The capillary covered alveoli inflate, deoxygenated blood flows through the capillaries. The carbon dioxide from the venous blood diffuses into the alveoli and the oxygen from the alveoli diffuses into the blood. This works through a process called diffusion in which gases move from where they have a high concentration to where they have a low concentration. The carbon dioxide is then breathed out. The oxygenated blood now is pumped to the mitochondria in cells so they can carry out respiration and produce ATP so humans have energy for life processes.
