Gas exchange气体交换 Pulmonary gas exchange Tissue gas exchange Tissue cells CO CO CO CO Pulmonary capillary Tissue capillaries
Gas exchange 气体交换 Tissue capillaries Tissue cells CO2 O2 CO2 O2 Pulmonary capillary CO2 CO2 O2 O2 Pulmonary gas exchange Tissue gas exchange
Physical principles of gas exchange Diffusion continuous random motion of gas molecules ■ Partial pressure:the individual pressure of -..o each gas, eg. PO ada
Physical principles of gas exchange ◼ Diffusion: continuous random motion of gas molecules. ◼ Partial pressure: the individual pressure of each gas, eg. PO2
P1V1=P2v2 Compression Decompression ↓v→↑P tv→4P Boyle's law states that the pressure of a fixed number of gas molecules is inversely proportional to the volume of the container
Boyle’s law states that the pressure of a fixed number of gas molecules is inversely proportional to the volume of the container
Laws governing gas diffusion P2 ■ Henry's law: The amount of dissolved gas is directl ty proportional to the partial pressure of the gas 88EEa 0100200300400500600700 Pao2(mmHg)
Laws governing gas diffusion ◼ Henry’s law: The amount of dissolved gas is directly proportional to the partial pressure of the gas
Laws governing gas diffusion ■ Grahan'sLaW When gases are dissolved in liquids, the relative rate of diffusion of a given gas is proportional to its solubility in the liquid and inversely proportional to the square root of its molecular mass diffusion rate of COz: 2232=19 diffusion rate of 02 44
Laws governing gas diffusion ◼ Graham's Law When gases are dissolved in liquids, the relative rate of diffusion of a given gas is proportional to its solubility in the liquid and inversely proportional to the square root of its molecular mass
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