Tuesday, 12 April 2011

MCQ 1

Which of the following would shift the oxygen-hemoglobin dissociation curve
to the right?
A. Carbon monoxide poisoning
B. Decreased PCO2
C. Decreased pH
D. Decreased temperature
E. Decreased 2,3-DPG 

Answer and explanation :

Answer to question 1: "c"
Explanation:  
The loading of O2 is facilitated when the oxygen dissociation curve shifts to the left, and the unloading of O2 is facilitated when the oxygen dissociation curve shifts to the right. A good way to remember the conditions that promote dissociation of O2 is to think of exercising muscle, which has decreased pH (choice C) because of the accumulation of lactic acid, increased PCO2 (compare with choice B) because of the increased rate of aerobic metabolism, increased temperature (compare with choice D), and increased 2,3-DPG (2,3-diphosphoglycerate; compare with choice E) because of increased glycolysis.
Carbon monoxide poisoning (choice A) left-shifts the oxygen dissociation curve, which interferes with the unloading of O2. Carbon monoxide also strongly binds to available sites on hemoglobin. 

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