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Respiration 2

Respiration 2. Xia Qiang, PhD Department of Physiology Zhejiang University School of Medicine Email: xiaqiang@zju.edu.cn. CO 2. O 2. Tissue cells. O 2. O 2. CO 2. CO 2. O 2. CO 2. O 2. Pulmonary capillary. CO 2. Tissue capillaries. Gas exchange.

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Respiration 2

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  1. Respiration 2 Xia Qiang, PhD Department of Physiology Zhejiang University School of Medicine Email: xiaqiang@zju.edu.cn

  2. CO2 O2 Tissue cells O2 O2 CO2 CO2 O2 CO2 O2 Pulmonary capillary CO2 Tissue capillaries Gas exchange Pulmonary gas exchange Tissue gas exchange

  3. Physical principles of gas exchange

  4. Laws governing gas diffusion • Henry’s law The amount of dissolved gas is directly proportional to the partial pressure of the gas

  5. Boyle’s law states that the pressure of a fixed number of gas molecules is inversely proportional to the volume of the container.

  6. 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

  7. 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

  8. Factors affecting gas exchange • D: Rate of gas diffusion • T: Absolute temperature • A: Area of diffusion • S: Solubility of the gas • P: Difference of partial pressure • d: Distance of diffusion • MW: Molecular weight

  9. Changes in the concentration of dissolved gases are indicated as the blood circulates in the body. Oxygen is converted to water in cells; cells release carbon dioxide as a byproduct of fuel catabolism.

  10. In lungs

  11. Oxygen diffusion along the length of the pulmonary capillaries quickly achieves diffusional equilibrium, unless disease processes in the lungs reduce the rate of diffusion.

  12. In tissue

  13. Factors that affect pulmonary gas exchange • Thickness of respiratory membrane • Surface area of respiratory membrane • Ventilation-perfusion ratio (V/Q)

  14. Respiratory membrane alveolus capillary endothelial cell surfactant CO2 epithelial cell O2 red blood cell interstitial space

  15. Ventilation-perfusion ratio • Alveolar ventilation (V) = 4.2 L • Pulmonary blood flow (Q) = 5 L • V/Q = 0.84 (optimal ratio)

  16. VA/QC Ventilation-perfusion ratio Effect of gravity on V/Q

  17. Gas transport in the blood • Forms of gas transported • Physical dissolve • Chemical combination Alveoli Blood Tissue O2 →dissolve→combine→dissolve→ O2 CO2 ←dissolve←combine←dissolve← CO2

  18. Transport of oxygen • Forms of oxygen transported • Physical dissolve: 1.5% • Chemical combination: 98.5% • Hemoglobin (Hb) is essential for the transport of O2 by blood

  19. Adding hemoglobin to compartment B substantially increases the total amount of oxygen in that compartment, since the bound oxygen is no longer part of the diffusional equilibrium.

  20. High PO2 Hb + O2 HbO2 Low PO2

  21. Oxygen capacity The maximal amount of O2 that can combine with Hb at high PO2 • Oxygen content The amount of O2 that combines with Hb • Oxygen saturation (O2 content / O2 capacity) x 100%

  22. Cyanosis • Hb>50g/L

  23. O2 CO O2 CO CO O2 Carbon monoxide poisoning • CO competes for the O2 sides in Hb • CO has extremely high affinity for Hb

  24. Oxygen-hemoglobin dissociation curve • The relationship between O2 saturation of Hb and PO2

  25. Factors that shift oxygen dissociation curve • PCO2 and [H+] • Temperature • 2,3-diphosphoglycerate (DPG)

  26. Bohr Effect • Increased delivery of oxygen to the tissue when carbon dioxide and hydrogen ions shift the oxygen dissociation curve

  27. Chemical and thermal factors that alter hemoglobin’s affinity to bind oxygen alter the ease of “loading” and “unloading” this gas in the lungs and near the active cells.

  28. Transport of carbon dioxide • Forms of carbon dioxide transported • Physical dissolve: 7% • Chemical combination: 93% • Bicarbonate ion: 70% • Carbaminohemoglobin: 23%

  29. CO2 transport in tissue capillaries tissues CO2 CO2 tissue capillaries CO2+H2O H2CO3 CO2 + Hb HbCO2 H+ + HCO3- carbonic anhydrase CO2 + H2O H2CO3 CO2 + R-NH2 R-NHCOO- + H+ HCO3- H+ +HCO3- Cl- plasma tissuescapillaries

  30. CO2 transport in pulmonary capillaries CO2 + Hb HbCO2 alveoli CO2 pulmonary capillaries CO2 carbonicanhydrase CO2 + H2O H2CO3 HCO3- H+ +HCO3- plasma Cl- Cl- pulmonary capillaries

  31. Carbon Dioxide Dissociation Curve

  32. PO2=40 mmHg PO2=100 mmHg Haldane Effect • When oxygen binds with hemoglobin, carbon dioxide is released

  33. Bohr effect and Haldane effect H2CO3 H+ +HCO3- HbO2 HbO2 Hb + O2 Hb + O2 tissue capillaries HbH Bohr effect Haldane effect CO2 HbCO2

  34. Regulation of respiration • Breathing is autonomically controlled by the central neuronal network to meet the metabolic demands of the body • Breathing can be voluntarily changed, within certain limits, independently of body metabolism

  35. Respiratory center • A collection of functionally similar neurons that help to regulate the respiratory movement • Respiratory center • Medulla • Pons • Higher respiratory center: cerebral cortex, hypothalamus & limbic system Basic respiratory center

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