The Complete Human Body Dr Alice Roberts

DR. ALICE ROBERTS



THE COMPLETE

HUMANBODY

THE DEFINITIVE VISUAL GUIDE



DR. ALICE ROBERTS

THE COMPLETE

HUMANBODY

THE DEFINITIVE VISUAL GUIDE

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THE INTEGRATED BODY THE INTEGRATED BODY

Linda Geddes Professor Mark Hanson, Southampton
General Hospital

ANATOMY ANATOMY

Dr. Alice Roberts Professor Harold Ellis, King’s College, London
Professor Susan Standring, King’s College London

HOW THE BODY WORKS HOW THE BODY WORKS

HAIR, NAILS, AND SKIN: Richard Walker HAIR, NAILS, AND SKIN:
MUSCULOSKELETAL: Richard Walker Professor David Gawkrodger, Royal Hallamshire
NERVOUS SYSTEM: Steve Parker
Hospital, Sheffield
RESPIRATORY SYSTEM: Dr. Justine Davies
CARDIOVASCULAR SYSTEM: Dr. Justine Davies MUSCULOSKELETAL SYSTEM:
Dr. Christopher Smith, King’s College London
LYMPHATIC AND IMMUNE SYSTEM:
Daniel Price NERVOUS SYSTEM:
Dr. Adrian Pini, King’s College London
DIGESTIVE SYSTEM: Richard Walker
URINARY SYSTEM: Dr. Sheena Meredith RESPIRATORY SYSTEM:
REPRODUCTIVE SYSTEM: Dr. Gillian Jenkins Dr. Cedric Demaine, King’s College London

LIFE CYCLE CARDIOVASCULAR SYSTEM:
Dr. Cedric Demaine, King’s College London
Authors: Dr. Gillian Jenkins, Dr. Sheena Meredith
Consultant: Professor Mark Hanson IMMUNE AND LYMPHATIC SYSTEM:
Dr. Lindsay Nicholson, University of Bristol
DISEASES AND
DISORDERS DIGESTIVE SYSTEM:
Dr. Richard Naftalin, King’s College London
Authors: Dr. Fintan Coyle (allergies, blood,
digestive, hair and nails, respiratory, skin) URINARY SYSTEM:
Dr. Gillian Jenkins (cardiovascular, endocrine, Dr. Richard Naftalin, King’s College London

infertility, reproductive, STDs, urinary) REPRODUCTIVE SYSTEM:
Dr. Mary Selby (cancer, eye and ear, infectious Dr. Cedric Demaine, King’s College London

disease, inherited disease, nervous system, ENDOCRINE SYSTEM:
mental health, musculoskeletal) Professor Gareth Williams, University of Bristol

Consultants: Cordelia T Grimm, MD, Researchers: Christoper Rao,
Dr. Rob Hicks Kathie Wong, Imperial College, London

Every effort has been made to ensure that the First American Edition, 2010
information contained in this book is complete and
First published in the United States by
accurate. This book is intended to give general DK Publishing
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damage allegedly arising from following any 178690—September 2010
suggestion in this book.
Copyright © 2010 Dorling Kindersley Limited
Foreword copyright © Alice Roberts.

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CONTENTS

010 028 274

THE INTEGRATED ANATOMY HOW THE BODY
BODY WORKS

012 Human evolution 030 ANATOMICAL TERMINOLOGY 276 SKIN, HAIR, AND NAILS
014 Human ancestors
016 Human genetic formula 036 BODY SYSTEMS 282 MUSCULOSKELETAL SYSTEM
020 The cell
022 Cells and tissues 038 Skin, hair, and nail structure 284 The working skeleton
024 Body composition 040 Skeletal system 286 Bones
026 Body systems 050 Muscular system 288 Joints
060 Nervous system 290 How muscles work
066 Respiratory system 292 Muscle mechanics
068 Cardiovascular system
074 Lymphatic and immune system 294 NERVOUS SYSTEM
078 Digestive system
080 Urinary system 296 How the body is wired
082 Reproductive system 298 Nerve cells
084 Endocrine system 300 Passing on the message
302 The brain and spinal cord
086 ANATOMY ATLAS 304 The CNS in action
306 Memory and emotion
088 Head and neck 308 How we move
136 Thorax 310 How we sense the world
168 Abdomen and pelvis 312 How we see
198 Shoulder and upper arm 316 Hearing and balance
222 Lower arm and hand 318 Taste and smell
236 Hip and thigh 320 Touch
260 Lower leg and foot
322 RESPIRATORY SYSTEM

324 Journey of air
326 Gas exchange
328 Mechanics of breathing
330 Instinctive breathing

332 CARDIOVASCULAR SYSTEM 392 414
334 Blood
336 Cardiac cycle LIFE CYCLE DISEASES AND
338 Controlling the heart DISORDERS
340 Blood vessels 394 Life’s journey
396 Inheritance 416 Inherited disorders
342 LYMPHATIC AND IMMUNE 398 Developing embryo 418 Cancer
SYSTEM 400 Fetal development 420 Infectious diseases
404 The newborn 422 Skin, hair, and nail disorders
344 Lymphatic system 406 Childhood 426 Bone and joint disorders
346 Innate immunity 408 Adolescence and puberty 430 Muscle, tendon, and ligament disorders
348 Adaptive immunity 410 Adulthood and old age 432 Back, neck, and shoulder problems
412 End of life 434 Limb joint disorders
350 DIGESTIVE SYSTEM 436 Cerebrovascular disorders
352 Mouth and throat 438 Brain and spinal cord disorders
354 Stomach 440 General nervous disorders
356 Small intestine 441 Nervous system infection
358 Liver 442 Mental health disorders
360 Large intestine 444 Ear disorders
362 Nutrition and metabolism 446 Eye disorders
448 Respiratory disorders
364 URINARY SYSTEM 452 Cardiovascular disorders
366 Kidney function 456 Peripheral vascular disorders
368 Bladder function 458 Blood disorders
460 Allergies and autoimmune disorders
370 REPRODUCTIVE SYSTEM 462 Upper digestive tract disorders
372 Male reproductive system 464 Lower digestive tract disorders
374 Female reproductive system 466 Liver, gallbladder, and pancreas disorders
376 Creation of life 468 Kidney and urinary problems
378 The expectant body 470 Female reproductive system disorders
380 Labor and birth 472 Male reproductive system disorders
474 Sexually transmitted diseases
382 ENDOCRINE SYSTEM 476 Infertility
384 Hormones in action 478 Disorders of pregnancy and labor
386 The pituitary gland 480 Endocrine disorders
388 Hormone producers
484 GLOSSARY
490 INDEX
512 ACKNOWLEDGMENTS



FOREWORD learn in this way is a great privilege and
depends entirely on the generosity of
people who bequeath their bodies to
medical science. But in addition to

dissection, we now have other techniques

with which to explore the structure of the

The study of the human body has human body: cutting it up virtually using

an extremely long history. The Edwin X-rays, computed tomography (CT) and

Smith papyrus, dating to around 1600 BCE, magnetic resonance imaging (MRI), or

is the earliest known medical document. studying the minute detail of its

It’s a sort of early surgical textbook, listing architecture using electron microscopy.

various afflictions and ways of treating The first section of this book is an atlas

them. Even if those are treatments that of human anatomy. The body is like a very

we wouldn’t necessarily recommend complicated jigsaw, with organs packed

today, the papyrus shows us that the closely together and nestled into cavities,

ancient Egyptians had some knowledge with nerves and vessels twisting around

of the internal structure of the body— each other, branching inside organs, or

they knew about the brain, heart, liver, piercing through muscles. It can be very

and kidneys, even if they didn’t understand hard to appreciate the way that all these

how these organs functioned. elements are organized, but the illustrators

Historically, finding out about the have been able to strip down and present

structure of the human body involved the anatomy in a way that is not really

dissection; the word “anatomy” literally possible in the dissection room—showing

means “to cut up.” After all, when you’re the bones, muscles, blood vessels, nerves,

trying to find out how a machine works, and organs of the body in turn.

it’s not particularly helpful just to look at Of course, this isn’t an inanimate

the outside of it and try to imagine the sculpture, but a working machine. The

machinery inside. I remember a physics function of the body becomes the main

practical at school, when we were tasked theme of the second part of the book,

with finding out how a toaster worked. as we focus on physiology. Many of us

We found out by taking it apart—although only start to think about how the human

I must admit that we miserably failed to body is constructed, and how it works,

put it back together again (so it’s probably when something goes wrong with it.

a good thing that I ended up as an The final section looks at some of the

anatomist rather than a surgeon). Most problems that interfere with the smooth

medical schools still have dissection running of our bodies.

rooms, where medical students can learn This book—which is a bit like a user’s

about the structure of the body in a manual—should be of interest to anyone,

practical, hands-on way. Being able to young or old, who inhabits a human body.

DR. ALICE ROBERTS

The body piece by piece
A series of magnetic resonance imaging
(MRI) scans show horizontal slices
through the body, starting with the head
and working downward, through the
thorax and upper limbs, to the lower
limbs, and finally the feet.

theintegrated
body

The human body comprises trillions of cells, each one a complex
unit with intricate workings in itself. Cells are the building blocks
of tissues, organs, and eventually, the integrated body systems that
all interact—allowing us to function and survive.

010

THE INTEGRATED BODY

012 Human evolution 016 Human genetic formula 022 Cells and tissues 026 Body systems
014 Human ancestors 020 The cell 024 Body composition



012

THE INTEGRATED BODY

HUMAN EVOLUTION

Who are we? Where are we from? We can attempt to answer these questions by
studying human evolution. Evolution provides a context for understanding the
structure and function of our bodies, and even how we behave and think.

ANCIENT ORIGINS blades on the back of the chest, supported by long Face is flatter than Robust, Braincase is slightly
collarbones; arms and hands designed for swinging in monkeylike apelike jaw larger than in
In placing our species within the animal kingdom, it is from branches; and the lack of a tail. species monkeylike species
clear that we are primates—mammals with large brains
compared to other mammals, good eyesight, and, usually, The earliest apes emerged in East Africa at least Possible ancestor
opposable thumbs. Primates diverged, or branched off, 20 million years ago, and for the following 15 million Proconsul lived in
from other mammal groups on the evolutionary tree at years a profusion of ape species existed across Africa, Africa 27–17 million
least 65 million years ago, and possibly as far back as Asia, and Europe. The picture today is very different: years ago. Although
85 million years ago (see below). humans represent one populous, globally distributed it has some more
species, contrasting with very small populations of other primitive primate
Within the primates, we share with a clutch of other apes, which are threatened with habitat loss and extinction. characteristics, it may
species—the apes—a range of anatomical features: a large be an early ape and
body with a chest that is flattened front-to-back; shoulder even a common
ancestor of living apes,
including humans.

UNUSUAL PRIMATE on our hands and feet; opposable thumbs, SCIENCE
which can be brought into contact with
From bush babies to bonobos, lorises and the tips of the fingers (other primates DATING SPECIES DIVERGENCE
lemurs, to gibbons and gorillas, primates have opposable big toes as well); large,
are a diverse bunch of animals, bound forward-facing eyes, which allow good Historically, figuring out evolutionary
together by a common ancestral heritage depth perception; nails rather than claws relationships between living species
(see below) and a penchant for living in on our fingers and toes; year-round depended on comparing their anatomy
trees. Humans are unusual primates, breeding and long gestation periods, with and behavior. Recently, scientists began to
having developed a new way of getting only one or two offspring produced compare species’ proteins and DNA, using
around—on two legs, on the ground. per pregnancy; and flexible behavior differences in these molecules to construct
However, we still share many with a strong emphasis on learning. family trees. Assuming a uniform rate of
characteristics with the other members change, and calibrating the tree using dates
of the wider primate family tree: five digits from fossils, the dates of divergence of each
branch or lineage can be calculated.

80

70

60

MILLIONS OF YEARS AGO 50

40

Primate family tree 30
This diagram explains the 20
evolutionary relationships 10
between living primates. It
shows how humans are most 0
closely related to chimpanzees,
and that apes are more closely Human
related to Old World monkeys Chimpanzee
(including baboons) than New
World monkeys (including Gorilla
squirrel monkeys). All monkeys Orangutan
and apes are shown to be more
closely related to each other Gibbon
than to prosimians (including Baboon
lemurs and bush babies). Macaque

Vervet
Squirrel
monkey
Marmoset

Titi
monkey

Mouse
lemur
Lemur
Bush baby

013

HUMAN EVOLUTION

GREAT APE OUR CLOSEST RELATIVE

Although we might like to think of ourselves relationship between the African apes Science has shown that humans and species is much younger. Reproduction is
as separate from other apes, our anatomy and humans, it makes more sense to chimpanzees shared a common ancestor quite similar, although human females
and genetic makeup places us firmly in group humans, chimpanzees, and gorillas some 5–8 million years ago. Comparing reach puberty later, and also live for a long
that group. Classically, the apes have been together as hominids. Humans and their ourselves with our closest relative gives time after menopause. Humans live up to
divided into two families: lesser apes ancestors are then known as hominins. us an opportunity to identify the unique 80 years, while chimpanzees may live up to
(gibbons and siamangs) and great apes features that make us human. 40 or 50 years in the wild. Chimpanzees
(orangutans, gorillas, and chimpanzees), Not only that, but humans are live in large, hierarchical social groups,
with humans and their ancestors placed in genetically closer to chimpanzees than Humans have developed two major with relationships strengthened by social
a separate family: hominids. But, since either humans or chimpanzees are to defining characteristics—upright walking grooming; humans have even more
genetic studies have shown such a close gorillas. It’s not surprising that humans on two legs, and large brains—but there complex social organization. Furthermore,
have been called the “third chimpanzee.” are many other differences between us and although chimpanzees can be taught to
Human skull chimpanzees. The human population is use sign language, humans are uniquely
The skull in humans is dominated High, huge and globally distributed, but we adept at communicating thoughts and
by a massive braincase, with a rounded are, in fact, less genetically diverse than ideas through complex language systems.
volume of 1,100–1,700 cubic braincase chimpanzees, probably because our
centimeters (cc). Its teeth, jaws, and
areas of attachment for chewing Flat face with High, rounded Comparing cousins
muscles are small in comparison projecting braincase Some parts of the human skeleton
with other apes. The brow ridges nasal bones are remarkably similar to that of the
over the eye sockets are subtle Skull positioned chimpanzee: the shoulder and upper
and the face is relatively flat. Pointed directly over spine arm are almost the same size and
chin shape. Chimpanzees walk on four legs,
Small Barrel-shaped rib which makes their lower skeletons
braincase Sloping cage allows arms quite different from a human’s, with
forehead to swing when a long pelvis and short, bent legs.
Chimpanzee skull walking
Chimpanzees have a relatively Sloping face with
small, rounded braincase, nonprojecting nasal Short, wide pelvis
accommodating a brain of bones positions torso
300–500 cubic centimeters above hips
in volume. The face is relatively
large, with a fairly prominent Small, low Spine attaches Cone-shaped rib
brow ridge and jaws that braincase to rear of skull cage allows
project forward. overhead
Short, slender reaching
Large canine fingers enable fine
teeth manipulation Long,
narrow
No chin pelvis

Occipital torus

Gorilla skull Large sagittal crest Legs extend
The occipital torus is high on fully during
the skull, with a large area for Massive brow
the attachment of strong neck ridge standing
muscles below it. The male and walking
gorilla has a massive brow ridge Long, Very long Short,
and a large sagittal crest for the sloping face Big toe forearms bent
attachment of strong jaw lined up relative to legs legs
muscles. The size of the braincase with other
is 350–700 cubic centimeters. Flat Long, curved Opposable
forehead toes fingers for big toe for

climbing trees and grasping
knuckle walking
Large,
Small projecting
jaw, but
no chin

Orangutan skull braincase

Like the chimpanzee, the Small brow
ridge
orangutan has a relatively

small braincase, with a volume Strongly
projecting
of 300–500 cubic centimeters, jaws Dependent young
A human baby is born
and a large face. The skull is at an earlier stage of brain
development than a
extremely prognathic, with chimpanzee baby, and is more
helpless and dependent on
strongly projecting jaws. The caregivers. Even so, the human
baby’s head is relatively large
brow ridge is much smaller than at birth, making for a longer
and more difficult delivery.
in gorillas or chimpanzees.

014

THE INTEGRATED BODY

HUMAN ANCESTORS

Humans and their ancestors are known as hominins. The hominin fossil record begins in
East Africa, with many finds from the Rift Valley. Early species walked upright, but large
brains and tool-making came along later, with the appearance of our own genus, Homo.

PRESENT DAY0 THE FOSSIL RECORD where the spinal cord exits) on its fossil skull, appears Until recently, it was thought that Homo erectus was
to have stood upright on two legs. Fossilized limb the first hominin to leave Africa, and its fossils are
In the last two decades, exciting discoveries have bones of Ardipithecus ramidus suggest that it found as far east as China. However, discoveries
pushed back the dates of the earliest hominin clambered around in trees as well as being able of small hominins in Indonesia suggest that there
ancestors, and provoked controversy over when to walk on two legs on the ground. From 4.5 million may have been an earlier expansion out of Africa.
humans first left Africa. years ago, a range of fossil species known collectively
as australopithecines emerged. These hominins were We are the only hominin species on the planet
Fossils of a few possible early hominins have well adapted to upright walking, but did not have today, but this is unusual: for most of human
been found in East and Central Africa, dating to the long legs and large brains of the Homo genus. evolutionary history, there have been several species
more than 5 million years ago. The oldest of these overlapping with each other.
is Sahelanthropus tchadensis, which, from the
position of the foramen magnum (the large hole

MYA1

MYA2 Australopithecus garhi
BRAIN: about 450 cc

About 2.5 MYA

MYA3 Paranthropus Paranthropus
boisei robustus
BRAIN: 410–550 cc BRAIN: about 530 cc Homo rudolfensis
BRAIN: 600–800 cc
2.3–1.4 MYA 2–1.5 MYA 2.4–1.6 MYA

MYA4 Paranthropus Australopithecus Australopithecus Kenyanthropus
aethiopicus africanus sebida platyops
BRAIN: about 410 cc BRAIN: 428–625 cc BRAIN: 420–450 cc BRAIN: unknown
3–2.4 MYA 1.95–1.78 MYA 3.5–3.2 MYA
2.5–2.3 MYA
Ardipithecus Australopithecus
MYA5 Australopithecus ramidus afarensis
anamensis BRAIN: unknown BRAIN: 380–485 cc
BRAIN: unknown 4.5–4.3 MYA 4–3 MYA

4.5–3.9 MYA Ardipithecus
kadabba
MYA6 Hominin time line BRAIN: unknown
Human evolution has not been a straightforward 5.8–5.2 MYA
process. Different groups of hominins lived in the
same time periods, and may even have encountered Orrorin tugenensis Sahelanthropus
one another. One species did not simply change into BRAIN: unknown tchadensis
the next in a linear pattern. Instead, new species BRAIN: about 300 cc
emerged in a more branching style, with some 6.6–5.7 MYA
succeeding, and others, such as the paranthropines, 7–6 MYA
MYA7 dying out and becoming evolutionary dead ends.
Homo sapiens is the only extant hominin species.

015

HUMAN ANCESTORS

MODERN HUMANS humans (Homo sapiens) in Africa, around 200,000 EXTINCT COUSINS

From around 600,000 years ago, a species called years ago. Although it is difficult to draw a line Neanderthals lived in Europe for
Homo heidelbergensis existed in Africa and Europe. hundreds of thousands of years
This ancestral species may have evolved into between the later fossils of Homo heidelbergensis before modern humans arrived
Neanderthals (Homo neanderthalensis) in Europe, on the scene some 40,000 years
about 400,000 years ago, and anatomically modern and the earliest fossils of Homo sapiens, the rounded ago. The last known evidence of
Neanderthals is from Gibraltar,
cranium of Omo II, discovered by the renowned around 25,000 years ago. The
question of whether Neanderthals
Kenyan paleoanthropologist Richard Leakey and his and modern humans met and
interacted is hotly debated. There
team in southern Ethiopia, and now dated to around are a few fossils that some
anthropologists believe show
195,000 years ago, is accepted by many to be the features of both species, leading to
the controversial suggestion that
earliest fossil of a modern human (see below). modern humans and Neanderthals
interbred with each other. Analysis
The fossil, archaeological, and climatic evidence of DNA from Neanderthal fossils
has not shown any genetic
suggests that modern humans expanded out of evidence for interbreeding.

Africa between 50,000 and

Modern behavior 80,000 years ago. People Varied diets
This piece of ocher spread out of Africa along Archaeological evidence from
Gibraltar suggests that, like humans,
found at Pinnacle Point, the rim of the Indian Ocean Neanderthals were eating a varied diet
South Africa, suggests to Australia, and northward, including shellfish, small animals and
that humans were using into Europe, northeast Asia, birds, and possibly even dolphins.
pigment more than and later, into the Americas.
160,000 years ago.

Homo floresiensis Homo sapiens
BRAIN: about 400 cc
95,000–12,000 YA Homo BRAIN: 1,000–2,000 cc

Homo erectus Homo antecessor Homo neanderthalensis 200,000 YA–present
BRAIN: 750–1,300 cc BRAIN: about 1,000 cc
780,000–500,000 YA heidelbergensis BRAIN: about 1,412 cc
1.8 MYA–30,000 YA
BRAIN: 1,100–1,400 cc 400,000–28,000 YA

600,000–100,000 YA

Homo habilis Homo ergaster
BRAIN: 500–650 cc BRAIN: 600–910 cc

2.4–1.4 MYA 1.9–1.5 MYA

OUR OLDEST REMAINS

In 1967, a team led by the
paleoanthropogist Richard Leakey
discovered fossils of our own
species in the dunelike hills
of the Kibish formation near the
Omo River in Ethiopia (shown
here). The fossils were found
sandwiched between layers of
ancient volcanic rock. In 2005,
scientists applied new dating
techniques to these volcanic
layers, and pushed back the date
of the fossils to around 195,000
years old. This makes them
the oldest known remains
of Homo sapiens in the world.

016

THE INTEGRATED BODY

HUMAN GENETIC FORMULA

DNA (deoxyribonucleic acid) is the blueprint for all life, from the humblest yeast to the human being.
It provides a set of instructions on how to assemble the many thousands of different proteins that
make us who we are. It also tightly regulates this assembly, ensuring that it does not run out of control.

THE MOLECULE OF LIFE

Although we all look different, the basic have a wide range of vital functions in the DNA micrograph
structure of our DNA is identical. It consists body. They form structures such as skin or Although DNA is extremely
of chemical building blocks called bases, or hair, they carry signals around the body,
nucleotides. What varies between individuals and they fight off infectious agents such as small, its structure can be
is the precise order in which these bases bacteria. Proteins also make up cells, the observed by using a scanning
are connected into pairs. When base pairs basic units of the body, and perform the tunneling microscope, which
are strung together they can form thousands of basic biochemical processes
functional units called genes, which “spell needed to sustain life. However, only has magnified this image
out” the instructions for making a protein. about 1.5 percent of our DNA encodes around two million times.
Each gene encodes a single protein, genes. The rest consists of regulatory
although some complex proteins are sequences, structural DNA, or has no
encoded by more than one gene. Proteins obvious purpose—so-called junk DNA.

DNA double helix DNA backbone
In the vast majority of organisms, Formed of alternating
including humans, long strands of
DNA twist around each other to form units of phosphate
a right-handed spiral structure called and a sugar called
a double helix. The helix consists of
a sugar (deoxyribose) and phosphate deoxyribose
backbone and complementary base
pairs that stick together in the middle.
Each twist of the helix contains
around ten base pairs.

Guanine
Cytosine

Thymine
Adenine

BASE PAIRS Three bonds Phosphate GENES
join C and G
DNA consists of building blocks A gene is a unit of DNA needed to make a protein. Genes
called bases. There are four types: adenine C G range in size from just a few hundred to millions of base pairs. Eye color
(A), thymine (T), cytosine (C), and guanine T They control our development, but are also switched on and The genetics of eye color are
(G). Each base is attached to a phosphate G A off in response to environmental factors. For example, when incredibly complex, and many
group and a deoxyribose sugar ring to form A an immune cell encounters a bacterium, genes are switched different genes are involved.
a nucleotide. In humans, bases pair up to C on that produce antibodies to destroy it. Gene expression
form a double-stranded helix in which Sugar is regulated by proteins that bind to regulatory sequences Exon
adenine pairs with thymine, and cytosine with T within each gene. Genes contain regions that are translated
guanine. The two strands are “complementary” Two bonds join into protein (exons) and noncoding regions (introns).
to each other. Even if they are unwound A and T
and unzipped, they can realign and rejoin. Regulatory sequence Intron

Forming bonds Gene
The two strands of the double helix join by
forming hydrogen bonds. When guanine binds
with cytosine, three bonds are formed, and when
adenine binds with thymine, they form two.

017

HUMAN GENETIC FORMULA

PACKAGING DNA COILED Histone Chromosome
X-shaped structure
The human genome is composed of approximately 3 billion composed of DNA
bases of DNA—about 61/2 ft (2 m) of DNA in every cell if it
was stretched from end to end. Therefore, our DNA must molecules
be packaged up in order to fit inside each tiny cell. DNA is
concentrated into dense structures called chromosomes, DNA double Chromatin Nondividing
and each cell contains 23 pairs of chromosomes (46 in helix cell
total)—one set from the mother and another set from the
father. To package up DNA, the double helix must first be SUPERCOILED Supercoiled Chromosome
coiled around histone proteins, forming a structure that looks region
a little like beads on a string. These histone “beads” then wind
up and lock together into densely coiled “chromatin,” which, Supercoiled DNA
when a cell prepares to divide, further winds back on Coils of DNA
itself into tightly coiled chromosomes. double-helix are
themselves twisted
Histone into a supercoil

Cell prepared Histone
for division Ball-shaped
protein
Core unit
Package of proteins
around which 2–5

turns of DNA is
wrapped; also
known as a
nucleosome

Adenine–thymine

link
Adenine and
thymine always form
base pairs together

Guanine–cytosine Helical repeat
Helix turns 360°
link
Guanine always for every 10.4
forms a base pair base pairs

with cytosine

MAKING PROTEINS TRANSCRIPTION AND TRANSLATION DNA strand

Proteins consist of building blocks called amino acids, C TGGCAG C TGGCAG
strung together in chains and folded. Every three base
pairs of DNA codes for one amino acid, and the body GA
makes 20 different amino acids—others are obtained from
the diet. Protein synthesis occurs in two steps: transcription GAC C GT C CC
and translation. In transcription, the DNA double helix
unwinds, exposing single-stranded DNA. Complementary mRNA strand GU C
sequences of a related molecule called RNA (ribonucleic
acid) then create a copy of the DNA sequence that can DNA strand Strands separate RNA nucleotide
be translated into protein. This “messenger RNA” travels to
1 Inside the nucleus of the cell, the DNA strands temporarily 2 RNA nucleotides with correctly corresponding bases lock onto
ribosomes, where it is separate. One will act as a template for the formation of the exposed DNA bases and join to form a strand of mRNA.
translated into strings of mRNA (messenger ribonucleic acid). In this process, thymine bases are replaced by uracil bases.
amino acids. These are
then folded into the 3-D Used tRNS Ribosome Amino acid Amino acid
structure of a protein. molecule

Cell nucleus tRNS
DNA is found in a structure at molecule
the center of the cell called the
nucleus. The first stage of protein mRNA Protein (chain of amino acids)
synthesis takes place here. strand
4 As the ribosome moves along the mRNA,
Ribosome moves along it produces a specific sequence of amino
acids, which combine to form a particular protein.
3 The mRNA strand attaches to a ribosome, which passes along the
strand. Within the ribosome, individual tRNS (transfer ribonucleic
acid) molecules, each carrying an amino acid, slot onto the mRNA.

018

THE INTEGRATED BODY

THE HUMAN GENOME and gene-poor sections. When GENETIC PROFILING Chromosome banding
chromosomes are stained, differences in Each chromosome has two arms,
Different organisms contain different these regions show up as light and dark Apart from subtle genetic variations, humans also vary in and staining reveals that these are
genes, but a surprisingly large proportion bands, giving chromosomes a striped their noncoding DNA. This so-called junk DNA accounts for divided into bands. Each band is
of genes are shared between organisms. appearance. We still don’t know exactly how vast tracts of our genetic material, and we still have little numbered, making it possible to
For example, roughly half of the genes many protein-coding genes there are in the understanding of what it does. However, that does not make locate a specific gene if you know
found in humans are also found in human genome, but researchers currently it useless. Forensic scientists look at variations in noncoding its address. These are the bandings
bananas. However, it would not be estimate between 20,000 and 25,000. DNA to match criminal suspects to crime scenes. To do this, on chromosome 7.
possible to substitute the banana version they analyze short, repeating sequences of DNA within
of a gene for a human one because Karyotype noncoding regions, called short-tandem-repeats (STRs). The Short arm is
variations in the order of the base pairs This is an organized profile of the chromosomes in precise number of repeats is highly variable between known as 7p
within each gene also distinguish us. someone’s cells, arranged by size. Studying someone’s
Humans all possess more or less the same karyotype enables doctors to determine whether individuals. In one method, Centromere,
genes, but many of the differences any chromosomes are missing or abnormal. forensic scientists compare where two
between individuals can be explained by ten of these repeating halves of
subtle variations within each gene. The regions, chopping them
extent of these variations is smaller than up and then separating chromosome
between humans and animals, and smaller them on the basis of their meet
still than the differences between humans size to generate a series of
and plants. In humans, DNA differs by bands called a DNA Long arm is
only around 0.2 percent, while human profile or fingerprint. known as 7q
DNA differs from chimpanzee DNA by
around 5 percent. Shared characteristics
Genetic profiling can also
Human genes are divided unevenly be used to prove family
between 23 pairs of chromosomes, and relationships. Here, two
each chromosome consists of gene-rich children are shown to share
bands with each parent,
proving they are related.

Chromosome complement There is no known function for 97 percent The cystic
The human genome is stored on 23 pairs of chromosomes—46 in total. of the DNA in the human genome— fibrosis gene is
Of these, 22 pairs store general genetic information and are called sometimes known as junk DNA. found at 7q31.2
autosomes, while the remaining pair determines whether you are male
or female. There are two types of sex chromosome: X and Y. Men have
one X and one Y, while women have two X chromosomes.

1 2 3 4 5 6 7 8 9 10 11 12

Number of Number of Number of Number of Number of Number of Number of Number of Number of Number of Number of Number of

genes: 4,234 genes: 3,078 genes: 3,723 genes: 542 genes: 737 genes: 2,277 genes: 4,171 genes: 1,400 genes: 1,931 genes: 1,776 genes: 546 genes: 1,698
Associations Associations Associations Associations Associations Associations Associations Associations Associations Associations Associations Associations
and conditions: and conditions: and conditions: and conditions: and conditions: and conditions: and conditions: and conditions: and conditions: and conditions: and conditions: and conditions:
Alzheimer’s Color blindness; Deafness; Blood vessel DNA repair; Cannabis Pain perception; Brain Blood group; Inflammation; Sense of smell; Cartilage and
disease; red hair; breast autism; growth; immune nicotine receptor; muscle, tendon development albinism; DNA repair; hemoglobin muscle strength;
Parkinson’s cancer; Crohn’s cataracts; system genes; addiction; cartilage and bone and function; bladder cancer; breast cancer; production; narcolepsy;
disease; disease; susceptibility to bladder cancer; Parkinson’s strength; formation; cleft lip and porphyria Usher’s autism; albinism; stuttering;
glaucoma; amyotrophic HIV infection; Huntington’s disease; Cri du immune system cystic fibrosis; palate; syndrome sickle-cell Parkinson’s
prostate cancer; lateral sclerosis diabetes; disease; Chat syndrome; genes; epilepsy; schizophrenia; schizophrenia; anemia; breast disease
brain size (ALS); high Charcot-Marie- deafness; breast cancer; type 1 diabetes; Williams Werner cancer; bladder
cholesterol Tooth disease hemophilia; Crohn’s disease rheumatoid syndrome; syndrome cancer
Parkinson’s arthritis deafness; type 2
disease diabetes

019

HUMAN GENETIC FORMULA

THE SUM OF ONE’S GENES Human diversity BREAKTHROUGHS
Although all humans carry more or less the same genes in terms
At the simplest level, each gene encodes a protein, and of the proteins they manufacture, the vast number of possible GENETIC ENGINEERING
each protein results in a distinct trait or phenotype. In combinations of genes, and the ways they are expressed, explains
humans, this is best illustrated by inherited diseases like the huge diversity in the human body across the world’s population. This form of gene manipulation enables us to substitute
cystic fibrosis. Here, a mutation in the CFTR gene, which a defective gene with a functional one, or introduce new
makes a protein found in mucus, sweat, and digestive Inherited traits genes. Glow-in-the-dark mice were created by introducing
juices, results in the accumulation of thick mucus in the Humans possess two copies of a jellyfish gene that encodes a fluorescent protein into the
lungs, leaving carriers of the defective gene more each gene, but not all genes are mouse genome. Finding safe ways of delivering replacement
susceptible to lung infections. If we know what a specific equal. Dominant genes show genes to the correct cells in humans could lead to cures for
gene looks like in a healthy person, and how it looks if it their effect even if there is only one in a pair, while recessive genes many types of inherited diseases—so-called gene therapy.
has gone wrong, it may be possible to devise a genetic need two copies (see p.397). Free-hanging earlobes are caused by
test to find out whether someone is at risk of disease. the dominant form of a gene, while attached earlobes are recessive.
For example, mutations in a gene called BRCA1 can
predict if a woman is at high risk of developing one form
of breast cancer. However, many traits—such as height or
hair color—are influenced by several genes working
together. And genes are only part of the equation. In the
case of personality or lifespan, multiple genes interact
with environmental factors, such as upbringing and diet,
to shape who we are and who we will become (see p.396).

13 14 15 16 17 18 19 20 21 22 X Y

Number of Number of Number of Number of Number of Number of Number of Number of Number of Number of Number of Number of

genes: 925 genes: 1,887 genes: 1,377 genes: 1,561 genes: 2,417 genes: 756 genes: 1,984 genes: 1,019 genes: 595 genes: 1,841 genes: 1,860 genes: 454
Associations Associations Associations Associations Associations Associations Associations Associations Associations
and conditions: and conditions: and conditions: and conditions: and conditions: and conditions: and conditions: Associations Associations Associations
LSD receptor; Antibody Connective tissue Edward’s Cognition; Celiac disease; Down syndrome;
breast cancer production; and conditions: and conditions: function; early syndrome; Alzheimer’s type 1 diabetes; Alzheimer’s and conditions: and conditions: and conditions:
(BRCA2 gene); Alzheimer’s onset breast Paget’s disease; disease; prion diseases disease;
bladder cancer; disease; Eye color; skin Red hair; obesity; cancer (BRCA1); porphyria; cardiovascular amyotrophic Antibody Breast cancer; Male fertility
deafness; amyotrophic brittle bone selective mutism disease; high lateral sclerosis production; color blindness; and testicular
Wilson’s disease lateral sclerosis color; Angelman Crohn’s disease; disease; bladder cholesterol; (ALS); deafness
(ALS); muscular cancer hereditary stroke
dystrophy syndrome; breast breast cancer; breast cancer; hemophilia; development

cancer; Tay-Sachs trisomy 16 schizophrenia; fragile X
amyotrophic syndrome;
disease; Marfan (most common lateral sclerosis Turner syndrome;

syndrome chromosomal

cause of (ALS) Klinefelter’s

miscarriage) syndrome

020 Nucleolus Nucleus
The region at the center of The cell’s control center,
THE INTEGRATED BODY the nucleus; plays a vital role containing chromatin and

THE CELL in ribosome production most of the cell’s DNA

It is hard to comprehend what 75 trillion cells looks like, but Nuclear membrane
observing yourself in a mirror would be a good start. That A two-layered membrane
is how many cells exist in the average human body—and we with pores for substances to
replace millions of these cells every single day. enter and leave the nucleus

CELL ANATOMY Generic cell
At a cell’s heart is the nucleus, where
The cell is the basic functional unit of the human body. the genetic material is stored and
Cells are extremely small, typically only about 0.01 mm the first stages of protein synthesis
across—even our largest cells are no bigger than the width occur. Cells also contain other
of a human hair. They are also immensely versatile: some structures for assembling proteins,
can form sheets like those in your skin or lining your including ribosomes, the
mouth, while others can store or generate energy, such as endoplasmic reticulum, and Golgi
fat and muscle cells. Despite their amazing diversity, there apparatus. The mitochondria
are certain features that all cells have in common, provide the cell with energy.
including an outer membrane, a control center called a
nucleus, and tiny powerhouses called mitochondria. Nucleoplasm
Fluid within the nucleus, in

which nucleolus and
chromosomes float

Microtubules
Part of cell’s cytoskeleton,

these aid movement of
substances through the

watery cytoplasm

Centriole
Composed of
two cylinders

of tubules;
essential to cell

reproduction

Liver cell Microvilli
These cells make protein, cholesterol, and bile, and detoxify and These projections
modify substances from the blood. This requires lots of energy, increase the cell’s
so liver cells are packed with mitochondria (orange).
surface area,
aiding absorption

of nutrients

CELL METABOLISM Released secretions
Secretions are released
When individual cells break down nutrients to generate from the cell by exytosis,
energy for building new proteins or nucleic acids, it is when a vesicle merges
known as cell metabolism. Cells use a variety of fuels to with the cell membrane
generate energy, but the most common one is glucose, and releases its contents
which is transformed into adenosine triphosphate (ATP).
This takes place in structures called Secretory vesicle
mitochondria through a process called Sac containing various
cellular respiration: enzymes within the
mitochondria react with oxygen and substances, such as
glucose to produce ATP, carbon dioxide, enzymes, that are produced
and water. Energy is released when ATP is
converted into adenoside diphosphate by the cell and secreted at
(ADP) via the loss of a phosphate group. the cell membrane

Mitochondrion Golgi complex Lysosome
While the number of mitochondria varies between A structure that processes Produces powerful
different cells, all have the same basic structure: an enzymes that aid in
outer membrane and a highly folded inner membrane, and repackages proteins digestion and excretion
where the production of energy actually takes place. produced in the rough of substances and
worn-out organelles
endoplasmic reticulum for
release at the cell membrane

021
THE CELL

Vacuole CELL TRANSPORT Cell
Sac that stores and membrane
transports ingested Materials are constantly being transported in and out of the cell via the cell
materials, waste membrane. Such materials could include fuel for generating energy, or Cell
products, and water building blocks essential for protein assembly, such as amino acids. Some interior
cells can secrete signaling molecules to communicate with neighboring
cells or the rest of the body. The cell membrane is largely composed of Fluid outside
phospholipids, but it is also studded with proteins that facilitate transport, cell
enable cells to communicate with one another, and identify a cell to other
cells. The membrane is permeable to some molecules, but other molecules Diffusion
need active transport through special channels in the membrane. Cells Molecules passively cross the membrane from
have three main methods of transport: diffusion, facilitated diffusion, and areas of high to low concentration. Water and
active transport (the last requires energy). oxygen both cross by diffusion.

Cytoskeleton Carrier Molecule at
Internal framework of the cell, protein receptor site
made up of microfilaments
and hollow microtubules

Microfilament Cell Protein forms
Provides support for the interior channel
cell; sometimes linked to
the cell’s outer membrane Facilitated diffusion Active transport
A carrier protein, or protein pore, binds with a Molecules bind to a receptor site on the cell
Mitochondrion molecule outside the cell, then changes shape membrane, triggering a protein, which changes
Site of fat and sugar digestion and ejects the molecule into the cell. into a channel that molecules travel through.
in the cell; produces energy

Cytoplasm MAKING NEW BODY CELLS
Jellylike fluid in which
organelles float; primarily Some cells are constantly replacing themselves; others last a lifetime. While the cells
water, but also contains lining the mouth are replaced every couple of days, some of the nerve cells in the brain
enzymes and amino acids have been there since before birth. Stem cells are specialized cells that are constantly
dividing and giving rise to new cells, such as blood cells, immune cells, or fat cells. Cell
Rough endoplasmic division requires that a cell’s DNA is accurately copied and then shared equally between
reticulum two “daughter” cells, by a process called mitosis. The chromosomes are first replicated
Consists of folded membranes, before being pulled to opposite ends of the cell. The cell then divides to produce two
studded with ribosomes, that daughter cells, with the cytoplasm and organelles being shared between the two cells.
extend throughout the cell;
helps transport of materials Nuclear membrane Centromere Single
through the cell; site of much Centromere chromosome
protein manufacture

Ribosome
Tiny structure that assists with
protein assembly (see p.17)

Duplicated Spindle
chromosome
Nucleus

Cell membrane 1 Preparation 2 Alignment 3 Separation
Encloses contents of the cell The cell produces proteins and The chromosomes line up along The chromosomes are pulled
and maintains the cell’s shape; new organelles, and duplicates a network of filaments called the apart and move to opposite
regulates flow of substances in its DNA. The DNA condenses spindle. This is linked to a larger ends of the cell. Each end has an
and out of the cell into X-shaped chromosomes. network called the cytoskeleton. identical set of chromosomes.

Peroxisome Single chromosome Nucleus Chromosome
Makes enzymes that oxidize
some toxic chemicals

Smooth endoplasmic Nuclear membrane 5 Offspring
Each daughter cell contains a complete copy of
reticulum 4 Splitting the DNA from the parent cell; this enables it to
Network of tubes and flat, The cell now splits in two, with the cytoplasm, cell continue growing, and eventually divide itself.
curved sacs that helps to membrane, and remaining organelles being shared
transport materials through the roughly equally between the two daughter cells.
cell; site of calcium storage;
main location of fat metabolism

022

THE INTEGRATED BODY

CELLS AND TISSUES

Cells are the building blocks from which the human body is made.
Some cells work alone—such as red blood cells, which carry
oxygen around the body, or sperm, which fertilize egg cells—but
many are organized into tissues, where cells with different
functions join forces to accomplish one or more specific tasks.

CELL TYPES 200 Integrated tissues
This section through the wall
There are more than 200 different types of cell in the body, The number of different types of cell in the human of the esophagus shows a
each type specially adapted to its own particular function. body. Most are organized in groups to form tissues. combination of different tissues:
Every cell contains the same genetic information, but not lining epithelium (pink, top);
all of the genes are “switched on” in every cell. It is this collagen connective tissue (blue);
pattern of gene expression that dictates what the cell blood vessels (circular); skeletal
looks like, how it behaves, and what role it performs in muscle fibers (purple, bottom).
the body. A cell’s fate is largely determined before birth,
influenced by its position in the body and the cocktail Red blood cells Concave Epithelial cells Fingerlike cilia
of chemical messengers that it is exposed to in that Unlike all other human cells, red surface These cells are barrier cells lining Nucleus
environment. Early during development, stem cells begin blood cells lack a nucleus and the cavities and surfaces of the
to differentiate into three layers of more specialized cells most organelles. Instead, they are Red from body. They include skin cells and
called the ectoderm, endoderm, and mesoderm. Cells packed with an oxygen-carrying haemoglobin the cells lining the lungs and
of the ectoderm will form the skin and nails, the epithelial protein called hemoglobin, which reproductive tracts. Some epithelial
lining of the nose, mouth, and anus, the eyes, and the gives blood its red color. Red cells have fingerlike projections
brain and spinal cord. Cells of the endoderm become the blood cells develop in the bone called “cilia” that can waft eggs
inner linings of the digestive tract, the respiratory linings, marrow and circulate for around down the fallopian tubes, or
and glandular organs including the liver and pancreas. 120 days, before being broken push mucus out of the lungs,
Mesoderm cells develop into the muscles, circulatory down and recycled. for example.
system, and the excretory system, including the kidneys.
Adipose (fat) cells Fat globule Nerve cells
SCIENCE These cells are highly adapted These electrically excitable cells
for the storage of fat, and the transmit electrical signals, or “action Dendrite
STEM CELLS bulk of their interior is taken up potentials,” down an extended stem
by a large droplet of semiliquid called an axon. Found throughout Nucleus
A few days after fertilization, an embryo consists of a ball of fat. When we gain weight, our the body, they enable you to move Axon
“embryonic stem cells” (ESCs). These cells have the potential adipose cells swell up and fill and feel sensations such as pain.
to become any type of cell in the body. Scientists are trying to with even more fat, though They communicate with each
harness this property to grow replacement body parts. As the eventually they also start to other across connections
embryo grows, the stem cells become increasingly restricted increase in number. called synapses.
in their potential. By the time we are born most of our cells
are fully differentiated, but a small number of adult stem cells Nucleus
remain in parts of the body, including in bone marrow. While
not as universal in their potential as ESCs, they do have some Sperm cells Head Ovum (egg) cells Nucleus Follicle
flexibility in terms of what they can become. Scientists believe Sperm are male reproductive One of the largest cells in cells
that these cells could also be used to help cure disease. cells with a tail that enables Middle the body, a human egg is still only
them to swim up the female piece just visible to the naked eye. Eggs
reproductive tract and fertilize are the female reproductive cells
an egg. Sperm contain just 23 Tail and, like sperm, they contain just
chromosomes; in fertilization, 23 chromosomes. Every woman is
these pair up with an egg’s born with a finite number of eggs,
23 chromosomes to create which decreases as she ages.
an embryo with the normal
46 chromosomes per cell. Jellylike film

Photoreceptor cells Smooth muscle cells
These occur at the back of the eye. They contain a light-sensitive One of three types of muscle cell, smooth muscle cells are spindle-
pigment and generate electrical signals when struck by light, shaped cells found in the arteries and the digestive tract that produce
enabling us to see. There are two main photoreceptor types: rods long, wavelike contractions. To do this, they are packed with
(below) see in black and white, and work well in low light; cones contractile filaments, and large numbers of mitochondria that supply
work better in bright light, and are able to detect colors. the energy they need.

Adult stem cells Nucleus Filaments Nucleus
Adult stem cells, such as the large white cell in this image, are
present in bone marrow, where they multiply and produce
millions of blood cells, including red blood cells, also seen here.

Pigment-containing part

TISSUE TYPES 023

Cells often group together with their own kind to form tissues that perform a specific CELLS AND TISSUES
function. However, not all cells within a tissue are necessarily identical. The four main
types of tissue in the human body are muscle, connective tissue, nervous tissue, Skeletal muscle
and epithelial tissue. Within these groups, different forms of these tissues can have very This tissue performs voluntary
different appearances and functions. For example, blood, bone, and cartilage are all movements of the limbs. Unlike
types of connective tissue, but so are fat layers, tendons, ligaments, and the fibrous tissue smooth muscle, skeletal muscle
that holds organs and epithelial layers in place. Organs such as the heart and lungs
are composed of several different kinds of tissue. cells are arranged into
bundles of fibers, which
Smooth muscle connect to bones via
Able to contract in long, wavelike tendons. They are
motions without conscious packed with highly
thought, smooth muscle is organized filaments
found in sheets on the walls that slide over one
of the blood vessels, another to produce
stomach, intestines, contractions.
and bladder. It is vital
for maintaining MUSCLE FIBERS
blood pressure and
for pushing food Spongy bone
through the Bone cells secrete a hard
digestive system. material that makes bones
strong and brittle. Spongy bone
SMALL INTESTINE
is found in the center of
Cartilage bones, and is softer and
This stiff, rubbery, connective weaker than the
tissue is composed of cells called compact bone.
chondrocytes embedded in a The latticelike
matrix of gel-like material, spaces in spongy
which the cells secrete. bone are filled with
Cartilage is found in bone marrow or
the joints between connective tissue.
bones, and in the
ear and nose. The END OF THE FEMUR
high water content
of cartilage makes it Loose connective tissue
tough but flexible. This type of tissue also contains
cells called fibroblasts, but the
NOSE CARTILAGE fibers they secrete are loosely

Dense connective tissue organized and run in
This contains fibroblast cells, random directions,
which secrete the fibrous protein making the tissue
called type 1 collagen. The fibers quite pliable. Loose
are organized into a regular connective tissue
parallel pattern, making holds organs in
the tissue very strong. place, and provides
Dense connective cushioning and
tissue occurs in the support.
base layer of skin,
and forms structures DERMAL TISSUE
such as ligaments
and tendons. Adipose tissue
A type of connective tissue,
KNEE LIGAMENTS adipose tissue is composed of
fat cells called adipocytes, as
Epithelial tissue
This tissue forms a covering well as some fibroblast
or lining for internal and cells, immune cells, and
external body surfaces. blood vessels. Its
Some epithelial tissues main function is to
can secrete substances act as an energy
such as digestive store, and to
enzymes; others can cushion, protect,
absorb substances and insulate
like food or water. the body.

STOMACH WALL SUBCUTANEOUS FAT

Nerve tissue
This forms the brain, spinal cord,

and the nerves that control
movement, transmit
sensation, and regulate
many body
functions. It is
mainly made up of
networks of nerve
cells (see opposite).

UPPER SPINAL CORD

024

THE INTEGRATED BODY

BODY COMPOSITION

If the 75 trillion cells that make up the human body led an isolated, anarchic existence, it would be no more
than a shapeless mass. Instead, those cells are precisely organized, taking their place within the hierarchical
structure that is a fully functioning human being.

LEVELS OF ORGANIZATION others to form molecules such as water (hydrogen and and lines cavities; connective, which supports and
oxygen atoms), and the many organic molecules, protects body structures; muscular, which creates
The overall organization of the human body can be including proteins and DNA. These organic molecules are movement; and nervous, which facilitates rapid internal
visualized in the form of a hierarchy of levels, as shown constructed around a “skeleton” of linked carbon atoms. communication (see p.23).
below. At its lowest level are the body’s basic chemical
constituents. As the hierarchy ascends, the number of Cells are the smallest of all living units. They are Organs, such as the liver, brain, and heart are discrete
components in each of its levels—cells, tissues, organs, created from chemical molecules, which shape their structures built from at least two types of tissue. Each has
and systems—decreases progressively, culminating in outer covering and inner structures, and drive the a specialized role or roles that no other organ can
a single organism at its apex. metabolic reactions that keep them alive. There are more perform. Where organs collectively have a common
than 200 types of cell in the human body, each adapted purpose, they are linked together within a system, such as
More than 20 chemical elements are found in the to carry out a specific role, but not in isolation (see p.22). the cardiovascular system, which transports oxygen and
body, with just four—oxygen, carbon, hydrogen, and Groups of similar cells with the same function form and nutrients around the body, and which is overviewed here.
nitrogen—comprising around 96 percent of body mass. cooperate within communities called tissues. The body’s Integrated and interdependent, the body’s systems
Each element is composed of atoms, the tiny building four basic tissue types are epithelial, which covers surfaces combine to produce a complete human (see pp.26–27).
blocks of matter, of which there are quadrillions in the
body. Atoms of different elements generally combine with

1 234

CHEMICAL CELL TISSUE ORGAN

CHEMICALS CELLS HEART TISSUE HEART

Key among the chemicals inside all cells is While cells may differ in size and shape One of three types of muscle tissue, cardiac Like other organs, the heart is made of
DNA (see pp.16–17). Its long molecules according to their function (see p.22), all muscle is found only in the walls of the several types of tissue, including cardiac
resemble twisted ladders, their “rungs” made possess the same basic features: an outer heart. Its constituent cells contract together muscle tissue. Among the other types
from bases that provide the instructions for boundary membrane; organelles, floating to make the heart squeeze and pump, and, present are connective tissues, which
making proteins. These, in turn, perform within a jellylike cytoplasm; and a nucleus, working as a network, conduct the signals protect the heart and hold the other tissues
many roles, from building cells to controlling which contains DNA (see pp.20–21). Cells that ensure that the pumping is precisely together, and epithelial tissues, which line its
chemical reactions. are the body’s most basic living components. coordinated. chambers and cover its valves.

DNA sequencing Stem cells Muscle fibers Complex structure
The bases of DNA can be isolated and These unspecialized cells have the unique The cells, or fibers, in cardiac tissue are The heart has a complex structure. Internally
separated by scientists. Such sequencing allows ability to differentiate, or develop, into a wide long and cylindrical and have branches that it has four chambers through which blood is
them to “read” the instructions coded within range of specialized tissue cells such as form junctions with other cells to create an pumped by its muscular walls. It is connected
the molecules. muscle, brain, or blood cells. interconnected network. to a vast network of veins and arteries.

025

BODY COMPOSITION

75trillion Neck arteries
The arteries of the neck
The total number of cells that make have the important role of
up the average human body. supplying blood to the brain

5 Central organ
The heart sits at the center

of the cardiovascular
system, pumping blood

around the body

Long vessels
Some of the longest blood
vessels in the body transport
blood through the legs to

and from the feet

BODY SYSTEM

CARDIOVASCULAR SYSTEM endocrine (hormonal), lymphatic, respiratory,
digestive, urinary, and reproductive systems. At
The heart, blood, and the blood vessels— the same time, the cardiovascular system
arteries (shown in red) and veins (blue)—that depends on those other systems to function
carry blood, make up the cardiovascular normally. The respiratory system, for example,
system. As the body’s key transportation system, provides the blood with oxygen, the nervous
its basic function is to pump blood around the system regulates the rate at which the heart beats,
body, delivering essentials to, and removing and the digestive system supplies the body with
waste from, the tissue cells that comprise the energy-rich fuel (see pp.26–27).
body’s other ten systems: the integumentary
(skin, nails, and hair), skeletal, muscular, nervous,

026 LYMPHATIC SYSTEM

THE INTEGRATED BODY The lymphatic system is composed of a network of
vessels and nodes, which drain fluid from blood
BODY SYSTEMS capillaries and return it to the veins. Its main functions
are to maintain fluid balance within the cardiovascular
The human body can do many different things. It can digest food, think, system and to distribute immune cells from the
move, even reproduce and create new life. Each of these tasks is performed immune system around the body. Movement of
by a different body system—a group of organs and tissues working lymph fluid relies on the contraction and relaxation
together to complete that task. However, good health and body efficiency of smooth muscles within the muscular system.
rely on the different body systems working together in harmony.

SYSTEM INTERACTION ENDOCRINE SYSTEM

Think about what your body is doing right now. You Like the nervous system, the endocrine system
are breathing, your heart is beating, and your blood communicates messages between the rest of
pressure is under control. You are also conscious and the body’s systems, enabling them to be closely
alert. If you were to start running, specialized cells called monitored and controlled. It uses chemical
chemoreceptors would detect a change in your body’s messengers called hormones, which are usually
metabolic requirements and signal to the brain to release secreted into the blood from specialized glands.
adrenaline. This would in turn signal to the heart to beat
faster, boosting blood circulation and enabling more
oxygen to reach the muscles. After a while, cells in the
hypothalamus might detect an increase in body
temperature and send a signal to the skin to produce
sweat, which would evaporate and cool you down.

The individual systems of the body are linked together
by a vast network of positive and negative feedback
loops. These use signaling molecules such as hormones
and electrical impulses from nerves to communicate
and maintain a state of equilibrium. Here, the basic
components and functions of each system are described,
and examples of system interactions are examined.

CONTROLLING THE HEART NERVOUS SYSTEM

Working together, nerves of the sympathetic The brain, spinal cord, and nerves work
and parasympathetic nervous systems together to collect, process, and
regulate the heart and cardiac output disseminate information from the body’s
(see p.339). Sympathetic nerves release internal and external environments. The
chemicals that increase heart rate and the nervous system communicates through
force of cardiac muscle contractions. networks of nerve cells, which connect with
The vagus nerve, from the parasympathetic every other body system. The brain controls
system, releases a chemical that slows the and monitors all of these systems to make
heart rate and reduces sure that they are performing normally
cardiac output. and receiving everything they need.

Spinal cord RESPIRATORY SYSTEM BREATHING IN AND OUT Accessory and
intercostal muscles
Vagus nerve Every cell in the body needs oxygen and The mechanics of breathing rely upon an
must get rid of the waste product carbon interaction between the respiratory and Diaphragm
Sympathetic dioxide in order to function—regardless muscular systems. Together with three
nerves of which body system it belongs to. The accessory muscles, the intercostal muscles
respiratory system allows this to happen by and the diaphragm contract to increase the
breathing air into the lungs, where the passive volume of the chest cavity (see pp.328–29).
exchange of these molecules occurs between This forces air down into the lungs.
the air and blood. The cardiovascular system A different set of muscles is used during
transports oxygen and carbon dioxide forced exhalation. These rapidly shrink the
between the cells and the lungs. chest cavity, forcing air out of the lungs.

027

BODY SYSTEMS

DIGESTIVE SYSTEM MUSCULAR SYSTEM CIRCULATING BLOOD

In addition to oxygen, every cell needs The muscular system is made up of three types of muscle: The veins of the cardiovascular system
energy in order to function. The digestive skeletal, smooth, and cardiac. It is responsible for generating
system processes and breaks down the food movement—both of the limbs and within the other body rely on the direct action of skeletal
we eat so that a variety of nutrients can be systems. For example, smooth muscle aids the digestive
absorbed from the intestines into the system by helping to propel food down the esophagus and muscles to transport deoxygenated
circulatory system. These are then delivered through the stomach, intestines, and rectum. And the
to the cells of every body system in order to respiratory system could not function without the muscles of blood from the body’s extremities
provide them with energy. the thorax contracting to fill the lungs with air (see opposite).
back to the heart (see p.341). As
SKELETAL SYSTEM
shown here, in the muscles
This system uses bones, cartilage, ligaments, and tendons to
provide the body with structural support and protection. It and veins of the lower leg, Blood
encases much of the nervous system within a protective skull muscle contractions forced
and vertebrae, and the vital organs of the respiratory and compress nearby veins, upward
circulatory systems within the rib cage. The skeletal system
also supports the circulatory and immune systems by forcing the blood
manufacturing red and white blood cells.
upward. When the Contracting
muscles relax, the muscle

one-way valves within the

veins prevent the blood from

flowing back down, and the vein

fills up with blood from below. The same process is used

by the lymphatic system as muscle contractions aid the

transportation of lymph through lymph vessels (see p.344).

CARDIOVASCULAR REPRODUCTIVE SYSTEM MAKING URINE
SYSTEM
Although the reproductive system is not essential for The kidney is the site of a key interaction between the
The cardiovascular system uses blood to maintaining life, it is needed to propagate it. Both the testes urinary and cardiovascular systems (see p.367). Urine is
carry oxygen from the respiratory system of the male and the ovaries of the female produce gametes produced as nephrons, the kidney’s functional units, filter the
and nutrients from the digestive system in the form of sperm and eggs, which fuse to create an blood. Within each nephron, blood is forced through a
to cells of all the body’s systems. It also embryo. The testes and ovaries also produce hormones glomerulus (cluster of capillaries) and filtered by its sievelike
removes products from these cells. At the including estrogen and testosterone, so also form part membranes. The filtrate passes through a series of tubules
center of the cardiovascular system lies of the endocrine system. through which some glucose, salts, and water are reabsorbed
the muscular heart, which pumps the into the blood stream. What remains, including urea and
blood through the blood vessels. URINARY SYSTEM waste products, is excreted as urine.

The urinary system filters and removes many of the waste products Blood Tubule
generated by the other body systems, such as the digestive system. supply
It does this by filtering blood through the kidneys and producing urine,
which is collected in the bladder and then excreted through the urethra Glomerulus
(see right). The kidneys also help maintain blood pressure within the
cardiovascular system by ensuring that the correct amount of water is
reabsorbed by the blood.

anatomy

The human body is a “living machine” with many complex
working parts. To understand how the body functions it is vital
to know how it is assembled. Advances in technology allow us
to strip back the outer layers and reveal the wonders inside.

030 Anatomical terminology

036

BODY SYSTEMS

038 Skin, hair, and nail structure 060 Nervous system 074 Lymphatic and 080 Urinary system
040 Skeletal system 066 Respiratory system immune system 082 Reproductive system
050 Muscular system 068 Cardiovascular system 084 Endocrine system
078 Digestive system

086

ANATOMY ATLAS

Head and Neck 150 Respiratory 192 Reproductive Hip and thigh
154 Cardiovascular 196 MRI scans
088 Skeletal 160 Lymphatic and immune 236 Skeletal
098 Muscular 162 Digestive Shoulder and upper arm 242 Muscular
104 Nervous 164 Reproductive 250 Nervous
122 Respiratory 166 MRI scans 198 Skeletal 254 Cardiovascular
124 Cardiovascular 204 Muscular 258 Lymphatic and immune
128 Lymphatic and immune Abdomen and pelvis 212 Nervous
130 Digestive 216 Cardiovascular Lower leg and foot
132 Endocrine 168 Skeletal 220 Lymphatic and immune
134 MRI scans 174 Muscular 260 Skeletal
178 Nervous Lower arm and hand 264 Muscular
Thorax 180 Cardiovascular 268 Nervous
182 Lymphatic and immune 222 Skeletal 270 Cardiovascular
136 Skeletal 184 Digestive 226 Muscular 272 MRI scans
142 Muscular 190 Urinary 230 Nervous
148 Nervous 232 Cardiovascular
234 MRI scans



030

ANATOMY

Pectoral region Midclavicular line
The chest; sometimes used A vertical line running
down from the midpoint
to refer to just the upper of each clavicle
chest, where the pectoral
Axilla
muscles lie Loosely, the armpit; more precisely,
the pyramid-shaped part of the body
Epigastric region between the upper arm and the side
Area of the abdominal wall of the thorax. Floored by the skin of
above the transpyloric plane, the armpit, it reaches up to the level
and framed by the diverging of the clavicle, top of the scapula,
and first rib
margins of the ribcage
Anterior surface of arm
Umbilical region “Anterior” means front, and always
Central region of the refers to the body when it is in the
“anatomical position” shown here.
abdomen, around Strictly speaking, “arm” only relates
the umbilicus (navel) to the part of the upper limb between
the shoulder and the elbow
Lumbar region
Refers to the sides of the Hypochondrial region
abdominal wall, between The abdominal region
under the ribs on each side
the transpyloric and
intertubercular planes Transpyloric plane
Horizontal plane joining the tips of
Intertubercular plane the ninth costal cartilages, at the
This plane passes through the iliac margins of the ribcage; also level
tubercles—bony landmarks on the with the first lumbar vertebra and
pelvis—and lies at the level of the the pylorus of the stomach

fifth lumbar vertebra Cubital fossa
Triangular area anterior to (in front
Iliac region of) the elbow, bounded above by a
The area below the intertubercular line between the bony epicondyles
plane and lateral to (to the side of) of the humerus on each side, and
the midclavicular line; may also be framed below by the pronator teres
and brachioradialis muscles
referred to as the “iliac fossa”
Anterior surface of forearm
Anatomically—and colloquially
—the forearm is the part of the body
between the elbow and the wrist

Suprapubic region
The part of the abdomen
that lies just above the
pubic bones of the pelvis

Inguinal region
Refers to the groin area, where
the thigh meets the trunk

031

ANATOMICAL TERMINOLOGY

Palmar surface of hand
Refers to the anterior
(front) surface of the hand
Anterior surface of thigh
As in common usage, the
term “thigh” refers to the part
of the body between the hip
and the knee
Anterior surface of knee
Anterior surface of leg
Anatomically, “leg” just
refers to the part between
the knee and ankle, and the
term “lower limb” is used for
the whole limb
Dorsum of foot
Standing upright, this is the
upper surface of the foot

ANTERIOR (FRONT)

ANATOMICAL Anatomical language allows us to describe the structure of the body
TERMINOLOGY clearly and precisely. It is useful to be able to describe areas and parts,
as well as the planes and lines used to map out the body, in much
more accurate and detailed terms than would be possible colloquially.
Rather than recording that a patient had a tender area “somewhere
on the left side of the belly,” a doctor can be more precise and say that
the patient’s painful area was “the left lumbar region,” and other
doctors will know exactly what is meant.

Superior Medial Lateral 032

ANATOMY

Proximal Occipital region
Medial The back of the head
Lateral
Distal Posterior surface of arm

Proximal Lumbar region
This term comes from the
Distal Latin for “loin.” On the back
of the body it refers to the
Inferior part between the thorax
and the pelvis
Relative terms
In addition to defining parts of the body, Gluteal region
anatomical terminology also allows us to precisely Refers to the buttock, and
and concisely describe the relative positions of extends from the iliac crest
various structures. These terms always refer back (the top of the bony pelvis)
to relative positions of structures when the body above, to the gluteal fold (the
is in the “anatomical position” (shown above). furrow between the buttock
Medial and lateral describe positions of structures and thigh) below
toward the midline, or toward the side of the
body, respectively. Superior and inferior refer to
vertical position—toward the top or bottom of the
body. Proximal and distal are useful terms,
particularly for structures in the limbs, describing
a relative position toward the center or the
periphery of the body.

Posterior surface
of forearm

033

ANATOMICAL TERMINOLOGY

Posterior surface of thigh
Popliteal fossa
A diamond-shaped cavity
at the back of the knee,
between the diverging
hamstring muscles above
and the converging calf
muscles below
Calf
This common term is
also used anatomically,
to describe the fleshy
back of the leg

POSTERIOR (BACK)

Dorsum of hand ANATOMICAL The illustration shows some of the terms used for the broader regions
The back of the hand TERMINOLOGY of the back of the body, and those used to describe relative position.
Where our everyday language may have names for larger structures—
such as the shoulder or hip—it soon runs out when it comes to finer
detail. So anatomists have created names for specific structures,
usually derived from Latin or Greek. The pages that follow show the
detailed structure of the head and neck, thorax, abdomen, and limbs.
The anatomical language is there to illuminate rather than confuse.
Some of the terms may seem unfamiliar and even unnecessary at first,
but they enable precise description and clear communication.

034

ANATOMY

Transverse plane Coronal plane
Cuts horizontally through Sagittal plane
the body, dividing it into upper
Transverse plane
and lower parts
Flexion
TRANSVERSE Extension

Adduction

Abduction

Anatomical terms for movement
The diagram above shows the three planes—sagittal, coronal,
and transverse—cutting through a body, and to the left are
examples of real MRI scans demonstrating views along those
planes. The above image also illustrates some medical terms that
are used to describe certain movements of body parts: flexion
decreases the angle of a joint, such as the elbow, while extension
increases it; adduction draws a limb closer to the sagittal plane,
while abduction moves it farther away from that plane.

035

PLANES AND MOVEMENT

PLANES AND MOVEMENT

Sometimes it is easier to appreciate and understand and relative positions of structures within the body
anatomy by dividing the three-dimensional body up (see pp.30–33), and to describe movements of joints,
into two-dimensional slices. Computed tomography such as abduction, adduction, flexion, and extension
(CT) and magnetic resonance imaging (MRI) scans are (see left). Some joints, such as the shoulder and hip
examples of medical imaging techniques that show joint, also allow rotation of a limb along its axis.
the body in slices or sections. The orientation of these A special type of rotation between the forearm bones
slices or sections are described as sagittal, coronal, allows the palm to be moved from a forward or
or transverse—as shown in these images. Precise upward-facing position (supination) to a backward
anatomical terms are also used to define the absolute or downward-facing position (pronation).

Sagittal plane
Cuts vertically down the
body, through or parallel
to the sternum

SAGITTAL

CORONAL
Coronal plane
Cuts vertically down the
body, through or parallel

to the shoulders

SKIN, HAIR, SKELETAL MUSCULAR
AND NAILS
• Front pp.40–41 • Front (superficial on right side of
• Skin, hair, and nail • Back pp.42–43 body; deep on left side) pp.50–51
structure pp.38–39 • Side pp.44–45 • Back (superficial on right side
• Bone and cartilage of body; deep on left side) pp.52–53
structure pp.46–47 • Side pp.54–55
• Joint and ligament • Muscle attachments pp.56–57
structure pp.48–49 • Muscle structure pp.58–59

CARDIOVASCULAR LYMPHATIC DIGESTIVE
AND IMMUNE
• Front pp.68–69 • Front pp.78–79
• Side pp.70–71 • Front pp.74–75
• Artery, vein, capillary • Side pp.76–77
structure pp.72–73

URINARY REPRODUCTIVE ENDOCRINE

• Front (male main; female • Front (female main; male inset) • Front pp.84–85
inset) pp.80–81 pp.82–83

NERVOUS RESPIRATORY BODY
SYSTEMS
• Front pp.60–61 • Front pp.66–67
• Side pp.62–63
• Nerve structure pp.64–65

The body has 11 main body systems. None of these
works in isolation, for example the endocrine and nervous
systems work together closely, as do the respiratory and
cardiovascular systems. However, in order to understand
how the body is put together, it helps to break it down
system by system. In this part of the Anatomy chapter,
an overview of the basic anatomy of each of the 11
systems is given before being broken down into more
detail in the Anatomy Atlas.

038

ANATOMY

Medulla Visible hair
Hair Cortex

Cuticle

Epithelial Internal root A hair in section
root sheath sheath A strand of hair has a multilayered
structure, from its root to the tip.
External root Hair’s color is determined by
sheath melanin within the cortex; the
medulla reflects light so the
Dermal root different tones of color are seen.
sheath
Sebaceous
Together with the gland
epithelial root

sheath, makes the
hair follicle

Bulb Hair matrix
Base of hair root
Melanocyte
Cell that makes the
pigment (melanin) that
gives hair its color

Papilla
Directs growth of
the hair follicle

Blood vessels
Bring nourishment

to the cells of
the matrix

SECTION THROUGH A HAIR

SKIN, HAIR, Nail matrix Nail Lunula
AND NAIL Adds keratinized root Cuticle Crescent shape
STRUCTURE cells to nail root on nail

The skin is our largest organ, weighing about 11 lb (5 kg) and Nail
covering an area of about 21 square feet (2 square meters). Hard plate made
It forms a tough, waterproof layer, which protects us from the of keratin
elements. However, it offers much more than protection:
the skin lets us appreciate the texture and temperature of our Nail bed
environment; it regulates body temperature; it allows excretion
in sweat, communication through blushing, gripping due to Bone
ridges on our fingertips, and vitamin D production in sunlight.
Fat
Thick head hairs and fine body hairs help to keep us warm
and dry. All visible hair is in fact dead; hairs are only alive at SECTION THROUGH A NAIL
their root. Constantly growing and self-repairing, nails protect
fingers and toes but also enhance their sensitivity.

Hair SECTION THROUGH SKIN 039
Hairs cover most
Touch of the body, apart Arrector pili muscle Sweat SKIN, HAIR, AND NAILS
sensor from the palms Tiny bundles of smooth droplet
of the hands, muscle, these contract Skin in section
soles of the feet, to raise the hairs in In just one square centimeter (1/6 in2) of the
nipples, glans response to cold skin, there are, on average, 211/2 in (55 cm) of
penis, and vulva nerve fibers, 271/2 in (70 cm) of blood vessels,
15 sebaceous glands, 100 sweat glands, and
Epidermal over 200 sensory receptors.
surface
Basal epidermal
layer
New skin cells are
made here

Epidermis
Outermost layer
of the skin,
comprising
constantly
renewing layers
of cells called
keratinocytes

Dermis
Inner layer,
composed of
dense connective
tissue, containing
the nerves and
blood vessels that
supply the skin

Hypodermis
Layer of loose
connective tissue
under the skin;
also known as
superficial fascia

Hair follicle Sebaceous gland Sweat gland Arteriole Venule
Cuplike structure in the Secretes a sebum into the hair follicle; Coiled tubes extend upward from
dermis or hypodermis this oily secretion helps to waterproof the dermis to open at a pore on
forms a socket for a hair the skin and keep it supple, and also the surface of the epidermis
has an antibacterial effect

040

ANATOMY

ANTERIOR (FRONT)
Cranium
Vertebral column Contains and protects the brain
Comprises stacked vertebrae and the organs of special sense—
the eyes, ears, and nose—and
and forms a strong, flexible provides the supporting framework
backbone for the skeleton of the face

Manubrium Mandible
A single bone, the jaw contains the
Sternum Gladiolus lower teeth and provides attachment
Breastbone; made up Xiphoid process for the chewing muscles
of the manubrium, the
body (gladiolus), and Clavicle
Traces a sinuous curve at the base
the xiphoid process. of the neck; it acts as a strut supporting
Anchors the upper the shoulder

seven costal cartilages Scapula
Connects the arm to the trunk, and
Costal cartilages provides a secure but mobile anchor for
Attach the upper ribs to the sternum, the arm, allowing the shoulders to be
and lower ribs to each other, and give retracted backward, protracted forward,
and elevated
the ribcage flexibility
Humerus
Ribs
Twelve pairs of curving Ulna
bones form the ribcage Wide at its proximal end, where it
articulates with the humerus at the
Pelvis elbow, this bone tapers down to a
Oddly shaped bone also called pointed styloid process near the wrist

the innominate bone (“bone Radius
without a name”) Forearm bone; it can rotate around the
ulna to alter the orientation of the hand
Sacrum
Formed from five fused vertebrae; it Carpals
provides a strong connection between Eight small bones in the base of the
hand. Two articulate with the radius
the pelvis and the spine to form the wrist joint

041

SKELETAL SYSTEM

Metacarpals
Five slender bones, hidden
in the base of the thumb
and the palm of the hand
Phalanges
Fourteen bones in each
hand: two form the thumb,
with three (proximal, middle,
and distal) in each finger
Femur
The largest bone in
the body at around
45cm (18in) long
Tibia
The shinbone; its
sharp anterior edge
can be felt along the
front of the shin
Fibula
Contributes to the
ankle joint and
provides a surface for
muscle attachment

Patella
The kneecap. This
bone lies embedded
in the tendon of the
quadriceps muscle

Tarsals
A group of seven
bones, including
the talus; contributes
to the ankle joint, and
the heel-bone or

calcaneus
Metatarsals
Five bones in the foot;
the equivalent of the
metacarpals in the hand

Phalanges
Fourteen phalanges form

the toes of each foot

SKELETAL The skeleton gives the body its shape, supports the The human skeleton differs between the sexes. This
SYSTEM weight of all our other tissues, provides attachment is most obvious in the pelvis, which must form the
for muscles, and forms a system of linked levers birth canal in a woman; the pelvis of a woman is
that the muscles can move. The skeleton also plays usually wider than that of a man. The skull also
an important role in protecting delicate organs and varies: men tend to have a larger brow and more
tissues, such as the brain within the skull, the spinal prominent areas for muscle attachment on the
cord within the protective arches of the vertebrae, back of the head. The entire skeleton tends to be
and the heart and lungs within the ribcage. larger and more robust in a man.

Cranium 042
Named after the Latin
word for skull ANATOMY

Parietal bone Occipital bone

Atlas Axis
Mandible
Cervical vertebrae Clavicle
Means key or bolt in Latin

Acromion Scapula
Means shoulder blade in
Thoracic vertebrae Latin, but may come from
the Greek word meaning
Rib to dig, as it resembles a
A teutonic word. small shovel
The Latin for rib, costa,
gives us the adjective Humerus
costal—of the ribs Latin for shoulder

Vertebral column Epicondyles
Vertebra simply means
Ulna
joint in Latin Latin for elbow

Lumbar vertebrae Radius
Slender bone
Ilium named after a
Named after the wheel-spoke in Latin

Latin for hip Carpals
Bones of the
Sacrum carpus, or wrist
Means sacred; several theories exist, but
it is not clear why this bone would have

been considered to be holy
Coccyx

End of the spine made up of three to five
tiny vertebrae; means cuckoo in Greek

043

SKELETAL SYSTEM

Metacarpals
Link the carpals to the
proximal phalanges
Phalanges
The plural of phalanx,
a Greek word that
calls to mind rows
of soldiers
Femur
Simply means thigh
in Latin. It gives us the
adjective, femoral—
of the thigh
Tibia
Latin name of this bone
means both shinbone and
flute—perhaps because
ancient flutes were made
from animal tibias
Fibula
Thin bone named
after a Roman
brooch
Calcaneus
Heel bone

POSTERIOR (BACK)

SKELETAL It is important to remember that bone is a living, dynamic tissue that
SYSTEM constantly restructures itself in response to mechanical changes. We
are familiar with the idea that if we work out at the gym our muscles
develop in response—we can see the effects. But deep under the
skin, our bones also respond to the change by slightly altering their
architecture. Bones are full of blood vessels, and bleed when broken.
Arteries enter bones through small holes in the surface, visible to the
naked eye, called nutrient foramina. The surface, or periosteum, of a
bone is supplied with sensory nerves, so it’s not surprising that when
we damage a bone it produces a lot of pain.

Frontal bone Cranium 044
Damage to the cranium, or skull, may
Nasal bone bruise the brain or damage blood ANATOMY
vessels and cause intracranial bleeding
Lateral radiograph of a skull and cervical spine Mandible Parietal bone
On radiographs—images produced using X-rays—bone appears Moves up and
bright, while air spaces are dark. The part of the skull just above down, and side to Temporal bone
the spine looks very bright here—this is the extremely dense side, in chewing
petrous, or “stony,” part of the temporal bone. Occipital bone
movements
Atlas
Hyoid bone Axis
U-shaped
Cervical vertebra
bone; provides
attachments for Clavicle
The most commonly
muscles of the fractured bone in the
tongue, as well as human body

the ligaments Scapula
suspending the Although very thin, the
larynx in the neck scapula is covered by
thick muscles, and is
Rib rarely fractured

Costal cartilage Thoracic vertebra

MRI of a lumbar spine Radius Humerus
Protected within the vertebral column, the tapering tail end of May be fractured Several nerves supplying
the spinal cord can be seen, in blue. The fluid and fat around close to the wrist by the arm and hand pass
the cord appears white. close to the humerus
a fall onto an and can be damaged
outstretched hand if this bone is fractured

Carpals Lumbar vertebra
These eight small carpal
Ulna
bones may also be The radius and ulna are
damaged in a fall on an joined together along
their length by a flat
outstretched hand ligament called the
interosseous membrane

Pelvis
Can be fractured in a bad fall
or a car accident, and the
fracture often leads to severe
internal bleeding

Coccyx
The coccyx can be painful
following trauma in childbirth
or after a fall onto the bottom

Metacarpal Phalanges
The first metacarpal Fingers tend to stick out and
get knocked, twisted, and
is the key to our crushed. If the finger swells up
opposable thumbs: and is very painful, a phalanx
it is very mobile and may have been fractured

can be brought Femur
across the palm, Large arteries pass
bringing the thumb close to this bone, and
fractures can lead to
into a position considerable bleeding
where it can touch

the other fingers

Patella SIDE SKELETAL
Usually held in place by ligaments, SYSTEM

muscles, and the shape of the
femur behind it, it can get

dislocated sideways in trauma

Lateral radiograph of a knee Fibula After teeth, bone is the hardest material in the human body. Bone
The knee is half flexed here, showing how the curved condyles An important nerve passes very mineral—made of calcium and phosphate salts—gives bone its
of the femur rotate on the tibia below. The patella is embedded close to the neck of the fibula at its hardness and rigidity. It also acts as the body’s calcium store: if the
in the quadriceps tendon (invisible on a radiograph), which upper end, and can be crushed in level of calcium in the blood drops, calcium will be freed from
runs over the front of the knee. the bones. Cartilage is another component of the skeleton. Many
car bumper injuries bones develop as cartilage “models” in the embryo, and later ossify, or
turn to bone. But cartilage persists into adulthood at certain sites, such
Tibia as at the surfaces of joints and as the costal cartilages that join the ribs
The anteromedial (inside front) to the sternum. Cartilage is not as hard as bone, but it has other useful
surface of the tibia lies just under properties. The costal cartilages give the rib cage some flexibility, and
the skin, and a fractured tibia will the cartilage lining the surface of joints resists compression well and
often stick out through the skin provides a smooth, low-friction surface.

Tarsals
The seven tarsal bones articulate
with each other with synovial joints
and are held together by ligaments.
They can twist against each other
to move the sole of the foot inward

or outward

Lateral radiograph of a foot Metatarsals 045
The hinge joint that forms the ankle can Fracture of the slender neck
be clearly seen here—between the tibia SKELETAL SYSTEM
and fibula of the leg and the uppermost of the fifth metatarsal is
tarsal bone, the talus. The bones of the common in ballet dancers
foot can be seen to form an arch, which
is supported by tendons and ligaments. Phalanx
African apes have opposable great toes,
somewhat like our thumbs. This opposability
was lost during human evolution because we
use our feet more as platforms to stand, run,
and walk on—rather than to grasp things

046

ANATOMY

LONG BONE Diaphysis
The shaft is a cylinder of
compact bone, around
a central marrow cavity

TYPICAL LONG BONE
Long bones are found in the limbs, and include the femur
(shown here), humerus, radius, ulna, tibia, and fibula,
metatarsals, metacarpals, and phalanges. A long bone has
flared ends (epiphyses), which narrow to form a neck
(metaphysis), tapering down into a cylindrical shaft (diaphysis).

Central osteonal canal TRANSVERSE Osteocyte
Bone cells, or osteocytes, lie in minute
(Haversian canal) cavities between the concentric,
Channel in the center of cylindrical layers of bone mineral,
each osteon, containing the cells communicate with each other
blood and lymphatic vessels via thin processes, which run through
microscopic canals in the mineral

Osteon
Basic unit in compact
bone; consists
of concentric layers of
tissue

Periosteal blood
vessels
Run around the
outside of the bone

Endosteal blood
vessels
These travel inside bone

Lymphatic vessel

STRUCTURE OF COMPACT BONE Medullary (marrow) cavity
Also known as cortical bone, compact bone is made
up of osteons: concentric cylinders of bone tissue,
each around 0.1–0.4 mm in diameter, with a central
vascular canal. Bone is full of blood vessels: those
in the osteons connect to blood vessels within the
medullary cavity of the bone as well as to vessels
in the periosteum on the outside.

Medullary (marrow) cavity Line of fusion of growth plate 047
Medullary cavities of long bones are filled A cartilage plate allows long bones
with blood-forming red marrow at birth, to grow quickly in length during SKELETAL SYSTEM
but this is replaced with fat-rich yellow childhood; the growth plate fuses
marrow by adulthood; red marrow persists by adulthood, but the line of fusion Spongy (cancellous)
in the skull, spine, ribs, and pelvis may still be evident for a few years bone

Compact bone

Periosteum Metaphysis
Outer lining of bones; Neck of bone; spongy
contains cells that can lay bone starts to encroach
down or remove bone tissue on marrow cavity

Epiphysis Articular surface
Expanded to form a joint surface The epiphysis forms the joint surface
at the end of the bone; covered (here the head of the femur), which
is covered in articular cartilage
with a relatively thin shell of
compact bone and full of

spongy or cancellous bone

BONE AND CARTILAGE
STRUCTURE

The adult skeleton is mainly made of bone, with just a little CARTILAGE
cartilage in some places—such as the costal cartilages which This tissue is made up of specialized cells
complete the ribs. Most of the human skeleton develops called chondrocytes (seen clearly here)
first as cartilage, which is later replaced by bone (see contained within a gel-like matrix embedded
pp.286–87). At just 8 weeks, a fetus already has cartilage with fibers, including collagen and elastin.
models of almost all the components of the skeleton, some The different types of cartilage include
of which are just starting to transform into bone. This hyaline, elastic, and fibrocartilage, which
transformation continues during fetal development and differ in the proportion of these constituents.
throughout childhood. But there are still cartilage plates near
the end of the bones in an adolescent’s skeleton, enabling
rapid growth. When growth is finally complete, those plates
close and become bone. Bone and cartilage are both
connective tissues, with cells embedded in a matrix, but they
have different properties. Cartilage is a stiff but flexible tissue
and good at load bearing, which is why it is involved in
joints. But it has virtually no blood vessels and is very bad at
self repair. In contrast, bone is full of blood vessels and
repairs very well. Bone cells are embedded in a mineralized
matrix, creating an extremely hard, strong tissue.

SPONGY BONE
Also known as cancellous bone, this is found in the epiphyses of long
bones, and completely fills bones such as the vertebrae, carpals, and
tarsals. It is made of minute interlinking struts or trabeculae (seen
in this magnified image), giving it a spongy appearance, with bone
marrow occupying the spaces between the trabeculae.

048

ANATOMY

JOINT AND LIGAMENT Fibula
STRUCTURE
Tibia
During development of the embryo, the connective tissue between developing bones
forms joints—either remaining solid, creating a fibrous or cartilaginous joint, or creating Inferior tibiofibular joint
cavities, to form a synovial joint. Fibrous joints are linked by microscopic fibers of The bones are united here by a
collagen. They include the sutures of the skull, the teeth sockets (gomphoses), and the ligament, whereas the superior
lower joint between the tibia and fibula. Cartilaginous joints include the junctions
between ribs and costal cartilages, joints between the components of the sternum, and tibiofibular joint is synovial
the pubic symphysis. The intervertebral discs are also specialized cartilaginous joints.
Synovial joints contain lubricating fluid, and the joint surfaces are lined with cartilage Syndesmosis
to reduce friction. They tend to be very mobile joints (see pp.288–89). From the Greek for joined
together; the lower ends of the
tibia and fibula are firmly bound
together by fibrous tissue. The
interosseous membranes of the
forearm and lower leg could also
be described as syndesmoses.

FIBROUS JOINTS

Gomphosis Alveolar bone Suture ANKLE
This name comes from the Greek word for Bone of the maxilla or These joints exist between flat bones
bolted together. The fibrous tissue of the mandible forming the of the skull. They are flexible in the Bone
periodontal ligament connects the cement tooth socket (alveolus) skull of a newborn baby, and allow
of the tooth to the bone of the socket. growth of the skull throughout
childhood. The sutures in the adult
skull are interlocking, practically Uniting layer
immovable joints, and eventually
fuse completely in later adulthood.

Cement
Covers the roots

of the tooth

Periodontal
ligament

Dense connective
tissue anchoring the

tooth in the socket

TOOTH SKULL Middle layer Capsular layer Cambial layer

CARTILAGINOUS JOINTS Intervertebral disc Atlas (first cervical
The fibrocartilage pad or disc between vertebra)
Pubic symphysis vertebrae is organized into an outer
At the front of the annulus fibrosus and an inner Zygapophyseal joint
bony pelvis, the two nucleus pulposus. Small synovial joints
pubic bones meet each between the neural
other. The articular surface Pubic bone arches at the back
of each is covered with Forms the front of the spine
hyaline cartilage, with a pad of the bony pelvis
of fibrocartilage joining Axis (second
them in the middle. Pubic symphysis cervical vertebra)

PELVIS Hyaline cartilage

Nucleus pulposus
Inner, gel-like center
of the disc

Annulus fibrosus
Outer, fibrous ring
of the disc

SPINE