DID YOU KNOW? Of the millions of people in the UK suffering from kidney disease, 50,000 will suffer end-stage renal failure
Domino Patient 1 Patient 2 Time is always of
transplants From patient 2 the essence
family member
Patient 1 needs a new kidney but their NON-COMPATIBLE NON-COMPATIBLE
family member isn’t compatible.
Patient 2 also needs a kidney and has From patient 1 COMPATIBLE
an incompatible family member as family member
well. However, patient 2’s relation is © Science Photo Library
compatible with patient 1 and vice
versa. The surgeon arranges a swap
– a ‘paired’ transplant. A longer line of
patients and family members
swapping compatible kidneys can be
arranged – a ‘daisy-chain’ transplant.
A ‘good Samaritan’ donor, who isn’t
related to any of the recipients, can
start the process. This first recipient’s
family member will subsequently
donate to someone else – a ‘domino’
transplant effect which can go on for
several cycles.
Who is Antibody Pack
suitable? carefully!
If the antigens are too dissimilar, the host’s existing
Of the several million people in immune system thinks the new kidney is a foreign invader The transport of harvested organs
the UK with kidney disease, and attacks it with antibodies, leading to rejection. is time critical – the sooner the
only around 50,000 will develop surgeon can put them into the
end-stage renal failure (ESRF). Antigens recipient the better. As soon as
For these people, dialysis or blood stops flowing to the
kidney transplantation are the Antigens from the recipient kidney’s ABO harvested tissue, the lack of oxygen
only options. Kidney damage blood group and HLA system should be as damages these cells, which is
from diabetes is the most close a match to the donor’s as possible. called ischaemia. The retrieval
common cause of team have a few tricks up their
transplantation. Other causes When things go wrong… sleeves to maximise the viability of
include damage from high blood the precious cargo they carry.
pressure, chronic kidney Kidneys need to be carefully matched to suitable donors, or rejection of the new organ
scarring (chronic will set in fast. Rejection occurs when the host body’s natural antibodies think the In the operating theatre, just
pyelonephritis) and polycystic new tissue is a foreign invader and attacks; careful pre-operative matching helps limit before they remove the harvested
kidney disease (the normal the degree of this attack. The most important match is via the ABO blood group type – kidney, it is flushed clean of blood
kidney tissue is replaced with the blood group must match or rejection is fast and aggressive. Next, the body’s HLA with a special cold, nutrient-rich
multiple cysts); many other less (human leukocyte antigen) system should be a close a match as possible, although it solution. Once removed, it is
common causes exist also. doesn’t need to be perfect. Incorrect matches here can lead to rejection over longer quickly put in a sterile container
periods of time. After the operation, patients are started on anti-rejection medicines with ice. The most modern
Patients must be selected which suppress the host’s immune system (immunosuppressants such as Tacrolimus, technique is to use a cold perfusion
carefully due to the scarcity Azathioprine or Prednisolone). Patients are monitored for the rest of their lives for machine instead of ice, which
of organs. Those with signs of rejection. These immunosuppressants aren’t without their risks – since they pumps a cooled solution through
widespread cancer, severely suppress the body’s natural defences, the risks of infections and cancers are higher. the kidney and improves its lasting
calcified arteries, persistent power. While hearts and lungs can
substance abuse and unstable only last around four hours,
mental problems mean that kidneys can last 24-48 hours.
transplants are likely to fail Transfer of the affected organ is
and so these patients are done via the fastest method
unsuitable to receive a precious possible; this often involves using
kidney transplant. helicopters or police escorts.
“Patients are All of these methods prolong the
monitored preservation time of the kidney,
for the rest although once ‘plugged’ back in, it
of their lives” can take a few days for the kidney
to start working properly
(especially if harvested from a
non-heart-beating donor).
51
HUMAN ANATOMY
Useless body parts
Why have humans and other animals stopped using certain Evolution’s
organs and functions which were once crucial for survival? leftovers
C harles Darwin is one of history’s most attributes and behavioural responses are 1Appendix
famous naturalists. Living in the 19th functional in other animals, but they do not seem The best known of the
Century, he became celebrated for his to be of any benefit to us; such as the appendix and vestigial organs, the
theories on evolution. In his seminal work On The your tailbone. These evolutionary remnants that appendix is used in animals
Origin Of Species he described how similar no longer serve any purpose are called vestigial to help digest cellulose found
animals were likely to be related by common organs, though this can apply as much to in grass, but in humans it
ancestors, rather than be completely unrelated. As behaviour and other body structures as it does to serves no clear function now.
subsequent generations are born, traits and actual organs.
features that did not bring a survival benefit to 2Tailbone
that species were eliminated. That, in a nutshell, Evolution has also adapted some existing The hard
is the theory of evolution. features to help us in new ways, in a process bone at the
known as exaptation. For example, birds’ wings bottom of
As a consequence, some organs and traits left in not only help them to fly but keep them warm too. your spine, the
the body lose their function and are no longer These changes may take thousands of years to coccyx, is a
used. This applies to modern human beings as develop, and in some cases the original role is remnant of our evolutionary
much as other creatures; some of our physical eventually eliminated altogether. ancestors’ tail. It has no
function in humans, but you
Appendicitis in focus could break it if you fall over.
What happens when your appendix gets inflamed?
Surgery Progression 3Goosebumps
Animals use body hair for
During surgery to remove The inflammation can insulation from the cold, by
the appendix, the surgeon lead to perforation of the trapping a warm layer of air
ties off the base to prevent appendix and around the body. Each hair
bowel contents leaking, and inflammation of the can stand on end when its
removes the whole surrounding tissues. The own tiny muscle contracts,
appendix organ. pain then worsens and but as human beings have
then localises to the lost most of their body hair, a
Blockage lower right-hand side of jumper is more effective.
the abdomen.
A blockage, caused by either a 4Plica semilunaris
tiny piece of waste or swollen The fleshy
lymphatic tissue in the bowel red fold found
wall, causes appendix swelling. in the corner
of your eye
Inflammation used to be a
transparent inner
Beyond the blockage, inflammation eyelid, which is still present
sets in, which causes intense in both reptiles and birds.
abdominal pain.
5Wisdom teeth
These teeth emerge
during our late teens in each
corner of the gums. Our
ancestors used them to help
chew dense plant matter, but
they have no function today,
but can cause a lot of pain.
© SPL
© SPL; Thinkstock
52
DID YOU KNOW? Around 15 per cent of us have an extra spleen – a small sphere close to but separate from the principal organ
How the spleen works
Perhaps not as well known as famous organs like the heart,
the spleen serves vital functions that help keep us healthy
he spleen’s main functions are to remove old blood Location
Inside the spleencells and fight off infection. Red blood cells have an The spleen sits underneath the
9th, 10th and 11th ribs (below
Taverage life span of 120 days. Most are created from the Wetakeyouonatourofthe the diaphragm) on the
left-hand side of the body,
marrow of long bones, such as the femur. When they’re old, majorfeaturesinthis which provides it with some
it’s the spleen’s job to identify them, filter them out and then often-overlookedorgan protection against knocks.
break them down. The smaller particles are then sent back Splenic vein
into the bloodstream, and either recycled or excreted from The waste products
from filtration and
other parts of the body. This takes place in the ‘red pulp’, Hilum pathogen digestion
which are blood vessel-rich areas of the spleen that make up
about three-quarters of its structure. The entrance to the spleen, are returned to the main
this is where the splenic artery circulation via this vein
The remainder is called ‘white pulp’, which are areas filled divides into smaller branches for disposal.
with different types of immune cell (such as lymphocytes). and the splenic vein is formed
They filter out and destroy foreign pathogens, which have from its tributaries.
invaded the body and are circulating in the blood. The white Splenic artery
pulp breaks them down into smaller, harmless particles.
The spleen receives a blood
It is surrounded by a thin, fragile capsule and so is prone to supply via this artery,
injury. It sits beneath the lower ribs on the left-hand side of which arises from a branch
your body, which affords it some protection, but car crashes, of the aorta called the
coeliac trunk.
major sports impacts and knife wounds can all rupture the
organ. In the most serious cases, blood loss can endanger the
person’s life, and in these situations it needs to be removed by
a surgeon. Since this reduces the body’s ability to fight
infections, some people will need to take antibiotics to boost
their immunity for the rest of their lives.
The immune system
Although the red blood that flows through our bodies gets all the
glory, the transparent lymphatic fluid is equally important. It has its
own body-wide network which follows blood vessel flow closely and
allows for the transport of digested fats, immune cells and more…
Spleen Adenoids © Alamy
One of the master co-ordinators These are part of the tonsillar White pulp Splenic capsule
that staves off infections and system that are only present in
filters old red blood cells. It children up until the age of five; Making up roughly a The capsule provides some
contains a number of in adults they have disappeared. quarter of the spleen, protection, but it’s thin
lymphocytes that recognise and They add an extra layer of the white pulp is
destroy invading pathogens defence in our early years. where white blood and relatively weak. Strong
present in the blood as it flows cells identify and blows or knife wounds can
through the spleen. Bone marrow destroy any type of easily rupture it and lead to
invading pathogens.
Thymus This forms the central, flexible life-threatening bleeding.
part of our long bones (eg femur). Red pulp
A small organ that sits just above Bone marrow is essential as it Sinusoid
the heart and behind the produces our key circulating Forming approximately
sternum. It teaches cells, including red blood cells, three-quarters of the Similar to those found in the
T-lymphocytes to identify and white blood cells and platelets. spleen, the red pulp is liver, these capillaries allow
destroy specific foreign bodies. The white blood cells mature where red blood cells are
Its development is directly into different types (eg filtered and broken down. for the easy passage of
related to hormones in the body lymphocytes and neutrophils), large cells into the splenic
so it’s only present until puberty which serve as the basis of the
ends; adults don’t need one. human immune system. tissue for processing.
Tonsils Lymph nodes 53
These are masses of lymphoid These are small (about 1cm/
tissue at the back of the throat 0.4in) spherical nodes that are
and can be seen when the mouth packed with macrophages and
is wide open. They form the first lymphocytes to defend against
line of defence against inhaled foreign agents. These are often
foreign pathogens, although linked in chains and are
they can become infected prevalent around the head,
themselves, causing tonsillitis. neck, axillae (armpits) and groin.
HUMAN ANATOMY
How the liver works
The human liver is T he liver is the largest internal organ in The liver is the body’s main powerhouse, producing
the ultimate the human body and, amazingly, has over and storing glucose as a key energy source. It is also
500 different functions. In fact, it is the responsible for breaking down complex fat molecules and
multitasker – it second most complex organ after the brain and is building them up into cholesterol and triglycerides, which
performs many intrinsically involved in almost every aspect of the body’s the body needs but in excess are bad. The liver makes
different functions metabolic processes. many complex proteins, including clotting factors which
all at the same time are vital in arresting bleeding. Bile, which helps digest fat
The liver’s main functions are energy production, in the intestines, is produced in the liver and stored in the
without you removal of harmful substances and the production of adjacent gallbladder.
even asking crucial proteins. These tasks are carried out within liver
cells, called hepatocytes, which sit in complex The liver also plays a key role in detoxifying the blood.
arrangements to maximise their overall efficiency. Waste products, toxins and drugs are processed here into
The hepatobiliary
region
Two halves Eight segments
The liver is anatomically split Functionally, there are
into two halves: left and right. eight segments of the
There are four lobes, and the liver, which are based
right lobe is the largest. upon the distribution
The gallbladder of veins draining
these segments.
The gallbladder and liver
are intimately related. Bile, The portal triad
which helps digest fat, is
produced in the liver and The common bile duct,
stored in the gallbladder. hepatic artery and
The common bile duct hepatic portal vein form
the portal triad, which
This duct is small, but vital in
the human body. It carries bile are the vital inflows and
from the liver and gallbladder outflows for this liver.
into the duodenum where it
helps digest fat.
Feel your liver
Take a deep breath in and feel
just under the right lower
edge of your ribs – in some
people the lower edge of the
liver can be felt.
The biggest organ Digestion
The liver is the largest of Once nutrients from food have
the internal organs, sitting in the been absorbed in the small
right upper quadrant of the abdomen,
just under the rib cage and attached to intestine, they are transported
the underside of the diaphragm. to the liver via the hepatic
54 portal vein (not shown here)
for energy production.
DID YOU KNOW? The liver can regenerate itself. If up to 75 per cent of the liver is removed, it can grow back to restore itself
“The liver also breaks A high demand organ
down old blood cells
and recycles hormones The liver deals with a massive amount of blood. branches from the aorta), carrying oxygen
such as adrenaline” It is unique because it has two blood supplies. 75 which the liver needs to produce this energy.
per cent of this comes directly from the The blood flows in tiny passages in between the
forms which are easier for the rest of the body to use or intestines (via the hepatic portal vein) which liver cells where the many metabolic functions
excrete. The liver also breaks down old blood cells, carries nutrients from digestion, which the liver occur. The blood then leaves the liver via the
produces antibodies to fight infection and recycles processes and turns into energy. The rest comes hepatic veins to flow into the biggest vein in the
hormones such as adrenaline. Numerous essential from the heart, via the hepatic artery (which body – the inferior vena cava.
vitamins and minerals are stored in the liver: vitamins A,
D, E and K, iron and copper. Liver lobules
Such a complex organ is also unfortunately prone to 3. Sinusoids The functional unit which
diseases. Cancers, infections (hepatitis) and cirrhosis (a performs the liver’s tasks
form of fibrosis often caused by excess alcohol These blood filled
consumption) are just some of those which can affect channels are lined by
the liver. hepatocytes and provide
the site of transfer of
molecules between blood The liver is considered a ‘chemical factory,’ as it
and liver cells.
forms large complex molecules from smaller
9. Central vein
1. The lobule ones brought to it from the gut via the blood
Blood from sinusoids, now stream. The functional unit of the liver is the
containing all of its new This arrangement of blood
molecules, flows into vessels, bile ducts and lobule – these are hexagonal-shaped
central veins which then
flow into larger hepatic hepatocytes form the structures comprising of blood vessels
veins. These drain into
the heart via the functional unit of the liver. and sinusoids. Sinusoids are the
inferior vena cava.
specialised areas where blood comes
into contact with the hepatocytes,
© Science Photo Library 2. The hepatocyte where the liver’s biological
These highly active cells processes take place.
perform all of the liver’s
key metabolic tasks.
4. Kupffer cells
These specialised cells sit
within the sinusoids and
destroy any bacteria which
are contaminating blood.
Stony 5. Hepatic
artery branch
Gallstones are
common but Blood from here supplies
oxygen to hepatocytes and
usually don’t cause
problems. carries metabolic waste
which the liver extracts.
The gallbladder 8. The portal triad
6. Bile duct
Bile, a dark green slimy liquid, is produced in the The hepatic artery, portal vein and bile duct are known as
hepatocytes and helps to digest fat. It is stored in a the portal triad. These sit at the edges of the liver lobule Bile, which helps
reservoir which sits on the under-surface of the liver, and are the main entry and exit routes for the liver. digest fat, is made in
to be used when needed. This reservoir is called the
gallbladder. Stones can form in the gallbladder hepatocytes and
(gallstones) and are very common, although most secreted into bile
don’t cause problems. In 2009, just under 60,000 ducts. It then flows
gallbladders were removed from patients within the into the gallbladder for
NHS making it one of the most common operations storage before being
performed; over 90 per cent of these are removed via
keyhole surgery. Most patients do very well without secreted into
their gallbladder and don’t notice any changes at all. the duodenum.
7. Portal vein
This vein carries nutrient-rich blood
directly from the intestines, which
flows into sinusoids for conversion
into energy within hepatocytes.
55
HUMAN ANATOMY
The surface area of Structure of the
the small intestine small intestine
is huge – in fact, Examine the anatomy of this vital
rolled flat it would organ in the human digestive tract
cover a tennis
court!
Lumen
This is the space inside the
small intestine in which the
food travels to be digested
and absorbed.
Exploring the Mucosal folds Mucosa
small intestine
These line the small The internal lining of the
Crucial for getting the nutrients we need from the intestine to increase small intestine where the
food we eat, how does this digestive organ work? surface area and help plicae circulares (mucosal
push the food on its way folds) and villi are situated.
by creating a valve-like
structure, stopping food Submucosa
travelling backwards.
This supports the mucosa
and connects it to the layers
of muscle (muscularis) that
make up the exterior of the
small intestine.
T he small intestine is one of the most duodenum is very important in breaking food increase the surface area dramatically to aid
important elements of our digestive down, using bile and enzymes from the this process.
system, which enables us to process food gallbladder, liver and pancreas, it is the shortest
and absorb nutrients. On average, it sits at a little element of the small bowel, only averaging about The ileum is the final section of the small bowel
over six metres (19.7 feet) long with a diameter of 30 centimetres (11.8 inches). and serves to catch nutrients that may have been
2.5-3 centimetres (1-1.2 inches), and it’s made up of missed, as well as absorbing vitamin B12 and
three distinctive parts: the duodenum, jejunum The jejunum follows the duodenum and its bile salts.
and the ileum. primary function is to encourage absorption of
carbohydrates and proteins by passing the Peristalsis is the movement used by the small
The duodenum connects the small intestine to broken-down food molecules through an area intestine to push the food through to the large
the stomach and is the key place for further with a large surface area so they can enter the bowel, where waste matter is stored for a short
enzyme breakdown, following the stomach bloodstream. Villi – small finger-like structures – period then disposed of via the colon. This process
turning food into an amino acid state. While the and mucosal folds line the passage and is generated by a series of muscles which make up
the organ’s outer wall.
56
DID YOU KNOW? The small intestine is actually longer than the large intestine, but is so called because of its narrower diameter
Serosa What exactly are nutrients?
This protective outer layer stops There are three main types of nutrient that we process in the body:
the small intestine from being lipids (fats), carbohydrates and proteins. These three groups of
damaged by other organs. molecules are broken down into sugars, starches, fats and smaller,
simpler molecule elements, which we can absorb through the
small intestine walls and that then travel in the bloodstream to our
muscles and other areas of the body that require energy or to be
repaired. We also need to consume and absorb vitamins and
minerals that we can’t synthesise within the body, eg vitamin B12
(prevalent in meat and fish).
Fat
Carbohydrate
Protein
Nutrients Blood vessels
Nutrients move through These sit close to the small intestine
the tube-like organ to be to allow easy diffusion of nutrients
diffused into the body, into the bloodstream.
mainly via the bloodstream.
Villi A closer look at villi
Villi are tiny finger-like What role do these little finger-like
structures that sit all over protrusions play in the bowel?
the mucosa. They help
Circular Longitudinal increase the surface area Epithelium Mucosa Lacteal
muscle layer muscle layer massively, alongside the (epithelial cells)
mucosal folds. The lining of the small The lacteal is a
This works in partnership This contracts and extends These individual cells that intestine on which lymphatic capillary
sit in the mucosa layer villi are located. that absorbs nutrients
with the longitudinal to help transport food with are where individual that can’t pass directly
microvilli extend from. into the bloodstream.
muscle layer to push the the circular muscle layer.
food down via a process
called peristalsis.
Microvilli
These are a mini version
of villi and sit on villi’s
individual epithelial cells.
Capillary bed © Corbis; Thinkstock
These absorb simple
sugars and amino acids as
they pass through the
epithelial tissue of the villi.
57
HUMAN ANATOMY
Inside the thoracic cavity
It may not look like it at first glance,
but there are more than two dozen
bones that make up the ribcage…
Clavicle
Also known as the
collarbone, this pair of
long bones is a support
between the sternum
and the shoulder blades.
True ribs
Rib pairs one through
seven attach to the
sternum directly via
a piece of cartilage.
The human False ribs
ribcage
Rib pairs eight through
Ribs are not merely armour for the organs ten connect to the
inside our torsos, as we reveal here… sternum via a structure
made of cartilage linked
to the seventh true rib.
T he ribcage – also known as the thoracic Rib pairs one through seven are called ‘true ribs’ What are hiccups?
cage or thoracic basket – is easily thought because they attach directly to the sternum. Rib
of as just a framework protecting your pairs eight through ten attach indirectly through Hiccupping – known medically as singultus, or
lungs, heart and other major organs. Although other cartilage structures, so they’re referred to as synchronous diaphragmatic flutter (SDF) – is an
that is one key function, the ribcage does so much ‘false ribs’. The final two pairs – the ‘floating ribs’ involuntary spasm of the diaphragm that can
more. It provides vital support as part of the – hang unattached to the sternum. happen for a number of reasons. Short-term
skeleton and, simply put, breathing wouldn’t be causes include eating or drinking too quickly, a
possible without it. Rib fractures are a common and very painful sudden change in body temperature or shock.
injury, with the middle ribs the most likely ones
All this means that the ribcage has to be to get broken. A fractured rib can be very However, some researchers have suggested
flexible. The conical structure isn’t just a rigid dangerous, because a sharp piece could pierce the that hiccupping in premature babies – who tend
system of bone – it’s both bone and cartilage. heart or lungs. to hiccup much more than full-term babies – is
The cage comprises 24 ribs, joining in the back to due to their underdeveloped lungs. It could be an
the 12 vertebrae making up the middle of the There’s also a condition called flail chest, in evolutionary leftover, since hiccupping in humans
spinal column. which several ribs break and detach from the is similar to the way that amphibians gulp water
cage, which can even be fatal. But otherwise and air into their gills to breathe.
The cartilage portions of the ribs meet in the there’s not much you can do to mend a fractured
front at the long, flat three-bone plate called the rib other than keep it stabilised, resting and
sternum (breastbone). Or rather, most of them do. giving it time to heal.
58
DID YOU KNOW? The condition known as flail chest is fatal in almost 50 per cent of cases
Manubrium Breathe in,
This broadest and thickest part breathe out…
of the sternum connects with
the clavicles and the cartilage Consciously take in a breath, and think about the
for the first pair of ribs. fact that there are ten different muscle groups
working together to make it happen. The
muscles that move the ribcage itself are the
intercostal muscles. They are each attached to
the ribs and run between them. As you inhale,
the external intercostals raise the ribs and
sternum so your lungs can expand, while your
diaphragm lowers and flattens. The internal
intercostals lower the ribcage when you exhale.
This forces the lungs to compress and release air
(working in tandem with seven other muscles). If
you breathe out gently, it’s a passive process
that doesn’t require much ribcage movement.
Sternal angle Inhalation Contraction
This is the angle formed by As you inhale, the The diaphragm contracts by
the joint between the intercostal muscles moving downward, allowing
contract to expand
manubrium and the body, and lift the ribcage. the lungs to fill with air.
often used as a sort of
‘landmark’ by physicians.
Body
The main body of the
sternum (breastbone) is
almost flat, with three
ridges running across its
surface and cavities for the
cartilage attaching to rib
pairs three through seven.
Xiphoid process Floating ribs
(not shown)
This extension from the
sternum starts as cartilage, Pairs 11-12 are only attached
but hardens to bone and
fuses to the rest of the to the vertebrae, not the
breastbone in adulthood.
sternum, so are often called
the floating, or free, ribs.
Ribs in other animals
Most vertebrates (ie animals with ribs overlap one another with hook-like Exhalation Relaxation © Thinkstock
backbones) have a ribcage of sorts – structures called uncinate processes,
however, ribcages can be very which add strength. Frogs don’t have The intercostal muscles The diaphragm relaxes,
different depending on the creature. any ribs, while turtles’ eight rib pairs relax as we exhale, moving upward to force
For example, dogs and cats have 13 are fused to the shell. A snake’s compressing and
pairs of ribs as opposed to our 12. ‘ribcage’, meanwhile, runs the length lowering the ribcage. air out of the lungs.
Marsupials have fewer ribs than of its body and can comprise hundreds
humans, and some of those are so tiny of pairs of ribs. Despite the variations
they aren’t much more than knobs of in appearance, ribcages all serve the
bone sticking out from the vertebrae. same basic functions for the
Once you get into other vertebrates, most part: to provide support and
the differences are even greater. Birds’ protection to the rest of the body.
59
HUMAN ANATOMY
How the pancreas works
Learn how the workhorse of the digestive system helps
to break down food and control our blood sugar levels
T he pancreas is a pivotal organ Anatomy of the pancreas Body of the
within the digestive system. It sits pancreas
inside the abdomen, behind the It might not be the biggest organ but the pancreas is a key
stomach and the large bowel, adjacent to facilitator of how we absorb nutrients and stay energised The central body sits
the spleen. In humans, it has a head, neck,
body and tail. It is connected to the first Pancreatic duct on top of the main
section of the small intestine, the
duodenum, by the pancreatic duct, and to Within the pancreas, the digestive artery to the spleen.
the bloodstream via a rich network of enzymes are secreted into
vessels. When it comes to the function of the pancreatic duct,
the pancreas, it is best to think about the which joins onto
two types of cell it contains: endocrine the common
and exocrine. bile duct.
The endocrine pancreas is made up of Common bile duct
clusters of cells called islets of Langerhans,
which in total contain approximately 1 The pancreatic enzymes are
million cells and are responsible for mixed with bile from the
producing hormones. These cells include gallbladder, which is all sent
alpha cells, which secrete glucagon, and through the common bile
beta cells which generate insulin. These duct into the duodenum.
two hormones have opposite effects on
blood sugar levels throughout the body: Duodenum
glucagon increases glucose levels, while
insulin decreases them. The pancreas empties
its digestive enzymes
The cells here are all in contact with into the first part of
capillaries, so hormones which are the small intestine.
produced can be fed directly into the
bloodstream. Insulin secretion is under the Head of the
control of a negative-feedback loop; high pancreas
blood sugar leads to insulin secretion,
which then lowers blood sugar with The head needs to be
subsequent suppression of insulin. removed if it’s affected by
Disorders of these cells (and thus cancer, via a complex
alterations of hormone levels) can lead to operation that involves the
many conditions, including diabetes. The resection of many other
islets of Langerhans are also responsible for adjacent structures.
producing other hormones, like
somatostatin, which governs nutrient
absorption among other things.
The exocrine pancreas, meanwhile, is
responsible for secreting digestive
enzymes. Cells are arranged in clusters
called acini, which flow into the central
pancreatic duct. This leads into the
duodenum – part of the small bowel – to
come into contact with and aid in the
digestion of food. The enzymes secreted
include proteases (to digest protein),
lipases (for fat) and amylase (for sugar/
starch). Secretion of these enzymes is
controlled by a series of hormones, which
are released from the stomach and
duodenum in response to the stretch from
the presence of food.
60
DID YOU KNOW? In the UK, 80 per cent of acute pancreatitis cases are caused by gallstones or excessive alcohol ingestion
Tail of the pancreas
This is the end portion of
the organ and is positioned
close to the spleen.
What brings on diabetes?
Diabetes is a condition where a other disorders of the pancreas.
person has higher blood sugar than Inflammation of the organ (ie acute
normal. It is either caused by a pancreatitis) causes severe pain in
failure of the pancreas to produce the upper abdomen, forcing most
insulin (ie type 1, or insulin- people to attend the emergency
dependent diabetes mellitus), or department as it can be life
resistance of the body’s cells to threatening. In contrast, cancer of
insulin present in the circulation (ie the pancreas causes gradually
type 2, or non-insulin-dependent worsening pain which can often be
diabetes mellitus). There are also mistaken for other ailments.
Beta cells Insulin released
It is the beta cells The vesicle releases its
within the islets of stored insulin into the
Langerhans which blood capillaries
control glucose through exocytosis.
levels and amount
of insulin secretion.
Blood supply High glucose Calcium
effects
The pancreas derives its blood When the levels of
supply from a variety of sources, glucose within the The calcium
including vessels running to the bloodstream are high, causes the
the glucose wants to
stomach and spleen. move down its diffusion vesicles that
gradient into the cells. store insulin to
Does the pancreas vary in move towards
humans and animals?
the cell wall.
Every vertebrate animal has a pancreas of some form,
meaning they are all susceptible to diabetes too. The GLUT2 Depolarisation Calcium channels © Corbis; Süleyman Habib
arrangement, however, varies from creature to creature. In
humans, the pancreas is most often a single structure that sits This is a glucose- The metabolism of glucose Changes in potassium
at the back of the abdomen. In other animals, the arrangement transporting channel, leads to changes in the levels cause voltage-gated
varies from two or three masses of tissue scattered around which facilitates the polarity of the cell wall calcium channels to open in
the abdomen, to tissue interspersed within the connective uptake of glucose and an increase in the
tissue between the bowels, to small collections of tissue within into the cells. number of potassium ions. the cell wall, and calcium
the bowel mucosal wall itself. One of the other key differences ions to flow into the cell.
is the number of ducts that connect the pancreas to the bowel.
In most humans there’s only one duct, but occasionally there
may be two or three – and sometimes even more. In other
animals, the number is much more variable. However, the
function is largely similar, where the pancreas secretes
digestive enzymes and hormones to control blood sugar levels.
61
HUMAN ANATOMY © Thinkstock THE COMPLETE
URINARY SYSTEM
When you’ve got to
go, you’ve got to go… Kidneys
but really our bodies
are reacting to our The kidneys
bladders’ direction turn unwanted
substances in the
blood into urine.
Ureters
Ureters carry
urine from
the kidneys to
the bladder.
How your Urethra
bladder works
The urethra runs
from the bottom
of the bladder to
the outside world.
As a key part of the urinary system, the bladder © SPL Bladder
is crucial to removing waste from your body
This muscular
bag generally
holds around a
pint of urine.
T he bladder is one of the key organs in the urinary system the bladder becomes full, or nearly full, the nerves in the
and it stores urine following production by the kidneys bladder communicate with the brain, which in turn induces an
until the body can release it. urge to urinate. This sensation will get stronger if you do not go
Urine is a waste substance produced by the kidneys as they – creating the ‘bursting for a wee’ feeling that you can
filter our blood of toxins and other unneeded elements. Up to 150 occasionally experience. When ready to urinate, both the
litres (40 gallons) of blood are filtered per day by your kidneys, internal and external sphincters relax and the detrusor muscles
but only around two litres (0.5 gallons) of waste actually pass in the bladder wall contract in order to generate pressure,
down the ureters to the bladder. forcing urine to pass down the urethra and exit the body.
Urine travels down the ureters and through the ureter valves, As well as telling you when you need to pass fluid, the urinary
which attach each tube to the organ and prevent any liquid system also helps to maintain the mineral and salt balance in
passing back. The bladder walls, controlled by the detrusor your body. For instance, when salts and minerals are too highly
muscles, relax as urine enters and allow the organ to fill. When concentrated, you feel thirst to regain the balance.
Incontinence explained
For the bladder to work correctly, urine without control. It is often caused pressure (eg while coughing, laughing
several areas within it must all function by involuntary spasms by the detrusor or sneezing). This kind of incontinence
properly. It is most commonly the muscles which can be a result of either is most common in the elderly.
failure of one of these features that nervous system problems or infections.
leads to incontinence. One modern remedy is a preventative
Another type is stress incontinence, implant that has been developed to
A common type of urinary caused when the external sphincter or replace post-event incontinence pads.
incontinence is urge incontinence. This pelvic floor muscles are damaged. This This comes in the form of a collagen-
is when an individual feels a sudden means urine can accidentally escape, based substance injected around the
compulsion to urinate and will release especially if the pelvic floor is under urethra in order to support it.
62
DID YOU KNOW? Everyone’s bladder differs slightly in size. The average maximum capacity is between 600-800ml (1.3-1.7pt)
Inside the bladder What is
urine made
How this organ acts as the middleman between up of?
your kidneys and excretion
A human bladder usually holds around
FULL Ureters Bla(dddeetrruwsaolrl 350 millilitres (0.7 pints) of urine, though
BLADDER muscles) male bladders can typically hold slightly
These tubes link the kidneys more than those of females. Urine is
Ureter valves and the bladder, transporting The detrusor muscles made up of urea, the waste by-product
make up a layer of the the body forms while breaking down
These sit at the end of the urine for disposal. protein across the body. The kidneys will
the ureters and let bladder wall. These filter this out and pass it with extra water
urine pass into the muscles cause the wall to the bladder for expulsion. Other waste
bladder without letting products produced or consumed by the
it flow back. to relax and extend as body that pass through the kidneys will
urine enters, while also exit the body via this route.
Pelvic floor muscles Typically, urine is made up of 95 per cent
nerves situated in the water and 5 per cent dissolved or
These hold the bladder in place, wall measure how full suspended solids including urea, plus
and sit around the urethra the bladder is and will chloride, sodium and potassium ions.
stopping unintended urination.
signal to the brain URINE
when to urinate. CONTENTS
Internal Uric acid
urethral sphincter 0.6g
The internal sphincter is Bicarbonate
controlled by the body. It ions
stays closed to stop urine 1.2g
passing out of the body.
Externaslpuhreintchtrearl
(distal sphincter)
This sphincter is controlled
by the individual, and they
control whether to open or
close the valve.
EMPTYING Creatinine
BLADDER 2.7g
Potassium ions
3.2g
Sodium ions
4.1g
Chloride ions
6.6g
Internal urethral Bladder wall Urea
sphincter (controlled by 25.5g
This relaxes when the detrusor
body is ready to expel muscles)
the waste liquid.
These muscles contract
to force the urine out
of the bladder.
2x © DK Images
Espxhteinrncatel rurethral Urethra
(distal sphincter)
Urine travels down this
This also relaxes for the urine passageway to leave the body.
to exit the body.
63
HUMAN ANATOMY
The urinary
system
explained Kidneys
This is where liquids are
filtered and nutrients are
absorbed before urine
exits into the ureters.
Every day the body produces waste
products that enter the bloodstream – Ureter
but how do we get rid of them? These tubes link the
kidneys and the bladder.
T he human urinary system’s water levels in the body, sodium and Inferior vena cava
primary function is to remove potassium levels among other
by-products which remain in the electrolytes, blood pressure, pH of This carries deoxygenated
blood after the body has metabolised the blood and are also involved in red blood back from the kidneys
food. The process is made up of several blood cell production through the to the right aorta of the heart.
different key features. Generally, this creation and release of the hormone
system consists of two kidneys, two erythropoietin. Consequently, they Abdominal aorta
ureters, the bladder, two sphincter are absolutely crucial to optimum
muscles (one internal, one external) body operation. This artery supplies blood
and a urethra and these work alongside to the kidneys, via the renal
the intestines, lungs and skin, all of After blood has been filtered by artery and vein. This blood
which excrete waste products from the kidneys, the waste products then is then cleansed by
the body. travel down the ureters to the bladder. the kidneys.
The bladder’s walls expand out to
The abdominal aorta is an important hold the urine until the body can Bladder
artery to the system as this feeds the excrete the waste out through the
renal artery and vein, which supply the urethra. The internal and external This is where urine
kidneys with blood. This blood is filtered sphincters then control the release gathers after being
by the kidneys to remove waste of urine. passed down the
products, such as urea which is formed ureters from
through amino acid metabolism. Generally, a human will produce the kidneys.
Through communication with other approximately 2.5-3 litres of urine a day,
areas of the body, such as the although this can vary dramatically
hypothalamus, the kidneys also control dependant on external factors such as
water consumption.
“Generally, a human will produce
2.5-3 litres of urine a day”
How do the kidneys work?
The kidneys will have around 150-180 litres of blood to filter per day, but only pass
around two litres of waste down the ureters to the bladder for excretion, therefore the
kidneys return much of this blood, minus most of the waste products, to the heart for
re-oxygenation and recirculation around the body.
The way the kidneys do this is to pass the blood through a small filtering unit called a
nephron. Each kidney has around a million of these, which are made up of a number of
small blood capillaries and a tube called the renal tubule. The blood capillaries sift the
normal cells and proteins from the blood for recirculation and then direct the waste
products into the renal tubule. This waste, which will primarily consist of urea, mixes
with water and forms urine as it passes through the renal tubule and then into the
ureter on its way to the bladder.
64
DID YOU KNOW? On average, you make the same amount of urine in the day as in the night
How do we store waste until
we’re ready to expel it?
The bladder stores waste products by allowing the urine to enter
through the ureter valves, which attach the ureter to the bladder.
The walls relax as urine enters and this allows the bladder to
stretch. When the bladder becomes full, the nerves in the bladder
communicate with the brain and cause the individual to feel the
urge to urinate. The internal and external sphincters will then
relax, allowing urine to pass down the urethra.
Bladder 1. Ureters
fills
These tubes connect to the kidneys and urine
flows down to the bladder through them.
Why do we 2. Internal urethral sphincter
get thirsty?
This remains closed to ensure urine does
Maintaining the balance between the not escape unexpectedly.
minerals and salts in our body and water is
very important. When this is out of balance, 3. External 5. Bladder walls
the body tells us to consume more liquids to urethral (controlled by
redress this imbalance in order for the body sphincter
to continue operating effectively. detrusor muscles)
This secondary
This craving, or thirst, can be caused by sphincter also The detrusor muscles in the wall of
too high a concentration of salts in the body, remains closed
or by the water volume in the body dropping to ensure no the bladder relax to allow expansion
too low for optimal operation. Avoiding urine escapes.
dehydration is important as long term of the bladder as necessary.
dehydration can cause renal failure, among 4. Ureter valves
other conditions.
These valves are situated
The human at the end of the ureters
urinary and let urine in.
system
Bladder 1. Internal urethral sphincter
Renal artery and vein empties
This relaxes when the body is ready to expel
This supplies blood to the kidneys the waste.
in order for them to operate, and
then removes deoxygenated blood 2. External
urethral sphincter
after use by the kidneys.
This also relaxes for the urine
to exit the body.
© DK Images Pelvis 3. Bladder 4. Urethra
walls
The bladder sits in the pelvis, (controlled Urine travels down this
and the urethra passes through by detrusor passageway to exit the body.
muscles)
it for urine to exit the body.
These muscles
Urethra
contract to force
The urethra is the tube
that urine travels the urine out of
through to exit the body. the bladder.
65
HUMAN ANATOMY
Inside the human stomach
Discover how this amazing digestive organ stretches, churns and holds
corrosive acid to break down our food, all without getting damaged
T he stomach’s major role is as a reservoir the rugae flatten, allowing the stomach to cells (G-cells) to make the hormone gastrin,
for food; it allows large meals to be expand, and the outer muscles relax. The which encourages even more acid production.
consumed in one sitting before being stomach can accommodate about a litre (1.8
gradually emptied into the small intestine. A pints) of food without discomfort. The stomach empties its contents into the
combination of acid, protein-digesting small intestine through the pyloric sphincter.
enzymes and vigorous churning action breaks The expansion of the stomach activates Liquids pass through the sphincter easily, but
the stomach contents down into an easier-to- stretch receptors, which trigger nerve solids must be smaller than one to two
process liquid form, preparing food for signalling that results in increased acid millimetres (0.04-0.08 inches) in diameter
absorption in the bowels. production and powerful muscle contractions before they will fit. Anything larger is ‘refluxed’
to mix and churn the contents. Gastric acid backwards into the main chamber for further
In its resting state, the stomach is contracted causes proteins in the food to unravel, allowing churning and enzymatic breakdown. It takes
and the internal surface of the organ folds into access by the enzyme pepsin, which breaks about two hours for half a meal to pass into the
characteristic ridges, or rugae. When we start down protein. The presence of partially small intestine and the process is generally
eating, however, the stomach begins to distend; digested proteins stimulates enteroendocrine complete within four to five hours.
Lining under the microscope Chief cell (yellow)
The stomach is much more than just a storage bag. Chief cells make pepsinogen; at the low pH
Take a look at its complex microanatomy now… in the stomach it becomes the digestive
enzyme pepsin, which deconstructs protein.
Gastric pits Mucous cell
The entire surface of the These cells secrete alkaline
stomach is covered in tiny mucus to protect the
holes, which lead to the
glands that produce mucus, stomach lining from damage
acid and enzymes. by stomach acid.
Mucosa G-cell (pink)
Submucosa Also known as
enteroendocrine cells,
these produce hormones
like gastrin, which regulate
acid production and
stomach contraction.
Muscularis Muscle layers
Parietal cell (blue) The stomach has three layers
of muscle running in different
These cells produce hydrochloric
acid, which kills off micro- orientations. These produce
organisms, unravels proteins and the co-ordinated contraction
activates digestive enzymes.
required to mix food.
66
DID YOU KNOW? Stomach rumbling, also known as borborygmus, is actually the noise of air movement in the intestines
Gastric anatomy Fundus
This major organ in the digestive system has several distinct The top portion of the
regions with different functions, as we highlight here stomach curves up and
Pyloric sphincter Cardia allows gases created
during digestion to
The pyloric sphincter is a strong The oesophagus empties into be collected.
ring of muscle that regulates the the stomach at the cardia. This
passage of food from the region makes lots of mucus, Body
stomach to the bowels. but little acid or enzymes.
Also called the corpus, this
Antrum is the largest part of the
The antrum contains cells that stomach and is responsible
can stimulate or shut off acid for storing food as gastric
production, regulating the pH juices are introduced.
level of the stomach.
Small intestine Pancreas Large intestine
The stomach empties into The bottom of the stomach The large intestine curls
the first section of the small is located in front of the around and rests just below
intestine: the duodenum. pancreas, although the two the stomach in the abdomen.
aren’t directly connected.
Vomit reflex
Why doesn’t it Produced by parietal step-by-step
digest itself? cells in the stomach
lining, gastric acid has a Vomiting is the forceful expulsion
Your stomach is full of corrosive acid and pH level of 1.5 to 3.5 of the stomach contents up the
enzymes capable of breaking down protein – if oesophagus and out of the mouth.
left unprotected the stomach lining would It’s the result of three co-ordinated © Thinkstock
quickly be destroyed. To prevent this from stages. First, a deep breath is
occurring, the cells lining the stomach wall drawn and the body closes the
produce carbohydrate-rich mucus, which forms glottis, covering the entrance to
a slippery, gel-like barrier. The mucus contains the lungs. The diaphragm then
bicarbonate, which is alkaline and buffers the pH contracts, lowering pressure in the
at the surface of the stomach lining, preventing thorax to open up the oesophagus.
damage by acid. For added protection, the At the same time, the muscles of
protein-digesting enzyme pepsin is created from the abdominal wall contract,
a zymogen (the enzyme in its inactive form) – which squeezes the stomach. The
pepsinogen; it only becomes active when it combined shifts in pressure both
comes into contact with acid, a safe distance inside and outside the stomach
away from the cells that manufacture it. forces any contents upwards.
67
HUMAN ANATOMY
T he human hand is an important The human hand
feature of the human body, which
allows individuals to manipulate We take our hands for granted, but they are
their surroundings and also to gather large actually quite complex and have been
amounts of data from the environment that crucial in our evolution
the individual is situated within. A hand is
generally defined as the terminal aspect of Bones in Distal phalanges
the human arm, which consists of prehensile
digits, an opposable thumb, and a wrist and the hand A distal phalange (fingertip) is situated
palm. Although many other animals have at the end of each finger. Deep flexors
similar structures, only primates and a The human hand contains 27 attach to this bone to allow for
limited number of other vertebrates can be bones, and these divide up into maximum movement.
said to have a ‘hand’ due to the need for an three distinct groups: the
opposable thumb to be present and the carpals, metacarpals and Intermediate
degree of extra articulation that the human phalanges. These also then phalanges
hand can achieve. Due to this extra further break down into three:
articulation, humans have developed fine the proximal phalanges, This is where the
motor skills allowing for much increased intermediate phalanges and superficial flexors attach
control in this limb. Consequently we see distal phalanges. Eight bones via tendons to allow the
improved ability to grasp and grip items and are situated in the wrist and digit to bend.
these are collectively called
development of skills such as writing. the carpals. The metacarpals, Proximal
A normal human hand is made up of five which are situated in the palm phalanges
of the hand account for a
digits, the palm and wrist. It consists of 27 further five out of the 27, and Each finger has three
bones, tendons, muscles and nerves, with each finger has three phalanges, and this phalange
each fingertip of each digit containing phalanges, the thumb has two. joins the intermediate to its
numerous nerve endings making the hand a Intrinsic muscles and tendons respective metacarpal.
crucial area for gathering information from interact to control movement of
the environment using one of man’s most the digits and hand, and attach Metacarpals
crucial five senses: touch. Muscles interact to extrinsic muscles that
together with tendons to allow fingers to extend further up into the arm, These five bones make up the
bend, straighten, point and, in the case of the which flex the digits. palm, and each one aligns
thumb, rotate. However, the hand is an area with one of the hand’s digits.
that sees many injuries due to the number of
ways we use it, one in ten injuries in A&E Carpals
being hand related, and there are also
several disorders that can affect the hand The carpals (scaphoid, triquetral, trapezium,
development in the womb, such as trapezoid, lunate, hamate, capitate and
polydactyly, where an individual is born with pisiform) sit between the ulna and radius
extra digits, which are often in perfect and the metacarpals.
working order.
68
DID YOU KNOW? Skin is attached to tendons and so when you bend you fingers back, dimples appear on the back of your hand
Muscles and other structures Opposable
thumbs
The movements and articulations of the hand and complex mix of tendons and intrinsic muscles to
by the digits are controlled by tendons and two operate (extensors). These muscles will contract in Increased articulation of
muscle groups situated within the hand and wrist. order to cause digit movement, and flexors and the thumb has been
These are the extrinsic and intrinsic muscle groups, extensors work in a pair to complement each to heralded as a key
so named as the extrinsics are attached to muscles straighten and bend digits. The intrinsic muscles factor in human
which extend into the forearm, whereas the are responsible for aiding extrinsic muscle action evolution. It allowed
intrinsics are situated within the hand and wrist. and other movements in the digits and have three for increased grip
The flexors and extensors, which make up the distinct groups; the thenar and hypothenar and control, and for
extrinsic muscles, use either exclusively tendons to (referring to the thumb and little finger tool use to develop
attach to digits they control (flexors) or a more respectively), the interossei and the lumbrical. among human
ancestors as well as other
Thenar space primates. This has later also facilitated
major cultural advances, such as writing. Alongside
Thenar refers to the thumb, the four other flexible digits, the opposable thumb
and this space is situated makes the human hand one of the most dexterous in
between the first digit and the world. A thumb can only be classified as
thumb. One of the deep opposable when it can be brought opposite to the
flexors (extrinsic muscle) is other digits.
located in here.
Left handed
Interossei © Wilfredor 2008 Ulnar nerve or right
muscle handed?
(intrinsic) Insertion of flexor tendon This nerve stretches
down the forearm into The most common theory for why some individuals
This interossei muscle sits This is where the tendon attaches the the hand and allows for are left handed is that of the ‘disappearing twin’. This
between metacarpal flexor muscle to the finger bones to supposes that the left-handed individual was
bones and will unite with allow articulation. sensory information actually one of a set of twins, but that in the early
tendons to allow extension to be passed from stages of development the other, right handed, twin
using extrinsic muscles. hand to brain. died. However, it’s been found that dominance of one
hand is directly linked with hemisphere dominance
Arteries, veins Hypothenar in the brain, as in many other paired organs.
and nerves muscle (intrinsic)
Individuals who somehow damage their dominant
These supply fresh Hypothenar refers to the little hand for extended periods of time can actually
oxygenated blood (and finger and this muscle group is one change to use the other hand, proving the impact and
take away deoxygenated importance of environment and extent to which
blood) to hand muscles. of the intrinsic muscles. humans can adapt.
Forearm Mid palmar space
muscles
Tendons and intrinsic muscles
primarily inhabit this space
within the hand.
Extrinsic muscles are so © Science photo library
called because they are
primarily situated outside Tendons and Thenars Superficial flexors Deep flexors Extensors
the hand, the body of the intrinsics
muscles situated along the The intrinsic group of The other flexor that acts on The digits have two extrinsic Extensors on the back of
underside or front of the These attach the muscles is used to flex the the digits is the superior flexor, flexors that allow them to bend, the forearm straighten the
forearm. This body of flexor muscles to the thumb and control its which attaches to the the deep flexor and the
muscles actually breaks phalanges, and facilitate sideways movement. intermediate phalanges. superficial. The deep flexor digits. Divided into six
down into two quite distinct bending. Tendons also attaches to the distal phalanges. sections, their connection
groups: the flexors and the interact with the intrinsics
extensors. The flexors run and extensors in the wrist, to the digits is complex.
alongside the underside of palm and forearm to
the arm and allow for the straighten the digits.
bending of the digits,
whereas the extensor
muscles’ main purpose is the
reverse this action, to
straighten the digits. There
are both deep and superficial
flexors and extensors, and
which are used at any one
time depends on the digit to
be moved.
69
HUMAN ANATOMY
What are our
fingernails
made of?
And how are they formed?
Fingernails are made of a tough protein called keratin (from the Greek
word ‘Kera’, meaning horn). Keratin is also what animals hooves and horns
are made from. Most animals have a supportive bone structure in their
horns, although rhinoceros horns are made completely of keratin compacted
together. The only other biological material which has a similar toughness
to keratinised tissue is chitin, the main component of exoskeletons
belonging to arthropods. The half-moon shape that you can see at the
bottom of your nail (apart from maybe your little finger) is called the lanula.
This is a group of cells that produce keratin and other living cells. As these
living cells are pushed forward by newer cells, they die and merge with the
keratin to become keritinised. They then become flattened, stiff and known
as your fingernails.
“The half-moon shape that you
can see at the bottom of your
nail is called the lanula”
What does
the Achilles’
tendon do?
Is it really a weak spot and how
important is it?
T his tendon, the strongest in your body, connects the calf muscles to the
heel. When everything is fine, it pulls the back of the foot up when the
calf muscles contract. This way, your heel raises and your weight goes to
your toes.
It enables us to do such things as sprinting, hopping or jumping. It also stores
elastic energy to do these tasks more efficiently. Biological anthropologists
believe all this was very important for the way we evolved to run around on two
legs and survive.
The Achilles’ tendon is seemingly named thus after the mythological Greek
character of Achilles, who during the Trojan War - made famous by Homer’s epic
poem The Illiad - is shot by a poisoned arrow in his unprotected heel - hence the
common phrase describing a person’s weak point.
70
DID YOU KNOW? Knee injuries are common within the sporting world due to the constant muscle strain
Inside © Science Photo Library Quadriceps
the knee
The quadriceps, made up
How do our knee joints of four muscles,
allow us to walk and run?
are on the front of the
The knee is the largest and also one of thigh and help to
the most complex joints in the body,
allowing us bipedal humans to move straighten the leg.
around and get from point A to point B.
Three different bones meet at the knee Hamstrings
joint and work together to allow for
movement and protection. At the top of Hamstring muscles running
the knee is the lower part of the from the thigh to the knee joint
thighbone (femur). This rotates on top of
the shinbone (tibia) and the kneecap are responsible for bending
(patella), the latter of which moves in a the leg at the knee.
groove between the femur and tibia.
Cartilage within the knee cushions it Femur
from shock caused by motion, while
ligaments prevent damage occurring to This bone runs from the hip to
the joint in case of unusual or erratic the knee joint. It is the thickest
motion. Muscles running from the hip
down to the knee joint are responsible and the longest bone in the
for working the knee joint and allowing human body.
our legs to bend, stretch, and ultimately
allowing us to walk, run and skip. The knee
structure
Cartilage
How does everything work in
The point at which the three tandem to allow for movement?
bones meet is covered in tough,
elastic articular cartilage, Synovial membrane
allowing smooth movement of
the joint and absorbing shock. The soft tissue at the centre of the
knee joint contains synovial fluid,
Patella providing lubrication for the
moving knee.
This bone slides at the front of
the femur and tibia as the knee Ligaments
moves, protecting the knee and
giving the muscles leverage. These elastic bands of tissue
connect the bones together
Menisci
and provide stability and
The three bones are separated strength to the knee joint.
with two discs of connective
tissue called ‘menisci’, also
acting as shock absorbers and
enhancing stability.
Tendons Tibia The patella, seen
separated above, is also
These tough cords of tissue This bone connects the knee to known as the kneecap
attach muscle to bone, so that the ankle, running parallel to the
the muscles can bend and thinner fibula bone.
straighten the leg as required.
71
HUMAN ANATOMY
How do your
feet work?
Feet are immensely complex structures,
yet we put huge amounts of pressure on
them every day. How do they cope?
T he human foot and ankle is crucial for locomotion and is Toes
one of the most complex structures of the human body.
This intricate structure is made up of no less than 26 Terminal aspects of the foot
bones, 20 muscles, 33 joints – although only 20 are articulated that aid balance by grasping
– as well as numerous tendons and ligaments. Tendons connect onto the ground. They are the
the muscles to the bones and facilitate movement of the foot, equivalent of fingers in the
while ligaments hold the tendons in place and help the foot foot structure.
move up and down to initiate walking. Arches in the foot are
formed by ligaments, muscles and foot bones and help to Muscles – including the extensor
distribute weight, as well as making it easier for the foot to digitorum brevis muscle
operate efficiently when walking and running. It is due to the
unique structure of the foot and the way it distributes pressure Muscles within the foot help the foot lift and
throughout all aspects that it can withstand constant pressure articulate as necessary. The extensor digitorum
throughout the day. brevis muscle sits on the top of the foot, and
helps flex digits two-four on the foot.
One of the other crucial functions of the foot is to aid balance,
and toes are a crucial aspect of this. The big toe in particular Blood vessels
helps in this area, as we can grip the ground with it if we feel we
are losing balance. These supply blood to the foot,
facilitating muscle operation by
The skin, nerves and blood vessels make up the rest of the supplying energy and oxygen and
foot, helping to hold the shape and also supplying it with all the removing deoxygenated blood.
necessary minerals, oxygen and energy to help keep it moving
easily and constantly. Ligaments
What happens when Ligaments support the
you sprain your ankle? tendons and help to form the
arches of the foot, spreading
A sprained ankle is the most common type of soft tissue weight across it.
injury. The severity of the sprain can depend on how you
sprained the ankle, and a minor sprain will generally Tendons (extensor digitorum
consist of a stretched or only partially torn ligament. longus, among others)
However, more severe sprains can cause the ligament
to tear completely, or even force a piece of bone to Fibrous bands of tissue which connect
break off. muscles to bones. They can withstand a lot
of tension and link various aspects of the
Generally a sprain happens when you lose balance or foot, facilitating movement.
slip, and the foot bends inwards
towards the other leg. This then Tibia
overstretches the ligaments and
causes the damage. Over a The larger and stronger of the lower
quarter of all sporting injuries leg bones, this links the knee and the
are sprains of the ankle. ankle bones of the foot.
Fibula
This bone sits alongside the tibia, also
linking the knee and the ankle.
© DK Images
© DK Images
The structure
of the foot
and how the
elements
work together
72
DID YOU KNOW? In a lifetime, a person will walk the equivalent of four times around the globe – more than 100,000 miles!
How do 4. Leg swing
we walk?
The lower leg will
‘Human gait’ is the term to describe how we then swing at the
walk. This gait will vary between each knee, under the body,
person, but the basics are the same to be placed in front
of the stationary,
2. Weight transfer weight- bearing foot.
The weight will transfer fully
to the foot still in contact
with the ground, normally
with a slight leaning
movement of the body.
The structure of the foot 3. Foot lift 5. Heel 1. Heel lift 6. Repeat
enables us to stay balanced placement process
After weight has The first step of walking is for
transferred and the The heel will normally be the foot to be lifted off the The process is
individual feels the part of the foot that’s ground. The knee will raise and then repeated with
balanced, the ball of placed first, and weight the calf muscle and Achilles the other foot. During
the first foot will then will start to transfer back tendon, situated on the back of normal walking or
lift off the ground, onto this foot as it hits the leg, will contract to allow running, one foot will
raising the thigh. the ground. the heel to lift off the ground. start to lift as the other
starts to come into
contact with the ground.
Bones of the foot
Distal Proximal Metatarsals Cuneiforms Navicular A baby is born with 22
phalanges phalanges bones (three) out of a total 26 bones in each foot
The five, long bones that are This bone, which is
The bones which These bones link the the metatarsals are located Three bones that fuse so named due
sit at the far end metatarsals and the between the tarsal bones together during bone to its resemblance
of the foot and distal phalanges and and the phalanges. These development and sit to a boat, articulates
make up the tips stretch from the are the equivalent of the between the metatarsals with the three
of the toes. base of the toes. metacarpals in the hand. and the talus. cuneiform bones.
Cuboid Talus Calcaneus © DK Images
One of five irregular bones The talus is the This bone
(cuboid, navicular and three second largest constitutes the
cuneiform bones) which make bone of the foot, heel and is crucial
and it makes up for walking. It is
up the arches of the foot. the lower part of the largest bone
These help with shock the ankle joint.
in the foot.
absorption in locomotion.
73
THE BODY
AT WORK
100 90
How our The lungs
bones heal explained
76 The science of sleep 99 Making protein 117 What is anxiety?
Understand why we sleep How are they manufactured? What causes us to feel uneasy?
84 The blood-brain barrier 100 The cell cycle 118 Circulatory system
What important role does it play? Inside a vital process How blood gets transported
85 Pituitary gland up close 102 Human pregnancy 120 How your blood works
The ‘master gland’ explored The different stages explained The miraculous fluid analysed
86 Human digestion explained 104 Embryo development 124 Blood vessels /
The digestion process revealed How a foetus evolves Hyperventilation
What are blood vessels made of
88 Altitude sickness / Synapses 106 How we taste / Taste buds and why do we hyperventilate?
What causes altitude sickness? The way we sense flavours
125 Tracheotomy surgery
89 Adrenaline 107 What is saliva? A look at the life-saving operation
How this hormone affects us Find out why there is moisture in
our mouths 126 Hormones
90 Human respiration Understand the human
The lungs explained 108 Neurotransmitters and your endocrine system
feelings
92 Dehydration / Sweating How do your emotions work? 128 Exploring the sensory system
Why we sweat and using fluids How we experience the world
109 Short term memory
93 Scar types How do we retain information in 132 Chickenpox
How different scar types form our heads? How harmful can it really be?
94 The immune system 110 White blood cells 133 Why do we cry?
Combating viruses How infection is fought The different types of tears
98 Healing bone fractures 112 The science of genetics 134 The other senses
How broken bones are mended How genes define who we are The ones you didn’t know about
074
114
DNA
explored
© Alamy
126
The role of
hormones
102 135
The cell cycle Why do
we cry?
© Thinkstock
“The cell damage © DK Images 128 © Corbis
from viruses
causes diseases” Tracheotomy
surgery
075
THE BODY AT WORK
SleepThe science of
Unravelling the mysteries behind insomnia, sleepwalking, dreams and more
We spend around a third of our lives There have been many ideas and theories
sleeping. It is vital to our survival, but proposed about why humans sleep, from a way to
despite years of research, scientists still rest after the day’s activities or a method for saving
aren’t entirely sure why we do it. The urge to sleep is energy, to simply a way to fill time until we can be
all-consuming, and if we are deprived of it, we will doing something useful. But all of these ideas are
eventually slip into slumber even if the situation is somewhat flawed. The body repairs itself just as well
life-threatening. when we are sitting quietly, we only save around 100
calories a night by sleeping, and we wouldn’t need to
Sleep is common to mammals, birds and catch up on sleep during the day if it were just to fill
reptiles and has been conserved through evolution, empty time at night.
despite preventing us from performing tasks such as
eating, reproducing and raising young. It is as One of the major problems with sleep deprivation
important as food and, without it, rats will die is a resulting decline in cognitive ability – our brains
within two or three weeks – the same period it takes just don’t work properly without sleep. We will find
to die of starvation. ourselves struggling with memory, learning,
76
DID YOU KNOW? Marine mammals sleep with just half of their brain at a time, allowing them to surface for air
Theories of why we sleep
Energy
conservation
We save around 100 calories per night
by sleeping; metabolic rate drops, the
digestive system is less active, heart
and breathing rates slow, and body
temperature drops. However, the
calorie-saving equates to just one cup
of milk, which from an evolutionary
perspective does not seem worth the
accompanying vulnerability.
Restoration
One of the major problems with sleep
deprivation is a decline in cognitive
function, accompanied by a drop in
mood, and there is mounting evidence
that sleep is involved in restoring the
brain. However, there is little evidence
to suggest that the body undergoes
more repair during sleep compared to
rest or relaxation.
Evolutionary Memory
protection consolidation
An early idea about the purpose of sleep One of the strongest theories regarding
is that it is a protective adaptation to fill sleep is that it helps with consolidation
time. For example, prey animals with of memory. The brain is bombarded
night vision might sleep during the day to with more information during the day
than it is possible to remember, so sleep
avoid being spotted by predators.
However, this theory cannot explain is used to sort through this information
why sleep-deprived people fall asleep in and selectively practise parts that need
the middle of the day. to be stored.
planning and reasoning. A lack of sleep can have memories, such as learning to associate pairs of based, whereas REM sleep dreams are more vivid
severe effects on our mood and performance of words, can be seriously impaired. Deep sleep is and emotional.
everyday tasks, ranging from irritability, through to important for transferring short-term memories into
long term problems such as an increased risk of long-term storage. Deep sleep is also the time of peak Some scientists argue that REM sleep allows our
heart disease and even a higher incidence of road growth hormone release in the body, which is brains a safe place to practice dealing with situations
traffic accidents. important for cell reproduction and repair. or emotions that we might not encounter during our
daily lives. During REM sleep our muscles are
Sleep can be divided into two broad stages: The purpose of REM sleep is unclear, with the temporarily paralysed, preventing us acting out
non-rapid eye movement (NREM), and rapid eye effects of REM sleep deprivation proving less severe these emotions. Others think that it might be a way
movement (REM) sleep. The vast majority of our than NREM deprivation; for the first two weeks to unlearn memories, or to process unwanted
sleep (around 75 to 80 per cent) is NREM, humans report little in the way of ill effects. REM feelings or emotions. Each of these ideas has its
characterised by electrical patterns in the brain sleep is the period during the night when we have flaws, and no one knows the real answer.
known as ‘sleep spindles’ and high, slow delta our most vivid dreams, but people dream during
waves. This is the time when we sleep the deepest. both NREM and REM sleep. One curiosity is that Over the next few pages we will delve into the
Without NREM sleep, our ability to form declarative during NREM sleep, dreams tend to be more concept- science of sleep and attempt to make sense of the
mysteries of the sleeping brain.
77
THE BODY AT WORK
The sleep cycle
During the night, you cycle through five separate stages of sleep every 90 to 110 minutes
The five stages of sleep can be distinguished by then by two stages of deep sleep. Your brain activity like wakefulness, and you enter rapid eye movement
changes in the electrical activity in your brain, starts to slow down, your breathing, heart rate and (REM) sleep – the time when your most vivid dreams
measured by electroencephalogram (EEG). The first temperature drop, and you become progressively occur. This cycle happens several times throughout
stage begins with drowsiness as you drift in and out more difficult to wake up. Finally, your brain perks the night, and each time, the period of REM sleep
of consciousness, and is followed by light sleep and up again, resuming activity that looks much more grows longer.
Growth How much 30% 20%
hormone time is spent Other
release REM sleep
stages
After you fall asleep, 50%
the pituitary gland in each sleep Stage 2
ramps up its stage? sleep
production of
growth hormone. Low temperature
Body temperature falls just
before you fall asleep, and is
maintained at a lower level
throughout the night.
Limited
movement
Muscle tone drops
during sleep, but you
still change position,
tossing and turning.
Different when Slow breathing
dreaming
As you fall into deeper and
During REM sleep, your deeper sleep, your breathing
heart rate rises, but your becomes slower and more rhythmic
larger muscles are and your heart rate drops.
paralysed. This mean just
your fingers, toes and eyes
twitch as you dream.
Stages of sleep
Not all sleep is the same. There are five separate stages, divided by brain activity
JFKRQBP
JFKRQBP
JFKRQBP
1 Drowsiness 2 Light sleep 3 Moderate sleep
During the first stage of sleep you are just drifting off; After a few minutes, your brain activity slows further, As you start to enter this third stage, your sleep
your eyelids are heavy and your head starts to drop. and you descend into light sleep. On the EEG monitor, spindles stop, showing that your brain has entered
During this drowsy period, you are easily woken and this stage is characterised by further slowing in the moderate sleep. This is then followed by deep sleep.
your brain is still quite active. The electrical activity on waves, with an increase in their size and short one- or The trace on the EEG slows still further as your brain
an electroencephalogram (EEG) monitor starts to slow two-second bursts of activity known as ‘sleep produces delta waves with occasional spikes of
down, and the cortical waves become taller and spindles’. By the time you are in the second phase of smaller, faster waves in between. As you progress
spikier. As the sleep cycle repeats during the night, you sleep, your eyes stop moving, but you can still be through stage-three sleep, you become much more
re-enter this drowsy half-awake, half-asleep stage. woken quite easily. difficult to wake up.
78
DID YOU KNOW? Sleeping in at the weekends causes ‘social jet lag’ and makes it more difficult to get up on Monday morning
WAKE Dreaming versus deep sleep
REM
First Second Third Fourth Fifth
STAGE 1 cycle cycle cycle cycle cycle
STAGE 2
STAGE 3 Deep sleep Dreaming (REM)
STAGE 4
Clearing Brain activity
the mind
Wide awake Deep sleep
The brain is a power-hungry organ; it
makes up only two per cent of the total The red areas in this scan During the later stages of
mass of the body, but it uses an show areas of activity in the NREM sleep, the brain is less
enormous 25 per cent of the total waking human brain, while active, shown here by the
energy supply. The question is, how the blue areas represent
does it get rid of waste? The areas of inactivity. cool blue and purple colours
Nedergaard Lab at the University of that dominate the scan.
Rochester in New York thinks
sleep might be a time to clean the REM (dream) sleep Light sleep
brain. The rest of the body relies
on the lymphatic drainage When dreaming, the In the first stages of NREM
system to help remove waste human brain shows a lot of sleep, the brain is less active
products, but the brain is a activity, displaying similar than when awake, but you
protected area, and these vessels red patterns of activity to remain alert and easy to
do not extend upward into the the waking brain. wake up.
head. Instead, your central
nervous system is bathed in a
JFKRQBP
clear liquid called cerebrospinal
fluid (CSF), into which waste can be
dissolved for removal. During the
day, it remains on the outside, but
the lab’s research has shown that,
during sleep, gaps open up between
brain cells and the fluid rushes in,
following paths along the outside of
blood vessels, sweeping through
every corner of the brain and helping to
clear out toxic molecules.
JFKRQBP
4 Deep sleep 5 REM sleep Sleep deprivation NREM sleep © Science Photo Library; Alamy; Thinkstock
There is some debate as to whether sleep stages three After deep sleep, your brain starts to perk up and its The sleep-deprived brain As you descend through the
and four are really separate, or whether they are part electrical activity starts to resemble the waking brain. looks similar to the brain four stages of NREM sleep,
of the same phase of sleep. Stage four is the deepest This is the period of the night when most dreams during NREM sleep, showing your brain becomes
stage of all, and during this time you are extremely happen. Your muscles are temporarily paralysed, and patterns of inactivity. progressively less active.
hard to wake. The EEG shows tall, slow waves known your eyes dart around, giving it the name rapid eye
as delta waves; your muscles will relax and your movement (REM) sleep. You cycle through the stages of
breathing becomes slow and rhythmic, which can lead sleep about every 90 minutes, experiencing between
to snoring. three and five dream periods each night.
79
THE BODY AT WORK
Sleep Sleepwalking Sleepwalkers can perform complicated
actions while in deep NREM sleep
disorders Sleepwalking affects between one
and 15 per cent of the population,
There are over 100 different and is much more common in
disorders that can get in the way children than in adults, tending to
of a good night’s sleep happen less and less after the age
of 11 or 12. Sleepwalkers might just
Sleep is necessary for our health, so disruptions to sit up in their bed, but can
the quality or quantity of our sleep can have a sometimes perform complex
serious negative impact on daily life, affecting both behaviours, such as walking,
physical health and mental wellbeing. getting dressed, cooking, or even
driving a car. Although
Sleep disorders fall into four main categories: sleepwalkers seem to be acting
difficulty falling asleep, difficulty staying awake, out their dreams, sleepwalking
trouble sticking to a regular sleep pattern and tends to occur during the
abnormal sleep behaviours. Struggling with falling deep-sleep phase of NREM sleep
asleep or staying asleep is known as insomnia, and and not during REM sleep.
is one of the most familiar sleep disorders; around a
third of the population will experience it during Sleep apnoea protective response, pulling the sufferer out of
their lifetime. Difficulty staying awake, or deep sleep to protect them from damage. This can
hypersomnia, is less common. The best-known Sleep apnoea is a dangerous sleep disorder. It is cause people to wake up, but often it will just put
example is narcolepsy, which is when sufferers when the walls of the airways relax so much them into a different sleep stage, interrupting their
experience excessive daytime sleepiness, during the night that breathing is interrupted for rest and causing feelings of tiredness the next day.
accompanied by uncontrollable short periods of ten seconds or more, restricting the supply of
sleep during the day. Trouble sticking to a regular oxygen to the brain. The lack of oxygen initiates a
sleeping pattern can either be caused by external
disruption to normal day-to-day rhythms, for Loud breathing Waking up Lack of oxygen
example by jet lag or shift work. It can also be the
result of an internal problem with the part of the People suffering with sleep apnoea The low oxygen level in the blood If the airway is obstructed for
brain responsible for setting the body clock. often snore, gasp and breathe triggers the brain to wake up in an ten seconds or more, the
loudly as they struggle for air attempt to fix the obstruction. amount of oxygen reaching
Abnormal sleep behaviours include problems during the night. the brain drops.
like night terrors, sleepwalking and REM-sleep
behaviour disorder. Night terrors and sleepwalking Muscle collapse
most commonly affect children, and tend to resolve
themselves with age, but other sleep behaviours The muscles supporting
persist into adulthood. In REM-sleep behaviour the tongue, tonsils and
disorder, the normal muscle paralysis that soft palate relax during
accompanies dreaming fails, and people begin to sleep, causing the throat
act out their dreams. to narrow.
Treatment for different sleep disorders varies
depending on the particular problem, and can be as
simple as making the bedroom environment more
conducive to restful sleep.
“Treatment for
different sleep
disorders varies”
A continuous Risk factors Reduced airflow Warning signs
positive airway
pressure (CPAP) Sleep apnoea is much more Soft-tissue collapse reduces the amount People may not know they have sleep
machine pumps common in patients who are of air entering the lungs or obstructing apnoea, but warning signs include
air into a overweight, male and over the airways completely. daytime sleepiness, headaches and
close-fitting the age of 40. Smoking, night sweats.
mask, alcohol and sleeping pills also
preventing the increase the risk.
airway from
collapsing
80
DID YOU KNOW? After 24 sleepless hours your cognition is at the same level as a person with a blood alcohol content of 0.10%
Narcolepsy People with narcolepsy fall Insomnia
asleep involuntarily
Narcolepsy is a chronic condition during the day Insomniacs have difficulty falling
that causes people to suddenly fall asleep or staying asleep. Sufferers can
asleep during the daytime. In the wake up during the night, wake up
United States, it affects one in every unusually early in the morning, and
3,000 people. Narcoleptics report report feeling tired and drained
excessive daytime sleepiness, during the day. Stress is thought to be
accompanied by a lack of energy one of the major causes of this sleep
and impaired ability to concentrate. disruption, but it is also associated
They fall asleep involuntarily for with mental health problems like
periods lasting just a few seconds at depression, anxiety and psychosis,
a time, and some can continue to and with underlying medical
perform tasks such as writing, conditions ranging from lung
walking, or even driving during problems to hormone imbalances.
these microsleeps. In 70 per cent of After underlying causes have been
cases, narcolepsy is accompanied ruled out, management of insomnia
by cataplexy, where the muscles go generally involves improving ‘sleep
limp and become difficult to control. hygiene’ by sticking to regular sleep
It has been linked to low levels of the patterns, avoiding caffeine in the
neurotransmitter hypocretin, evening and keeping the bedroom
which is responsible for promoting free from light and noise at night.
wakefulness in the brain.
Sleep studies One in three people in the UK will © BSIP SA / Alamy
experience insomnia in their lifetime
The most common type of sleep
study is a polysomnogram (PSG), Electrodes monitor brain activity,
which is an overnight test eye movement, heart rate and
performed in a specialist sleep breathing in sleep studies
facility. Electrodes are placed on the
chin, scalp and eyelids to monitor 81
brain activity and eye movement,
while pads are placed on the chest
to track heart rate and breathing.
Blood pressure is also monitored
throughout the night, and the
amount of oxygen in the
bloodstream can be tracked using a
device worn on the finger. The
equipment monitors how long it
takes a patient to fall asleep, and
then to follow their brains and
bodies as they move through each
of the five sleep stages.
THE BODY AT WORK
How to get a good night’s sleep
Understanding your biological clock is the key
to a healthy night’s sleep
Your body is driven by an internal late at night can confuse your The blue light from televisions, mobile phones and
circadian master clock known as brain, preventing the production of computer screens disrupts your circadian rhythm
the suprachiasmatic nucleus, melatonin and delaying your sleep.
which is set on a time scale of
roughly 24 hours. This biological Ensuring you see sunlight in the
clock is set by sunlight; blue light morning can help to keep your
hits special receptors in your eyes, circadian clock in line, and sticking
which feed back to the master to a regular sleep schedule, even at
clock and on to the pineal gland. the weekends, helps to keep this
This suppresses the production of rhythm regular.
the sleep hormone melatonin and
tells your brain that it is time to Another important factor in a
wake up. good night’s sleep is winding
down before bed. Stimulants like
Disruptions in light exposure can caffeine and nicotine keep your
play havoc with your sleep, so it is brain alert and can seriously
important to ensure that your disrupt your sleep. Even
bedroom is as dark as possible. depressants like alcohol can have
Many electronic devices produce a negative effect; even though it
enough light to reset your biological calms the brain, it interferes with
clock, and using backlit screens normal sleep cycles, preventing
proper deep and REM sleep.
The dangers of sleep deprivation
Lack of sleep doesn’t just make you tired – it can have dangerous unseen effects
1 IMPAIRED JUDGEMENT 2 WEIGHT GAIN 3 RAISED BLOOD PRESSURE
Sleep deprivation impacts your visual working Sleep deprivation affects the levels of hormones Poor sleep can raise blood pressure, and in the long
memory, making it hard to distinguish between involved in regulating appetite. Levels of leptin (the term is associated with an increased risk of diseases
relevant and irrelevant stimuli, affecting emotional hormone that tells you how much stored fat you have) such as coronary heart disease and stroke. This danger
intelligence, behaviour and stress management. drop, and levels of the hunger hormone ghrelin rise. is increased in people with sleep apnoea.
4 INCREASED ACCIDENTS 5 MOOD DISORDERS 6 HALLUCINATIONS
In the USA it is estimated that 100,000 road accidents Mental health problems are linked to sleep disorders, Severe sleep deprivation can lead to hallucinations –
each year are the result of driver fatigue, and over a and sleep deprivation can play havoc with seeing things that aren’t really there. In rare cases , it
third of drivers have admitted to falling asleep behind neurotransmitters in the brain, mimicking the can lead to temporary psychosis or symptoms that
the wheel. symptoms of depression, anxiety and mania. resemble paranoid schizophrenia.
82
DID YOU KNOW? Sleep deprivation was found to have played a significant role in the nuclear meltdown at Chernobyl in 1986
Sleep myths debunked SLEEP STATS
The science behind five of the most common myths What are the most common
relating to sleep sleeping positions?
“Counting sheep 41% 15% 13%
helps you sleep”
Foetus Log Yearner
This myth was put to the test by the University of Oxford,
who challenged insomniacs to either count sheep,
imagine a relaxing scene, or do nothing as they tried to
fall asleep. When they imagined a relaxing scene, the
participants fell asleep an average of 20
minutes earlier than when they tried
either of the other two methods.
“Yawning 8% 7% 5%
wakes you up”
Soldier Freefaller Starfish
Yawning has long been associated with
tiredness and was fabled to provide more How does 16 hours
oxygen to a sleepy brain, but this is not the sleep time vary
case. New research suggests that we actually with age? INFANTS
yawn to cool our brains down, using a deep
intake of breath to keep the brain running at 9 hours
its optimal temperature. 7 hours TEENS
ADULTS
“Teenagers What keeps the
are lazy” UK up at night?
Sleep habits start to change just before puberty, 67% 36% 13% 34% 19%
and between the ages of ten and 25, people need
around nine hours of sleep every night. Teens can Discomfort Noise Partner Temperature Light
also experience a shift in their circadian rhythm,
called sleep phase delay, pushing back their Which country UK
natural bedtime by around two hours, and sleeps the longest?
encouraging them to sleep in. 6h49
Canada
“You should never wake
a sleepwalker” 7h03
Many people have heard that waking a sleepwalker might kill USA Japan
them, but there is little truth behind these tales. Waking a
sleepwalker can leave them confused and disorientated, but 6h31 6h22
the act of sleepwalking in itself can be much more dangerous.
Gently guiding a sleepwalker back to their bed is Mexico Germany
the safest option, but waking them carefully
shouldn’t do any harm. 7h06 7h01
“Cheese gives What do Other © Thinkstock; Dreamstime
you nightmares” people
dream 14%
The British Cheese Board conducted a study in an about?
attempt to debunk this myth by feeding 20g (0.7oz) of Sex
cheese to 200 volunteers every night for a week and Sadness,
asking them to record their dreams. There were no apprehension, 1%
nightmares, but strangely 75 per cent of men and 85 per anger
cent of the women who ate Stilton reported vivid dreams.
65%
Happiness
& excitement
20%
83
THE BODY AT WORK
What is the blood-
brain barrier?
How does this gateway control the molecules
that pass from the blood into the brain
The blood-brain barrier (BBB) is an Breaking down the barrier Lipophilic
essential group of cells that line the
blood vessels in the central nervous This built-in gateway is the main line of Substances rich in
system (brain and spinal cord). They allow defence for the central nervous system lipids can diffuse
passage of materials between the clear fluid across the barrier
surrounding the brain (cerebrospinal fluid) Just passing through
and the red blood cells in arteries, veins and with relative ease.
capillaries. The key advantage of having such a Some ions are transported
barrier is that it prevents large micro- out of the blood cells and A tight squeeze
organisms passing into the brain and causing into the astrocytes, and then
infections. While infections in other areas are out of the astrocytes and The tiny gaps between
common (such as after a cut finger, or mild into neurons in the brain. cells regulate the size
chest infections), those affecting the brain are
much rarer. However when they do occur (eg Astrocyte and type of particle that
meningitis), they are potentially life are able to fit through.
threatening as they are very difficult to treat. These numerous
star-shaped cells provide
The tight junctions between cells regulate biochemical support to the
the size and type of particle that pass between endothelial cells, and also
them, including oxygen molecules, carbon play an important role in
dioxide molecules, nutrients and hormones. transportation and repair.
Since it’s so effective, it also stops medications
from entering the brain (such as certain
antibiotics), so while they are effective in the
rest of the body, they are ineffective in this
vital organ. Overcoming this is a major aim of
doctors in the next decade, and the battle has
already started. Manipulating the blood-brain
barrier’s natural transport mechanisms and
delivering drugs within nanoparticles to
squeeze through the tight junctions are just
two examples of the modern techniques that
are under development.
Crossing the BBB Special transport © Thinkstock; SPL
The endothelial lining of the blood-brain barrier Active and passive
loves lipids (fatty molecules), but it hates transporters across this
particles with high electrical charges (ions) and membrane can overcome
large substances. Thus the ideal substance is some of these problems,
small, rich in lipids and has a low electrical and be manipulated to
charge. Barbiturates are such an example, as they deliver medications to
freely flow across the blood-brain barrier to the correct place.
suppress brain function; they act as sedatives and
antidepressants. However this free movement Highly charged
comes with risks – too much of it will accumulate
and slow the brain to a point where you can lose Highly charged ions are
consciousness and even stop breathing. repelled, meaning that
some medications are
ineffective in the brain.
84
DID YOU KNOW? In fish, the intermediate lobe controls skin colour change, while birds have no intermediate lobe at all
Pituitary gland up close
What does this hormone factory do and why couldn’t we live without it?
The pea-sized pituitary gland is found at The master gland in context
the base of the brain, close to the
hypothalamus. It looks a relatively Where does this vitally important hormone
insignificant part of the brain, but it plays a role manufacturer sit within the human brain?
in many vital systems.
Hypothalamus
Often referred to as the ‘master gland’, it not
only releases hormones that control various The secretion of hormones
functions, but it also prompts the activity of from the pituitary gland is
other glands like the ovaries and testes. directly controlled by this
part of the brain, which
The pituitary gland comprises three sections links the nervous and
called lobes: the anterior, the posterior and the endocrine systems.
intermediate – the latter of which is considered
part of the anterior lobe in humans. These work Pituitary stalk
together with the hypothalamus, which
monitors hormones in the blood and stimulates This is what connects
the pituitary gland to produce/release the the pituitary lobes to
appropriate hormone(s) if levels fall too low. the hypothalamus.
The anterior lobe produces seven important Posterior lobe
hormones, which include those that regulate
growth and reproduction. Adrenocorticotropic This doesn’t produce any
hormone (ACTH) targets the adrenal glands to hormones itself, but
produce cortisol and controls metabolism, stores and releases some,
while luteinising hormone triggers ovulation in like ADH, made elsewhere
women and stimulates testosterone production in the hypothalamus.
in men. The posterior lobe, meanwhile, doesn’t
generate any hormones itself, but stores two: Capillaries
antidiuretic hormone (ADH), which decreases
urine production by making the kidneys return Hormones are exchanged
more water to the blood, and oxytocin, which between the anterior lobe
tells the uterus to contract during childbirth and the hypothalamus via
and also prompts milk production. a network of capillaries.
Gigantism in focus Anterior lobe Thyroid
The pituitary gland also produces growth Subdivided into three One of the largest
hormone, which in adults controls the amount parts, including the thin endocrine glands that
of muscle and fat in the body and plays a key intermediate lobe, this regulates metabolism
role in the immune system. In children, of produces seven kinds is in turn regulated by
course, growth hormone has a very noticeable of hormone which each the pituitary gland.
effect in increasing height and bulk until target specific organs.
adulthood. However, sometimes the pituitary
gland becomes hyperactive – often as a result of © Alamy
a benign tumour – and produces excess growth
hormone. In these cases, a person can grow to a
far-beyond-average height, with hands, feet and
facial features growing proportionally. While this
might not seem so bad, gigantism is nearly
always accompanied by other health issues,
such as skeletal problems, severe headaches
and more life-threatening conditions like heart
disorders. If diagnosed early, treatment such as
drugs that inhibit growth hormone production
and surgical removal of the tumour can help
avert the more serious conditions of gigantism.
85
THE BODY AT WORK
Human
digestion
How does food get Large intestine Rectum
turned into energy?
The colon, as the large This is where waste
The digestive system is a group of organs that process intestine is also known, is material (faeces) exits
food into energy that the human body where waste material will the digestive system.
can use to operate. It is an immensely complex be stored until expelled
system that stretches all the way between the mouth and from the digestive system
the anus. through the rectum.
Primary organs that make up the system are the Small intestine
mouth, oesophagus, stomach, small intestine, large
intestine and the anus. Each organ has a different function so Nutrients that have been
that the maximum amount of energy is gained from the food, released from food are
and the waste can be safely expelled from the body. absorbed into the blood
Secondary organs, such as the liver, pancreas and gall stream so they can be
bladder, aid the digestive process alongside mucosa cells, transported to where they are
which line all hollow organs and produce a secretion which needed in the body through
helps the food pass smoothly through them. Muscle the small intestine wall.
contractions called peristalsis also help to push the food Further breaking down occurs
throughout the system. here with enzymes from the
liver and pancreas.
The whole digestive process starts when food is taken into
the body through the mouth. Mastication (chewing) breaks How
down the food into smaller pieces and saliva starts to break your
starch in these pieces of food into simpler sugars as they are body
swallowed and move into the oesophagus. Once the food has digests
passed through the oesophagus, it passes into the stomach. food
It can be stored in the stomach for up to four hours.
Many different organs
The stomach will eventually mix the food with the are involved in the
digestive juices that it produces, which will break down the digestion process
food further into simpler molecules. These molecules then
move into the small intestine slowly, where the final stage of
chemical breakdown occurs through exposure to juices and
enzymes released from the pancreas, liver and glands in the
small intestine. All the nutrients are then absorbed through
the intestinal walls and transported around the body
through the blood stream.
After all nutrients have been absorbed from food
through the small intestine, resulting waste material,
including fibre and old mucosa cells, is then pushed into
the large intestine where it will remain until expelled by a
bowel movement.
“Nutrients are then
absorbed through the
intestinal walls and
transported around
the body”
86
DID YOU KNOW? The human digestive system is between 20 to 30 feet long!
Mouth How does our
stomach work?
This is where food enters the body and first gets broken into
more manageable pieces. Saliva is produced in the glands
and starts to break down starch in the food.
Oesophagus Oesophageal © DK Images The stomach is one of the most crucial
sphincter organs within the digestive system
The oesophagus passes the food
into the stomach. At this stage, it This is the control
has been broken down through valve for letting food
mastication and saliva will be into the stomach.
breaking down starch.
Corpus body
The stomach’s function is to break down food
This is where stomach into simple molecules before it moves into
acid is situated, the small intestine where nutrients are
consequently it is
where food is broken absorbed. The organ actually splits into four
down into molecules distinct parts, all of which have different
that the small intestine functions. The uppermost section is the
can then process.
cardia, where food is first stored, the fundus
Mucosa is the area above the corpus body, which
makes up the main area of the stomach
These cells line all of the
stomach to aid movement of where food is mixed with stomach acid. The
final section is the antrum, containing the
food throughout the organ. pyloric sphincter, which is in control of
emptying the stomach contents into the
small intestine. Food is passed down into the
stomach by mucosa and peristalsis through
the oesophageal sphincter, and then mixed
in the stomach with acids and juices by
muscle contractions.
Stomach Duodenum How the
intestine works
This is where food is broken The area at the top of the
down to smaller molecules small intestine, this is
which can then be passed into where most chemical
the small intestine. Stomach breakdown occurs.
acid and enzymes produced
by the stomach aid this.
Rectum The intestine is a crucial
part of the digestive
This is where
waste is stored system that is heavily
involved in breaking
briefly until it down and absorbing
is expelled by nutrients released from
the body. ingested food
Villi © DK Images The intestine splits into two distinct parts,
the small intestine and the large intestine.
These cells are shaped like fingers The small intestine is where the food goes
and line the small intestine to increase
surface area for nutrient absorption. through final stages of digestion and
nutrients are absorbed into the blood stream,
the large intestine is where waste is stored
until expelled through the anus. Both the
small and large intestines can be further
divided into sections, the duodenum,
jejunum and ileum are the three distinct
sections of the small intestine and the
cecum, colon and rectum are the sections of
the large intestine. As well as storing waste,
the large intestine removes water and salt
from the waste before it is expelled. Muscle
contractions and mucosa are essential for the
intestine to work properly, and we see a
variation of mucosa, called villi, present in
the lower intestine.
87
THE BODY AT WORK
What causes High altitude sickness can have a
altitude sickness? severe physical effect on the
human body. Descending to
lower altitudes is the only way to
ease symptoms
Discover the effects that dizzying heights can have on
the human body
Adventurous explorers can spend months In order to compensate, your heart rate will
training prior to scaling mountain peaks, but increase and the body will produce more red blood
regardless of fitness level, high altitudes can cells, making it easier to transport oxygen around
take its toll on the human body. the body.
Between around 1,524 and 3,505 metres (5,000 and The low humidity levels at high altitude can also
11,500 feet) above sea level is considered ‘high cause moisture in the skin and lungs to evaporate
altitude’. At this level, most travellers will start to feel quicker, so dehydration is a real threat. Your face,
the effects of high altitude sickness as they attempt legs and feet may start to swell as the body attempts
to acclimatise to the change in atmosphere that to retain fluid by holding more water and sodium in
happens at this height. the kidneys.
The most common symptom is shortness of Difficulty sleeping is also common, and symptoms
breath, which is due to a lack of atmospheric of high altitude sickness can get progressively worse
pressure. At these heights, air molecules are the higher you climb, including mood changes,
more dispersed, so less oxygen can be inhaled. headaches, dizziness, nausea and loss of appetite.
How does a synapse work?
Dendrite Neuron Neurotransmitter molecules
As well as a long extension The ‘sending’ nerve cell When the nerve signal reaches the synapse, it
called the axon, each neuron contains a nucleus, which is converted into neurotransmitters, which are
has multiple branch-like holds the cell’s genes and
extensions called dendrites, controls its functions. the chemicals that bind to the receptor nerve
which take in nerve messages cell, causing an electrical impulse.
from other neurons. Axon
Vesicle
The nerve signals travel in
one direction along the axon This is the tiny membrane that stores
to the synaptic knob at the neurotransmitter molecules. The vesicles travel
end of the axon. from the sending neuron to the synapse, where
Nerve impulse they fuse with the presynaptic membrane and
release the neurotransmitters.
A nerve impulse is initiated
when a stimulus (change in Ions
the internal or external
environment) alters the The flow of these charged
electrical properties of the particles is the basis of
neuron membranes. the propagation of a
nerve impulse.
Trillions of neurons carry messages around Presynaptic © DK Images
the body, but how do they pass them on? membrane Ongoing message
Synaptic cleft
The nervous system involves a complex collection of nerve cells called Postsynaptic Once the neurotransmitters
neurons. Nerve messages can travel along individual neurons as membrane cross the gap between the two
electrical nerve impulses caused by the movement of lots of electrically neurons, ion channels in the
charged ion particles. In order to cross the minuscule gaps between two The cell membranes of receiving neuron open allowing
neurons, the nerve message must be converted into a chemical message the sending neuron the positive ions to flow into the
capable of jumping the gap. These tiny gaps between neurons are called (presynaptic membrane) receiving neuron.
synapses, forming the main contact zone between two neurons. Each neuron and the receiving neuron
consists of a cell body and branching structures known as axons and (post-synaptic
dendrites. Dendrites are responsible for taking information in via receptors, membrane) are separated
while axons transmit information away by passing electrical signals across the by a fluid-filled gap called
synapse from one neuron to another. the synaptic cleft.
88
Adrenaline Medulla Cortex
Discover the science behind your body’s At the core of the At the edge of the adrenal gland, the
amazing chemical coping mechanism adrenal gland, the cortex produces steroid hormones that
adrenal medulla include cortisol (for balancing blood sugar
produces, stores and and carb metabolism) and aldosterone
releases adrenaline. (for balancing the body’s salts and water).
Nestling on a layer of fat located as adrenaline. Identified in 1900, Kidney
just above each of your adrenaline is a fast-acting hormone
kidneys are the body’s that helps the body deal with The organ that
adrenal glands. Around 8cm long, unexpected stresses – not to mention filters waste
the adrenal glands produce high levels of excitement – by upping
hormones that affect your body’s your heart rate and the flow of blood from the blood.
consumption of energy as well as to your muscles.
your stress responses. Fat
The effect of this is that your blood
Adrenal glands consist of two main vessels and air passages dilate, Each adrenal
layers of hormone-secreting cells: the meaning that more blood passes to gland is protected
outer cortex and the inner medulla. the muscles and more oxygen gets to
While the cortex produces energy- the lungs quicker, temporarily by a layer of fat.
balancing hormones, the medulla improving the body’s physical
produces a chemical called performance and potentially saving
epinephrine, which we know better your life.
“Adrenaline is a fast-acting Your
hormone that helps the adrenal glands
body deal with stresses”
89
THE BODY AT WORK
Human
respiration
Respiration is crucial to an organism’s survival. The
process of respiration is the transportation of oxygen
from the air that surrounds us into the tissue cells of
our body so that energy can be broken down
The primary organs used for the heart rate to ensure that oxygen 1. Nasal passage/
respiration in humans are the reaches tissues that need it. Oxygen is oral cavity
lungs. Humans have two then used to break down glucose to
lungs, with the left lung being divided provide energy for the body. This These areas are where air
into two lobes and the right into happens in the mitochondria of cells. enters into the body so that
three. Lungs have between 300–500 Carbon dioxide is one of the waste oxygen can be transported into
million alveoli, which is where gas products of this, which is why we get and around the body to where
exchange occurs. a build up of this gas in our body that it’s needed. Carbon dioxide
needs to be transported back into the also exits through these areas.
Respiration of oxygen breaks into lungs to be exhaled.
four main stages: ventilation,
pulmonary gas exchange, gas The body can also respire
transportation and peripheral gas anaerobically, but this produces far
exchange. Each stage is crucial in less energy and instead of producing
getting oxygen to the body’s tissue, co2 as a byproduct, lactic acid is
and removing carbon dioxide. produced. The body then takes time
Ventilation and gas transportation to break this down after exertion has
need energy to occur, as the finished as the body has a so-called
diaphragm and the heart are used to oxygen debt.
facilitate these actions, whereas gas
exchanging is passive. As air is drawn 5. Alveoli
into the lungs at a rate of between
10-20 breaths per minute while The alveoli are tiny little sacs which are situated
resting, through either your mouth or at the end of tubes inside the lungs and are in
nose by diaphragm contraction, and direct contact with blood. Oxygen and carbon
travels through the pharynx, then the dioxide transfer to and from the blood stream
larynx, down the trachea, and into through the alveoli.
one of the two main bronchial tubes.
Mucus and cilia keep the lungs clean Pulmonary How our
by catching dirt particles and artery lungs work
sweeping them up the trachea.
Pulmonary Lungs are the major
When air reaches the lungs, oxygen vein respiratory organ in humans
is diffused into the bloodstream
through the alveoli and carbon Capillary beds
dioxide is diffused from the blood
into the lungs to be exhaled. Diffusion
of gases occurs because of differing
pressures in the lungs and blood. This
is also the same when oxygen
diffuses into tissue around the body.
When blood has been oxygenated by
the lungs, it is transferred around the
body to where it is most needed in the
bloodstream. If the body is
exercising, the breathing rate
increases and, consequently, so does
90
DID YOU KNOW? Trained free-divers can hold their breath underwater for up to nine minutes
2. Pharynx How do we breathe? Chest cavity
This is part of both The intake of oxygen into the body is complex This is the space that
the respiratory and is protected by the
digestive system. A flap Breathing is not something that we have to the alveoli at the ends, which are the final
of connective tissue think about, and indeed is controlled by muscle branching. The chest will be seen to rise ribs, where the lungs
called the epiglottis contractions in our body. Breathing is because of this lung expansion. Alveoli are and heart are
closes over the trachea controlled by the diaphragm, which contracts surrounded by blood vessels, and oxygen and
to stop choking when and expands on a regular, constant basis. carbon dioxide are then interchanged at this situated. The space
an individual takes food When it contracts, the diaphragm pulls air into point between the lungs and the blood. Carbon changes as the
into their body. dioxide removed from the blood stream
the lungs by a vacuum-like effect. The lungs and air that was breathed in but not diaphragm moves.
3. Trachea expand to fill the enlarged chest cavity used is then expelled from the
and air is pulled right through lungs by diaphragm expansion.
Air is pulled into the maze of tubes that Lungs deflate back to a reduced
the body through make up the size when breathing out.
the nasal passages lungs to
and then passes into
the trachea.
4. Bronchial tubes Lungs © DK Images
These tubes lead to either the © DK Images Deoxygenated blood Rib cage
left or the right lung. Air passes arrives back at the
through these tubes into the lungs, where another This is the bone
lungs, where they pass gas exchange occurs at structure which
through progressively smaller the alveoli. Carbon protects the organs.
and smaller tubes until they dioxide is removed and The rib cage can
reach the alveoli. oxygen is placed back move slightly to
into the blood.
6. Ribs allow for lung
Diaphragm expansion.
These provide protection
for the lungs and other This is a sheet of muscle situated
internal organs situated at the bottom of the rib cage
in the chest cavity. which contracts and expands to
draw air into the lungs.
© DK Images
Heart
The heart pumps oxygenated
blood away from the lungs,
around the body to tissue,
where oxygen is needed to
break down glucose
into a usable form
of energy.
Tissue
Oxygen arrives
where energy is
needed, and a gas
exchange of
oxygen and carbon
dioxide occurs so
that aerobic
respiration can
occur within cells.
Why do we need oxygen?
We need oxygen to live as it is crucial for the release
of energy within the body
Although we can release energy through more than a few minutes, an individual will die.
anaerobic respiration temporarily, this method Oxygen is pumped around the body to be used
is inefficient and creates an oxygen debt that in cells that need to break down glucose so that
the body must repay after excess exercise or energy is provided for the tissue. The equation
exertion has ceased. If oxygen supply is cut off for that illustrates this is:
C6H12O6+6O2 = 6CO2+6H2O + energy
91
THE BODY AT WORK
Pore Skin
Sweat is Once the sweat is on the skin’s
released directly surface, its absorbed moisture
into the dermis
via the secretary evaporates, transferring the
duct, which then heat into the atmosphere.
© Science Photo Libraryfilters through
© DK Imagesthe skin’s pores
to the surface.
Beads of sweat from the pores in
human skin, taken with a
scanning electron microscope
Why do we sweat?
As your doctor may tell you, it’s glandular…
Sweat is produced by dedicated sweat glands, a salty, water-based substance to the skin’s surface. Secretary Secretary part Nerve fibres
and is a mechanism used primarily by the This liquid then cools the skin and the body duct
body to reduce its internal temperature. through evaporation, storing and then transferring This is where the Deliver messages to
There are two types of sweat gland in the human excess heat into the atmosphere. Secreted sweat
body, the eccrine gland and the apocrine gland. majority of the gland’s glands to produce
The former regulates body temperature, and is the Both the eccrine and apocrine sweat glands travels up to the
primary source of excreted sweat, with the latter only appear in mammals and, if active over secretary cells can sweat when the body
only secreting under emotional stresses, rather the majority of the animal’s body, act as the skin via this duct.
than those involved with body dehydration. primary thermoregulatory device. Certain be located. temperature rises.
mammals such as dogs, cats and sheep only
Eccrine sweat glands are controlled by the have eccrine glands in specific areas – such as paws
sympathetic nervous system and, when the and lips – warranting the need to pant to control
internal temperature of the body rises, they secrete their temperature.
Dehydration Dangers of dehydration
What happens if we don’t How does a lack of water vary from mild to fatal?
drink enough?
1% Mild Thirst is triggered by a
Just by breathing, sweating and sugar levels going haywire. 2% Moderate concentration of particles
and urinating, the average Enzymatic activity is slowed, toxins in the blood, indicating a
person loses ten cups of accumulate more easily and your need to hydrate.
water a day. With H2O making up breathing can even become more
as much as 75 per cent of our difficult as the lungs are having to Other symptoms
body, dehydration is a frequent work harder.
risk. Water is integral in maintaining 3% Dizziness Dry skin at this level
our systems and it performs Babies and the elderly are most Headaches
limitless functions. susceptible as their bodies are not as include fatigue, a
resilient as others. It has been
Essentially, dehydration strikes recommended to have eight glasses dry mouth and
when your body takes in less fluid of water or two litres a day. More
than it loses. The mineral balance in recent research is undecided as to 4% constipation.
your body becomes upset with salt how much is exactly needed.
5% Severe Fever Racing pulse Lack of sweat
Dehydration levels 6%
Dehydration is Other symptoms
7% now so severe include sunken eyes,
that IV fluid low blood pressure
Too much H O? replacement and dark urine.
2
8% is necessary.
Hydration is all about finding the perfect
balance. Too much hydration can be 9% Fatal Delirium Loss of Here symptoms
harmful as well as too little; this is 10% consciousness become much more
known as water intoxication. If too 11% ? extreme and
much liquid is in your body, nutrients 12% cognitive abilities
such as electrolytes and sodium are may also suffer.
diluted and the body suffers. Your cells
bloat and expand and can even burst, Risk of heat exhaustion or
and it can be fatal if untreated. The best heat stroke is prevalent
treatment is to take on IV fluids and can even be fatal.
containing electrolytes.
92
DID YOU KNOW? There are lots of products on the market to help reduce the appearance of scars
Why does skin scar?
Scars are made up of the same proteins as normal skin, so why
do they look so different?
Scars are a natural part of the healing form. The most common is a flat scar – these tend to surrounding skin, and are hard, shiny and hairless.
process, with most of us having some form of initially be dark and raised, but will fade and flatten The reason behind why keloids form is poorly
them on our body. The reason why scars look over time as the scar matures. A hypertrophic scar understood, but it is known that people with darker
different compared to normal skin stems from their can be identified by its red appearance and elevated skin tones are more likely to form keloids.
proteins’ composition. nature. This scar type typically forms when the
dermis is damaged, and this can become itchy and Pitted scars are generally formed from acne or
Normal skin benefits from a weaved protein painful over time. chicken pox, and tend to be numerous in areas
structure, whereas the proteins in scars are aligned where these conditions were prevalent. Scar
in one direction. This results in a different Keloid scars are by far the most extreme scar type contractures, meanwhile, usually form after a burn,
appearance compared to normal, healthy skin. Scars when compared to the others. Unlike most scars, and are caused by the skin shrinking and tightening.
are smoother due to a lack of sweat glands and hair they extend beyond the confines of the original The severity of these kinds of scars can depend on
follicles, so they can often become itchy. There are injury and are formed due to excessive scar tissue their bodily location; if they form around a joint they
also a number of different types of scar that can being produced. Keloid scars are raised above the can lead to movement being restricted.
Clotting Epithelial cells Newly formed scar
Clotting occurs due to a combination of By rapidly multiplying, the Once the newly formed epithelium
proteins in the blood, which help a scab to epithelial cells fill in over the thickens, the area contracts and forms
form, protecting the wound from infection. newly formed granulation tissue. a scar on the skin’s surface.
illustration by Nicholas Forder
Inflammatory chemicals White blood cells Granulation tissue Scar tissue
The body recognises that it has sustained To help fight off potential The new granulation tissue Once fully formed, this tissue is known as scar
an injury, and white blood cells release infection, white blood cells replaces the clotted blood, and tissue. Due to excessive collagen production this
inflammatory chemicals to help protect seep into the area and flock helps restore the blood supply to tissue often lacks in flexibility, which can lead to pain
the area. to the wound. the damaged area. and dysfunction.
Can scars be treated? This can be used to change the shape of the scar, however A neat, even scar is the best
there is a risk of worsened scarring if unsuccessful. you can hope for even with
Scars cannot be stopped from forming, but there are today’s technology
various treatments available to help reduce their There are also certain steps that can be taken to help
appearance. Silicone gels or sheets have been shown to reduce the risk of an unsightly scar forming from an © Dreamstime
effectively minimise scar formation and are often used injury. By cleaning dirt and dead tissue away from the
when people have been burnt. These must be applied or wound, you are increasing the chance that the scar will
worn throughout the scar’s maturation phase to maximise form neatly. It is also vital that you don’t pick or scratch the
their efficacy. Corticosteroid injections can be used to scar, as this will slow down its formation, resulting in a
reduce any inflammation (swelling) around the scar and to more obvious appearance.
flatten it as well. A riskier treatment for scars is surgery.
93
THE BODY AT WORK
How your immune
system works
Your body is locked in a constant Physical
war against a viscous army defences
Human anatomy subscribes to the notion
that good fences make good neighbours.
Your skin, made up of tightly packed cells
and an antibacterial oil coating, keeps
most pathogens from ever setting foot in
body. Your body’s openings are well-
fortified too. Pathogens that you inhale
face a wall of mucus-covered membranes
in your respiratory tract, optimised to
trap germs. Pathogens that you digest end
up soaking in a bath of potent stomach
acid. Tears flush pathogens out of your
eyes, dousing bacteria with a harsh
enzyme for good measure.
It’s true: while you’re sitting around watching TV, replicate inside them; and fungi, a type of plant life. teeming with these microscopic intruders...
trillions of foreign invaders are launching a full Bacteria and viruses are by far the very worst including you. The bacteria in your stomach alone
scale assault on the trillions of cells that outnumber all the cells in your body, ten-to-one.
constitute ‘you’. Collectively known as pathogens, offenders. Dangerous bacteria release toxins in the Yet, your scrappy microscopic soldiers usually win
these attackers include bacteria, single-celled body that cause diseases such as E. coli, anthrax, the day against pathogens, through a combination
creatures that live to eat and reproduce; protists, and the black plague. The cell damage from viruses of sturdy barriers, brute force, and superior
larger single-cell organisms; viruses, packets of causes measles, the flu and the common cold, battlefield intelligence, collectively dubbed the
genetic information that take over host cells and among numerous other diseases. immune system.
Just about everything in our environment is
94
DID YOU KNOW? Dr Karl Landsteiner first identified the major human blood groups – A, B, AB and O – in 1901
The adaptive immune system
Fighting the good fight, and white blood cells are 2. Bacterium antigen
right on the front line…
These distinctive molecules allow your
immune system to recognise that the
When a pathogen is tough, wily, either disarm a specific 4. Engulfed bacterium is something other than a body cell.
or numerous enough to survive pathogen or bind to it, marking it bacterium
non-specific defences, it’s up to as a target for other white blood 3. Macrophage 1. Bacterium
the adaptive immune system to cells. When T-cells find their During the initial
clean up the mess. The key forces target, they lock on and release These white blood Any bacteria that enter
in the adaptive immune system toxic chemicals that will destroy inflammation reaction, cells engulf and digest your body have
are white blood cells called it. T-cells are especially adept at
a macrophage engulfs any pathogens they characteristic antigens
come across. on their surface.
the bacterium.
lymphocytes. Unlike their destroying your body’s cells that
macrophage cousins, are infected with a virus.
lymphocytes are engineered to This entire process takes
attack only one specific type of several days to get going and
pathogen. There are two types of may take even longer to
lymphocytes: B-cells and T-cells. conclude. All the while, the
These cells join the action raging battle can make you feel
when macrophages pass along terrible. Fortunately, the
information about the invading immune system is engineered to
pathogen, through chemical learn from the past. While your
messages called interleukins. body is producing new B-cells
After engulfing a pathogen, a and T-cells to fight the 7. Non-
macrophage communicates pathogens, it also produces matching B-cells
details about the pathogen’s memory cells – copies of the
antigens – telltale molecules that B-cells and T-cells, which stay in Other B-cells, engineered to
characterise a particular the system after the pathogen is
pathogen. Based on this defeated. The next time that attack other pathogens,
don’t recognise the antigen.
information, the immune pathogen shows up in your body, 5. Presented
system identifies specific B-cells these memory cells help launch bacterium antigen
and T-cells equipped to a counter-attack much more
recognise and battle the quickly. Your body can wipe out After engulfing the bacterium, the
macrophage ‘presents’ the
pathogen. Once they are the invaders before any infection bacterium’s distinctive antigens,
successfully identified, these takes hold. In other words, you communicating the presence of
cells rapidly reproduce, develop immunity. the specific pathogen to B-cells.
assembling an army of cells that Vaccines accomplish the same 6. Matching B-cell 9. Memory cell
are ready and equipped to take thing by giving you just enough
down the attacker. pathogen exposure for you to The specific B-cell that The matching B-cell also
develop memory cells, but not recognises the antigen, and replicates to produce
The B-cells flood your body enough to make you sick. can help defeat the pathogen,
with antibodies, molecules that receives the message. memory cells, which will
rapidly produce copies of
Non-specific itself if the specific
defences bacteria ever returns.
As good as your physical defence system is, pathogens How B-cells
do creep past it regularly. Your body initially responds attack
with counterattacks known as non-specific defences,
so named because they don’t target a specific type B-cells target and
destroy specificbacteria
and other invaders
of pathogen.
After a breech – bacteria rushing in through a cut, for 11. Phagocyte
example – cells release chemicals called inflammatory
mediators. This triggers the chief non-specific defence, White blood cells
known as inflammation. Within minutes of a breach, called phagocytes
recognise the antibody
your blood vessels dilate, allowing blood and other fluid marker, engulf the
to flow into the tissue around the cut. bacteria, and
The rush of fluid in inflammation carries various types digest them.
of white blood cells, which get to work destroying 10. Antibodies 8. Plasma cell
intruders. The biggest and toughest of the bunch are
macrophages, white blood cells with an insatiable The plasma cells release The matching B-cell
appetite for foreign particles. When a macrophage detects antibodies, which replicates itself,
a bacterium’s telltale chemical trail, it grabs the intruder, disable the bacteria by
engulfs it, takes it apart with chemical enzymes, and latching on to their
antigens. The antibodies
also mark the bacteria
spits out the indigestible parts. A single macrophage can for destruction. creating many
swallow up about 100 bacteria before its own digestive plasma cells to fight
chemicals destroy it from within. all the bacteria of this
type in the body.
95
THE BODY AT WORK
Your tonsils can help 1. Tonsils
fight bacteria
Lymphoid tissue loaded with
lymphocytes, which attack
bacteria that get into the body
through your nose or mouth.
© Klem 2007
© Ed Uthman, MD
2. Left subclavian vein
One of two large veins that serve
as the re-entry point for lymph
returning to the bloodstream.
Disorders of 3. Right lymphatic duct 6. Lymph
the immune node cluster
system Passageway leading from lymph vessels
to the right subclavian vein. Located along lymph vessels
Who watches the throughout the body, lymph nodes
watchmen? 4. Right subclavian vein filter lymph as it makes its way back
The immune system is a powerful set of The second of the two subclavian into the bloodstream.
defences, so when it malfunctions, it veins, this one taking the opposite
can do as much harm as a disease. path to its twin. 7. Left
Allergies are the result of an lymphatic duct
overzealous immune system. In 5. Spleen
response to something relatively Passageway leading from
benign, like pollen, the immune system An organ that houses white lymph vessels to the left
triggers excessive measures to expel the blood cells that attack subclavian vein.
pathogen. On the extreme end, allergies pathogens in the
may cause anaphylactic shock, a body’s bloodstream. 8. Thymus gland
potentially deadly drop in blood
pressure, sometimes accompanied by 10. Lymph vessels Organ that provides area for
breathing difficulty and loss of lymphocytes produced by bone
consciousness. In autoimmune Lymph collects in tiny capillaries,
disorders such as rheumatoid arthritis, which expand into larger vessels. marrow to mature into
the immune system fails to recognise Skeletal muscles move lymph specialised T-cells.
the body’s own cells and attacks them. through these vessels, back into
the bloodstream. 9. Thoracic duct
The The largest lymph vessel
lymphatic in the body.
system
11. Peyer’s patch
In an allergic reaction, the body may resort to The lymphatic system is a network of © DK Images
sneezing to expel a fairly harmless pathogen organs and vessels that collects lymph Nodules of lymphoid tissue supporting
– fluid that has drained from the white blood cells that battle pathogens
bloodstream into bodily tissues – and
returns it to your bloodstream. It also in the intestinal tract.
plays a key role in your immune
system, filtering pathogens from 12. Bone marrow
lymph and providing a home-base for
disease-fighting lymphocytes. The site of all white blood
cell production.
Lymph
nodes
explained
Lymph nodes
filter out
pathogens moving
through your
lymph vessels
Your immune system depends
on these .04-1-inch swellings
to fight all manner of
pathogens. As lymph makes
its way through a network of
fibres in the node, white blood
cells filter it, destroying any
pathogens they find.
96
DID YOU KNOW? In 2008, approximately 33 million people worldwide were living with HIV or AIDS
3. Capsule 1. Flagella Know your
enemy:
Protects the Flagella swish
inner contents for movement Bacteria
6. Cell wall 2. Pili Bacteria are the smallest and, by far, the most populous form of
life on Earth. Right now, there are trillions of the single-celled
Provides structural The pili anchor to creatures crawling on and in you. In fact, they constitute about
integrity cell surfaces four pounds of your total body weight. To the left is a look at
bacteria anatomy…
7. Cell membrane
4. Nucleoid What is HIV…
The cell’s interior barrier
The nucleoid contains … and how does it affect the
genetic material immune system?
8. Cytoplasm The human immunodeficiency virus (HIV) is a retrovirus (a
virus carrying ribonucleic acid, or RNA as it’s known),
5. Ribosomes Home of all material transmitted through bodily fluids. Like other deadly
outside the nucleoid viruses, HIV invades cells and multiplies rapidly inside.
These help with protein Specifically, HIV infects cells with CD4 molecules on their
surface, which includes infection-fighting helper T-cells.
HIV destroys the host cell, and the virus copies go on to
infect other cells. As the virus destroys helper T-cells, it
steadily weakens the immune system. If enough T-cells are
lost, the body becomes highly susceptible to a range of
infections, a condition known as acquired immune
deficiency syndrome (AIDS).
manufacturing
Bacteria
anatomyInsidethese
microorganisms
1 3 Major points of the lymph node
2 4
1. Outgoing lymph 7. Sinus
11 5
10 6 vessel A channel that slows the
flow of lymph, giving
9 7 The vessel that carries macrophages the
filtered lymph out of the opportunity to destroy any
88 lymph node detected pathogens Scanning electron micrograph of HIV-1 budding (in green) from
cultured lymphocyte. This image has been coloured to highlight the
8 2. Valve 8. Incoming lymph most important features. Multiple round bumps on the cell surface
represent sites of assembly and budding of virions.
A structure that prevents vessel
lymph from flowing back
into the lymph node A vessel that carries lymph
into the lymph node
3. Vein
9. Lymphocyte
Passageway for blood
leaving the lymph node The T-cells, B-cells and
natural killer cells that
4. Artery fight infection
Supply of incoming blood 10. Germinal centre
for the lymph node
This is the site of
5. Reticular fibres lymphocyte multiplication
and maturation
Divides the lymph node
into individual cells 11. Macrophage
6. Capsule Large white blood cells that
engulf and destroy any
The protective, shielding detected pathogens
fibres that surround the
lymph node
97
THE BODY AT WORK
Bone fracture
healing process
Learn how your body mends broken bones
If a bone has too much pressure put on it, or is hit together, like a bridge being constructed from All-star cast
or landed on in a particular way, there is a either side of a river until both ends meet in
chance it will break. Your body has ways of the middle. Most breaks on an arm or a leg will have a plaster
repairing these breaks, but it takes time and care. cast put on them to prevent the bone from
There are different kinds of break, ranging from a Once both sections of bone are connected again, setting at a wonky angle or not setting at all.
hairline fracture to a fully shattered bone, but they specialised cells called osteoblasts enter to
all mend in a similar way. produce bone cells. These new cells replace the It will generally be made from plaster of Paris.
callus, returning the bone to its original shape. This is a mixture of water and gypsum that sets
As a bone breaks, the blood vessels are also really hard once it has dried. The broken bone is
severed. Blood leaks out and forms a clot called a Much like repairing a broken toy with glue, bandaged and the wet mixture is applied to the
fracture haematoma. This stops blood flow to the the bone needs to be kept straight and steady gauze. Once it has dried then it should provide
area and also helps keep both pieces of bone for the fusion to happen correctly. This is why safety and stability for the bone.
aligned, ready for healing. doctors will put a cast on the broken bone. The
cast provides essential support, protection Fibreglass is an increasingly common cast
The body then makes fibrous cells and and stability, ensuring the broken bone doesn’t material. As with the plaster cast, the broken
cartilage, which reinforce the bond and strengthen move. A cast will generally stay on for a few bone is bandaged up. Next, another bandage,
it. This creates a callus, which is essentially a weeks until the bond has become strong enough, made of fibreglass and layered with resin, is
weakened bone. Over time, the callus builds up but it could take months for a properly set bone to soaked in water. This makes it flexible enough to
and the two parts of the bone gradually fuse fully recover. be wrapped around the bone before it hardens as
it dries. This is much lighter than a plaster cast
and the outer layer is waterproof.
The stages of bone repair
Blood Marrow New Healed
clot blood fracture
forms Internal callus vessels
(fibrous tissue
and cartilage)
Ruptured Hard
blood bone
vessels callus
External Blood flow
callus improves
Blood clot Tissue growth Remodelling © Thinkstock
When a bone breaks, the blood vessels A few days later, the blood clot – called the fracture Bone-forming cells called osteoblasts work in
that run through the bone are severed. haematoma – is gradually replaced by tougher teams to build a new bone, creating a more solid
The blood forms a clot to align the bones. tissue, which becomes a soft callus. Fibrous tissue structure called a hard bone callus. It takes
This creates a solid yet weak structure to and cartilage are produced that begin to bridge the several months to fill the cavity with harder bone,
prepare for mending. The clot also cuts off gap between the fractured ends. New blood vessels strengthened by nutrients like calcium and
blood flow to the edges of the broken bone, begin to form and the callus usually lasts around phosphorus. However, it may take longer for the
so these cells die. three weeks. bone to be completely healed.
98
DID YOU KNOW? Around half of your body’s ‘non-water’ mass is made up of proteins
1. Cell Protein production
The body is made up of millions Protein is generated in the nucleus of a cell using genetic
of cells, none of which could coding information held within our DNA. To produce
survive without protein, for
repair and replacement. protein, DNA unravels to allow messenger RNA (or mRNA) to
copy it and form a template. This template is translated by
ribosomes into amino acids, which then line up to form a
protein. Parts of DNA code will
serve as punctuation, telling
the ribosome when to start
and stop, and some parts
will instruct the cell how
frequently it must produce
the specific protein.
6. mRNA 7. Ribosome 5. DNA
This type of genetic acid This is the ‘protein-making DNA (deoxyribonucleic
forms a template based on machine’ in the cell. It uses acid) holds the information
DNA sequences, which is mRNA templates to synthesise
then used to produce amino the specific protein needed. necessary for amino acid
acids by the ribosome. – and ultimately protein
– production in the letter
sequence in its structure.
9. Protein 8. Amino acid 4. Nucleosomes
Proteins are made up of long chains of These small molecules These are balls formed of
amino acids. Each protein has a specific combine in specific string DNA strands and histones
function which suits its role and is sequences to generate the (spool-like proteins) which
crucial to our bodies being able to different types of protein.
operate effectively. sit inside chromosomes.
2. Nucleus 3. Chromosome Why are © SPL
amino acids
This is the control centre of Most human cells have a set of important?
the cell where all important 46 chromosomes and these
genetic data is stored. Amino acids are vital to
contain our genetic information our bodies being able to
which, among other things, operate as they are the
building blocks of
instructs the cell which protein proteins. Each type of
to make and also how. amino acid performs a
different job, which aids
How do we make protein? protein activity in the
body and determines the
Proteins are the building blocks of the human body, protein’s primary
but how do we go about manufacturing them? function(s). Without these,
proteins would not be
Proteins are large complex molecules made up of a chain and T) and these short sequences, which are known as triplets able to help the body with
of amino acids. Every cell in our body needs protein to or codons, then code mRNA templates; these templates are movement, defence
stay alive as it is necessary for tissue repair and ‘translated’ by cell ribosomes into amino acids. against disease,
replacing dead cells. processing food or
Each protein is made up of hundreds of thousands of amino co-ordinating general
They have many other functions as well as aiding cell repair acids, which are in long chains. There are 20 different types of growth and development.
and production including forming antibodies to help fight off amino acid that can be combined to build a protein and it is the
disease, forming enzymes which speed up or trigger chemical sequence of amino acids that determines each protein’s unique There are nine
reactions and co-ordinating processes within the body (via three-dimensional structure and its function. essential amino acids for
hormone regulation, for instance). Proteins also provide humans that must be
support for cells and form structural elements of the body, such However, not all amino acids can be made by the body. The absorbed from external
as nails and teeth, as well as facilitating the transportation of ones that need to be consumed via our diet are called essential protein sources (eg meat/
some small molecules around various systems. amino acids. If possible, the body will also conserve energy by fish) as they cannot be
using amino acids from food rather than producing them itself. synthesised by the body.
We build proteins using information encoded in our genetic Protein deficiency can cause diseases such as kwashiorkor, a Without the required
code. DNA code utilises groups of three letters (a mix of A, G, C form of malnutrition common in poverty-stricken areas. amount of amino acids,
the body can really suffer.
99
THE BODY AT WORK
The cell cycle
Inside one of the body’s most vital processes
The continuous cycle of cell division and
growth is essential to all life on Earth.
Without it, no organism on the planet
would be able to reproduce or develop. The cell
cycle consists of three main stages: interphase,
mitosis and cytokinesis.
During interphase, the cell expands and
makes the new proteins and organelles it will
need for division. It then makes copies of its
chromosomes, doubling the amount of DNA in
the cell and ensuring the conditions are right to
begin the next phase.
In mitosis, the membrane surrounding the
nucleus breaks down, exposing the
chromosomes, which are pulled to opposite
sides of the cell by tiny spindle fibres. A new
nuclear envelope then forms around the
chromosomes at each end of the cell. During
cytokinesis the cytoplasm splits in half to create
two ‘daughter’ cells, each with their own
nucleus and organelles.
The cycle is managed by regulating enzymes
known as CDKs . These act as a checkpoint
between the phases of division, giving the
signal for the next stage in the cycle to begin.
The cell cycle of prokaryotic cells (those
without a nucleus) is slightly different. Bacteria
and other prokaryotes divide via a process
called binary fission, in which the cell
duplicates its genetic material before doubling
in size and splitting in two. Meiosis is another
type of cell division and is concerned with
sexual reproduction as opposed to the asexual
organic growth of tissue in mitosis.
Cancer and the cycle Cell duplication
If the cell cycle goes wrong, cancerous Explore the key stages of mitosis now
tumours are a possible consequence. It all
depends on the levels of proteins in the cycle. A Prophase Prometaphase Metaphase Anaphase
protein called p53 halts the process if DNA is
damaged. This provides time for the protein to Chromosomes The nuclear envelope In this phase, all the Now, the spindle fibres
repair the DNA as the cells are then killed off condense, becoming breaks down and spindle spindle fibres are pull the chromosomes
and the cycle begins anew. On the rare thicker and shorter. fibres extend from attached and the apart, with the
occasions this process fails, cells can Sister chromatids form either side of the cell to chromosomes are chromatids moving to
reproduce at a rapid rate and tumours can when the chromosomes attach to the middle of arranged in a line along opposite ends or ‘poles’
form. Chemo- and radiotherapy work by replicate themselves. each chromatid. the equator of the cell. of the cell.
destroying these mutated cells. A p53 mutation
is the most frequent one leading to cancer. An
extreme case is Li Fraumeni syndrome, where
a genetic defect in p53 leads to a high
frequency of cancer in those affected.
100
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