Circulation in the lungs and microcirculation in the alveoli

Human lungs weighing ca 600 g permit the passage of 5–6 l of blood per minute. The blood capacity of the human lungs is about 0.5 l. Consequently, each 0.5 l of blood is during 5 s. The questions arise of how such a large mass of blood passes through such a small mass of lungs and what the reasons are for such a high rate of blood oxygenation. Since the structure of lungs in mammals is almost the same, we tried to solve these issues studying the rats, in which 20–22 ml of blood pass through the lungs of 1.5–2.0 g mass. A great blood flow appeared to be associated with a large diameter of the lung arterioles and a high rate of the blood flow in them. The high rate of oxygenation is accounted for by a special structure of alveoli and special conditions of the blood flow, which create ideal conditions for oxygen diffusion.