Oxygen is transported mainly (about 97 percent) by binding to the haemoglobin of red blood cells, forming oxyhaemoglobin; a small amount is dissolved in the plasma. Carbon dioxide is transported in three ways: mostly (about 70 percent) as bicarbonate ions in the plasma, about 20 to 25 percent bound to haemoglobin as carbaminohaemoglobin, and a small amount dissolved in the plasma.

Tidal volume (TV) is the volume of air breathed in or out during a normal (quiet) breath, about 500 mL. Residual volume (RV) is the volume of air that remains in the lungs even after a forceful expiration, about 1100 to 1200 mL. Vital capacity (VC) is the maximum volume of air that a person can breathe out after the deepest possible inspiration (it equals tidal volume plus inspiratory reserve volume plus expiratory reserve volume).

VC = TV + IRV + ERV

Blood is a fluid connective tissue made of a liquid plasma (about 55 percent) and formed elements (about 45 percent). Plasma carries dissolved nutrients, wastes, hormones and proteins. The formed elements are: red blood cells (erythrocytes), which carry oxygen using haemoglobin; white blood cells (leucocytes), which defend the body against infection (immunity); and platelets (thrombocytes), which help in the clotting of blood.