Childrens Illustrated Encyclopedia

TONGUE

The surface of the muscular

tongue is covered by tiny

bumps called papillae. Some

house taste buds that detect

five basic tastes in foods: sweet,

salty, sour, bitter, and umami

(a savory taste). Before tastes

can be detected by taste buds,

they have to dissolve in saliva.

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Digestion

Digestion begins in the mouth, as teeth crush
the food. Watery saliva moistens the food and
makes it easy to chew and swallow. The
muscular walls of the stomach churn food
into a soup-like liquid that is released in spurts
into the small intestine. This is where most
digestion takes place and
where simple
nutrients are
absorbed
through the
lining of the small
intestine into the
bloodstream.

STOMACH

This bag is lined with

a thick layer of slimy

mucus. Tiny glands

in the lining produce

strong digestive juices,

which contain substances

such as enzymes and acids.

THE HUMAN BODY NEEDS FOOD to

supply energy and to grow and repair itself. Food

contains water and five vital nutrients—proteins,

carbohydrates, fats, vitamins, and minerals. For food

to be useful, the body has to break it down, or

digest it, to release simple, usable

nutrients. The digestive system

consists of a long tube called

the alimentary canal, which

runs from the mouth

to the anus. It pushes

the food along by a

squeezing action called

peristalsis. Each part of

the system does a

particular job. The

stomach is like a bag

where chewed food is

mixed with acids and

digestive juices. The tiny

particles of digested food

pass easily through the walls of

the small intestine and into the

bloodstream, to be used by the body.

The large intestine absorbs water,

minerals, salts, and some vitamins

from the food and turns the waste

into semisolid lumps called feces.

VILLI
Each fold of the lining of the
small intestine has thousands
of microscopic finger-shaped
projections called villi. The
villi allow the small intestine
to absorb more nutrients.

ENZYMES

Digestive juices

contain proteins

called enzymes,

which break

down food into

simple substances

the body can absorb.

Find out more

Health and fitness

Human body

Lungs and breathing

Muscles and movement

DIGESTION

EATING FOOD

When you swallow food, it enters your throat.

A flap called the epiglottis folds over the

entrance to the windpipe so that food goes

into the oesophagus and not into the trachea,

where it could cause choking.

LIVER

The liver is the body’s “chemical factory”. It

receives digested nutrients, such as glucose

(sugar), from the small intestine, and either

stores them, converts them, or dispatches

them to another part of the body.

Anus is where

waste products

leave the body

as feces.

LARGE INTESTINE

The large intestine is

much shorter than

the small intestine,

but three times as

wide, measuring up

to 2.5 in (7 cm)

in width.

Stomach is where food

is mixed with acid and

digestive juices and

churned by muscles into

a semiliquid form. The

pancreas rests on

top of the stomach and

produces digestive juices.

SMALL INTESTINE

The small intestine is coiled into

the lower part of the body. It

is very long, measuring

about 20 ft (6 m) in

length. Its lining has

many folds and ridges,

so that it can absorb

nutrients efficiently.

Rectum is the last part

of the large intestine.

Oesophagus pushes

swallowed food down

through the chest,

behind the windpipe

and heart, into the

stomach.

Salivary glands

produce a watery

liquid containing

enzymes to mix with

the food and help

with swallowing.

Tongue tastes

different flavors.

Teeth chew,

crunch, and grind

food into a pulp.

Small intestine

absorbs digested

food into the body.

Large intestine

absorbs water from

the intestinal contents.

Liver

Papillae are

tiny bumps

on the tongue.