Biology 2672a: Comparative Animal Physiology

1. Biology 2672a: Comparative Animal Physiology Gas Exchange I: Principles & breathing in water

2. Gas Exchange • Getting O2 out of the external medium and into the cells • Often via the circulatory system • Getting CO2 out of the cells and into the external medium C6H12O6 + 6O2 6CO2 + 6H2O + 2820 kJ/mol

3. Where is the oxygen? (Cold)(Sea) water: ~0.8% O2 in solution Air: ~21% O2 as a gas

4. Partial pressure • Each gas in a mix (either as a gas or in solution) exerts pressure • Partial pressure is the amount of pressure that the gas of interest exerts

5. Partial pressure of gas x Partial pressure Px=FxPtot Fractional concentration of the gas (moles or by volume) Total pressure of the gas mixture Eqn. 21.2

6. Partial pressure • Air • 20.95 % O2 • 78.09 % N2 • 0.93 % Ar • 0.038 % CO2 Px=FxPtot PO2 = 0.2095 × 101.3 kPa = 21.22 kPa

7. Partial pressure on Mt Everest Px=FxPtot • Air • 20.95 % O2 • 78.09 % N2 • 0.93 % Ar • 0.038 % CO2 PO2 = 0.2095

8. Gases dissolve in liquids • Not the same as having air bubbles! • Pliquid is proportional to Pair • Amount of gas in solution depends on • Temperature • Salinity • Gas • Gases that have reacted chemically do not contribute to partial pressure in solution

9. Henry’s Law Concentration in solution C=AP Partial pressure Absorption coefficient (solubility) Eqn. 21.3

10. All gases are not equal

11. P1-P2 J=K X Diffusion of gases Partial pressure Rate of net movement of the gas Diffusion coefficient Distance to be diffused Eqn. 21.4

12. Diffusion coefficient • Depends on gas, temperature, medium • Also depends on the permeability of any barriers, e.g. cell membranes, cuticle, epidermis (m2/sec × 10-9)

13. Gas transport in organisms - a combination of convection and diffusion Unidirectional flow (convection) in circulatory system Tidal convection ventilates lungs Diffusion from capillaries into tissues Diffusion into bloodstream

14. Breathing water • Getting rid of CO2 isn’t a problem • High diffusivity & absorption • Getting O2is • Low absorption in water = low PO2

15. How to breathe water? • Fast ventilation • More water across respiratory surface = more O2 to absorb • Efficient absorption • Would predict countercurrent exchange • Highly vascularised system with a large surface area

16. Ventilatory structures • Gas exchange surfaces • Usually highly vascularised • Need to open to the ‘outside world’ • Are usually actively ventilated (convective flow of medium)

17. Ventilatory structures • Skin • Gills • Evaginations (outpocketings) • Lungs • Invaginations (inpocketings) • (or some combination of the above…)

18. Cutaneous respiration Fig. 22.8 (top half)

19. Blood vessel terminology • Afferent • Entering the structure (Arriving) • Efferent • Leaving the structure (Exit)

20. Gill structure in fishes Primary Lamellae Buccal Cavity (mouth) Blood is oxygenated while flowing through 1° lamella Operculum Gill Arch Fig. 22.10b

21. Gill structure in fishes Afferent (deoxygenated) Efferent (oxygenated) 2° Lamellae Fig. 22.10b&c

22. Counter-current gas exchange Fig. 22.10d Fig 22.4b

23. Ventilating the gills Buccal-opercular pumping Ram Ventilation Water in at mouth, pumped out of buccal cavity with positive pressure Water pumped out of opercular cavity with positive pressure Fig 22.11

24. Flow rates & Efficiency

25. Breathing through your butt Dragonfly nymph

26. Breathing through your butt • The Fitzroy River turtle can satisfy 70% of its oxygen requirements via cloacal respiration • 12 h at 25 °C (normoxic water) • Tidal ventilation of a ‘lung’

27. Thursday • Guest Lecture: Prof Ken Storey (Carleton U) (Freezing frogs) • Reading on OWL • Tues 21 Oct: Mid-term revision lecture • Thurs 23 Oct: Ethics of Animal Use • Reading on OWL