Respiration

External respiration is the exchange of gases between the alveoli and the blood. Here oxygen diffuses from the alveoli into the pulmonary capillaries and carbon dioxide diffuses from the pulmonary capillary into the alveoli.

Internal respiration is the exchange of gases between the systemic capillaries and the tissues. Here oxygen diffuses from the blood in capillaries to the tissues and carbon dioxide diffuses from the tissues into the capillaries.