Question

Explain the oxygen dissociation curve and describe the significance of the flat portion and the steep portion of the curve.

Answer 1

The oxygen dissociation curve is a graph that plots the proportion of haemoglobin in its oxygen laden saturated form on the vertical axis and partial pressure of oxygen on the horizontal axis. As successive molecules of oxygen bind,Hemoglobin's affinity for oxygen increases . The oxygen partial pressure increases until the maximum amount that can be bound is reached. when limit is reached very little additional binding occurs and the curve levels out as the hemoglobin becomes saturated with oxygen. Hence the curve has a sigmoidal or S-shape. The standard dissociation curve is relatively flat, at pressures above about 60 mmHg, which means that the oxygen content of the blood does not change significantly even with large increases in the oxygen partial pressure. To get more oxygen to the tissue would require blood transfusions to increase the hemoglobin count (and hence the oxygen carrying capacity), or supplemental oxygen that would increase the oxygen dissolved in plasma.Although binding of oxygen to hemoglobin continues to some extent for pressures below about 60 mmHg, as oxygen partial pressures decrease in this steep area of the curve, the oxygen is unloaded to peripheral tissue readily as the hemoglobin's affinity diminishes.The partial pressure of oxygen in the blood at which the hemoglobin is 50% saturated, typically about 26.6 mmHg for a healthy person, is known as the P₅₀. The P₅₀ is a conventional measure of hemoglobin affinity for oxygen. In the presence of disease or other conditions that change the hemoglobin's oxygen affinity and, consequently, shift the curve to the right or left, the P₅₀ changes accordingly. An increased P₅₀ indicates a rightward shift of the standard curve, which means that a larger partial pressure is necessary to maintain a 50% oxygen saturation. This indicates a decreased affinity. Conversely, a lower P₅₀ indicates a leftward shift and a higher affinity.