1. Gas Exchange in Animals Principles & Processes

2. Gas Exchange respiratory gases –oxygen (O 2 ) required as final electron acceptor for oxidative metabolism –carbon dioxide (CO 2 ) discarded byproduct of oxidative metabolism

3. Gas Exchange respiratory mechanisms –system to deliver oxygenated/remove deoxygenated medium –membrane for gas exchange –system to carry O 2 to cells/CO 2 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) –O 2 content of air is greater than O 2 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 surfaces Figure 48.1

7. Gas Exchange problems for water breathers –an ectotherm’s O 2 demand increases with increased temperature –O 2 content of water decreases with increased temperature –compensatory increase in breathing increases O 2 demand

8. the problem with warm water Figure 48.2

9. Gas Exchange problems for (adventurous) air breathers –air pressure decreases with altitude O 2 partial pressure decreases with altitude rate of O 2 diffusion decreases with decreased O 2 partial pressure

10. increased altitude decreases the availability of O 2

11. Gas Exchange CO 2 removal –[CO 2 ] in air is ~350 ppm gradient for outward diffusion is always steep –[CO 2 ] 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·(P 1 -P 2 )/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·(P 1 -P 2 )/L –increase diffusion (Q) by increasing D (use air instead of water?) increasing A (increase exchange surface) increasing P 1 -P 2 (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 water Figure 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 air Figure 48.3

18. Gas Exchange animal gas exchange surfaces (increase P 1 - P 2 /L) –exchange membranes are very thin (L small) –breathing ventilates external surface (O 2 at P 1 is high; CO 2 at P 2 is low) –circulatory system perfuses internal surface (O 2 at P 2 is low; CO 2 at P 1 is high)

19. Gas Exchange animal gas exchange surfaces (increase P 1 - P 2 /L) –exchange membranes are very thin (L small) –breathing ventilates external surface (O 2 at P 1 is high; CO 2 at P 2 is low) –circulatory system perfuses internal surface (O 2 at P 2 is low; CO 2 at P 1 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 system Figure 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 lamellae Figure 48.5

24. Gas Exchange fish gills –maximize diffusion gradient (P 1 -P 2 ) by countercurrent flow water flow is unidirectional and constant blood flows in lamellae in opposite direction –low O 2 blood low O 2 water –partially oxygenated blood partially depleted water –high O 2 blood high O 2 water

25. counter-current flow maximizes the diffusion gradient Figure 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, trachea Figure 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 and air 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 cycle second breath cycle Figure 48.8

30. Gas Exchange bird lungs –maximize diffusion gradient (P 1 -P 2 ) 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 breathing Figure 48.9 tidal volume residual volume expiratory reserve 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 (P 1 -P 2 ) is limited by low P 1

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. big A, little L Figure 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 breathing Figure 48.11