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Chapter 18a

Chapter 18a. Gas Exchange and Transport. About this Chapter. Diffusion and solubility of gases Gas exchange in lungs and tissues Gas transport in the blood Regulation of ventilation. Overview. Oxygen and carbon dioxide move into and out of the blood at pulmonary and systemic capillaries

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Chapter 18a

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  1. Chapter 18a Gas Exchange and Transport

  2. About this Chapter • Diffusion and solubility of gases • Gas exchange in lungs and tissues • Gas transport in the blood • Regulation of ventilation

  3. Overview • Oxygen and carbon dioxide move into and out of the blood at pulmonary and systemic capillaries • Internal respiration O2 CO2 Airways Alveoli of lungs O2 CO2 6 CO2 exchangeat alveolar-capillaryinterface 1 Oxygen exchangeat alveolar-capillaryinterface O2 CO2 Pulmonarycirculation 2 Oxygen transport 5 CO2 transport Systemiccirculation CO2 O2 4 CO2 exchangeat cells Oxygen exchangeat cells 3 CO2 O2 Cellularrespiration Cells Nutrients ATP Figure 18-1

  4. Diffusion and Solubility • Constants influencing diffusion in the lungs • Surface area • Contact between air and blood • Membrane thickness • Alveoli and endothelium • Diffusion distance • Distance between blood and air • Concentration gradient • Most important factor as others usually are constant

  5. Movement of Gases • Pressure gradient • Partial pressure change • Solubility • Gas into liquid • Temperature • Higher faster

  6. Gases in Solution PO2 =100 mm Hg PO2 = 100 mm Hg [O2] =5.20 mmol/L PO2 =100 mm Hg PO2 = 0 mm Hg [O2] =0.15 mmol/L (a) (b) (c) Figure 18-2a–c

  7. Gases in Solution P = O2 P = CO2 100 mm Hg 100 mm Hg [O2] =5.20 mmol/L [CO2] =5.20 mmol/L P = P = O2 CO2 100 mm Hg 100 mm Hg [O2] =0.15 mmol/L [CO2] =3.00 mmol/L (d) (c) Solubility difference between O2 and CO2 Figure 18-2c–d

  8. PO2 < 40 mm Hg – PCO2 > 46 mm Hg – Gas Diffusion Alveoli Alveoli PO2 = 100 mm Hg PCO2 = 40 mm Hg PO2 = 40 PO2 = 100 PCO2 = 46 PCO2 = 40 Circulatorysystem Circulatorysystem PCO2 = 46 PCO2 = 40 PO2 = 100 PO2 = 40 Peripheral tissue Peripheral tissue (a) Oxygen diffusion (b) CO2 diffusion Figure 18-3

  9. Gas Exchange PLAY Interactive Physiology® Animation: Respiratory System: Gas Exchange

  10. Partial Pressures Table 18-1

  11. Gas Exchange Table 18-2

  12. Causes of Low Alveolar PO2 • Inspired air has abnormally low oxygen content • Altitude • Alveolar ventilation is inadequate • Decreased lung compliance • Increased airway resistance • Overdose of drugs • What types??

  13. Alveolar Ventilation • Pathological conditions that reduce alveolar ventilation and gas exchange Figure 18-4a

  14. Alveolar Ventilation Fewer alveoli Figure 18-4b

  15. Alveolar Ventilation Low compliance Figure 18-4c

  16. Alveolar Ventilation Figure 18-4d

  17. Alveolar Ventilation Figure 18-4e

  18. Gas Exchange • Oxygen diffuses across alveolar epithelial cells and capillary endothelial cells to enter the plasma – respiratory membrane Surfactant Alveolarair space O2 Alveolarepithelium Fused basementmembranes 0.1–1.5 m Nucleus ofendothelialcell O2 Capillarylumen Plasma RBC Figure 18-5

  19. Gas Exchange • Pathological changes • Decrease in amount of alveolar surface area • emphysema • Increase in thickness of alveolar membrane • fibrosis • Increase in diffusion distance between alveoli and blood • pneumonia

  20. Oxygen Transport ARTERIAL BLOOD Capillaryendothelium O2 dissolved in plasma (~PO2) < 2% O2 O2 + Hb Hb•O2> 98% Red blood cell Alveolus Alveolarmembrane Transportto cells Cells Hb + O2 Hb•O2 O2 Used incellularrespiration O2 dissolved in plasma Figure 18-6

  21. Oxygen Transport (a) Oxygen transport in blood withouthemoglobin. Alveolar PO2 = arterial PO2 • Hemoglobin increases oxygen transport by blood PO2 = 100 mm Hg O2 molecule Alveoli Arterialplasma PO2 = 100 mm Hg Oxygen dissolves in plasma. O O2 content of plasma = 3 mL O2/L blood O2 content of redblood cells = 0 Total O2 carryingcapacity 3 mL O2/L blood Figure 18-7a

  22. Oxygen Transport (b) Oxygen transport at normalPO2 in blood with hemoglobin PO2 = 100 mm Hg PO2 = 100 mm Hg Red blood cells with hemoglobin are carry-ing 98% of their maximum load of oxygen. O2 content of plasma = 003 mL O2/L blood O2 content of redblood cells = 197 mL O2/L blood Total O2 carryingcapacity 200 mL O2/L blood Figure 18-7b

  23. Oxygen Transport (c) Oxygen transport at reduced PO2in blood with hemoglobin PO2 = 28 mm Hg PO2 = 28 mm Hg Red blood cells carrying 50% of theirmaximum load of oxygen. O2 content of plasma = 000.8 mL O2/L blood O2 content of redblood cells = 099.5 mL O2/L blood Total O2 carryingcapacity 100.3 mL O2/L blood Figure 18-7c

  24. The Hemoglobin Molecule  Chain  Chain • Hemoglobin consists of 4 subunits, each centered around Fe2+ Hemegroup (a) Porphyrinring (b) R = additional C, H, O groups Figure 18-8

  25. Oxygen-Hemoglobin Dissociation Curve Figure 18-9

  26. Oxygen Binding • Physical factors alter hemoglobin’s affinity for oxygen shift curve right or left • pH • Temperature • pCO2 • BPG • RBCs produce during hypoxia • Hb type • Fetal HbF Figure 18-10a

  27. Oxygen Binding Figure 18-10b

  28. Oxygen Binding Figure 18-10c

  29. Oxygen Binding • 2,3-DPG decreases hemoglobin’s affinity for oxygen Figure 18-11

  30. Oxygen Binding • Maternal and fetal hemoglobin have different oxygen-binding properties Figure 18-12

  31. Oxygen Binding • The total oxygen content of arterial blood depends on the amount of oxygen dissolved in plasma and bound to hemoglobin TOTAL ARTERIALO2 CONTENT Oxygen dissolved inplasma (PO2 of plasma) Oxygenbound to Hb helpsdetermine is influenced by Adequateperfusionof alveoli Oxygen diffusionbetween alveoliand blood % Saturationof Hb Total number ofbinding sites Composition ofinspired air Alveolarventilation x affected by Rate anddepth ofbreathing Hb contentper RBC Numberof RBCs Diffusiondistance Surfacearea PCO2 Airwayresistance Lungcompliance pH Temperature 2,3–DPG x Membranethickness Amount ofinterstitial fluid Figure 18-13

  32. Carbon Dioxide Transport • Dissolved: 7% • Converted to bicarbonate ion: 70% • Bound to hemoglobin: 23% • Hemoglobin also binds H+ • Hb and CO2: carbaminohemoglobin H20 + CO2H2CO3 H+ + HCO3-

  33. Carbon Dioxide Transport in the Blood VENOUS BLOOD CO2 Dissolved CO2(7%) Cellularrespirationinperipheraltissues Red blood cell CO2 + Hb Hb•CO2 (23%) Cl– HCO3– HCO3– inplasma (70%) CA CO2 + H2O H2CO3 H+ + Hb Hb•H Capillaryendothelium Cell membrane Transportto lungs Dissolved CO2 Dissolved CO2 CO2 Hb + CO2 Hb•CO2 Cl– Alveoli CA H2O + CO2 HCO3– H2CO3 HCO3–inplasma Hb•H H+ + Hb Figure 18-14

  34. – PO2 < 40 mm Hg – PCO2 > 46 mm Hg Summary of O2 and CO2 Exchange and Transport Dry air = 760 mm Hg PO2 = 160 mm Hg PCO2 = 0.25 mm Hg Alveoli PO2 = 100 mm Hg PCO2 = 40 mm Hg O2 CO2 CO2 transport HCO3– = 70%Hb•CO2 = 23%Dissolved CO2 = 7% Arterial blood PO2=100 mm Hg Pulmonarycirculation PCO2=40 mm Hg O2 transportHb•O2 > 98%Dissolved O2 < 2%(~PO2) Venous blood PO2 = 40 mm Hg PCO2 = 46 mm Hg Systemiccirculation O2 CO2 Cells Figure 18-15

  35. Gas Transport PLAY Interactive Physiology® Animation: Respiratory System: Gas Transport

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