1. Biology 2672a: Comparative Animal Physiology
Why is blood red (or green, or blue)?

2. 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

3. Blood must be thicker than water
Solubility of O2 in water (especially warm salty water) not enough to provide O2 to active tissues
Many organisms use respiratory pigments to bind O2 and transport it to tissues

4. Respiratory pigments Diffusion into solution O2 in solution Air Blood
O2 molecule bound to respiratory pigment is no longer in solution
PO2 in blood, allows more to diffuse across (and more to bind to pigment)

5. What it means to have a respiratory pigment
Species
Total Oxygen carrying capacity
(ml O2/l)
Water
Blood of an efficient bony fish

6. What it means to have a respiratory pigment
Can not only suck a lot of O2 out of water, but can transport a lot per unit volume as well!
Fig 22.4b

7. Respiratory pigments Can be in solution or enclosed in blood cells
Hematocrit
Centrifuge whole blood and measure proportion of ‘solids’ (=cells)
A pretty good measure of blood oxygen carrying capacity in vertebrates

8. Components of a respiratory pigment
Protein
Metal-containing ‘Heme’ group – site of oxygen binding
Fig. 23.1

9. Kinds of respiratory pigments
Colour
Structure
O2 binding
Hemoglobin
Protein + Heme + Fe2+
1/Fe2+
Chlorocruorin
Green
Protein + Porphyrin + Fe2+
Hemerythrin
Violet/ Colourless
1/2Fe2+
Hemocyanin
Protein + Cu2+
1/2Cu2+

10. Chlorocruorins Found in four polychaete families: Serpulidae
Sabellidae
Chlorhaemidae
Ampharetidae

11. Hemerythrins
Sipunculida
Priapulida
Brachiopoda

12. Hemocyanins
Some arthropods
Many Molluscs

13. Hemoglobins
Fig. 23.3

14. Hb Oxygen association curve
Sigmoid shape
Fig. 23.4a

15. Why is it a sigmoid curve?
Cooperativity
Cumulative increase in affinity as O2 binds to the heme groups
Subunit changes conformation slightly, increasing affinity of other heme groups in that tetramer
Subunit interaction

16. Offloading O2
Lungs
Tissues at rest
Tissues in exercise
Fig. 23.6

17. Affinity can change
Fig. 23.4a

18. The Bohr effect Exercising tissues produce CO2 and thus have  pH
As PCO2 increases (and pH decreases), affinity of Hb decreases
This allows more O2 to be unloaded at sites where it is needed
Affinity is still high at the blood-gas barrier for initial O2 uptake

19. The Bohr Effect
(~pH)
Fig b

20. The Bohr Effect
Fig

21. Does CO2 bind to hemoglobin?
Short answer: No
Hb doesn’t drop off an O2 and pick up a CO2 to return to the lungs
Most transport of CO2 is in solution (and often as carbonic acid/bicarbonate)
Long answer: Yes
CO2 binds to the Hb molecule (but not at the heme group)
This binding alters the conformation of the protein (and contributes to the Bohr effect)
But it isn’t the main means of CO2 transport.

22. Other modulations of O2 affinity
Temperature = O2 affinity
Metabolic products, e.g. 2,3-DPG = O2 affinity
Inorganic ions?

23. The Root Effect
A change in amount of O2 bound at saturation, not (just) in affinity
Used by fishes
to offload O2 against gradients to fill swim bladder
to supply O2 to oxygen-demanding retina
Fig

24. Myoglobin A monomeric globin found in muscle (esp. heart)
Has a higher O2 affinity than Hb
A sort of oxygen store for the cell
Fig. 22.7a

25. Neuroglobins Discovered in 2000 Monomeric, high O2 affinity
Present in brain and retina of humans
Protection from hypoxia

26. Cytoglobins Discovered in 2002 Apparently present in all cells
Also monomeric?

27. Reading for Tuesday Osmoregulation in general Pp 663-679
Fish Osmoregulation
Pp ; Box 4.1