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Understanding the Human Body

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With 6 trillion cells, 206 bones, and 600 muscles, the human body is an amazing living mechanism that is in intense and constant activity.
For all curious readers, the Knowledge Guides open the door to a world of complex and captivating phenomena.
Accurate, detailed visual information is all defined in lay language to make it readily accessible to the non-expert. Definitions to scientific terms are given either in the explanation itself, or in the comprehensive glossary.

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Published by
Published 09 August 2012
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EAN13 9782764408926
Language English
Document size 41 MB

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Exrait

Human Body
Understanding
The

THE VISUAL GUIDES

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The
body

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Dr Alain Beaudet
Department of Neurology and Neurosurgery
McGill University
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Department of Obstetrics and Gynaecology
Queen’s University
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Département de dermatologie
Centre hospitalier universitaire de Québec
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KGK Synergize
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Département d’ophtalmologie
Centre hospitalier universitaire de Québec
Dr Pierre Duguay
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School of Communication Sciences
and Disorders
Faculty of Medicine
McGill University
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Orthopedic Trauma Service
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Dr Michael Hawke
Department of Otolaryngology
Faculty of Medicine
University of Toronto
DrPatrice Hugo
Dr fM-ruAnntSfeei l
Procrea BioSciences Inc.
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Division of Urology
The Montreal Children’s Hospital
Dr Michael S. Kramer
Departments of Pediatrics and of
Epidemiology and Biostatistics
Faculty of Medicine
McGill University
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Department of Ophthalmology
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MD Multimedia Inc.
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Department of Physiology
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4

6 | The body’s
building blocks

8
10
12
14

The human cell

Chromosomes and DNA

Cellular activity

Body tissues

41
40

38
36
34
32
30
28
27
26
24
22
20
18

The movements of the hand
The action of the skeletal
muscles
The muscles of the head
Muscle tissue
The skeletal muscles
The joints
The hand and the foot
The spine
The head
Types of bones
The human skeleton
Bone growth
Bone structure
The skin

16 | The architecture
of the body

Ta b l e

42 | The nervous system
44 Neurons
46The central nervous system
48The brain
50The cerebrum
52The peripheral
nervous system
54The motor functions
of the nervous system

72
70
68
67
66
64
62
60
58

o f

Smell
Taste receptors
Taste
Balance
Perception of sound
The organ of hearing
Sight
The eye
Touch

56 | The five senses

c

o

74 | Blood circulation
76 Blood
78The cardiovascular system
80Arteries and veins
82 The heart
84The cardiac cycle
86The lymphatic system
88 Immunity
90The endocrine system
92The hypothalamus and
the pituitary gland
94The urinary system

n

t

110The liver, pancreas,
and gallbladder
109 The intestines
108The stomach
106 The teeth
104The digestive system
102 Speech
100 Respiration
98The respiratory system

96 |Respiration and
nutrition

e

n

112 | Reproduction

114
116
118
120
122

t

The male genital organs
The female genital organs
Fertilization
The life of the embryo
Maternity

s

124 | Glossary
126 | Index

5

What is the human body made of? Although our bodies are very complex, they are composed of fundamental units
microscopic basic components
that are very similar to each other. These
assembled to form the different tissues that form all the body’s organs. Cells are also the sites of intense and
constant activity: they manufacture living matter, and continually reproduce
consume energy,

themselves.

are

The body’s building blocks

8

10

12

14

The human cell
The body’s basic component

Chromosomes and DNA
The code of life deep within cells

Cellular activity
Cell division and protein synthesis

Body tissues
Groupings of cells

T h e h u m a n c e l l
The body’s basic component

The human body contains about 60 billion human cells. These cells, the basic
components of the human body, are invisible to the naked eye, as their diameter
generally is less than a few hundredths of a millimeter. Although they take many
forms, depending on their location and their function, they always have a
welldefined structure: an exterior membrane, a nucleus, and a number of internal
elements floating in a gelatinous medium, the cytoplasm.

DIFFERENT TYPES OF CELLS
The body’s building blocks
The human body contains a great many types of cells, which are differentiated
according to their function. Despite their different sizes and shapes, all have the
same general structure.

8

The rods eht fo cnatireintaon
light-sensitive pigments.

The nucleus of the
has several lobes.

neutrophil

Erythrocytes)ls(red blood cel
color the blood red.

The ovumt cergese las thinlli
the human body.

Spermatozoidsgnolvah a e
flagellum.

Neurons(nesl )ac nerbuul acp le
to 1 meter in length.

The irregular shape of osteocytes
(bone cells) enables them to lodge in
very narrow cavities of bony tissue.

Cytoplasm w,il fchhils the
intracellular space, is a
jellylike substance composed of
water, proteins, lipids, ions,
and glucose.

Lysosomesmyszene niatnoc
that perform intracellular
digestion.

Microtubuleseh, which form t
skeleton of the cell, make it
easier for organelles to move
within the cytoplasm.

Made mainly of lipid molecules,
the cell membrane amsorf
selective water-insoluble barrier.

Enveloped in a double
membrane, mitochondria
produce and store energy.

Enzymes enclosed in
peroxisomesperform
oxidization.

Cilialestubugra p ou mofroicof ,demr fo
covered by the cellular membrane, can propel
the cell or move a substance outside the cell.
Large cilia are called flagella.

THE STRUCTURE OF HUMAN CELLS

Human cells (like those of all higher orders of life) are called eukaryotes – that is, their genetic material is
enclosed in a nucleus defined by a nuclear membrane. The rest of the cell is composed of cytoplasm, a
semiliquid medium structured by a network of microtubules and microfilaments. The organellesthat float in the
cytoplasm (mitochondrion, Golgi apparatus, endoplasmic reticulum, lysosome) perform different cellular
functions, such as storing energy, synthesis and transportation of proteins, and digestion of foreign bodies.

Chromatinnenopmoceht fo tusleuc n,, the main
is a filament formed of DNA and proteins.

The nuclear membranehas
a large number of pores.

free ribosome

Each cell has two centriolesof ,edrm
of bundles of microtubules placed at
aright angle to each other. They play
a le lnic lo er.siondivi

Ribosomes are made in the
in the center of the nucleus.

nucleolus,

The endoplasmic reticulumacol detraen(E, R)
the nucleus, consists of a network of membranous
pockets and canals. The rough ER is covered with
ribosomes that synthesize proteins, while the
smooth ER does not have ribosomes and produces
other types of substances.

The Golgi apparatussieer s aesblemser
of membranous sacs attached to the
rough ER. It collects the proteins
synthesized by the ribosomes, sometimes
changes them by adding carbohydrates,
then releases them into vacuoles.

Microfilamentsare made of a protein,
actin. With the microtubules, they
form the cytoskeleton, which gives
the cell its shape.

Vacuoles, small liquid-filled vesicles,
move from the Golgi apparatus
to the cellular membrane, where
theyrelease the proteins that
they contain.

TRANSPORT OF PROTEINS IN THE CELL

Protein synthesis, one of the main functions of the cells,
is performed in small particles called ribosomes. There are
two types of ribosomes: free ribosomes, which secrete
their products directly into the cytoplasm, and ribosomes
attached to the endoplasmic reticulum, which release
their proteins outside the cell. Proteins move through
the network of membranous sacs in the endoplasmic
reticulum, are processed by the Golgi apparatus, and then
migrate toward the cellular membrane inside a vacuole.

9

The body’s building blocks

Chromosomes and DNA
The code of life deep within cells

Each cell in our body has a nucleus. Although nuclei are only a few microns
in diameter, they are the site of fundamental mechanisms, such as cell division
and protein synthesis. The substance responsible for these phenomena,
deoxyribonucleic acid (DNA), is in the form of very long helicoidal molecules in
constant motion. During the process of cell division, these filaments twist around
on themselves to form chromosomes.

DNA molecules are unique in that they are formed of two strands linked by several
The body’s building blocks
billion successive bonds. The sequence of these components constitutes a code
that is capable of commanding the production of a large number of specific
proteins and also replicating itself.

10

nucleolus

The nucleus is separated from
the cytoplasm by a porous
nuclear membrane.

The chromosomes float in a gelatinous
substance, the nucleoplasm.

Human cells have 46 chromosomesauxes ro,sllec l, pt fexce
which have only half this number. Chromosomes cannot be
observed except during cell division. At that time, they divide
into two sister chromatids that remain attached to each other
for a short time by a central zone, the centromere.

INSIDE THE NUCLEUS

sister chromatids

centromere

With the exception of red blood cells, all cells in the body contain a nucleus. Some, like the muscle cells,
even have several. The nucleus of a cell contains one or several nucleoli and filaments of chromatin floating
in the nucleoplasm. Chromatin, which generally looks like a string of beads, is composed of long DNA
molecules wound around proteins called histones. When cells divide, this filament rolls up into a spiral,
becomes condensed, and is organized to form characteristic small rods, the chromosomes.

THE MOLECULAR STRUCTURE OF DNA

DNA is a polymer – that is, its molecule is formed by the grouping together of a large
number of simpler molecules. It can be visualized as a very long, twisted ladder whose
two uprights are linked by billions of rungs, each of which is composed of two smaller
molecules, nitrogenous bases. There are only four different nitrogenous bases in DNA:
adenine, thymine, cytosine, and guanine. These molecules are linked up not at
random but according to a strict rule resulting from their molecular structure: adenine
can link only with thymine, and cytosine only with guanine. These bases are called
complementary.

The nucleotideo fentnmoopcic bas theiseth
DNA molecule. It is composed of a phosphate
group and a sugar, deoxyribose, to which one
of the four bases attaches.

deoxyribose

phosphate group

The nitrogenous basebose,d oeyxir,nile k dot
links up with its complementary base to form
a rung in the DNA molecule.

chromatin

When the DNA molecule wraps around
eight histone molecules, it forms a mass,
the nucleosome, which supports it.

guanine

Adeninepu knil nac
only with thymine.

thymine

Cytosinesit eh
complementary base
for guanine.

Each chromosome has a single
DNA moleculefo mi2 , hsntioll
a millimeter wide but several
centimeters long.

THE GENETIC HERITAGE AND HEREDITY

All of the cells in an individual’s body have resulted from
the division of a single initial cell, and so they all contain
absolutely identical DNA filaments. The sequence of
nitrogenous bases is always different from one human
beingto another; the DNA composition of each human
being is thqinu.eufere ero

Much of our genetic heritage is linked to our belonging to
the human race: all humans, for instance, have the same
organs. However, other, more specific, genetic characteristics
(physical features, predisposition to certain diseases) are
transmitted from one generation to the next at the time
the sexual cells merge. This mode of transmission is called
heredity.

11

The body’s building blocks

newly synthesized
strand

nucleotide

DNA
molecule

matrix

Like more complex living organisms, the cells in our bodies are born and die.
Different cells have very different life spans: a few hours for white blood cells,
four months for red blood cells. When they die, most cells are replaced by
identical cells. Their life can thus be described as a cycle during which they
prepare for and complete their reproduction by cellular division.

nucleus
W

T

Q

a c t i v i t y
Cell division and protein synthesis

phase G1

C e l l u l a r

CELL DIVISION
Cell division, or mitosis, comprises several distinct steps. The DNA
molecules, deployed as chromatin during the interphase, coil and
thicken during the prophase Q, which makes the chromosomes
visible. The nucleolus disappears and the two pairs of centrioles
move apart and migrate to opposite ends of the cell, while a system
of microfilaments, the mitotic spindle, forms between these two
poles. Gradually, the nuclear membrane disintegrates and the
chromosomes move along the filaments of the mitotic spindle.
During the metaphase W, the chromosomes line up at the center
of the cell. When their centromeres divide, the anaphase begins E:
the chromatids, which have become complete chromosomes, are
drawn to one or the other end of the cell. In the telophase Ra
new nucleus forms at each end of the cell. The chromosomes uncoil
to become chromatin once more, while a new nuclear membrane is
formed. The mitotic spindle disappears and the cytoplasm begins
to separate during a phase called cytocinesis T. At the end of the
process, the original cell is replaced by two new identical cells Y.

12

Y

cytoplasm

An essential step in cell division consists of
copying the cell’s genetic material, its DNA.
To do this, the two strands of the double
helix separate and become matrices for the
synthesis of two new strands according to
the principle of base pairing. When the DNA
molecule has completely replicated, the cell
has two absolutely identical molecules.

chromosome
pair of
centrioles

mitotic
spindle

new
nucleus

E

R

phase S

The cell cyclecomprises four successive stages: the three phases of the
interphase (phases G1, S, and G2) and phase M. Phases G1 and G2 are
phases of growth and intense metabolic activity. G1 is the longest and
most variable phase (from 10 hours to several months, depending on
the cell; even an entire life for neurons). Phase G2 lasts one to two
hours. Phase S, which can last from four to eight hours, is the period
during which replication of DNA takes place. Phase M corresponds to
cell division itself and lasts only a few minutes.

REPLICATION OF DNA

phase M
The body’s building blocks
phase G2