Carbon monoxide (CO) binds avidly to hemoglobin (Hb), to form carboxyhemoglobin,
ID: 63438 • Letter: C
Question
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). Oxygen unloading is not affected in anemic patient. In case of carboxyhemoglobin (COHb), carbon monoxide prevents the release of oxygen from hemoglobin. The affinity of CO is 250 times greater than that of oxygen.
B. The atmospheric pressure of oxygen decreases at high altitudes. People living at heigher altitudes are adapted to lower PO2 levels. One of the key change observed in this adaptation is increased 2,3-BPG (2,3- bisphosphoglycerate), which shift P50 to higher values.
2,3-BPG decreases the oxygen binding affinity of hemoglobin by decreasing its affinity for oxygen due to alteration in conformational changes, oxygen is loosely bound to hemoglobin in the presence of BPG. So, increased levels of 2,3-BPG makes more oxygen available to cells.
C). During pregnancy, the oxygen demands increase due to increased metabolic activities. So, 2,3-BPG (2,3- bisphosphoglycerate) levels increase.