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Chapter 18

Chapter 18. Gas Exchange and Transport. About this Chapter. Getting CO 2 & O 2 dissolved for transport How oxygen is transported, role of hemoglobin How carbon dioxide is transported Regulators that sense and coordinate respiration with circulation for gas transport.

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Chapter 18

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  1. Chapter 18 Gas Exchange and Transport

  2. About this Chapter • Getting CO2 & O2 dissolved for transport • How oxygen is transported, role of hemoglobin • How carbon dioxide is transported • Regulators that sense and coordinate respiration with circulation for gas transport

  3. Overview of Respiratory Exchange Figure 18-1: Overview of oxygen and exchange and Transport CO2

  4. Solubility of Gasses • Pressure gradient: lower at high altitudes • Temperature: constant in warm blooded humans • Solubility (solute & solvent): O2 or CO2 in water Figure 18-2: Gases in solution

  5. Gas Exchange in the Lungs and Tissues: Oxygen • Diffusion through alveolar thin cells • Down diffusion gradient • Higher in alveoli • Lower in blood • Diffusion from blood • Also down gradient • To ECF • To tissue cells (convert O2 to CO2)

  6. Gas Exchange in the Lungs and Tissues: Oxygen Figure 18-3a: Gas exchange at the alveoli and cells

  7. Gas Exchange in the Lungs and Tissues: Carbon Dioxide • Diffusion out of cells (down diffusion gradient) • Into blood • Buffer role • Conversions: • Plasma • Bicarbonate • On Hb • Into alveolus & expiration

  8. Gas Exchange in the Lungs and Tissues: Carbon Dioxide Figure 18-3b: Gas exchange at the alveoli and cells

  9. Movement of Gases in Body

  10. Alveolar Exchange and Diseases Related to Exchange • Wet surface • Thin epithelia • Little ECF • Diseases: • Emphysema • Fibrotic Lung • Pulmonary edema • Asthma

  11. Alveolar Exchange and Diseases Related to Exchange Figure 18-5: Oxygen diffuses across the alveolar and endothelial cells to enter the plasma

  12. Diseases of the Lung Figure 18-4: Pulmonary pathologies that affect alveolarventilation and gas exchange

  13. Gas Transport in the Blood: Oxygen • 2% in plasma • 98% in hemoglobin (Hb) • Blood holds O2 reserve Figure 18-6: Summary of oxygen transport in the blood

  14. Gas Transport in the Blood: Oxygen Figure 18-7 : The role of hemoglobin in oxygen transport

  15. Hemoglobin Transport of Oxygen: Disassociation Curve • 4 binding sites per Hb molecule • 98% saturated in alveolar arteries • Resting cell PO2 = 40 mmHg • Working cell PO2 = 20 mmHg • More unloaded with more need • 75% in reserve at normal activity

  16. Hemoglobin Transport of Oxygen: Disassociation Curve Figure 18-8: Oxygen-hemoglobin dissociation curve

  17. Factors that Modify Hb Transport of Oxygen • Bohr effect: pH  causes  O2 binding -releasing it •  2,3 DPG decreases O2 binding to hemoglobin (response to high altitude) •  PCO2 decreases O2 binding–releasing it • (Temperature affects the curve but doesn't vary in humans)

  18. Factors that Modify Hb Transport of Oxygen Figure 18-9: Physical factors alter oxygen binding to hemoglobin

  19. Summary of Oxygen Transport • How many of these choices are likely to be variable? Figure 18-12: Factors contributing to the total oxygen content of arterial blood

  20. Gas Transport in the Blood: Carbon Dioxide • Excess CO2 in blood (Hypercapnia) • Leading to: acidosis, CNS depression & coma • 7% in plasma, 23% bound to Hb • 70% as HCO3- acts as a buffer [H+]

  21. Gas Transport in the Blood: Carbon Dioxide Figure 18-13: Carbon dioxide transport in the blood

  22. Review of Respiratory Exchange & Transport Figure 18-14: Summary of gas transport

  23. Regulation of Ventilation: Central pattern generator • Integrates input from cortex, limbic & chemoreceptors • Rhythmic contractions of ventilation

  24. Regulation of Ventilation: Central pattern generator Figure 18-15: Reflex control of ventilation

  25. Regulation of Ventilation: Pons Center Figure 18-16: Rhythmic breathing

  26. Regulation of Ventilation: Chemoreceptors • Carotid & aortic bodies: O2, CO2 & H+ receptors • Medullary CO2 receptor • Low [O2], high [CO2] & low pH  ventilation Figure 18-17: Carotid body oxygen sensor releases neurotransmitter when decreases PO2

  27. Regulation of Ventilation: Chemoreceptors Figure 18-18: Central chemoreceptor monitors in cerebrospinal fluid

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