1. Biology 272a: Comparative Animal Physiology Diving mammals

2. Dive record of a male northern elephant seal Fig. 25.4

3. Dive durations of Weddell seals Fig. 25.1a

4. Problems with diving  Oxygen  Nitrogen  Waste products CO 2 Lactate

5. Forced diving  Led to an extreme diving response The seal didn’t know how long it would be underwater!

6. “Natural” Diving

7. Natural diving

8. The classical diving response  Apnoea  Bradycardia  Vasoconstriction and reduced blood flow

9. Oxygen  …or lack thereof Blood lactate Aerobic dive limit Fig 25.12

10. Oxygen stores Fig. 25.6

11. Conserving oxygen  Peripheral vasoconstriction  Hypoperfusion of viceral organs  Brain & retina remain normoxic

12. Body and heart-lung-brain become separate compartments Muscle O2 depleted Blood O2 remains high Fig. 25.10a

13. Harbor seal breathing air 0.5 s 2 s6 s Fully perfused kidney and other viceral organs Fig. 25.7 a-c

14. Harbor seal in forced dive 0.5 s 2 s6 s No perfusion of kidney and other viceral organs Breathing Air Fig. 25.7 d-e

15. Waste products – CO 2  High blood buffering capacity Reduced changes in blood pH  Reduced ventilatory response to CO 2 Or increased threshold  Post-dive hyperventilation

16. Waste products - lactate Anaerobic metabolism is compartmentalised Fig. 25.10b

17. Waste products - lactate Fig. 25.11

18. “The Bends”  Workers in pressurised mine shafts and tunneling projects in 19 th C Caisson disease  PN 2 (lungs) > PN 2 (blood & tissue) results in increased N2 in tissues and fluids  Rapid decompression results in N 2 coming out of solution Bubbles of N 2 gas in joints cause “the bends” Other symptoms also due to bubbles and/or high [N 2 ]

19. Why don’t seals get the bends? Compressible thorax Fig. 25.5 Air is compressed out of gas exchange surfaces, so N2 cant diffuse into bloodstream … but nor can O2… Fig. 24.14

20. Compressed alveoli… an oxygen supply for resurfacing? Decreasing depth and pressure More O2 becomes available during ascent

21. Gradations of the diving response Fig. 25.1Fig. 25.2

22. Gradations of the diving response Fig. 25. 9

23. The classical diving response  Apnoea  Bradycardia  Vasoconstriction and reduced blood flow

24. That’s it! See you Thursday for the review session “Fun” (ie: non-examinable) lecture about my research next Tuesday.