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136 Human Body

The process of taking in oxygen and

expelling carbon dioxide is called

respiration. When you breathe in,

oxygen from the air enters the

bloodstream. When you breathe out,

waste carbon dioxide is removed.

WHY DO WE NEED TO BREATHE?

Breathing is essential to keep us alive, because every

living cell in the body needs a continual supply of

oxygen. Inside each cell, oxygen combines with food

molecules in a chemical reaction called oxidation,

which releases energy. This energy powers every

process in the human body.

HOW DO THE AIRWAYS STAY CLEAN?

The inner lining of the airways constantly produces a

sticky fluid, called mucus, to trap particles of dirt. The

mucus is always moving. In the nose, it is pushed by

cilia towards the back of the throat where it is

swallowed. Mucus also moves up from the airways of

the lungs to the throat to be swallowed.

HOW DOES AIR REACH THE LUNGS?

Air enters the body through the nose and mouth and

travels to the pharynx (throat). The pharynx splits into

the oesophagus for food, and the trachea (windpipe)

for air. The trachea leads to the chest, where it divides

into two branches, or bronchi, one to each lung.

The larynx is made up of nine pieces of cartilage (bound

together by muscles and ligaments to form several larger

structures) at the top of the trachea, and the two flaps

of tissue, called vocal cords, stretched across them. If the

vocal cords are open, air passes silently through them.

If drawn together, air makes the cords vibrate, creating

sound. The tighter the vocal cords, the higher the pitch.

The mouth and tongue alter the sound to make words.

FIND OUT MORE. Cells 73 • Mouth 142 • Nose 143 • Sound 176–177

RESPIRATORY SYSTEM 3

The respiratory system is made up

of many organs, including the

lungs, nose, mouth, airways

leading to the lungs, and the

network of blood vessels running

through the lungs.

1 CILIA IN THE NOSE

Tiny beating hairs, called cilia, line the inside of the nose. The cilia clean,

warm, and moisten the air to protect the sensitive airways of the lungs.

Respiration

Pulmonary vessels

run throughout the lungs,

bringing blood from the

heart to pick up oxygen,

then taking it back to the

heart to be pumped around

the body

The epiglottis

swings down to cover

the larynx when we

swallow, to stop food

entering the air passages

The trachea

(windpipe) is made

up of rings of

cartilage that hold

the air passage open

HOW SOUND IS MADE IN THE LARYNX

Bronchi

divide again and

again, to form a

network of ever

smaller airways

The diaphragm

is a dome of muscle

between the chest and

abdomen

Vocal cords

in the larynx (voice

box) produce sound

Cartilage rings

of the trachea

Pharynx (throat)

THE LARYNX VOCAL CORDS CLOSED VOCAL CORDS OPEN

Ligaments

Adam’s apple

Vocal cords

Heart

respiration