Laws governing gas diffusion ■ Fick's law The net diffusion rate of a gas across a fluid membrane is proportional to the difference in partial pressure, proportional to the area of the membrane and inversely proportional to the thickness of the membrane
Laws governing gas diffusion ◼ Fick’s law The net diffusion rate of a gas across a fluid membrane is proportional to the difference in partial pressure, proportional to the area of the membrane and inversely proportional to the thickness of the membrane
Factors affecting gas exchange △P·S·T·A D∝ d·√MW Rate of gas diffusion D△sTAd Difference of partial pressure Solubility of the gas Absolute temperature Area of diffusion Distance of diffusion MW Molecular weight
▪ D: Rate of gas diffusion ▪ P: Difference of partial pressure ▪ S: Solubility of the gas ▪ T: Absolute temperature ▪ A: Area of diffusion ▪ d: Distance of diffusion ▪ MW: Molecular weight d MW P S T A D Factors affecting gas exchange
Gas partial pressure(mmHg) Atmosphere Alveoli Arterial Venous Tissue Po,159 104 100 4030 Pco.3 40 40 4650
Gas partial pressure (mmHg) Atmosphere Alveoli Arterial Venous Tissue Po2 159 104 100 40 30 Pco2 0.3 40 40 46 50
Begin 840 ml/min 590 ml/min 200 ml/min Alveoli Alveolar ventilation 4 U/min 200 ml co2 250mO2 750mo2→1000mO2 2800mCo2→2600mCo ung capillaries Lung capillaries Right Left Cardiac output/Right heart heart heart Tissue capillaries Tissue capillaries 750mO2 1000mO2 2800mCo2+2600mCo2 250mO2 200 ml cO2 Cells Cells In the lungs, the concentration gradients favor the diffusion of oXygen toward the blood and the diffusion of carbon dioxide toward the alveolar air; owing to the metabolic activities of cells these gradients are reversed at the interface of the blood and the active cells
In the lungs, the concentration gradients favor the diffusion of oxygen toward the blood and the diffusion of carbon dioxide toward the alveolar air; owing to the metabolic activities of cells, these gradients are reversed at the interface of the blood and the active cells
Factors that affect the velocity of pulmonary gas exchange Thickness of respiratory membrane呼吸膜 a Surface area of respiratory membrane The diffusion coefficient扩散系数 of the gas a The pressure difference of the gas between the two sides of the membrane
Factors that affect the velocity of pulmonary gas exchange ◼ Thickness of respiratory membrane呼吸膜 ◼ Surface area of respiratory membrane ◼ The diffusion coefficient 扩散系数of the gas ◼ The pressure difference of the gas between the two sides of the membrane