CHAPTER 48 Gas Exchange in Animals

1. CHAPTER 48Gas Exchange in Animals

2. Chapter 48: Gas Exchange in Animals Respiratory Gas Exchange Respiratory Adaptations for Gas Exchange Mammalian Lungs and Gas Exchange Blood Transport of Respiratory Gases Regulating Breathing to Supply O2

3. Respiratory Gas Exchange • Most cells require a constant supply of O2 and continuous removal of CO2. • These respiratory gases exchange between the body fluids of an animal and its environment by diffusion. 3

4. Respiratory Gas Exchange • In aquatic animals, gas exchange is limited by low diffusion rate and low O2 level in water. • As water temperature rises, aquatic animals face a double bind in that O2 in water decreases, but • Their metabolism and work required to move water over gas exchange surfaces increases. Review Figure 48.2 4

5. figure 48-02.jpg Figure 48.2 Figure 48.2

6. Respiratory Adaptations for Gas Exchange • The evolution of large animals with high metabolic rates required adaptations to maximize respiratory gas diffusion rates: • Increasing surface areas • maximizing partial pressure gradients • decreasing their thickness • ventilating the outer surface with gases • perfusing the inner surface with blood. Review Figure 48.4 6

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8. Respiratory Adaptations for Gas Exchange • Insects distribute air throughout their bodies in a system of tracheae, tracheoles, and air capillaries. Review Figure 48.5 8

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10. Respiratory Adaptations for Gas Exchange • Fish have maximized gas exchange rates by having large gas exchange surface areas ventilated continuously and unidirectionally with fresh water. • Countercurrent blood flow helps increase gas exchange efficiency. Review Figures 48.6, 48.7 10

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12. figure 48-07.jpg Figure 48.7 Figure 48.7

13. Respiratory Adaptations for Gas Exchange • The gas exchange system of birds includes air sacs that communicate with the lungs but are not used for gas exchange. • Air flows unidirectionally through bird lungs in parabronchi. • Gases are exchanged in air capillaries running between parabronchi. Review Figures 48.8, 48.9 13

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16. Respiratory Adaptations for Gas Exchange • Each breath of air remains in the bird respiratory system for two breathing cycles. • The air sacs work as bellows to supply the air capillaries with a continuous, unidirectional flow of fresh air. Review Figure 48.10 16

17. figure 48-10a.jpg Figure 48.10 – Part 1 Figure 48.10 – Part 1

18. figure 48-10b.jpg Figure 48.10 – Part 2 Figure 48.10 – Part 2

19. Respiratory Adaptations for Gas Exchange • Breathing in vertebrates other than birds is tidal, thus less efficient than gas exchange in fishes or birds. • Even though the volume of air exchanged with each breath can vary considerably, inhaled air is always mixed with stale air. Review Figure 48.11 19

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21. Mammalian Lungs and Gas Exchange • In mammalian lungs, the gas exchange surface area provided by the millions of alveoli is enormous, and • The diffusion path length between the air and perfusing blood is very short. Review Figure 48.12 21

22. figure 48-12a.jpg Figure 48.12 – Part 1 Figure 48.12 – Part 1

23. figure 48-12b.jpg Figure 48.12 – Part 2 Figure 48.12 – Part 2

24. Mammalian Lungs and Gas Exchange • Surface tension in the alveoli would make their inflation difficult if the lungs did not produce surfactant. 24

25. Mammalian Lungs and Gas Exchange • Inhalation occurs when contractions of the diaphragm and intercostal muscles create negative pressure in the thoracic cavity. • Relaxation of the diaphragm and some intercostal muscles and contraction of other intercostal muscles increases pressure in the thoracic cavity causing exhalation. Review Figure 48.13 25

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27. Blood Transport of Respiratory Gases • Oxygen is reversibly bound to hemoglobin in red blood cells. • Each hemoglobin molecule can carry four O2 molecules maximum. • Because of positive cooperativity, affinity of hemoglobin for O2 depends on the <PO2 to which the hemoglobin is exposed. • Therefore, hemoglobin gives up O2 in metabolically active tissues and picks it up as it flows through respiratory exchange structures. Review Figure 48.14 27

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29. Blood Transport of Respiratory Gases • Myoglobin has a very high affinity for oxygen and serves as an oxygen reserve in muscle. 29

30. Blood Transport of Respiratory Gases • Fetal hemoglobin has a higher affinity for O2 than does maternal hemoglobin, allowing fetal blood to pick up O2 from maternal blood in the placenta. Review Figure 48.15 30

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32. Blood Transport of Respiratory Gases • The affinity of hemoglobin for oxygen is decreased by the presence of hydrogen ions or 2,3 diphosphoglyceric acid. Review Figure 48.16 32

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34. Blood Transport of Respiratory Gases • Carbon dioxide is carried in the blood principally as bicarbonate ions. Review Figure 48.17 34

35. figure 48-17a.jpg Figure 48.17 – Part 1 Figure 48.17 – Part 1

36. figure 48-17b.jpg Figure 48.17 – Part 2 Figure 48.17 – Part 2

37. Regulating Breathing to Supply O2 • Breathing rhythm is an autonomic function generated by neurons in the medulla of the brain stem and modulated by higher brain centers. Review Figure 48.18 37

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39. Regulating Breathing to Supply O2 • The most important feedback stimulus for breathing is level of CO2 in the blood. Review Figure 48.19 39

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41. Regulating Breathing to Supply O2 • Breathing rhythm is sensitive to feedback from chemoreceptors on the ventral surface of the brain stem and in the carotid and aortic bodies on the large vessels leaving the heart. Review Figure 48.20 41

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