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Physiology 3120 Lecture Notes - Hemoglobin, Partial Pressure, Carbonic Anhydrase

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Tom Stavraky

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Human Physiology
Friday, February 5, 2010
“Respiration IV”
Oxygen Transport
Transported (I) as a dissolved gas (minor component), or (II) bound to haemoglobin
Binding to haemoglobin
Major component
Bound = oxy-H; unbound = deoxy-H
4 subunits, each with heme group (has an iron molecule to which O can bind)
1g haemoglobin can carry 1.34mL oxygen
O capacity of blood perform experiment; have blood equilibrate and measure the amount
bound to H
H-O dissociation curve
In the lung, the H saturation is almost 100% (at 100mmHg)
If the PO drops in the lung, still have high saturation (at 60mmHg, saturation is still 90%
or so); not a linear curve
PO in tissue is low, and there is a steep drop in affinity, which allows dissociation of O in
Shape is “sigmoidal”; results from binding of H to O; binding one O molecule is hard,
but once it binds, the other 3 O’s can bind relatively easily
Factors that influence it. . .(doesn’t transform curve, but only shifts it)
Shifted to the right; at the same partial pressure, you have less saturation
P-CO2 (shifts right); higher T (shifts right); lower pH (shifts right) think of
these 3 in terms of exercise
CO has 210-fold higher affinity for H than O
If you have PO of 210mmHg, then 100% bound to H
If you have PO of 210mmHg, but a PCO of 1%, then get a 50-50 split in binding
Carbon Dioxide Transport
3 ways
1. Dissolved gas
Henry’s Law; concentration = pressure * solubility
Much more soluble than O
About 10% of transport
2. Bicarbonate
70% of total
Formed in RBCs and involves enzyme called carbonic anhydrase
Bicarbonate formed diffuses out of cell, and chloride diffuses in to maintain neutrality
3. Haemoglobin
20% of total
In RBC, hydrogen binds to deoxygenated H to form HHb
CO2 binds HHb to form carbamino-Hb
Unloading of oxygen in tissue enhances the ability to transport CO2 (Haldane effect)
Effects on volumes due to O and CO2 transport
When you exercise, the whole process speeds up
High content in arteries; very little bound to H (most of it bound to O)
In tissue, CO2 enters blood, and some binds to H because of O unloading
In veins, CO2 content is substantially higher
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