Question 3 Carbon monoxide (CO) binds avidly to hemoglobin (Hb), to form carboxy

Question

Question 3 Carbon monoxide (CO) binds avidly to hemoglobin (Hb), to form carboxyhemoglobin, COHb. The diagram shows plots of the oxygen content of whole blood as a function of the partial pressure of oxygen. Curves are shown for normal blood, for blood containing 50% COHb, and for blood from a patient with 50% anemia (that is half the normal content of hemoglobin). (a) A patient with 50% anemia appears normal. However, if an otherwise healthy individual is exposed to CO such that 50% of heme sites in Hb are occupied by CO (50% COHb), then the individual is incapacitated. Look carefully at the curves and explain why 50% COHb is more dangerous than 50% anemia. (b) Acclimatization to high altitude involves numerous physiological and biochemical changes, including an increase in the concentration of 2,3 bisphosphoglycerate in red blood cells. Why is increased 2,3 bisphosphoglycerate advantageous at high altitude? (c) The 2,3 bisphosphoglycerate concentration in red blood cells also increases during pregnancy. Why?

Explanation / Answer

a)

The CO is a poisonous gas. The CO shifts the oxygen dissociation curve to left. The CO generally occupies oxygen binding site on hemoglobin. This results in less O2 binding with hemoglobin and less oxygen delivered to tissues and binding of CO results hypoxic conditions in tissues and impair the tissue function. In anemic conditions the binding affinity of O2 to hemoglobin remains same but the transportation to tissues is lowered. Low oxygen conditions may prevail in tissues but not cause poisoning like CO. Thus, 50% of CO binding to hemoglobin is much dangerous than 50% of anemia.

b)

The increase in 2, 3 biphosphoglycerate results in reduced P50 of oxygen. Hence, results in increasing the binding affinity of oxygen. Thus, at high altitudes the increased 2, 3 BPG causes more oxygen overloading and shifts the oxygen dissociation curve to right. Increased 2, 3 BPG concentration increases oxygen affinity in pulmonary capillaries would be advantageous.

c)

In pregnant women, the increase in 2, 3 BPG would be 30% more. This results in lowering the maternal hemoglobin affinity for oxygen, and therefore increases oxygen supply to the fetus in the maternal uterine arteries. The fetus hemoglobin shows low sensitivity to 2, 3-BPG and higher affinity for oxygen.

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