3- The respiratory system

Our cells need oxygen and produce carbon dioxide that has to be expelled from the body. To obtain oxygen and get rid of carbon dioxide we use our respiratory system.

Respiration

Air enters through the nose and mouth and passes down the pharynx and then to the trachea (or windpipe).

The trachea divides into two tubes called bronchi and each of them subdivides into smaller and smaller bronchi called bronchioles.

The alveoli are tiny air sacs at the end of the bronchioles. The alveoli are where the blood exchange oxygen and carbon dioxide. Oxygen passes from the alveoli to the capillaries and into the blood and carbon dioxide leaves the blood and enters the alveoli,  goes out through the mouth and nose.