How the Body Works: The Respiratory System

The network of air tubes spreading out just like the branches and twigs of a tree, form the structure of the lungs. The trachea, or windpipe, divides into two bronchi and these on entering the lungs, divide into bronchioles, alveolar ducts, alveolar sacs and individual alveoli. The right ventricle of the heart pumps deoxygenated blood to the lungs via the pulmonary arteries. At the alveoli, gaseous exchange of oxygen and carbon dioxide takes place between air in the lungs and blood in surrounding capillaries.