What are the different concentrations and partial pressures of the gases in the alveoli?
In the lungs, oxygen diffuses from alveolar air into the blood because the venous blood has a lower partial pressure. The oxygen dissolves in the blood. Only a small amount is carried as a physical solution (0.31 ml per 100 ml). The remainder of the oxygen is carried in chemical combination with the hemoglobin in red blood cells (erthrocytes). Hemoglobin (molecular weight of 68,000) is made from 4 hemes, a porphyrin ring containing iron and globin, a 4 protein chains. Oxygen is bound to the iron for the transport process. Hemoglobin (HHgb) behaves as a weak acid (K = 1.4 x 10-8; pKa = 7.85). Oxyhemoglobin (HHgbO2) also behaves as a weak acid (K = 2.5 x 10-7; pKa = 6.6) Because both forms of hemoglobin are weak acids, and a relationship of the numerical values of the equilibrium constants, the net reaction for the interaction of oxygen with hemoglobin results in the following equilibrium: HHgb + O 2 <===> HgbO 2 + H+ If 2 is increased in the blood at the lungs, the equilibrium shifts to
