Gas Exchange in Animals

1. Gas Exchange in Animals Principles & Processes

2. Gas Exchange • respiratory gases • oxygen (O2) • required as final electron acceptor for oxidative metabolism • carbon dioxide (CO2) • discarded byproduct of oxidative metabolism

3. Gas Exchange • respiratory mechanisms • system to deliver oxygenated/remove deoxygenated medium • membrane for gas exchange • system to carry O2 to cells/CO2 from cells

4. Gas Exchange • physical factors affecting gas exchange • gases cross respiratory membranes by diffusion • diffusion occurs much faster in air than in water (~8000 X) • O2 content of air is greater than O2 content of water (<20 X) • air is less dense (~800 X) & less viscous (50 X) than water • air is a better respiratory medium than water

5. Gas Exchange • problems for water breathers • cells must be near oxygenated medium • solutions • thin (2-D) body • perfused body • specialized external exchange surfaces • specialized internal exchange surfaces

6. specialized external exchange surfacesFigure 48.1

7. Gas Exchange • problems for water breathers • an ectotherm’s O2 demand increases with increased temperature • O2 content of water decreases with increased temperature • compensatory increase in breathing increases O2 demand

8. the problem with warm waterFigure 48.2

9. Gas Exchange • problems for (adventurous) air breathers • air pressure decreases with altitude • O2 partial pressure decreases with altitude • rate of O2 diffusion decreases with decreased O2 partial pressure

10. increased altitude decreases the availabilityof O2

11. Gas Exchange • CO2 removal • [CO2] in air is ~350 ppm • gradient for outward diffusion is always steep • [CO2] in water varies depending on aeration • gradient for outward diffusion may be very shallow

12. Gas Exchange • Fick’s law of diffusion indicates how to increase diffusion rates Q = D·A·(P1-P2)/L Q is the rate of diffusion from a => b D is the diffusion coefficient of a system A is the cross-sectional area of diffusion P1, P2 are the partial pressures of the diffusing particle at a & b L is the distance between a & b

13. Gas Exchange • using Fick’s law of diffusion Q = D·A·(P1-P2)/L • increase diffusion (Q) by • increasing D (use air instead of water?) • increasing A (increase exchange surface) • increasing P1-P2 (replenish fresh air) • decreasing L (decrease thickness of exchange surface)

14. Gas Exchange • animal gas exchange surfaces (increase A) • external gills • large surface area • no breathing system needed • exposed to possible damage or predation • internal gills • same large surface area, plus • protection against damage, but • requires breathing mechanism

15. gas exchange with waterFigure 48.3

16. Gas Exchange • animal gas exchange surfaces (increase A) • lungs • internal, highly divided, elastic cavities • transfer gases to transport medium • tracheae (insects) • internal, highly branched air tubes • transfer gases to all tissues

17. gas exchange with airFigure 48.3

18. Gas Exchange • animal gas exchange surfaces (increase P1-P2/L) • exchange membranes are very thin (L small) • breathing ventilates external surface (O2 at P1 is high; CO2 at P2 is low) • circulatory system perfuses internal surface (O2 at P2 is low; CO2 at P1 is high)

19. Gas Exchange • animal gas exchange surfaces (increase P1-P2/L) • exchange membranes are very thin (L small) • breathing ventilates external surface (O2 at P1 is high; CO2 at P2 is low) • circulatory system perfuses internal surface (O2 at P2 is low; CO2 at P1 is high) • specific systems vary in the details of ventilation, perfusion & exchange surface

20. Gas Exchange • insect tracheae • spiracles open into tubes (tracheae) • tubes branch into smaller tubes (tracheoles) • network ends in dead end air capillaries entering all tissues • gases diffuse from cell to atmosphere entirely in air • rate of diffusion is limited by • A = diameter of tubes • L = length of tubes

21. spiracles and tubular systemFigure 48.4

22. Gas Exchange • fish gills • opercular flaps protect gills • gill arches support gill filaments • gill filament surfaces bear lamellar folds (L) • oxygenated water flows • in mouth • through gill filaments • over lamellae • out opercula

23. filament lamellaeFigure 48.5

24. Gas Exchange • fish gills • maximize diffusion gradient (P1-P2) by countercurrent flow • water flow is unidirectional and constant • blood flows in lamellae in opposite direction • low O2 blood <=> low O2 water • partially oxygenated blood <=> partially depleted water • high O2 blood <=> high O2 water

25. counter-current flow maximizes the diffusion gradientFigure 48.6

26. Gas Exchange • bird lungs • continuous airway without dead end spaces • trachea delivers inhaled air to posterior air sacs • air moves from posterior air sacs through lung to anterior air sacs • air moves through parabronchi • gases exchange in air capillaries (L) • air moves out from anterior air sacs through trachea

27. trachea,posterior air sacs,lung,anterior air sacs,tracheaFigure 48.7

28. Gas Exchange • bird lungs • unidirectional flow through lung • inhalation moves air into posterior air sacs • exhalation moves air out of anterior air sacs andair from posterior air sacs to lung • inhalation refills posterior air sacs and moves air from lung to anterior air sacs • exhalation moves air out of anterior air sacs

29. first breath cyclesecondbreath cycleFigure 48.8

30. Gas Exchange • bird lungs • maximize diffusion gradient (P1-P2) by providing a continuous flow of fresh air

31. Gas Exchange • mammalian lungs • tidal ventilation • fresh air is inhaled (tidal volume) • fresh air mixes with depleted air (tidal volume + expiratory reserve volume + residual volume) • gas exchange occurs between blood and mixed air • depleted air is partially exhaled (tidal volume)

32. tidal breathingFigure 48.9 tidal volume expiratory reserve volume residual volume

33. Gas Exchange • mammalian lungs • tidal ventilation • fresh air is introduced only during inhalation • fresh air mixes with depleted air • lung dead space does not receive fresh air • dead end exchange surfaces do not provide countercurrent flow • diffusion gradient (P1-P2) is limited by low P1

34. Gas Exchange • mammalian lungs - structure/function • air enters through oral and nasal openings • passages join at pharynx • larynx (voice box) admits air to trachea • trachea conduct air to two bronchi • bronchi carry air to lungs • bronchi branch into smaller tubes (bronchioles) • smallest bronchioles terminate in thin-walled gas exchange sacs (alveoli)

35. Gas Exchange • mammalian lungs - structure/function • large number of alveoli provides massive gas exchange surface (A) • thin membranes of alveoli & alveolar capillaries minimizes diffusion path length (L)

36. bigA, little LFigure 48.10

37. Gas Exchange • mammalian lung ventilation • lungs are contained in thoracic cavity • each lung is enclosed by a pleural membrane • thoracic cavity is contained by muscular boundaries • diaphragm • rib cage • external intercostal muscles • internal intercostal muscles

38. Gas Exchange • mammalian lung ventilation • exhalation • relaxation of diaphragm allows elastic expulsion of air from lung • internal intercostal muscles decrease thoracic volume

39. mechanism of tidal breathingFigure 48.11