Possible role for membrane Lipids in the function of the normal and ab normal pulmonary circulation.

We have proposed that the necessity of transporting large quantities of a relatively insoluble molecule, 02, from alveolar air to blood may have led to the evolution of an extremely thin but extensive membrane. The very structure of the membrane has required specialized machinery to maintain low vascular pressures within it, to divert blood flow to the better oxygenated areas, and to defend the membrane from external or internal attack. The purpose of this paper is to consider whether membrane lipids (platelet-activating factor and the metabolities of arachidonic acid) constitute some of this specialized machinery, and, if so, how this machinery might work.