Diffusion of Respiratory Gases PDF

Diffusion of respiratory gases Dr. Ghada Elgarawany Assistant professor of Medical Physiology www.gmu.ac.ae COLLEGE OF MEDICINE Describe the difference between atmospheric and alveolar air. Enumerate the components of the respiratory membrane. List and explain the factors affecting the diffusion...

Diffusion of respiratory gases Dr. Ghada Elgarawany Assistant professor of Medical Physiology www.gmu.ac.ae COLLEGE OF MEDICINE Describe the difference between atmospheric and alveolar air. Enumerate the components of the respiratory membrane. List and explain the factors affecting the diffusion of respiratory gases. Composition of atmospheric air and alveolar air Atmospheric air contain N2, O2, CO2 and H2O. Atmospheric pressure = 760 mmHg Difference in partial pressure of respiratory gases between alveolar air and atmospheric air Gas exchange across respiratory membrane Gas exchange across pulmonary membrane occurs by simple diffusion. Respiratory membrane: It is a thin membrane that allows for the diffusion and exchange of oxygen (O2) and carbon dioxide (CO2) between the alveoli and capillary blood. Thickness: 0.6 micron Consists of : 1. Alveolar membrane. 2. Interstitial fluid. 3. Capillary wall. Gas exchange across respiratory membrane Diffusion of gases (D) Fick’s law , 𝑫 𝜶 Directly proportionate to 1. Pressure gradient 𝚫𝑷 2. Cross-sectional area 𝑨 3. Solubility of the gas 𝑺 𝚫𝑷 𝒙 𝑨 𝒙 𝑺 𝐝 𝐱 𝑴𝑾 Inversely proportionate to 1. Distance (thickness of the respiratory membrane d. 2. Molecular weight of the gas 𝑴𝑾 Gas exchange across respiratory membrane Diffusion coefficient = 𝑺 𝑴𝑾 Considering the diffusion coefficient for O2 is 1, the relative diffusion coefficients for different gases are as follows: From this table, what do you detect? Factor affecting Gas diffusion across respiratory membrane 1- Pressure gradient of gases across respiratory membrane (Henry’s Law) PO2 PCO2 Alveolar air Venous blood 100mmHg 40mmHg 40mmHg 46mmHg  O2 diffuse from higher pressure (alveolar air) to lower pressure (venous blood).  CO2 diffuse from higher pressure (venous blood) to lower pressure (alveolar air). Factor affecting Gas diffusion across respiratory membrane 2- Surface area of the respiratory membrane Surface area of the respiratory membrane = 70m². DαA Surface area increases in exercise: due to opening of closed pulmonary capillaries, dilatation of the capillaries and more expansion of the alveoli →increase gas diffusion across respiratory membrane. Surface area decreases in 1. Lung diseases 2. Old age. Factor affecting Gas diffusion across respiratory membrane 3- Nature and thickness of the respiratory membrane 𝟏 D d Lung fibrosis → change the nature of the respiratory membrane → decrease gas diffusion. Pulmonary edema → increase the thickness of the respiratory membrane → decrease gas diffusion. 4- Ventilation perfusion ratio (V/Q) High V/Q ratio: Pulmonary thrombi or emboli→ less perfusion → decreased gas exchange. Emphysema → destruction of alveolar blood vessel→ decreased gas exchange. Low V/Q ratio: Bronchial asthma →less ventilation → decreased gas exchange. Diffusion coefficient = 𝑺 𝑴𝑾 Diffusion capacity of the respiratory membrane to CO2 is 20 times O2 diffusion capacity. Blood leaving the lungs is in complete equilibrium with the alveolar air i.e. PO2 = 100mmHg and CO2 = 40 mmHg. PO2 leaving the alveoli capillaries is 100 mmHg, but in the systemic arteries is 98-99 mmHg due to Physiological shunt. 11 Review questions Which of the following would most increase diffusion of oxygen across the respiratory membrane? A. Decrease in membrane surface area B. Decrease in the number of alveoli C. Increase in membrane thickness D. Increase in the alveolar-capillary oxygen pressure gradient. https://exchange.scholarrx.com/brick/alveolar-gas-exchange Summary Describe the difference between atmospheric and alveolar air. Enumerate the components of the respiratory membrane. List and explain the factors affecting the diffusion of respiratory gases. Learning Resources  Hall JE, Hall ME. Guyton and Hall textbook of medical physiology e-Book. 14ed, Elsevier Health Sciences; 2021. Chapter 40, 511-520. https://www-clinicalkeycom.gmulibrary.com/#!/content/book/3-s2.0-B9780323597128000412  Power-point presentation in the Moodle. www.gmu.ac.ae COLLEGE OF MEDICINE Thank you