山东大学：《医学生理学 Medical Physiology》课程教学资源（PPT课件讲稿，人体生理学 Human Physiology）Chapter 5 Respiratory Physiology Part 3 respiratory gases exchange

Part 3 Respiratory gases Exchange

1 Part 3 Respiratory Gases Exchange

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I Physical Principles of Gas Exchange

3 I Physical Principles of Gas Exchange

Partial pressure The pressure exerted by each type of gap n a mixture Concentration of a gas in a liquid determined by its partial pressure and its solubility coefficient

4 • Partial pressure – The pressure exerted by each type of gas in a mixture • Concentration of a gas in a liquid – determined by its partial pressure and its solubility coefficient

Partial Pressures of gases Basic Composition of Air 79% Nitrogen o Oxygen 0% Carbon Dioxide In a mixture of gases, each gas exerts a partial pressure proportional to its mole fraction Total Pressure =sum of the partial pressures of each gas Total Pressure(at sea level) barometric 760 mm hs 760mm Hs Pgas=Pb X Fgas PN2=760X0.79=600.4mmHg PO2=760X0.21=1596mmHg

5 Partial Pressures of Gases Basic Composition of Air • 79% Nitrogen • 21% Oxygen • ~ 0% Carbon Dioxide In a mixture of gases, each gas exerts a partial pressure proportional to its mole fraction. Total Pressure = sum of the partial pressures of each gas Pgas = Pb x Fgas PN2 = 760 x 0.79 = 600.4 mm Hg P02 = 760 x 0.21 = 159.6 mm Hg Total Pressure (at sea level) Pbarometric = 760 mm Hg Pb 760 mm Hg Pb

Partial Pressure of gases in fluids Each gas has a specific solubility 0, Solubility coefficient=0.003 ml/100 ml Blood C02=0.06 ml/100 ml Blood(x 20 of02) Gases dissolve in fluids by moving down a Partial Pressure gradient rather than a concentration gradient Consider a container of fluid in a vacuum That is opened to the air Molecules of gas begin to enter the fluid

6 Consider a container of fluid in a vacuum Partial Pressure of Gases in Fluids Each gas has a specific solubility O2 Solubility coefficient = 0.003 ml/100 ml Blood C02 = 0.06 ml/100 ml Blood (x 20 of 02) Gases dissolve in fluids by moving down a Partial Pressure gradient rather than a concentration gradient That is opened to the air Molecules of gas begin to enter the fluid

Partial Pressure of gases in fluids After a short time the number of molecules the number of molecul ENTERING LEAVING At equilibrium, if the gas phase has a PO2=100 mm Hg. ne liquid phase also has a po2=100 mm Hg ● An easy way to talk about gases in fluids 7

7 Partial Pressure of Gases in Fluids After a short time, the number of molecules the number of molecules ENTERING = LEAVING At equilibrium, if the gas phase has a PO2 = 100 mm Hg, the liquid phase also has a PO2 = 100 mm Hg An easy way to talk about gases in fluids

Diffusion: Blood Transit Time in the Areo Alveolus Blood capil Time for exchange P mm Hg 100 g Saturated very quickly Reserve diffusive capacity of the 40 Ing Co2 Time 0.75 sec

8 Alveolus Blood capillary Time for exchange PO2 Time 0 0.75 sec 40 100 Saturated very quickly Reserve diffusive Capacity of the lung 45 mm Hg PCO2 Diffusion: Blood Transit Time in the Alveolus

II Gas exchange in the lung and in the tissue

9 II Gas exchange in the lung and in the tissue

Diffusion Gradients of Respiratory Gases at Sea Level Partial pressure(mmHg) in Dry Alveolar Venous Diffusion Gas dry air air alr blood gradient Tota100.007600760 760 2O 0.00 0.0 00 20.93159.1105 0 65 CO20.030 40 46 79.04600.7569 573 60 NB. CO is -20X more soluble than o2 in blood = large amounts move into out of the blood down a relatively small diffusion gradient

10 Diffusion Gradients of Respiratory Gases at Sea Level Total 100.00 760.0 760 760 0 H2O 0.00 0.0 47 47 0 O2 20.93 159.1 105 40 65 CO2 0.03 0.2 40 46 6 N2 79.04 600.7 569 573 0 Partial pressure (mmHg) % in Dry Alveolar Venous Diffusion Gas dry air air air blood gradient NB. CO2 is ~20x more soluble than O2 in blood => large amounts move into & out of the blood down a relatively small diffusion gradient