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

Blood

Air

Diffusion into solution

O2 in solution

O2 molecule bound to respiratory pigment is no

longer in solutionPO2 in blood, allows more to diffuse

across (and more to bind to pigment)

Respiratory pigment

What it means to have a respiratory pigment

Species Total Oxygen carrying capacity

(ml O2/l)

Water

Blood of an efficient bony fish

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

Respiratory pigmentsCan be in solution or enclosed in

blood cellsHematocrit

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

Pigment 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+

Kinds of respiratory pigments

ChlorocruorinsFound in four polychaete

families: Serpulidae Sabellidae Chlorhaemidae Ampharetidae

HemerythrinsSipunculidaPriapulidaBrachiopoda

HemocyaninsSome arthropodsMany Molluscs

Hemoglobins

Fig. 23.3

Hb Oxygen association curve

Fig. 23.4a

Sig

moid

shape

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 affinityMetabolic products, e.g. 2,3-

DPG = O2 affinity Inorganic ions?

The Root EffectA 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

MyoglobinA monomeric globin found in

muscle (esp. heart)Has a higher O2 affinity than HbA sort of oxygen store for the

cell

Fig. 22.7a

NeuroglobinsDiscovered in 2000Monomeric, high O2 affinityPresent in brain and retina of

humansProtection from hypoxia

CytoglobinsDiscovered in 2002Apparently present in all cellsAlso monomeric?

Reading for TuesdayOsmoregulation in generalPp 663-679Fish Osmoregulation

Pp 681-699; Box 4.1