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Biology 2672a:
Comparative Animal
Physiology
Why is blood red (or
green, or blue)?
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
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
Respiratory pigments
Diffusion into solution
Respiratory pigment
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)
What it means to have a
respiratory pigment
Species
Water
Blood of an
efficient bony fish
Total Oxygen
carrying capacity
(ml O2/l)
What it means to have a
respiratory pigment

Fig 22.4b
Can not only
suck a lot of O2
out of water, but
can transport a
lot per unit
volume as well!
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

Components of a respiratory
pigment
Protein
Metal-containing
‘Heme’ group –
site of oxygen
binding
Fig. 23.1
Kinds of respiratory pigments
Pigment
Colour
Hemoglobin
Chlorocruorin
Green
Hemerythrin
Violet/
Colourless
Hemocyanin
Structure
O2
binding
Protein +
Heme + Fe2+
1/Fe2+
Protein +
Porphyrin +
Fe2+
1/2Fe2+
Protein +
Cu2+
1/2Cu2+
Chlorocruorins
 Found
in four polychaete
families:
Serpulidae
 Sabellidae
 Chlorhaemidae
 Ampharetidae

Hemerythrins
 Sipunculida
 Priapulida
 Brachiopoda
Hemocyanins
 Some
arthropods
 Many Molluscs
Hemoglobins
Fig. 23.3
Hb Oxygen association curve
Fig. 23.4a
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

Offloading O2
Lungs
Tissues
at rest
Tissues in
exercise
Fig. 23.6
Affinity can change
Fig. 23.4a
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

The Bohr Effect
(~pH)
Fig. 23.10b
The Bohr Effect
Fig. 23.11
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.
Other modulations of O2 affinity
 Temperature
= O2 affinity
 Metabolic products, e.g. 2,3DPG = O2 affinity
 Inorganic ions?
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. 23.12
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
Neuroglobins
 Discovered
in 2000
 Monomeric, high O2 affinity
 Present in brain and retina of
humans
 Protection from hypoxia
Cytoglobins
 Discovered
in 2002
 Apparently present in all cells
 Also monomeric?
Reading for Tuesday
 Osmoregulation
in general
 Pp
663-679
 Fish Osmoregulation

Pp 681-699; Box 4.1