The relation between structure and function in the airways of the lung

Abstract

discussion is concerned with the relationships between the way in which gas moves in the airways of the human lung and the morphology and structure of the airways in which it moves. Fluid dynamic details, although of importance, will be deliberately avoided in order to keep the discussion simple. The problems are best viewed in terms of what the lung is required to do. The body uses oxygen and produces carbon dioxide and these gases are exchanged in opposite directions between the blood and the air. Since blood has to be retained within the vascular system it must be separated from the air by a tissue membrane through which the gases diffuse. Land animals have also to conserve water so this exchange membrane cannot be in the form of gills, but must be situated within the body. Diffusion is a relatively slow process in tissues and to compensate for this the membrane must be thin and also have a large enough surface area for gas exchange at times of physiological stress. The surface area required is about 60-80 m2 and this has to be contained within the volume available to the lungs, say 0.005 m3 or 5 litres. To achieve this the lung is divided up by many partitions into volumetric units, the alveoli, which are roughly spherical,