1. Gas Exchange and Transport
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. Figure 18-2: Gases in solution
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)

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

9. 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

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

11. Movement of Gases in Body

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

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

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

23. 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

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

25. 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

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

32. 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)

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

34. 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

35. 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+]

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

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

38. Movement of Gases in Body

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

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

41. Regulation of Ventilation: Pons Center
Dorsal respiratory group – inspiration
Ventral respiratory group – forced breathing

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

50. 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

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

54. Summary of Regulatory Ventilation Reflexes
Figure 18-19: Chemoreceptor response to increased PCO2

59. Protective Reflexes Bronchoconstriction Irritant receptors
Toxic particles
Irritating particles (i.e. pollen)
Hering-Breuer Reflex prevents over inflation via the activation of stretch receptors (present in smooth muscle of the airways)
Unconscious reflexes take over voluntary breathing

65. Summary
Oxygen is transported bound to Hb and this is affected by temperature, pH, CO2 , and DPG
Carbon dioxide is transported in plasma, bound to Hb and acts as the buffer bicarbonate
Respiration is regulated by CNS central pattern generator, pons center and peripheral carotid and aortic receptors
Feedback reflexes coordinate circulation and ventilation to maintain blood O2, CO2, and H+ concentrations