Describe how carbon dioxide (CO2) is carried in the blood.
It was expected answers would describe each of the main categories of how CO2 is carried:
Dissolved (10%), Plasma Bicarbonate (70%) and conjunction with plasma proteins and Hb as
Carbamino Hb (20%). An opening statement quantifying the amount of CO2 dissolved in
arterial (48mL/100mL) and venous blood (52mL/100mL) (4mL/100mL) and how this
compares with Oxygen was expected (20 times more soluble).
For dissolved CO2, the application and description of Henry’s Law was awarded marks.
A description of the consequences of the Haldane effect: difference in CO2 carriage of
oxygenated and deoxygenated blood was expected. A diagram of pCO2 v CO2 content was
helpful
That "opening statement" they ask for would probably sound something like this:
CO2 is transported by three (maybe, four) major mechanisms:
There is a difference between arterial and venous CO2 content:
Though this answer is already growing overlong, one cannot help but add a "a table of the contribution of each form of carriage to arterial and venous content and the AV difference". This is put together using data from Geers & Gross (2000):
Arterial (mmol/L) |
Venous (mmol/L) |
Difference in mmol/L |
|
Dissolved | 1.08 | 1.24 | 0.16 (9.5%) |
Bicarbonate | 18.53 | 19.97 | 1.44 (85.2%) |
Carbamates | 1.05 | 1.14 | 0.09 (5.3%) |
Total (mmol/L) | 20.66 | 22.35 | 1.69 (100%) |
Geers, Cornelia, and Gerolf Gros. "Carbon dioxide transport and carbonic anhydrase in blood and muscle." Physiological Reviews 80.2 (2000): 681-715.
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Cherniack, NEIL S., and G. S. Longobardo. "Oxygen and carbon dioxide gas stores of the body." Physiol Rev 50.2 (1970): 196-243.
Arthurs, G. J., and M. Sudhakar. "Carbon dioxide transport." Continuing Education in Anaesthesia Critical Care & Pain 5.6 (2005): 207-210.
Klocke, Robert A. "Carbon dioxide transport." Comprehensive Physiology (2011): 173-197.
Groeneveld, AB Johan. "Interpreting the venous-arterial PCO2 difference." Critical care medicine 26.6 (1998): 979-980.