(4)Gas_exchange(1).pptx and respiratory physiology

Respiratory physiology

1. Gas exchange By: Dr. Abdalla.M.Osman

2. The exchange of oxygen and carbon dioxide between the alveoli and blood is a purely passive process of gas diffusion . Several factors influence the diffusion of gases:

3. Partial pressure gradient of gases The movement of gases from the alveoli to the blood and vice versa are occur according to pressure gradient

4. PO 2 100mmHg in the alveoli 40mmHg in the blood The gradient is 100-40 = 60mmHg ( from the alveoli to capillary)

5. PCO 2 46 mmHg in the blood 40 mmHg in the alveoli The gradient is 46-40 = 6 mmHg ( from the capillary to the alveoli).

6. Alveolar – capillary membrane This is a semi permeable membrane which separates the alveolar air from the pulmonary capillary blood. It contain several layers Fluid lining the alveoli Alveolar wall Interstitial fluid Capillary wall The thick of its wall affect the rate of diffusion.

7. Pathophysiology note Oxygen diffusion is impaired by: decreases the O 2 pressure gradient (e.g., high altitude ), decreases the surface area of the pulmonary membrane (e.g ., emphysema ), or increases the diffusion distance (e.g ., pulmonary fibrosis ).

8. The physical properties of gases a- Solubility: The more soluble the gas the faster it will diffuse through the alveolar –capillary membrane b- Molecular weight of the gases: The higher the molecular weight of the gas the slower it will diffuse

9. Surface area Increase with depth of respiration as in severe exercise by: Increase alveolar ventilation Increase cardiac out put

10. Ventilation/blood flow ratio Ventilation/blood flow ratio = Alveolar ventilation Blood flow = 4 liters/min = 4 = 0.8 5 liters/min 5

11. Mechanisms of maintaining V/Q matching Optimal matching of pulmonary ventilation and perfusion is achieved by hypoxia induced vasoconstriction and by changes in response to exercise.

12. Chemical reactions The reaction between oxygen, carbon dioxide and hemoglobin is reversible. Oxygenation not oxidation.

13. Temperature The rate of diffusion of gases is normally dependent on temperature. Because body temperature is constant it has no significant influence on rate of exchange