Download How It Works. Book of the Human Body 3rd Revised Edition 2015 PDF

TitleHow It Works. Book of the Human Body 3rd Revised Edition 2015
File Size42.3 MB
Total Pages180
Document Text Contents
Page 1

NE
W

THE BODY AT WORK CURIOUS QUESTIONSHUMAN ANATOMY

Anatomy of
the tongue

PACKED WITH AMAZING FACTS AND STUNNING ILLUSTRATIONS

BOOK OF

Respiration
and

oxygenation

Uncover
the science

of DNA

Understanding
hormones

Everything you need to know about the human body

HUMAN
BODY

THE

Explore the
sensory
system

Inside a
human heart

How many
bones are in

a foot?

The evolution
of the hand

A look
inside

the eye

Food and
the brain

How do our
muscles work?

Guides to
the essential

organs

Fracture
healing
process


INCREDIBLE IMAGES

300
OVER

Operating
on the
brain

Kidney
function

explained

Page 2

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Page 90

090

The digestive tract is a long, muscular tube that
runs the entire length of your body. It is separated
into fi ve distinct sections, each with its own
particular and specialised function.

Digestion begins in the mouth. As you chew your food,
saliva is released, providing a slippery lubricant and

kick-starting the break down of carbohydrates with an
enzyme known as amylase. Touch receptors in your

mouth tell you when it is time to swallow, and as your
tongue comes upward, the food is pushed to the back

of your throat.
As you swallow, you pass control of digestion

over to your automatic motor functions. A fl ap of
skin called the epiglottis folds down to cover the
voice box, and the entrance to the lungs, and
then a wave pushes the mouthful all the way
down the oesophagus. When the food reaches
your stomach, it passes through a ring of muscle
known as the cardiac sphincter, which prevents
it from coming back out the way it came in.

The inside of the stomach is a hostile
environment, where the cells lining the walls

pump out hydrochloric acid and protein-digesting
enzymes. The presence of food triggers stretch

receptors in the stomach lining, which in turn trigger a series
of rhythmic contractions. These churn the stomach contents,
mixing in the acid and enzymes, grinding down the food.

At the bottom of the stomach there is a second ring of muscle
called the pyloric sphincter, which acts as a gatekeeper to the
small intestine. The sphincter prevents anything larger than
about two centimetres (0.8 inches) in diameter passing
through, returning it to the body of the stomach until it has

Food
& your

body
Join us as we unravel all nine

metres of your digestive system

THE BODY AT WORK

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Page 91

Chew
Digestion begins in the

mouth, where our teeth start

work on grinding food into

manageable chunks.

Add bile
As the liquid passes into the

intestines, stomach acid

is neutralised by

alkaline bile from

the liver.

Ferment waste
Bacteria living in the

large intestine help

with the breakdown of

waste, releasing even

more nutrients.

Absorb nutrients
As the enzymes begin to

release nutrients, they are

absorbed across the lining

of the small intestine into

the bloodstream.

Churn
The muscles of the

stomach rhythmically

churn its contents,

mechanically

breaking food down

into a lumpy paste.

Remove water
The large intestine

absorbs excess water

from the food as it

passes through.

Get rid of waste
All that is left at the

end of the digestive

process is a

combination of

indigestible material,

dead cells and bacteria.

Swallow
Saliva makes each mouthful

slippery, allowing it to slide

easily down the oesophagus

to the stomach.

Add acid and enzymes
The stomach produces

hydrochloric acid, and

protein-digesting enzymes.

Add more enzymes
The pancreas produces

digestive enzymes, which

are added to the mixture as

it enters the small intestine.

It can take up to 48
hours for a meal to travel
through your body

Journey of
your food

LENGTH OF THE
SMALL INTESTINE

7
metres

Shellfi sh
Shellfi sh allergies tend to

develop during

adulthood. Foods to avoid

include barnacles, crabs,

shrimps, lobsters,

crawfi sh and krill.

Milk
Children under the age of

three are the most likely

to develop an allergy to

milk, but they usually

outgrow it by the time

they reach adulthood.

Peanuts
By far the most

common food

allergy is peanuts. In

the UK, as many as

one in 50 children

are sensitive.

HEAD
HEAD2
FOOD ALLERGIES

1. COMMON 2. MORE COMMON 3. MOST COMMON

091

Biological washing powder uses digestive enzymes to break down the stains on dirty laundryDID YOU KNOW?

been ground down further. This ensures that by
the time it reaches the small intestine, your food
is a runny, slightly lumpy paste, and is ready for
the next stage of digestion.

The small intestine is the site of chemical
digestion. Here, the pancreas adds digestive
enzymes, and the liver adds a generous squirt of
alkaline bile, delivered via the gall bladder. This
bile not only neutralises the burning stomach
acid, it also acts a little like washing-up liquid on
dirty dinner dishes, helping to separate the
food particles and forcing fats to disperse into
tiny bubbles.

Muscles in the small intestine continue to
squeeze and mix the contents together, allowing
the enzymes to get to work inside the paste. As
the nutrients are released, they are then
absorbed over the walls of the intestine and into
the bloodstream.

To ensure that everything keeps moving
through the system, every fi ve to ten minutes a
wave of muscle contractions begins at the
stomach and travels all the way down the
intestines. Known as the migrating motor
complex (MMC), this wave squeezes the digestive
system like a tube of toothpaste, urging its
contents further toward the colon.

As the food progresses through the small
intestine, more and more of the nutrients are
released by enzyme activity, and by the time it
gets to the large intestine, most of the useful
material has been absorbed into the
bloodstream. However, the digestive process is
not over, and here, bacteria help to break down
even more of the undigested food.

The large intestine also absorbs most of the
remaining water, leaving behind a combination
of undigested material, dead cells and bacteria.
When the waste has completed its journey
through the large intestine it goes to the rectum
for storage until there is a convenient time to get
rid of it.

Food chain
Energy from the Sun is converted into

to chemical energy by photosynthetic

organisms like plants. The plants use

the energy to build biological

materials from nutrients in the air

and soil. Herbivores then consume

the plants, releasing some of the

energy, and using the components to

build their own bodies. Carnivores

then eat the herbivores. When plants

and animals die, decomposers break

their bodies down, returning

nutrients to the ground for reuse, and

the cycle begins again.

1 The Sun
On average, every minute the

Sun delivers 2kcal of energy for

every cm2 (0.2in2) of Earth.

4 Herbivore
Herbivores can digest plant

material, but the process is

diffi cult, and they can only

extract around ten per cent of

the energy.

3 Producer
Plants use the energy from the

Sun to combine CO2 and water,

producing chemical energy in

the form of sugars.

6 Carnivore
Carnivores get easy

energy by digesting the

tissues of other animals.

2 Ineffi cient
conversion
Less than fi ve per cent of the

available energy from the

Sun is converted into

chemical energy by plants.

5 Energy loss
At every step up in the food

chain, some of the energy is

lost, mostly as heat.

1 3 5

2 4 6

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Page 179

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Page 180

Human
respiration

Human anatomy
Discover how our hearts beat, our

brains think and our ears hear and
everything in between

The body at work
Find out how our bodies work, from
genetics and the immune system to

respiration and white blood cells

Curious questions
Uncover amazing facts that explain some of

life’s biggest questions, such as what
powers cells and how anaesthesia works

170+
PAGES
OF FACTS



AND TRIV
IA

INSIDE

The structure
of the skeleton

How do we
combat viruses?

The development
of an embryo

The
importance

of teeth

The science
behind a

sprained ankle

BOOK OF

HUMAN
BODY

THE

PACKED WITH AMAZING FACTS AND STUNNING ILLUSTRATIONS

Inside the eye

Understand
our sense of

taste

How do we
smell?

The circulation
system

The science
of genetics

Functions
of the liver

THE BODY AT WORK CURIOUS QUESTIONSHUMAN ANATOMY

3RD REVISED EDITION

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