Diffusion of Gases
Gases diffuse from areas of higher partial pressure to areas of lower partial pressure. The diffusion along the partial pressure gradient ceases only when the partial pressure in both areas becomes equal. This is true in aquous solutions: within mixtures of gases and across gas-water inter phase. Very seldom diffusion in direction of partial pressure gradient also means diffusion along a concentration gradient. In later sections we shall see how the movement of oxygen and carbon dioxide depends on the partial pressure gradient that exists at the inter phase between vascular: fluids and air in lungs. Within the body at the capillary level the intracellular fluids and vascular fluids develop opposed partial pressure gradients and hence gases move opposite directions.
Having studied the physical basis of gas diffusion we can now proceed to see how animals exchange gases across their respiratory surfaces. First, we shall discuss various arrangements for respiratory gas exchange in animals.