BIO2242 Lecture Notes - Lecture 9: Intrapleural Pressure, Pulmonary Pleurae, Partial Pressure
Document Summary
There are two separate but interrelated respiratory processes: cellular respirator, the oxidative processes that occur within the cells, and external respiration, the exchange of oxygen and carbon dioxide between the organism and its environment across a respiratory surface. An animal"s mechanism of external respiration is determined largely by the nature of its environment. The two great arenas of animal evolution water and land are vastly different in their physical characteristics. The most obvious difference is that air contains far more oxygen than does water. The density and viscosity of water are approximately 800 to 50 times greater, respectively, than those of air. Furthermore, gas molecules diffuse 10,000 times more rapidly in air than in water. Respiratory surfaces must be thin and always kept wet with a thin film of fluid to allow diffusion of gases across an aqueous phase between the environment and the underlying circulation.
