How It Works Book Of The Human Body

How epidurals work

The science behindblocking pain explained

What is a An epidural(meaning 'above 1. Epidural space 6. Processing
memory? the dura') is a form oflocal
anaesthetic used to The outer part of the Anaesthetic in the blood is filtered
Memory Is the brain's completely block pain while spinalcanal, this cavity is out by theliver and kidneys, then
a patient remains conscious. It involves typically about 7mm
t 9 ability torecaII the careful insertion ofa fine needle (0.8il1) wide in adults. leaves the body in urine. The effects
information from the past deep into an area ofthe spine between usually wear off a couple of hours
• and itgenerallyfalls Into two vertebrae ofthe lower back. 2. Epidural needle after the initial injection.
three categories- sensory, short-term This cavity is called the epidural
and long-term. space. Anaesthetic medication is After sterilising the area, a Bladder
injected into this cavity to relieve pain needle is inserted into the
Lookat this page then close your or numb an area ofthe body by reducing interspinous ligament until
eyes and try to remember what It sensation and blocking the nerve roots there is oo more
looks like. Your ability to reca II what that transmitsignals to the brain. resistance to the injection
this page looks like isan exampleof The resultinganaesthetic medication ol air or saline solution.
causesa warm feelingand numbness
yoursensorymemory. Dependingon leading to thearea beingfully
whetherornot this pageis Important anaesthetised afterabout20 minutes.
to you will be the determInlng factor Dependingon the length of the
in how likely illsthatit wlli get passed procedure, a top-up may berequired.
on toyourshort-term memory. This form of pain relief bas been used
widely for manyyears, particularly
Can you rememberthe last thing post-surgery and during childbirth.
youdid before reading thls?That is
your short-term memory and Is a bit 3. Anaesthetic ------..
like a temporary storage facility where
Through a fine catheter in the
the less-Importantstuffcan decay. needle, anaesthetic is carefully
whereas the moreImportantstuffcan introduced to the space
end up inthe long-term memory. surrounding the spinal dura.

Oursensesareconstantly belng M --"-- 4. Absorption 5. Radicular arteries
bombarded with Information.
Over about 20 minutes The anterior and posterior radicular
Electrical and chemical signals travel the anaesthetic arteries run with the ventraland
from our eyes, ears, nose, touch and medication is broken dorsal nerve roots, respectively,
tastereceptorsand thebrain then down and absorbed Into which are blocked by the drug.
makessenseoftheseslgnals. When the local fatty tissues.

we remembersomething, ourbrain How does toothpaste for
sensitive teeth work?
refiresthesame neural pathways
alongwhich theoriginal information Imaginejustoneofyour teeth. It has two thinner and they may havea recededgum line
travelled. You are almost reliving the primarysections: the crown locatedabove exposlngmoredentine. Therefore, the enameland
experience by remembering lt. the gum lineand the root below it. Tbe gumsoffer less protection and, assuch, this is what
crowncomprises the foUowinglayers from makes their teeth sensitive.

top to bottom: enamel. dentine and the pulp gum. Sensitive toothpaste works byeithernumbing tooth
Nerves branch from theroot to the pulp gum. Tbe sensitivity, or by blockingthe tubules in the dentine.
dentine runs ro therootand containsa large number of Thosethai numb usually contain potassium nitrate,
tubules or microscopicpores, which run from the which calms the nerve ofthe tooth.The toothpastes
that block tbe tubules in the dentine usually containa
outside of the tooth rightto the nerve in the pulpgum. chemicalcalledstrontiumchloride. Repeated use
People with sensitive teeth experience pain when builds up a strong barrier by pluggingthe tubules more
and more.
their teeth are exposed tosomething bot. cold orwhen
pressure is applied. Their layerof enamel may be

151

·ne I Blushing 1 Fointin Whyandhow
do we blush?
Red glow
Blushingoccurs when an excessof blood
Oled<s l1n1redwlile blushing flows Into the small blood vesselsjust
under the surfaceof the skin. Facial skin
ca.e to blood vesselsbeing near has more capillaryloops and vessels, and
vesselsare nearerthesurfaceso blushingis most
thesl<ns suface. visible on the cheeks, but may beseenacross the
whole face. Thesmall muscles in the vesselsare
Nervousness controlled by the nervous system.
Blushingcan beaffected by factorssuchasheat,
Being embarrassed releases illness, medicines, alcohol, spicyfoods, allergic
adrenaline, which stimulates reactions and emotions. Ifyou feelguilty, angry,
excited orembarrassed, you will involuntarily
the ne''"''" system. releaseadrena II ne, which sends the automatic
nervous system Into overdrive. Your breathingwUI
What makes , increase, heart rate quicken, pupilsdilate, blood will
be redl rected from your digestive system toyour
caffeine so --...___ muscles, and you blush because your blood vessels
dilate to Improve oxygen flow around the body; this
addictive? is all to prepare you for a Hght or flight situation.The
psychologyof blushing remains elusive; some
When we are awake the naturally scientistseven believe we have evolved to display
occurring brainchemicaladenosine ouremotions, toactasa publicapology.
is drawn to fastmoving receptors In
the brain. As adenosine attaches to "Blushing con
the receptors itslows them down, which causes us
to feel sleepy. be affected by
The receptor cellsconfusecaffeine for
adenosine cellsand as such willingly bond to lt. heat, illness,
Theaction doesn't slowdown the receptor's medicines and
spicy foods"
movement as adenosine would and as the spaceIs
usurped theyare unable to senseadenosl ne so the Fainting, or'syncope', is a
cellsspeed up, Increasingneuron firing in the temporary loss ofconsciousness
brain.The pltuarygland interprets thisas a fight due to a lack ofoxygen to the
or flightscenario so releases hormones to alert the brain. It Is preceded bydizziness,
adrenal glands to produceadrenaline. This results nausea, sweatingand blurred Vision.
In dilated pupils, a racing heartand an Increase In The most common cause is
blood pressure.The liveralso releasessugar Into overstlmulallon ofthe body's vagus nerve.
the bloodstream foran instantenergy boost. Possible triggers of this includeintense
stressand paIn, standing up for long pertods
or exposure to something unpleasant.
Severe coughing, exerclseand even
urinating can sometimes producea similar
response. Oversll mulation of the vagus
nerve results In dilation of the body's blood
vessels and a reduction of the heart rate.
These two changes together mean that the
bodystruggles to pump blood up to the
brainagal nstgravlry. Alack of blood to the
brain means there Is not enoughoxygenfor
it to funcllon properlyand fainting occurs.

152

LTea 2.lnstant 3. Ground
coffee
In a survey by the coffee
Food Standards Gr'ound coffee. however',
Agency. the mean The level of caffeine pl'esent contains the most c-affeine.
In instant coffee was oot
amount of caffeine The meanlevel was lOSmg.
fOIXld in too was much mote withanavefage
400>;1 percup. in SOI"'lecases tanglng as
of 54mg ot caffeine per
high as 254mg perserving.
fegular sef'Vlng.

What is Where is the self
earwax?
in the brain?
Earwax is a substance that can be
Until recently, neuroscientists had thought it
found in the earcanal ofhumans
and other mammals. Medicallyit fanciful to speculateabout the physicalsubstrates
ofsuch high-level phenomenaas consciousness
is referred to as cerumenand and 'the self', but recentadvances in functional
consists ofdead skin, hairand water-soluble neuroimagingareenabling us to makesignificantin-roads into
these questions. Researchers have identifieda core brain
secretions from the outerearcanal. ltserves
network, the 'default-mode network', which accounts for much
several functions - one ofwhich Is as an ofthe brain's metabolismand appears to supporta background
antibacterial, self-cleaning lubricant. Excess levelofconsciousness,of the sortassociated with day-
cerumen usuallyfinds its way outofthe ear dreaming or mind-wandering. Crucially, the default-mode
canal through the washing ofhair andjaw
network becomes especiallyactivated during self-judgments,
movement. Occasionallyitcancollectand get aswell as other high-level, species-specificbehaviourssuchas
taklnganotherperson's pointofview, or thinking outsideofthe
compacted whichcanlead to tinnitus. moment to contemplate the pastorfuture. The default-mode
network decreasesInactivityand connectivityduring statesof
Why do we have eyebrows?
reduced consciousnesssuch assleep oranaesthesia, and is
Eyebrowsare very importantfor diverting we weresweatinga lot ltis quite easy known to existonlyin a primitiveform In infantsand lower
primates. Using functional magnetic resonance imaging
moisture, suchas saltysweat, away from our to see how this could have had an (fMRI), we recentlyfound that the psychedelicdrug, psilocybin,
eyesdue to their distinctive arch shape. evolutionary advantage in terms of
escaping predators. Sweatalso causes the active component of'maglc mushrooms', also decreases
This would obviouslybe useful for irritation in the eyes. activityand connectivityin the default-mode network - in a
allowing us to see clearly ifit was raining or If manner that correlates with loss ofself, or'ego-disintegration'.

153

I

72-hour deodorants 1 Fillings

How 72-hour deodorants work

Discover the chemistry that helps us combat body odour for up to days at a time

Deodorants prevent Most deodorants also contain Antiperspirants cause cells
the odourassociated antiperspirants, which prevent
with sweating, either sweating from occurring at aLL to swell and the ducts to
by masking it, or by These are usually aluminium- close up, preventing
killing the bacteria responsible. To based compounds. Thealuminium sweating altogether
make the effects lastlonger, the is taken up by the cells that line the
active ingredientsare sometimes openings of the ducts that carry
encased within microcapsules. As sweat to the surface of the skin.
the capsules take up water from
sweat they burst, releasing As the aluminium moves into
deodorisingchemicals. By the cells, it takes water with it,
including capsules ofa varietyof causing the cells to swell and
sizes, each requiring a different closing off the ducts. Depending on
amount of water to burst, the the type ofaluminium compound
duration can be extended. used, the effect will last for
different lengths oftime.

odern fillings Is metal bad?

Composite resins are replacingtraditional Traditional silver-coloured 'amalgam' fillings are
metal fillings, but what are theymade of?
made from mixed metals, and are often
Curing - - - - - - - - - - - - - , . -- layering comprised ofaround 50 percent mercury.
Historical evidence suggests that this type of
!Aight is used to trigger a The liqlid composite resn is filling has been in use since around 650 A.D, and
applied in layers. Aftereacll despite the advances in composite materials, the
chemical reaction within layer, the composite is cased amalgam filling is still in use to this day.
the resil\ causing the
material to harden. Composite resin There has been much controversy over the
biological safety of amalgam fillings though, and
Finishing touches - - - - - - - - - , Dental composites are concerns have been raised regarding mercury
made from a resin matrix released into the body, as well as into the
Apiece of carbon paper is used containing ilorganic environment. However, as it stands, no causal
to test whether thebite lines materials, ll<e silica, for link between health complaints and amalgam
up properly, and the filling is durability. fillings has been proven. In fact, they still provide
smoothed down accordingly. some advantages over composite fillings, and
' - - - - -- Acid reQuire significantly less repair and replacement.
Primer - -------.J
Acontrolled amount of acid ~::::::::~::::::::::::::::::::~ ~
A priming agent is brushed is appled to thedrilled tooth
onto the prepared tooth togenerate mic~holes for
su1ace to enable the filing the filing to bind to.
to adhere properly.
' - - Base
Decay - -
In deeper filings, • cement
The decayed poi WIdthe base made fromglass

tooth isren MJ'IIed u:sng a iolo 11er orzh: phosphate IS
added to ns.Jate the nene
~IW;tNs
from lelo-ature changes.
generates a solid platform
for the filng to stick to.

154

STRANGE Who do you inherit Answer:
BUT TRUE mitochondria from?
The DNA within mltochoodr'la is only from youl'
INHERITED AT BIRTH A Father B Mother C Grandparent mothel''s egg. The corresponding DNA fl'om yout

father's sperm is destroyed aftel' fer-tlisatioo. This
means l'eseal'cherscao ttack back unchanged
maternal inheritance lines many b.Jndteds ofyears.

l•){•m!I!Il:i~~WJP Mitochondrial disease occurs when mitochondria malfunction - there is o huge variety ofsymptoms

at rs your •

Discover how mitochondria produce all the energyyour body needs

Mitochondria are knownas the maintain life- by controlling Krebs Cycle which They are deeply linked with evolution ofall
batteries ofcells because they use is the set of reactions that produce ATP.
food to make energy. Muscle fibres life. It is believed mitochondria formed over a
need energy for us to move and Mitochondriaare found in nearly everycell billion years ago from two different cells, where
brain cells need powerto communicatewith the in your body. They are found in most eukaryotic
rest of the body. Theygenerate energy, called cells, which have nucleus and otherorganelles the larger cell enveloped the other. The outer
adenosine triphosphate (ATP), by combining bound by a cell membrane. This means cells cell became dependent on the inner one for
without these features, such as red blood cells, energy, while the inner cell was reliant on the
oxygen with food molecules like glucose. don't contain mitochondria. Their numbers outer one for protection.
However, mitochondria are true biological also vary based on the individual cell types,
with high-energycells, like heart cells, This innercell evolved to become a
multi-taskers, as theyare also involved with containing many thousands. Mitochondriaare mitochondrion, and the outer cells evolved to
signalling between cells, cell growth and the vital for most life - human beings, animals and
cell cycle. Theyperform all of these functions by plants all have them, although bacteria don't. form building blocks for larger cell structures.
This process is known as the endosymbiotic
regulating metabolism -the processes that theory, which is Ancient Greek for 'living

together within.'

Inside the mitochondria ,... --- - - - - Phospholipid
bilayer
Take a t our of the cell's energy f actory
Every mitochondria has
ATP synthesis - - - - - - - - - - . . . . , a double-layered

ATP is the basic energy unit of the cell surface composed of
and is produced by ATP synthase phosphates and lipids.
enzymes on the inner membrane at its
interaction with the matrix. .---- Outer membrane

Mit ochondrial DNA - - The outer membrane contains
large gateway proteins, which
Mitochondria have their control passage of substances
own DNA and can divide to
pro'dlJ(:e copies. through the cell wall.

- - Inner membrane How many are e;
in a cell?
This layer contains the Q
key proteins that The numberofmitochondria in a
regulate energy cell depends on how active that
particular cell is and how much
production inside the energy it requires to function. As a
m itochondria, including
general rule, they can either be low
ATP synthase.
energy without a single
Inter-membrane mitochondrion, or high energy with
space thousands per cell. Examples of
high-energy cells are heart muscles
This contains proteins or the busy liver cells, which are
and ions that control activeeven when you're asleep,
and are packed with mitochondria
what is able to pass in to keep functioning. If you train
and out of the organelle your muscles at the gym, those
cells will develop more
via concentration mitochondria as an adaptive
gradientsand ion pumps.
mechanism to help provide energy.
- - - - - Cristae

The many folds ofthe
inner membrane

increase the surface
area, allowing greater
energy production for

high·activity cells.

:;-- - - - - - Matrix

The mitochondrial matrix
contains the enzymes, ribosomes

and DNA, which are essential to
allowing the complex energy-
producing reactions to occur.

155

ind reading

How can we view the brain?

Computed Magnetic n!SOflai1Ce Functional MRI (fMRO
~<en
ima!jng (MRO This formof MRJ uses blood-
ThlscomblnesmultlpleX-rays oxygen-level-dependent
MRI uses strong magnetic
to see the bones of tbeskull fields toalign lhe protons In (BOLD) contrast. followed bya
water molecules Invarious strong magneticfield, to detect
and soft tissue of tbe brain-It's body parts. When used In tinychanges In oxygen-rich
lhe most common scan used tbe braln, It allows lnlrlcale and oxygen-poor blood. By
afte.r trauma, to detect injuries anatomical detail to be showing pictures to lnvoke
to blood vessels and swelllng. visualised. It has formed the certainemotions, fMRI can
However, It can only givea baslsofnoveltechnlques to
snapshot of tbe structureso revealwhichareas are active
visualise thought processes.
can't captureour thoughts. durlngpartlculartboughts.

CTscan ' 2 . BRAIN 1\JMOURSj 3DMRI PET scan
el
Fast and easily accessible t"",· '• TheSI! 3Dscans show lntrlcato This functional imaging
24 hours a day, these a~ . anatomical details of b<aln
scans can identify ~. tumours, partk:ula~y In relotlon to isalowh) researchers
life-dveatering bleeding g ·'.~: . the SUf'T'OU"'dWlg stl\iCtwts. This
withW. the sku:Ufor enables doct01'5 to de\Ormlne W to test nO'oi'el drugsand

net.II'OSU'geon to stop. they ean bo safely removed 0< not treatments to preven1

train disorder.__progression of this

=::~=~~==~,..~~:lo~ous

l•ll•fil•IIH3~1•1Vd CT sconnrng of the brorn wos invented in the early-Seventies

Diffusion tensor Posibon emission Imag
inaging (0I I) •
tDmography (PE I)
This MRivarlant rel.leson the Alzheimer's disease isa potentially
direction ofwater diffusion This bleeding-edge technology debiUtatlng condition, which can lead
within tissue. Whena magnetic detectsgamma rays emitted to severe dementia. The ability to
gradient lsappUed. thewater from blologlcallyacttve tissues diagnoseitaccuratelyand earlyon has
alignsand. when t.befield Is basedonglurose.ltcan pick driven the need for modem imaging
removed. t.be wate.r dllluses up unusual biological activity, techniques. The above imageshowsa
according to a tissue's Internal suchas that from cancer.There PETscan.The right-hand sideof the
structure. Thlsallowsa)D bave been recent advances to Image (as you lookat it)showsa normal
romblne PET with CTor MRI to brain, with a good volume and activity
Image ofactivity to he built up. range. On the left-handsideisa patient
obtain lots of data quickly, affected by Alzheimer's. The brain is
shrunken with fewer folds, and a lower
range ofactivity- biologicallyspeaking,
there are far fewer neurons firing.

I

Anaesthesia

owanaest 1• awo

Byinterfering with nerve transmission these special drugs stop

pain signals from reaching the brain during operations - - - - - - - Memory

Anaestheticsare a form ofdrug widely The body under General anaesthetic affects
used to prevent painassociated with the ability to form memot ies;
surgery.They fall Into two main general anaesthetic
categories: localand general. Local the patientdoesnl remember
anaesthetics can bee!therappl!ed directly to the What happens to various parts of the operationand often woo'!
the body when we're put under?
recall coming to either.

skin orinjected. They are used to numb small areas Brain activity - - - - - ' Airway

without affecting consciousness,so the patient wi ll Electroencephalograms (EEGs) Loss ofconsciousness and
remain awake throughout a procedure. muscle relaxation suppress
show that the electrical
Local anaesthetics providea short-term blockade activity in the brain drops to a breathing and prevent
of nerve transmission, prevent! ngsensory neurons
from sending palnsignals to the bra! n. Information state deeperthan sleep, coughing, so a tube and
is transmitted along nerves by the movement of
sodium ions down a carefully mal ntalned mimicking a coma. ventilator areused to
electrochemicalgradient Localanaestheticscut maintain the airway.
offsodiumchannels, preventing the Ions from Nil by mouth - - - - - -
travelling through the membrane and stopping
electricalsignals travellingalong the nerve. Generalanaesthetics .._-ess
the gag reflex and cancause
Local anaesthesia isn'tspeciHcto pain nerves, soit
'«ll'l')jti~sotoprevent

cholcing pal:ieiots must not eat

beforeanopeatioo.

will also stop information passingfrom the brain to
tbe muscles, causing temporary paralysis.

Generalanaesthetics, meanwhile, are Inhaled Thecirruatory systEm is
and injected medications that act on the central slowed by anaesthetic, so
nervoussystem (brainand spinal cordi to Induce a heart rate, blood preSSlR
temporary coma, causing unconsciousness, muscle
relaxation, pain reliefand am nes!a. and blood oxygen areal

continuously monitored

It's not known for sure how general anaesthetics Pain neurons Many anaesthetics
'shut down· the brain, but thereareseveral proposed
mechanisms. Many general anaesthetics dissolve In Unlikewith local cause nausea. Often
fats and are thought to Interfere with the lipid antiemetic drugs that
membrane that surrounds nerve cells In the brain. anaesthetic, pain prevent V<miting are
They also disrupt neurotransmitter receptors, neurons still fire under given after su-ge<y.
altering transmission of the chemical signals that let generala naesthesia,
nerve cellscommunicatewith oneanother.
but the brain does
not process the
signals properly.

Comfortably numb

If large areas need to be anaesthetised while the Muscle relaxation ----~~
patient is still awake, local anaesthetics can be
A mJSde relaxa-lt isoften
injected around bundles of nerves. By preventing administeredwiththe
anaesthetic; thiscauses
transmission through a section of a large nerve, paralysis and enableslower
the signals from all of the smaller nerves that doses of anaesthe!ic to beused
feed into it can't reach the brain. For example,
injecting anaesthetic around the maxillary nerve
will not only generate numbness in the roof of
the mouth and aHof the teeth on that side, but
will stop nerve transmission from the nose and
sinuses too. local anaesthetics can also be
injected into the epidural space in the spinal
canal. This prevents nerve transmission through
the spinal roots, blocking the transmission of
information to the brain. The epidural procedure
is often used to mollify pain during childbirth.

158

2005

Stressand diet are blamed StOf'l'lach add Isproposed as TwoAustralian scientists The fii'St antibiotics ar~ Barty M..WII and Robin

for stomach ulcer'S.Patients the cause ofgastric ulcers .shov.l that HP)lfori causes approved fortreatment Warrenare awa(ded a
ate prescribed rest and of the infectionthat
bland food, like oatmeal and antacid treatment is stomach uk:ers, but some joint Nobel prize fOf'
introduced to countes-il ~sceptical to begin with. causes stomach ulcers. their 1982 discovery.

l•){•m!I!Il:i~~W.A'P The scientists who revealed bacteria caused gastric ulcers had to drink their own experiment to prove it!

causes stomach ulcers?

Originallythought to be the result ofstress, we now know that bacteria are the culprits...

Normallya th id< layer of An ulcer in the making Gastrin
alkaline mucus
effectively protects the Once bacteria breach the stomach lining, it can TheInflammatory
cellslining the stomach no longer protect itself from its acidic contents... responseIncreases
production ofthe
from the low pHofstomachacid. If Neutralising Helicobacter pylori hormonegastrin.This
this mucus becomesdisrupted, In tum stimulates the
however, add comes into contact stomach Bacteria burrow tbrougb the formation of more
with the organ'slining_ damaging mucusInthe stomach toescape
the cellsand resulting inan ulcer. acid ~--- Damage
damagebyadcL Theystlcktothe
Around 6o percentofstomach Hpylori break ceUsofthelnleriorUnlng. As the cellsbecome
ulcers are caused byinflammation damageda woundopens
due to chronicInfection by the downurea to upln !bestomachwall. If
bacteriumHelicobacter pylori. this becomes deepenough It
Bacterial by-products damage the makeammonia. can perforatebloodvessels
causingbleeding.
Thlslsusedto

produce ,-

bicarbonate to ~

neutralise

dangerous

stomach add.

cells lining thestomach, causinga

breakdownofthe top layers of tissue.

Non-steroidal anti -inflammatory

drugs (NSAIDs}, like ibuprofenand

aspirin, also causestomach ulcers in

large doses. They disrupt the

enzymes responsible for mucus

production, diminishing the

protective barrier.

Enzymes Theammonlamadeby
the bacteriaasa defence
Hpylori produceproteases againstadddamagesthe
cellslining !bestomach,
and phosphoUpases-
causing Inflammation.
enzymes thatdamage the
proteins and cell

membranes ofthe
stomach cells.

Why do we sometimes

get mouth ulcers?

Ulcers are smalllesions usually In othercases, recurrent ulcers may

triggered by physical damage to the be symptomatic of conditions
inside ofthe mouth, for example including812or iron deficiencies,
biting your cheel<accidentally, gastrointestinal diseases or
eatingsharp food or brushing your immunosuppressant diseases such
teeth. Theyare very rarely
as HIV. Ulcersare sometimes
contagiousand usually heal within triggered bysensitivity to certain
tendays. Recurrent ulcers have a foods includingstrawberries,
varietyofcauses, the most common almonds, tomatoes, cheese,
beingstress and hormonal changes.
chocolateand coffee.

~ "The.Y ore rarely contagious

i onousuol/y heal in ten days"

159

Why does blond
hair look darker
when it's wet?

Dry blond hair has a rough, Uledsurface - somethinglikefish
scales. When light rays hit these scales, they bounceoffin all
directions.Some ofthelight reachesyour eyesand makes the
hair look brighter; It's likeshininga torch on the hair.
When you wash your hair, a thin Him of water forms around each fibre.
Ught rays pass Into the film ofwater, bouncearound Inside, and there's
achance they'll get absorbed by the hair.Since the lightgets trapped
inside the water, less of It reachesyour eyes, so the hairactually appears
lot darker.

"A thtn film of water forms
around each fibre"

How quickly does
human ha·

Human hair grows onaverage 1.25 centimetres (0.5 inches)

t 9 permonth, which Isequivalent toabout15 centimetres
(six Inches) peryear. Thereare several variables that can
• affect hair'sgrowth rate suchas age, health and genetics.
Each hair grows In threestages, the first being the anagen phase
where mostgrowth occurs. The longeryour halrremalnsin this stage
dictates how longand quickly It develops; this can last between two

and eight years and Is followed by the catagen(transitional)and
telogen (resting) phases. Halrgrowth rates vary across differentareas
ofthe head, with that on the crowngrowing the fastest.

I "Each hair grows in three
stages, the first being the
onogen phose where most

growth occurs"

160

Correcting heart hms

How can a little electricity be used to fix a heart that's beating off-kilter?

rr - - - - - - 8. low energy 3. Timing the shock ~

ResettWlg anabo mal The heilrt iswherable when it
is between beats, so to prE'IIeOt
heart beat uses fairly
law-energy shocks ofjust a cardiac arrest, the shock is

50·200 joules. ti'ood to coincidewith the
pumping of the ventricles.
6. Natural pacemaker
4. Arrhythmia - --+.... BEFORE CARDIOVERSION
The hearthas i1S own internal
~the heart bealS too fast, or Atrial fibrillation
pacemaker known as the skloatrial at an irregular pace~ it
node. Delivering a small electric
shock to this resynchronises the becomes unable to
orgoo's natural electrical activity. effectively p~ blood
around the body.
5. Electric shocks
~ -- L Paddles
low-energy electric shocks
are deiM!red to the heilrt Two metalic plates are
tlvough the electrodes. placed on the patient's
chest across theheart.

AFTER CARDIOVERSION

7. Cardioversion A. ,..- A. ~
machine
2. Conductive gel NonnaiECG
The maciWle recoods the
A saltwateM>ased gel is electrical activity ofthe

used so the current can heilrt and calculates the
electric shocks reqund
triM!! from the elect1'0des
and tlvough the skln. to restore the orgoo to
its nonnal mytlm.

Why's salt Do women have
Adam's apple?
bad for
You may not realise, but actually everyone bas an
the heart?
t 9 Adam'sapple, butmen'sare usuallyeasiertoseein
Simply put, too much salt Is bad for their throat. It's a bump on the neck that moves
youasIt increases thedemand on • when you swallow, named after the biblical Adam
your heartto pump blood around the Supposedly, It'sa chunk of the Garden ofEden's forbidden fruit
body. This is because when you eat stuck in hisdescendants' throats, butit'sactuallya bump onthe
saltitcauses the body to retain thyroid carUiagesurroundlngthevoicebox. Thyroid cartilage is
Increased quantities of water, which shield-shaped and theAdam'sapple is the bitat the front.
increasesyour blood pressure, and
this places morestralnonyour heart. Whydo men'sAdam·sapplesstlck outmore?Tbls is partly
Assuch, most doctors recommend because they have bonier necks, but It isafso because their
moderating daUy salt intake. larynxes grow differently from women's during puberty to
accommodate their longer, thickervocal cords, wbicbgivetbem
deepervoices.

161

I

mbling stomach 1 Seasickness

ca

ab

Discover how the small Oesophagus
intestine is really to blame...
Thismuscular pipe

connectsthe throat
to thestomach.

Waves ol Involuntary muscle Stomach
contractions called peristalsischurn
the food we eat to soften It and rood Ischurnedand

transport It through the digestive mixedwith gastric
system.The contractionsare caused bystrong
muscles in the oesophagus wall, which takejust juices to help Itto
ten seconds to push food down to the stomach. breakdown.
Musclesin the stomach churn food and gastric
Smal intestine
juices to break it down further.
Then,aIter lour hours, the sem1-dlgested Here. liquidfood

liquefied food moves on to thesmall Intestine combinedwith trapped
where yet more powerful muscle contractions
gasescan makelorsome
force the food down through the Intestine's bends
and folds. This is where the rumblingoccurs. Air embarrassingnoises.
from gaseous foods or that swallowed when we eat
-oftendue to talking or Inhaling through the nose
while chewingfood- also ends up In the small

intestine, and it's this combinationof liquidand
gas in a smallspace that causes the gu rgling noise.

Rumbling is louder the less food presentIn the
small intestine, which Is partlywhy people

associate rumbling tummies with hunger. The
otherreason is that although the stomach may be
clear, the brain still triggers perlstaIsis at regular
intervals to rid the intestinesofany remaining
food. This createsa hollow feeling that causes you

to feel hungry.

"Then, after four Large intestine --;.-~.
hours, the semi-
digested liquefied roodpasses from the

smallIntestineto the

largelntesllnewbere

ItIs turned Into faeces.

food moves to the
small intestine"

Are seasickness and altitude
sickness the same thing?

No, they're not -altitudesicknessIs a collection signals'about a moving environment-for

ofsymptoms broughton when you're suddenly Instance, whenyour eyes tellyou thatyour

exposed to a high-altitude environmentwith lnunediatesurroundings(such as a ship's

lowerair pressureso lessoxygen enters our body. cabin) are still as a rock, whileyour sense of

Thesymptomscan includea headache, fatigue, balance(andyourstomachl)teUyousomething

d lzzi ness and nausea. quite different.

Seasickness, on the otherhallQ, Isa more Thlslsthereason wbyclosingyoureyesor
general feelingof nausea that's thought to be taking a turn outon deckwill often help, as it
causedwhen your brain and sensesget'mixed reconciles the two opposingsensations.

162

are

These small skin blemishes are
common, but what are they andwhy
must we keep a close eye on them?

Amole on the skl n, ora vigilant ifa new oneappears on the skin or "A malignant melanoma is o
melanocyticnaevus, !san Ifan existing mole begins to change. A rare k1nd of skin cancer that
abnormal collecllon ofthe malignant melanoma is a rare kindolskin con occur 1n melonocytes"
pigment cells called
cancer that canoccurin melanocytes.
melanocytes.Some moles can be presentat Although rare, malignant melanomas
birth (congenital melanocytlc naevi) but
most develop spontaneously later In life, cause the majority of the deaths related to
usually as a result ofexposure to sunlight. skincancer.llyou're partlcularlymoley
Molesare often brown or black(pigmented you're more susceptible to melanoma and
should try to avoid too muchsunlight.
naevl)andareusually round oroval, but
they can bea variety ordlllerentshapes Moles to watch are dysplastic naevi,
and sizes.Growth and change over tlme Is which are large, irregularly shaped moles
quite normal. of mixed colouration.They often have
paler, jaggededges with darker centres
Molessound pretty unremarkable and and tend to beaccompanied bya lot or
are harmless In natttre, and yet we must be
other moles on the body.

Melanocyte Hairs

The sldn's natur.11 Dipigla111nelelnt'lt, melanin, is a protein liarsare made from filamentous bicrnaterialthat
produce.d in eels caled melanocytes. Melanocytes
areusually spn>adevenly tlroughaut ll1e sldn for Epidermis
...,., colow. Melanin alsoabsorbs IN raciation.
Thisis the outer layerof
you' sldn anditcontar.s

lolJ!jl, flateels.
Melanocytesare
b::ated in the dellIMs

and epidermis.

•

MeJanoma Dennis

"""'*' with • farrily history ol The denuisis the layerthat
COIISisls of bloodwssels,
~melanomasand those who glands and"""""encings.

haYe beenexposed toa lot of Slright 163

aremost at risk from tl'is 1.11000 •trollable

!J'OWih ofP9nel 11 eels.

I f

rain control 1Laughing

Do we control our brains or
do our brains control us?

. An experimentat the Max Planck Institute, Berlin, in2008

t 9 showed that when you decide to move your hand, thedecision
can beseen In your brain, with an MRI scanner, before you are
• aware you have made a decision.The delay Isaround six
seconds. During that lime, your mind Is made up but yourconsciousness
doesn'tacknowledge the decision unUI your hand moves. One
interpretallon oflhlsIs that your consciousness- the thingyou think ofas
'you'-isjusta passengerinsidea deterministicautomaton. Your
unconsdous brain and your bodyget on with runnl ng yourltfe, and only
report back to your conscious mind to preservea sense offree wHI. But it's
justas valid to say that when you make a decision, there's always
background processinggoing on, which the conscious mind Ignores for
convenience. In the sa me way, your eye projectsan upside-down image
onto your retina, but your unconscious brain turns It the right way around.

we

Wsomhiechthminugsfculensllryeaanctdwwhheyniws e find

laughter so harcfto fake?

Laughing can pull the facial expression upward;
somellrnes be on top of this, the zygomaticus major
completely involuntary also pulls the upper lip upward

and involvesa complex and outward.

seriesof muscles, which is why It'sso The sound ofour laugh is

difficult to fake and also why an produced by the same mechanisms

active effort is required to suppress which are used for coughingand
laughterin moments ofsudden speaking: namely, the lungs and the
hilarity at inopportune moments. Ia rynx. When we're breathing
normally, air from the lungs passes
In the face, the zygomaticus major
and minoranchor at the cheekbones freely through the completely open

and stretch down towards thejaw to vocal cords In the larynx. When they

close, alrcannotpass, however
when they'repartlallyopen, they

generatesome form ofsound.

Laughter is the result when we

exhale while the vocal cords close,
with the respiratory muscles

perlodically activating to produce

the characteristicrhythmicsound

of laughing.

The risorius muscleis used to

smile, butaffects a smaller portion

of the face and iseasier to control
than the zygomatic muscles. As a

resu It, the risorius is more often

used to feign amusement, hence

why fake laughteriseasy to detect

byother humans.

"Laughter is produced by the some mechanisms

used for coughing ond speaking"

164

What is the maximum What is dandruff?

distance the hu DandruffIs when dead skin cellsfall offthe scalp. This
Is normal,asourskin Isalways being renewed. About
eye see? half the populatlon ofthe world suffers from an
excessiveamount of this shedding, which can be
Dust. water vapourand pollution In thealrw!ll rarelyletyouseemorelhan triggered by things like temperature or the increasedactivity ofa
20 kilometres, evenona clearday. Often, the curvatureofthe Earth gets in microorganism that normally lives In everyone'sskin, known as
the way first- egatsea level, the horl20n Is only 4-Bkmaway. On the top of Mt malassezla globosa. DandruffIs not contagiousand there are many
Everest. you could theoreticallysee for339km, bulln practice cloudgets In treatments available, the most common Isspecialisedshampoo.
the way. Fora truly unobstructed view, look up. Ona clear night, you cansee
the Andromeda galaxy with the naked eye, which Is2.25 million lightyears away.

Why do eyes

take a while to
adjust to dark?

At the backof the eyeon the retina, there
are two types ofphotoreceptors (cells
which detect light). Conesdeal with
colourand Hnedetallandactin bright
light, while rods deal with vision in low-light
situations. In the Hrst few minutes of moving intoa
dark room, conesare responsible for vision but
providea poor picture. Once the rods become more
active, they take overand createa much better
pictureIn poor llghLOnce you move backinto light
the rods are resetandso dark-adaption will take a
lew momentsagain. Soldiersare trained to closeor
coverone eyeat night when moving in and outofa
bright room, or when usinga torch, to protect their
nightvision. Once back In the dark, they reopen the
closedeye with the rods still working and, as a
result, maintain goodvision. This allows them to
keep operatingIn a potentiallyhostile environment
at peakoperational efficiency.Give it a try next time
you get up In the middle of the night, it may helpyou
avoid tripping over In the dark.

165

I
Allergies 1 Eczema

do SOtne people

haveal and

don't?

Allergies can be caused by two things: hostand
environ mental factors. Host Isifyou inherit an allergy or are
likely to get It due to your age, sex or racial group.
Environmental factors can Include things such as pollution,
epidemic diseases and diet. People who are likely to develop allergies
have a cond ilion known as 'atopy'. Atopy is not an illness but an
inherited feature, which makes individuals more likely to develop an
allergic disorder. Atopy tends to run In families.
The reason why atopic people have a tendency to develop allergic
disorders is because they have the ability to produce the allergy
antibody called 'Immunoglobulin E' or'lgE' when they come into
contact with a particularsubstance. However, not everyone who has
inherited the tendency to be atopicwiLl develop an allergic disorder.

"People who ore likely
to develop allergies
hove a condition known
as 'atopy"'

Eczema explained •

What causes the skin to react to otherwise harmless material? Allergen
entry route
Eczema ls a broad term for a Under the skin
Thecells of the skn are
t 9 range ofskin conditions, but What happens insidethe body when eczema flares up?
the most common form is normallytightlybound
• atopicdermatitis. Peoplewith Ceramides together to prevent
this condition havevery reactiveskin, contaminants from
which mountsan inflammatory response The membranes of skin cells contain waxy lipids entemg the body, but in
when in contact with Irritantsand to prevent moisb.re evaporation, but these are eczema there are gaps..
allergens. Mastcells release histamine,
which can lead to itching and scratching, often deficient in eczema Inflammatory
forming sores open to Infection.
There is thought to be a genetic Allergen • * ** response
element to the disease and a gene
involved in retainingwater in the skin Eczema is commonly triggered The irnrnu1esystem
has been identified as a potentiaI
contributor, but there are manyfactors. by the same things as many -gelproducesa response to
Eczema can be treatedwith steroids, ISbeneath the skin,
which suppress immunesystem allergies- anything from pet leading to redrII!SS, itd1i1!1
activity, dampeningthe inflammation and also inflammation
soskin can heaL In serious cases, hair to certaintypes of food
immunosuppressantdrugs- used to
prevent transplant rejection - can Water loss •
actually be used to weaken the immune
system so it no longer causes Theskin is lessable ••
inflammation in theskin. toretai1waler,
leading todcyness

and inlatiol L

166

do Is it for to

go have an allergy to

Sometimeswe trip overor hurt Arare conditioncalledaquagenlc contains water, the condition hinders intimacy.
ourselves In otherways. When It urticaria is often referred to as an Death could occur when water isswallowed if
happens some ofour blood vessels
break, blood plies up under ourskin allergy to water. The symptomsof the throat swells up, blocking the airway. The
and we can see this as a bruise.These nasty aquagenlc urticaria are painful but root cause Is unknown. One hypothesis is that
things have the famlllar 'blackand blue· or generally not fatal. Contactwith water- H20 generatesa toxic compound in the outer
purpleappearance In the beginning but containingsubstancescan bringoutsore hives layers of the skin, prompting the release of
graduallychange Into different colours.
The purplecolour Is given by haemoglobl n, a on thesurfaceoftheskin, causea burning histamines. Reactions cansometimes be
protein that carries the oxygen In our red blood sensationand induce headaches. Becausesaliva controlled with antihistamines.
cells. Our body reacts to this with some white
blood cells called phagocytes·eating up· the
materials in the bruise. As the phagocytes
degrade the haemoglobin, they turn It Into other
molecules. Different moleculesshowdifferent
coloursand the bruise will changecolourwlth
time to green, yellow and brown. When
everything has beencleared up by your
immunesystem the bruise disappears and
you're ready to bump into somethingelse.

The purple 1s given
by haemoglobin"

Is

bad for you?

Is thissubstance as evil aswe hear?

Cholesterol Is a fatty molecu le In the bloodand, generally

t 9 speaking, having too much is bad: itcanstickto the walls of
yourarteries and increase the rtskofheart disease. Most
• foods, with the exception ofoffal, eggsand shellfish, don't
containany cholesterol, but many containsaturatedfats, which are
turned Into cholesterolby the liver. However, cholesterol itselfisn't
unhealthy-In fact. you wouldn't beabletollvewlthoutilThe body uses
cholesterolas a kind of padding.coating the outer membranes ofallour
cellsand insulallng nerve Hbres, helpingslgnals travel properly to and
from the brain.lt'salsoa fundamental partoftheendocrinesystem,as
all steroid hormones (eg oestrogen)aresynthesised from cholesteroL
Importantly,a good, balanceddiet and regular exercisecan keep
cholesterol easily within a healthy range for most people.

"Cholesterol itself isn 't

unhealthy - in fact, you

wouldn'toe able to ffve
without it"

167

I
Alveoli onotom

I•

you reat e?

The lungs are filled with tiny
balloon-like sacs that keep you alive

Gas exchange occurs in the lungs, blod<s of eachare the tiny alveolus. They are blood within the capillary venous system on
where toxic gases (carbon dioxide) the final point of the respiratory tract, as the the other side of the epithelial layer.

are exchanged for fresh air with its bronchi break down into smallerand smaller The alveoli of the lungs have evolved to
unused oxygen content. Ofall the tubes, leading to the alveoli, whichare grouped become specialised structures, maximising
processes in the bodythat keep us functioning together and look like microscopic bunches of their efficiency. Their walls are extremely thin
and alive, this is the most important. Without it, grapes. Around the alveoli is the epithelial layer and yet very sturdy. Pulmonary surfactant is a
we would quickly become unconscious through -which isamazingly onlya single cell thick- thin liquid layermade from lipids and proteins
accumulation of carbon dioxide within the and this is surrounded by extremelysmall that coats ofall the alveoli, reduces their
bloodstream, which would poison the brain. blood vessels called capillaries. It is here that surface tension and prevents them crumpling
The two lungs (left and right) are made up of vital gas exchange takes place between the when we breathe out. Without them, the lungs
several lobes, and the fundamental building fresh air in the lungs and the deoxygenated would collapse.

Alveoli anatomy Type I pneumocytes Breathe in,
breathe out
How alveoli enable gas exchange These large, flattened cells form
95 per cent of the surface area of The alveoli function to allow gas
an alveolus, and are the very thin
diffusion barriers for gases. exchange, but since they're so
small, they can't move new air
Type II inside and out from the body
r - - -pneumocytes without help. That's what your

These thicker cells form respiratory muscles and ribs do,
the remaining surface area hence why your chest moves as
of the alveoli. They secrete you breathe. The diaphragm,
surfactant, which prevents which sits below your heart and
the thin alveoli collapsing. lungs but above your abdominal

Oxygenated blood organs, is the main muscle of
respiration. When it contracts, the
The freshly oxygenated normally dome-shaped diaphragm
blood is taken away by f lattens and the space within the
capillaries and enters the chest cavity expands. This
reduces the pressure compared to
left side of the heart,
to be pumped the outside atmosphere, so air
through the body. rushes in. When the diaphragm

relaxes, it returns to its dome
shape, the pressure within the
chest increases and the old air-
now full of expired carbon dioxide

- is forced out again. The muscles
between the ribs (called
intercostal muscles) are used
when forceful respiration is
required, such as during exercise
Try taking a deep breath and
observe how both your chest
expands to reduce the pressure!

One cell thick ---''"' The capillary veins bring Macrophages
deoxygenated blood from the
The alveolus wall is just right side of the heart, which These are defence
one cell thick, separated has been used by the body cells that digest
from the blood capillaries and now contains toxic C0 •
by an equally thin bacteria and particles
basement membrane. 2 present in air, or that
have escaped from the
168
blood capillaries.

Blue eyes •••• Blil*ing •• 3Sight •••• Tears 5••••••••'Measure ments

1PeoPle with blue eyes all • 2 Your eyes wiU blink around •• Technically. you see with 4 Toars are not only an On average, a human eyebatl
share acommon ancestor. A • 15-20times per minute and your brain and not your is around 2.Scm (lin) in
genetic mutation about • ctmOllonal response; they
LO.OOO years ago gave •• it last for around 100 • eyes. Poor vision sometimes •• diameter and weighs as
miUiseconds. You also blink also hnlp prevent your eyes Utile as 7.5g (0.25oz). A
someone blue eyes. whm • sterns from problems with from drying up and get rid ••••
everyOne elso's were brown. more when talking than the visual cortex of the brain giant squid's eyeball Is ten
•• and not the eye itsetf. of any IITltatlng particles times as big as a human1s.
when reading. that could cause damage. -

(I)(•M•I!NtW•l!j!G> SAD is more common in women and people between the ages of 15 and 55

How do dilating eye
drops work?

Discover how they are used to diagnose and treat eye conditions

Sight is one ou r most Important
senses, so maintalnlnggood eye
health is absolutely essential.
However, eyes ight problems can be
difficult to detect or treat on the surface, so
specialist eye doctors will often use dilating
eye drops in order to get a better took Inside the
eye a t the lens, retina and optic nerve.
The drops contain the active Ingredient
atropine, which works by temporarily relaxing
the muscle that constricts the pupil, enabling it
to remain enla rged for a longer period of time
so a thorough examination can be performed.
Some dilating eye drops also relax the muscle
that focuses the lens inside the eye, which
allows an eye doctor or optometrist to measure
a prescription for young children who can't
perform traditional reading tests.
Dilating eye dropsare not only used to help
perform procedures, they mayalso be
administered after treatment, as they can
prevent scar tissue from forming. Theyare a lso
occasionally prescribed to ch lid ren with
lazy-eye conditions, as they will temporarily
blur vision in the strong eye, causing the brain
to use and strengthen the weaker eye.

I

Those who suffer from also often reported, with pain
migraines know theyare sometimes subsidingafter the
a constant concernas sufferer has been sick.
they are liable to strike
at any time. Essentially, a migraine It is thought that migraines occur
isan intense pain at the front or on when levels ofserotonin in the brain
one side ofthe head. This usually drop rapidly. This causes blood
takes the form ofa heavy throbbing vesselsin the cortex to narrow,
sensation and can lastas little asan which is caused bythe brain
hourortwoand up to a few days. spasrning. The bloodvessels widen
Other symptoms ofa migraine again in response, causing the
include increasedsensitivity to intense headache. Emotional
light, soundand smell, so isolation upheaval is often cited as a cause for
ina darkand quiet room often the drop in serotonin inthe brain, as
brings relief. Nausea and vomiting is is a dlet in which blood-sugar levels
rise and fall dramatically.

I

1\Nins are becoming more prevalent due to medical
developments, but how and why do they occur?

The number of twins, or multiples, dizygotic twins. Also, ifthe mother is going but
through fertility treatments,sheis much more
being born Is actual tyon the rise likely to become pregnant with multiples. true...
due to the Increase In use offertility
It will becomeapparentquite earlyon that a Thereare many storiesof Identical twins being
treatmentssuchas tvr as people mother is carrying twins as this is often picked separatedat birthand then growingup to lead
up during early ultrasound scans.There can be very similarlives. Oneexampledescribed in the
wait longer to have ch Udren. The number of other indicationssuchas increased weight gain
orextreme fatigue. Although twins are often 198<>januaryedition of Reader'sDigesttells of
twins survivingearly birthsIs also Increasing bornentirely healthyandgo on to develop
due to improved medical knowledge. without problemslater in lifedue to medical two twins separatedat birth, both namedjames,
advances, twins can be prematureand smaller who both pursued law-enforcement trainingand
However, twins are still a relatively rare than single birthsdue to spaceconstrictions had a talent for carpentry. One named his son
occurrence making up onlyaround two per within the womb during development jamesAlan, and the other named hisjamesAllan
centofthe living world's population.Within
this, monozygotic twinsIfrom oneovum) make "It is believed twins and both named thelr dogsToy.There were also
up around eight percent with dizygoticIfrom the Mowforth twins, two Identical brotherswho
two ovum)seen to be far more common. 'run in the ft:;Jmily ', lived 8o miles apart In theUK, dyingofexactly the
samesymptomson thesamenlghtwithin hoursof
While the.re is no known reason for often seemtng to
skip generations" each other.
the occurrenceofthe splitof the ovum that
causes monozygotic twins, the chancesof
having twins is thought to beaffected by
several different factors. It Is believed twins
'runin the family', oftenseeming toskip

generations, while the age, weight, height. race
and even diet ofthe mother are thought to
potentiallyImpact the chancesofconceiving

170

•••••• Nonuplets exist ••• ••• ••• 5Quad•••••••••••
• children••
• 2 AMalaysianmother gavebirth
• 3 • 4•••••••

••
STOP 112foetus wolid record Race affects conception : Most gestation
Although sadlyttwspregnancy •••
FACTS cid not reachfuU termand no rrve:•• With regard to OZ twins, there ••••••• The highestrecorded number With regard toquadruplets.
babiesSUI"o'ived, a woman in •••• to boysand fourgirls in is seen to bea higher ofchildren hadbyone woman the average gestation period is
MULTIPLE BIRTHS March 1999... none survived prevalenceofthesetwins in isthe firstwife ofF'eoclor just 32 weeks - that's eight
Algentina wasobserved to have black Africans, and a lower Vassilyev, whoived in the weeks shcw'ter thanusua~
0'\lef six OOLrS. Anotherset of 1700s. She gavebirth to an primarilydue to the size
12 foetusesinside herworrtl norupletssuffered a similar fate incidence than tobe expected incredible 69dlldren. •• restriction ofthewomb.
from natural conception. in Oriental mothers.
• ;n~neym197L

I•U•~•I!l!3N•1MP Female monozygotic twins ore more common due to the increased likelihood of mole mortality in the womb

M•

Thereare many difficulties with twin they'rejoined.lfit is bya vital organor bone
pregnancies- mainlydue to the limitedsize
structure. one or both may die following birth
of the mother's womb. Multiple pregnandes as theygrow - orduring an operation to
rarely reach fullterm due to these limits, separate them.

twins averaging ataround 37weeks. Also, It isalso suspected thatas many as one in
becauseofthe lack ofspaceand eggssplitting eight pregnandes may have startedoutas a

in the womb, further complicationssuch as potential multiple birth, butone or more of the
conjoined twins canoccur. Conjoined twins foetuses does not progress through
can bea problem dependanton where development to full term.

Placenta Twins inside

Provides a metabolic the womb
interchange between
Uterine wall
thetwils and mother.
• - - - - The protective wall

of the uterus.

Amniotic sac - - - LSpenn

Athin-walled sac that ferti6ses egg
surroundsthe fetus
during pregnancy. 2. Fertilised + In MZ twins, only ooe
egg and one sperm
eAtgsgomsepp<lMitnst ~ are irwolved.

early on, the fertili~ "

egg will split and two

separate foetuses wiD

start to form. These

wil begenetically

identical. I \

Umbilical cord I

A rope-like cord Cervix
connecting the fetus
to the placenta. The lower partof the

uterus that projects 3.Spenn
into the vagina. fertilise

Fromstudying identical, monozygotic twins, different parents. Oftenwe seea similarIQ 4 . S epara t e separate
we can attempt to decipher the level ofimpact
and personalitydisplayed, whether or not eggs '------ eggs
environment has onan individualand the they grow up together, buteven these and
influencegenes have. As the genetics of the otherlifestyle choicescan vary dependant continue InDZ twins, two
on environment.
individuals would be Identical, we cansay to develop separate eggs are
Ultimately, itishardtodrawfirm
that differencesdisplayed between two conclusions from twin studiesas theywill be In DZ twins, both fertilised by
MZ twins are likely to be down to an unrepresentativelysmallsample within a foetuses will different sperm.
much larger populationand we often find that continue to develop These will implant
environmental influences. independently to independently in
Some ofthe most Interestingstudies look at both environmentand genetics interact to
influencean individual's development. each other. the mother's
twins that have beenseparatedat birth, often womb wan,
when individuals have beenadopted by commonly on
opposite sides.

171

I

'ns and needles 1 Burns 1 Funny bones

What is 'pins ~-

and les'? ••

The numb sensation ofyour leg Are there other 'funny
'going to sleep'lsn't caused by bones' in the body?
cuttingoff the bloodcirculation.
It's the pressureon the nerves that The term 'funnybone'is misleading
is responsible. Thissqueezes the Insulating because It refers to the painfulsensation
sheatharound the nerve and 'shortsIt out', youexpertencewhenyoutrapyourulnar
blocking nerve transm lsslon. When pressure nerve between the skinand the bonesof
Is released, the nerves downstream from the the elbow joint.This happens In the so-calledcubital
pinch pointsuddenlyall begin firing at once. tunnel, which directs the nerve 011ertheelbow but has
Thisjumbleofunco-ordlnated signals Is a little padding to protectagainst externalimpacts.The
mixture ofpainand touch, hot and coldall ulnar nerve takes Its name from the ulna bone, which is
mixed together, which Is why It's excruciating. oneoftwo bones that runs from thewrtstto the elbow;
the otherIs the radial bone, or radius.
"Thts squeezes the No otherjointIn the human skeletoncombines these
insulating sheath conditionsand duplicates the this erroneously named
reaction so we only have one 'funny bone'.
around tfle nerve

and 'shorts it out'"

Why do
paper
cuts hurt
so much?

Papercan cutyourskin
as itis incredibly thin
and, ifyou were to look
at it undera high-
powered microscope, it has
serrated edges. Critically though, a
sheetofloose paper isfar too soft
and flexible to exertenough
pressure to pierce the skin, hence
why they are not a more frequent
occurrence.However, ifthe paper
is fixed in place- maybe by being
sandwiched within a packof
paper- a sheetcan becomestiff
enough toattainskin-cutting
pressure. Papercutsare so painful
onceinflictedas theystimulatea
large number ofpain receptors-
nociceptorssend nervesignals to
the spinalcordand brain-in a
very smallarea due to the
razor-type incision. Because paper
cuts tend not to bedeep, bleeding
islimited, leavingpain receptors
open to the environment

172

do our muscles ache?

Learn what causes stiffness and pain in our muscles for days after exercise

Normally, when our muscles contract Weightlifting and the body Bending
theyshorten and bulge, much like a
bodybuilder's biceps. However, ifthe What happens to your biceps when you pump iron? NormaJJywhen thebleeps
muscle happens to be stretchedas it
contracts it can cause microscopic damage. Pain musclegroupoontracts it
The quadriceps muscle group located on the
front of the thigh is involved in ex tending the Thesorenessassoclated shortens, puJJlng theforearm
knee joint, and usua lly contracts and shortens to with exerciseIs theresult t o w a r d s the s h o ul der.
s traighten the leg. However, when walking ofrepetitive stretchingof
down a steep slope, say, the quadriceps contract oontracted muscles. Stretching
to support your body weight as you step
forward, butas the knee bends, the muscles are Straightening ---' As themuscle tries to
pulled in the opposite direction. This tension cootract, theweightpullsin
resu lts in tiny tears in the muscle and this is the Astheannstraightensout. the
reason thatdownhill running causesso much hlcepsarestretcbed, hutthe the oppositedirectiorl.
delayed-onset pain. welghtisstlllpnllingdownon
At the microscopic level, a muscle is made up causing mlcroscoplctears
of billionsofstacked sarcomeres, containing the band.so themuscles remain
molecular ratchets that pull agaJnst oneanother part.Jyoontracted to supportit within themusclecells.
to generate mechanical force. Ifthe muscle is
taut as it tries to contract. the sarcomeres get
pulled out of line, causing microscopic damage.
The muscle becomes inflamed and fills with
fluid, causing stiffn ess and activating pain
receptors- hence that achy feelIng you getafter
unfamiliar exercise.

i Why do the Why shouldn't
upper arm
and per we eat raw

meat?

Meat can harbour many different bacteria, viruses

and even parasites.Cooking meat properly

leg have only destroys them, making meat much saferfor
consumption. Bacteriaand viruses can make you

• one bone? ill, while parasitescangrowinsideyourgut and even migrate
to your brain. Food poisoningis avery serious businessand
by not cook! ng meat thoroughly, you are greatly increasing

your chancesofgettingsomething nasty. Peoplequite often

t 9 Themakeup ofthe eat rawmeatsuch as steak tartare, butit requires extracare
human skeleton is a In the preparation. Besidessafety; cooking meatalso makes it
taste better. Bycooking meat and otherfoods, humans can
fantastic display of get much more energy than from chewing raw foodalone.
• evolution that has left us

with the ability to perform

Incrediblycomplex tasks without

even thinkingabout them. There

are severaldifferent types ofjoint

between bones in your body, which

reflect their function; someare

strongandallowlittle movement,

othersare weak butallow free

movement.The forearm and tower

leg have two bones, which form

planejointsat the wrist and ankle.

This type ofjointallows fora range

offine movements, includinggliding

and rotation. The hingejointsat

yourelbowsand knees allow for less

lateral movement, buttheyare

strong.Shouldersand hips, though,

are ball-and-socketjoints, which

allow for a wide range of motion.

How do

•I

work?

The terms 'inoculation' and 'vaccination'are
used interchangeably.They involve
Introducinga foreign substance(antlgens) into
the body, causingantibodyproduction.These
caneltherbedead, made tess harmful, orjustcontain
certain bits that causedisease.
White bloodcellscalied Blymphocytes recognise these
antigens, and produce antibodies to neutralise them.
Afterthe initial encounter,a group of Blymphocytesare
made calied 'memorycells', which producea ntlbodles
faster ifexposed to the sameantigen again.

"They involve introducing
antigens into the body"

174

Why do we

develop gout?

Excessivelevelsofuricadd In the blood
causegout We producewicactdasawaste
productfrom digesting protein.Uricadd is
removed by the kidneys and excretedas a
dllutesolutlon.lfkldneyfunction Is impaired, the
concentration rises to the point where it prectpltatesas
monosodium urate crystals.
These normally form In thejoints ofyourtoes,
because your feetare coolerand cold temperatures
reduce thesolubility of uric acid. Gout is partlygenetic,
butexacerbated by excessivedrinking - particularly
beer-and not enough exercise,so there are things
that can be done to help avoid suffering.

"Your feet ore cooler
ond cold temperatures
reduce the solubility
of uric ocid"

175

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