Pneumocytes, Surfactant and Design of Gas Exchangers

Abstract

According to Young-Laplace’s law, the pressure (P) needed to distend a spherical body is directly proportional to the surface tension at the air-liquid interface (T) and inversely proportional to the radius of curvature (r⁻¹), i.e. P = T r⁻¹. Although an intensely subdivided lung grants an extensive respiratory surface area (Sect. 10), the process engenders higher ventilatory cost (e.g. Wilson and Bachofen 1982). Therefore, for optimal design, a compromise must be conceived between fabrication of an extensive respiratory surface area (by intensification of internal subdivision of a gas exchanger) with minimization of respiratory cost of operation. The surfactant [a mixture of phospholipids (dipalmitoylphosphatidylcholine), neutral lipids and a small quantity of proteins] lines the respiratory surface of the air bladder (e.g. Maina et al. 1996a; Maina 2000d) (Figs. 63, 112) and all those gas exchangers (lungs) that subsequently developed from it.

The availability of multiple solutions to a given structural problem is one of the reasons why animals have evolved into such an enormous variety of forms . Gordon (1988)