Question

In Figure showing blood carbon dioxide dissociation curves: 

a. A fall in blood PO₂ would shift the curve from A to B. 

b. If point X represents the situation at the venous end of systemic capillaries, then point Y represents the situation of the same blood at the venous end of the pulmonary capillaries. 

c. A rise in blood P_CO2 would shift the curve from B to A. 

d. The decrease in the slope of the curves as P_CO2 rises is related to the saturation of plasma with CO₂ as P_CO2 rises. 

e. At a P_CO2 of 50 mmHg, the amount of CO₂ in solution is lower in curve B than in curve A.

Answer 1

a. False The reverse is true; deoxygenated blood can carry more CO₂ than oxygenated blood at a given carbon dioxide pressure. 

b. True In the lungs the blood oxygen saturation rises shifting the curve from A to B and the CO₂ content and pressure fall from point X to point Y. 

c. False It would merely shift the position on a given dissociation curve. 

d. False Plasma does not become saturated with CO₂; CO₂ content remains proportional to P_CO2; the initial sharp rise is due to formation of carbamino compounds – this falls off sharply as the number of free amino groups declines. 

e. False The amount of CO₂ in solution is the same for both curves for any P_CO2; differences in total CO₂ content are due to differences in bicarbonate and carbamino content; at low oxygen pressures, the desaturated hemoglobin is increasingly more effective in buffering hydrogen ions and, by the law of mass action, favours formation of bicarbonate ions from carbon dioxide.