The New Childrens Encyclopedia

284

Take a breath

You need to breathe constantly to take in oxygen.

You do this by breathing in air, which is taken

down your windpipe and into your lungs, where

the oxygen is removed and enters the blood. At the

same time, carbon dioxide passes into the lungs.

TAKE A LOOK: CHEST SECTION

Your left lung is smaller than your right lung to

make room for the heart, which is positioned

toward the left side of the chest cavity. The heart’s

position can be seen in a scanned cross-section of

the chest, taken from above.  ALVEOLI Oxygen passes

through the walls of the

alveoli into capillaries

(thin-walled blood vessels:

( see p.279–280).

What happens inside your lungs?

Inside each lung, air tubes (known

as bronchi) get smaller and

smaller, becoming bronchioles,

each of which end in clusters

of small, flexible air sacs, or

bags, called alveoli. This is

known as the bronchial

tree, because it resembles

an upside-down tree.

Breathing is helped by your ribs

moving up and out. A dome-shaped

muscle called the diaphragm also

helps the process. It flattens a little

to increase the size of your chest

cavity when you breathe in.

Diaphragm moves

up as we exhale.

BREATHE IN, BREATHE OUT

Diaphragm moves

down as we inhale.

O

Flattened out, a pair of lungs would cover a tennis court.

O

An average person takes about 12 to 15 breaths a minute when at rest.

After physical activity they take in about 60 breaths a minute.

O

The trachea is about 4 in (11 cm) in length.

O

Your lungs act like giant sponges. They take in air instead of water.

O

Each minute around 1^1 ⁄ 3 -1^1 ⁄ 2 gallons (5 and 6 liters) of air pass into and out

of your lungs.

FAST FACTS

 BRONCHIOLI This greatly magnified

image shows the end of a bronchiole (in blue)

surrounded by a group of alveoli. There are

more than 300 million alveoli in the two lungs.

Each of the branching

networks ends in a

bronchiole, which leads

into groups of alveoli.

Area of right lung

is slightly larger.

Vertebra

Heart

Rib

Area of left lung

is slightly smaller.

Windpipe (trachea)

Left bronchus

Diagram shows

groups of alveoli.

Capillary

Terminal bronchiole

THE HUMAN BODY