Oxygen Dissociation Curve

OXYGEN-HEMOGLOBIN DISSOCIATION CURVE
  • Oxygen-hemoglobin dissociation curve is the curve that demonstrates the relationship between partial pressure of oxygen and the percentage saturation of hemoglobin with oxygen. It explains hemoglobin’s affinity for oxygen.
  • Myoglobin has much higher affinity for 02 than hemoglobin.Hence 02 is bound more tightly with myoglobin than with hemoglobin.
  • Further, pO2 needed for half saturation (50% binding) of myoglobin is about 1 mm Hg compared to about 26 mm Hg for hemoglobin.
Cooperative binding of Oxygen to hemoglobin
  • The oxygen dissociation curve for hemoglobin is sigmoidal in shape .This indicates that the binding of oxygen to one heme increases the binding of oxygen to other hemes. Thus theNaffinity of Hb for the last 02 is about 100 times greater than the binding of the first 02 to Hb.
  • This phenomenon is referred to as cooperative binding of 02 to Hb or simply heme-heme interaction.On the other hand, release of 02 from one heme facilitates the release of 02 from others.
  • The oxygen dissociation curve of myoglobin & hemoglobin is different due to Cooperative binding of Oxygen to hemoglobin.
  • As myoglobin is monomeric (consists of one polypeptide chain only), it can bind only one molecule of oxygen and for the same reason myoglobin cannot show the phenomenon of cooperative binding. Hence, the oxygen?myoglobin dissociation curve is hyperbola as compared to sigmoid shape of Hb-O2 curve.
FACTORS AFFECTING OXYGEN HEMOGLOBIN DISSOCIATION CURVE

Oxygen-hemoglobin dissociation curve is shifted to left or right by various factors:

1. Shift to right : indicates dissociation of oxygen from hemoglobin.
Oxygen-hemoglobin dissociation curve is shifted to right in the following conditions:
  1. Decrease in partial pressure of oxygen / Hypoxia
  2. Increase in partial pressure of carbon dioxide (Bohr effect)/Hypercarbia
  3. Increase in hydrogen ion concentration and decrease in pH (acidity)
  4. Increased body temperature
  5. Excess of 2,3-diphosphoglycerate (DPG) in RBC. It is also called 2,3-biphosphoglycerate (BPG).
  6. High altitude
  7. Anemia
  8. Diabetic ketoacidosis
  9. Systemic capillaries : in response to increase in blood CO2 and Hydrogen ions.
  10. Exercise
2. Shift to left : indicates acceptance (association) of oxygen by hemoglobin
Oxygen-hemoglobin dissociation curve is shifted to left in the following conditions:
  • In fetal blood because, fetal hemoglobin has got more affinity for oxygen than the adult hemoglobin
  1. Fetal hemoglobin has higher affinity for oxygen due to decreased 2,3 -DPG concentration.
  • Decrease in hydrogen ion concentration and increase in pH (alkalinity).
Exam Question
  • Oxygen-hemoglobin dissociation curve shifts to the right within the systemic capillaries .
  • Fetal hemoglobin has higher affinity for oxygen due to decreased 2,3 DPG concentration.
  • Oxygen dissociation curve shifts to right in Anemia.
  • Fetal hemoglobin has higher affinity for oxygen due to decreased 2,3-DPG concentration.
  • A rise in temperature or a fall in pH shifts the Oxygen-hemoglobin dissociation curve to the right.
  • Oxygen dissociation curve shifts to right in Diabetic Ketoacidosis.
  • 2,3-DPG shifts the Oxygen dissociation curve to the right.
  • Oxygen dissociation curve shift to right in Hypercarbia.
  • Right shift of oxygen dissociation curve is caused by Hypoxia.
  • The oxygen dissociation curve of myoglobin & hemoglobin is different due to Cooperative binding in Hb.
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