Partial Pressures of Gases in Blood

The enormous surface area of alveoli and the short diffusion distance between alveolar air and the capillary blood quickly help to bring the blood into gaseous equilibrium with the alveolar air. This function is further aided by the tremendous number of capillaries that surround each alveolus, forming an almost continuous sheet of blood around the alveoli (fig. 16.21).

When a liquid and a gas, such as blood and alveolar air, are at equilibrium, the amount of gas dissolved in the fluid reaches a maximum value. According to Henry's law, this value depends on (1) the solubility of the gas in the fluid, which is a physical constant; (2) the temperature of the fluid—more gas can be dissolved in cold water than warm water; and (3) the partial pressure of the gas. Since the temperature of the blood does not vary significantly, the concentration of a gas dissolved in a fluid (such as plasma) depends directly on its partial pressure in the gas mixture. When water—or plasma—is brought into equilibrium with air at a PO2 of 100 mmHg, for example, the fluid will contain 0.3 ml of O2 per 100 ml fluid at 37° C. If the PO2 of the gas were reduced by half, the amount of dissolved oxygen would also be reduced by half.

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Blood Pressure Health

Blood Pressure Health

Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...

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