Text С. The Physiology of the Lungs

The physiology of the lungs is associated with their structure. There are over 700,000,000 alveoli in the lungs. The total surface of the alveoli is about 90 sq. m (square metres). The lungs have many capillaries with the total surface of about 80 sq. m. This particular structure of the lungs enables the exchange of gases between the alveolar air and the blood.

Elastic fibers of connective tissue composing the walls of the alveoli, alveolar passages and the visceral pleura enable the lungs to dilate.

When one breathes normally not all the alveoli and capillaries of the lungs are opened. When respiration becomes deep, the number of the opened alveoli and capillaries increases. The flow of blood into the lungs increases when one breathes in and it decreases when one breathes out.

The regulation of the vital capacity of the lungs is of particular importance to the exchange of oxygen and carbon dioxide taking place in the lungs. It is considered that in the adult the vital capacity of the lungs is about 3-4 litres. When the depth of respiration increases the vital capacity may be 6 litres and even more.

The lungs take part in the production of physiologically active substances, in the regulation of blood coagulation, in the metabolism of proteins, fats and carbohydrates.

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