Breathing and respiration

We can live for weeks without food and for days without water, but only for a few minutes without air. Yet breathing is only the first step. The real purpose of taking in air is to release energy from food, and that happens inside every cell of the body.

Breathing and respiration are not the same

Breathing is the physical act of taking air into the lungs (inhaling) and pushing it out (exhaling). Respiration is the chemical process inside the cells in which food, mainly glucose, is broken down with the help of oxygen to release energy. Carbon dioxide and water are produced as waste.

Glucose + Oxygen → Carbon dioxide + Water + Energy

The path of air

1. Nose: air enters through the nostrils. Hairs and sticky mucus trap dust and germs, and the air is warmed and moistened. This is why we should breathe through the nose.
2. Windpipe (trachea): a tube kept open by rings of cartilage. It carries the air down the neck.
3. Bronchi: the windpipe divides into two branches, one to each lung. Inside the lungs they divide again and again into finer tubes.
4. Air sacs (alveoli): the finest tubes end in clusters of tiny balloon-like sacs. Their walls are extremely thin and covered with fine blood vessels.

Exchange of gases

In the air sacs, oxygen passes from the air into the blood. Red blood cells carry it to every cell of the body. At the same time, carbon dioxide brought by the blood from the cells passes into the air sacs and is breathed out. The air we breathe out has less oxygen and more carbon dioxide and water vapour than the air we breathe in. Breathe on a cold mirror and it fogs up with that water vapour.

How we breathe in and out

The lungs have no muscles of their own. They sit in the chest, protected by the ribs, above a dome-shaped sheet of muscle called the diaphragm.

• Inhaling: the ribs move up and out and the diaphragm moves down. The chest becomes bigger and air rushes into the lungs.
• Exhaling: the ribs move down and in and the diaphragm moves up. The chest becomes smaller and air is pushed out.

An adult at rest breathes about 15 to 18 times a minute. During running or cycling the muscles need more energy, so we breathe faster and deeper to bring in more oxygen.

Respiration in other living things

• Fish have gills that take in the oxygen dissolved in water.
• Earthworms breathe through their moist skin; frogs can breathe through both skin and lungs.
• Insects such as cockroaches have small openings called spiracles along the sides of the body, leading to a network of air tubes.
• Plants respire too, day and night. Leaves exchange gases through stomata, and roots take in air from the spaces in the soil.

Keeping the lungs healthy

Play outdoors, sit up straight, practise deep breathing, cover your nose in dust and smoke, and never smoke. Tobacco smoke damages the air sacs and causes diseases of the lungs and heart.