Gas Exchange in Animals

1. 37 Gas Exchange in Animals

2. Chapter 37 Gas Exchange in Animals • Key Concepts • 37.1 Fick’s Law of Diffusion Governs Respiratory Gas Exchange • 37.2 Respiratory Systems Have Evolved to Maximize Partial Pressure Gradients • 37.3 The Mammalian Lung Is Ventilated by Pressure Changes

3. Chapter 37 Gas Exchange in Animals • Key Concepts • 37.4 Respiration Is under Negative Feedback Control by the Nervous System • 37.5 Respiratory Gases Are Transported in the Blood

4. Chapter 37 Opening Question How are bar-headed geese able to sustain the high metabolic cost of flight at altitudes higher than Mount Everest?

5. Concept 37.1 Fick’s Law of Diffusion Governs Respiratory Gas Exchange • Organisms must exchange O2 and CO2—respiratory gases exchanged only by diffusion along their concentration gradients. • Partial pressure is the concentration of a gas in a mixture. • Barometric pressure—atmospheric pressure at sea level is 760 mm Hg. • Partial pressure of O2 (PO2)is159 mm Hg.

6. In-Text Art, Ch. 37, p. 730

7. Concept 37.1 Fick’s Law of Diffusion Governs Respiratory Gas Exchange • P1– P2 • Q = DA • L • Fick’s law of diffusion applies to all gas exchange systems. • Q = the rate of diffusion • D = the diffusion coefficient: A characteristic of the diffusing substance, the medium, and the temperature

8. Concept 37.1 Fick’s Law of Diffusion Governs Respiratory Gas Exchange • P1– P2 • Q = DA • L • A = the area where diffusion occurs. • P1 and P2 = partial pressures of the gas at two locations. • L = the path length between the locations. • (P1 – P2)/L is a partial pressure gradient.

9. Concept 37.1 Fick’s Law of Diffusion Governs Respiratory Gas Exchange • Oxygen is easier to obtain from air than from water: • O2 content of air is higher than that of water • O2 diffuses much faster through air • Air and water must be moved by the animal over its gas exchange surfaces—requires more energy to move water than air

10. Concept 37.1 Fick’s Law of Diffusion Governs Respiratory Gas Exchange • The slow rate of diffusion of oxygen in water limits the size and shape of species without internal systems for gas exchange. • These species have evolved larger surface areas, or central cavities, or specialized respiratory systems.

11. In-Text Art, Ch. 37, p. 731 (1)

12. In-Text Art, Ch. 37, p. 731 (2)

13. Concept 37.1 Fick’s Law of Diffusion Governs Respiratory Gas Exchange • O2 availability is limited in some environments due to temperature. • For water-breathers, body temperature and metabolic rate rise with an increase in water temperature—need for oxygen increases while the available oxygen decreases. • For air-breathers, increase in altitude reduces available oxygen due to lower partial pressure of oxygen at high altitudes.

14. Concept 37.1 Fick’s Law of Diffusion Governs Respiratory Gas Exchange • Respiratory gas exchange is a two-way process: CO2 diffuses out of the body as O2 diffuses in. • The concentration gradient of CO2 from air-breathers to the environment is always large. • CO2 is very soluble in water and is easy for aquatic animals to exchange.

15. Concept 37.2 Respiratory Systems Have Evolved to Maximize Partial Pressure Gradients • Gas exchange systems are made up of surfaces and the mechanisms that ventilate and perfuse those surfaces. • Adaptations to maximize the exchange of O2 and CO2: • Increase surface area • Maximize partial pressure difference • Minimize diffusion path length • Minimize the diffusion that takes place in an aqueous medium

16. Concept 37.2 Respiratory Systems Have Evolved to Maximize Partial Pressure Gradients • Surface area (A) is increased by: • External gills—also minimize the diffusion path length (L) of O2 and CO2 in water • Internal gills—protected from predators and damage • Lungs—internal cavities for respiratory gas exchange with air • Tracheae—air-filled tubes in insects

17. Figure 37.1 Gas Exchange Systems

18. Concept 37.2 Respiratory Systems Have Evolved to Maximize Partial Pressure Gradients • Transporting gases optimizes partial pressure gradients—increased by: • Minimization of the diffusion path length (L) of O2 and CO2 • Ventilation—active moving of the respiratory medium over the gas exchange surfaces • Perfusion—circulating blood over the gas exchange surfaces

19. Concept 37.2 Respiratory Systems Have Evolved to Maximize Partial Pressure Gradients • Insects have a tracheal system throughout their bodies. • Spiracles in the abdomen open to allow gas exchange and close to limit water loss. • Spiracles open into tracheae that branch to tracheoles, which end in air capillaries.

20. Figure 37.2 The Tracheal Gas Exchange System of Insects (Part 1)

21. Figure 37.2 The Tracheal Gas Exchange System of Insects (Part 2)

22. Figure 37.2 The Tracheal Gas Exchange System of Insects (Part 3)

23. Concept 37.2 Respiratory Systems Have Evolved to Maximize Partial Pressure Gradients • Fish gills use countercurrent flow to maximize gas exchange. • Gills are supported by gill arches that lie between the mouth and the opercular flaps. • Water flows unidirectionally into the mouth, over the gills, and out from under the opercular flaps.

24. Figure 37.3 Countercurrent Exchange Is More Efficient

25. Figure 37.4 Fish Gills (Part 1)

26. Concept 37.2 Respiratory Systems Have Evolved to Maximize Partial Pressure Gradients • Constant water flow maximizes PO2 on the external gill surfaces and blood circulation minimizes PO2 on the internal surfaces. • Gills are made up of gill filaments that are covered by folds, or lamellae. • Lamellae are the site of gas exchange and minimize the diffusion path length (L) between blood and water.

27. Figure 37.4 Fish Gills (Part 2)

28. Concept 37.2 Respiratory Systems Have Evolved to Maximize Partial Pressure Gradients • Afferent blood vessels bring blood to the gills and efferent vessels take blood away. • Blood flows through the lamellae in the direction opposite to the flow of water. • The countercurrent flow optimizes the PO2 gradient.

29. Concept 37.2 Respiratory Systems Have Evolved to Maximize Partial Pressure Gradients • Most terrestrial vertebrates use tidal ventilation in lungs—air flows in and out by the same path. • Lungs and airways are never completely empty—contain some dead space • The residual volume (RV) is the air that cannot be expelled from the lungs and contains “stale” (low O2) air. • Each inhalation brings a mixture of outside air and stale air to the exchange area.

30. Concept 37.2 Respiratory Systems Have Evolved to Maximize Partial Pressure Gradients • Bird lungs use unidirectional air flow to maintain a high PO2 gradient. • Air enters through the posterior end of the lung and flows through parabronchi, and then into air capillaries—the sites of gas exchange. • Birds have air sacs that receive inhaled air but are not sites of gas exchange. • Posterior air sacs store fresh air and release it to lungs during exhalation—anterior sacs receive air from lungs.

31. Figure 37.5 The Respiratory System of a Bird (Part 1)

32. Figure 37.5 The Respiratory System of a Bird (Part 2)

33. Concept 37.3 The Mammalian Lung Is Ventilated by Pressure Changes • In mammals, air enters the lung through the oral cavity and nasal passage, which join in the pharynx. • Below the pharynx, the esophagus directs food to the stomach, and the trachea leads to the lungs—at the beginning is the larynx, or voice box. • The trachea branches into two bronchi, then into bronchioles, and then into alveoli—the sites of gas exchange.

34. Figure 37.6 The Human Respiratory System (Part 1)

35. Figure 37.6 The Human Respiratory System (Part 2)

36. Concept 37.3 The Mammalian Lung Is Ventilated by Pressure Changes • Capillaries surround and lie between the alveoli—diffusion path between blood and air is less than two micrometers. • Mammalian lungs produce two secretions that affect ventilation—mucus and surfactant. • Mucus lines the airways and captures dirt and microorganisms. • A surfactant reduces the surface tension of liquid lining the alveoli.

37. Figure 37.6 The Human Respiratory System (Part 3)

38. Figure 37.6 The Human Respiratory System (Part 4)

39. Figure 37.6 The Human Respiratory System (Part 5)

40. Concept 37.3 The Mammalian Lung Is Ventilated by Pressure Changes • Tidal volume (TV)—the amount of air that moves in and out per breath, at rest. • Inspiratory (IRV) and expiratory (ERV) reserve volumes are the additional amounts of air that we can forcefully inhale or exhale. • The vital capacity (VC) is the sum of TV + IRV + ERV.

41. Figure 37.7 Measuring Lung Ventilation

42. Concept 37.3 The Mammalian Lung Is Ventilated by Pressure Changes • Mammalian lungs are suspended inside a thoracic cavity. • The diaphragm is a sheet of muscle at the bottom of the cavity. • The pleural membrane covers each lung and lines the thoracic cavity. • The space between the membranes contains fluid to help them slide past each other during breathing.

43. Concept 37.3 The Mammalian Lung Is Ventilated by Pressure Changes • Inhalation begins when the diaphragm contracts—it pulls down, expanding the thoracic cavity and pulling on on the pleural membranes. • The pleural membranes pull on the lungs, which expand and draw air in from outside. • Exhalation begins when the diaphragm relaxes. • The elastic lung tissues pull the diaphragm up and push air out of the airways.

44. Figure 37.8 Into the Lungs and Out Again (Part 1)

45. Figure 37.8 Into the Lungs and Out Again (Part 2)

46. Concept 37.3 The Mammalian Lung Is Ventilated by Pressure Changes • Additional musclesare used during exercise. • The external intercostal muscles lift the ribs up and outward, expanding the cavity. • The internal intercostal muscles decrease the volume by pulling the ribs down and inward.

47. Concept 37.4 Respiration Is under Negative Feedback Control by the Nervous System • Breathing is controlled in the medulla oblongata, in the brain stem. • Groups of respiratory motor neurons increase their firing rate just before an inhalation. • The breathing rate is modulated to meet demands for O2 supply and CO2 elimination.

48. Concept 37.4 Respiration Is under Negative Feedback Control by the Nervous System • In humans and mammals, the breathing rate is more sensitive to increases in CO2 than to falling levels of O2. • The PCO2 of blood is the primary metabolic feedback for breathing. When breathing or metabolism changes, it alters PO2 and PCO2 in the blood. • Ventilation increases rapidly with exercise, in anticipation of a rise in PCO2.

49. Figure 37.9 Sensitivity of Respiratory Control System Changes With Exercise (Part 1)

50. Figure 37.9 Sensitivity of Respiratory Control System Changes With Exercise (Part 2)