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The Oxygen-Hemoglobin Association and Dissociation Curve : USMLE Step 1 Physiology
The oxygen-hemoglobin association and dissociation curve describes the relationship between the partial pressure of oxygen (PO2) and the saturation of hemoglobin (Hb) with oxygen (O2). Hemoglobin is the protein in red blood cells that binds to oxygen and carries it from the lungs to the tissues in the body.
When hemoglobin binds to oxygen, it undergoes a conformational change that increases its affinity for oxygen. This means that as the PO2 in the blood increases, the saturation of hemoglobin with oxygen also increases, up to a maximum of 100%.
The relationship between PO2 and Hb-O2 saturation is described by the oxygen-hemoglobin dissociation curve, which is an S-shaped curve. At low PO2 values, such as those found in the tissues, the curve is relatively steep, indicating that a small change in PO2 results in a large change in Hb-O2 saturation. This is because at low PO2 values, hemoglobin has a low affinity for oxygen and readily releases it to the tissues.
As PO2 increases, the curve flattens out, indicating that a large change in PO2 results in only a small change in Hb-O2 saturation. This is because at high PO2 values, hemoglobin is almost fully saturated with oxygen and has a high affinity for it.
Factors that can shift the oxygen-hemoglobin dissociation curve include pH, temperature, and the partial pressure of carbon dioxide (PCO2). For example, a decrease in pH (such as occurs during exercise) shifts the curve to the right, indicating that hemoglobin has a lower affinity for oxygen and releases it more readily to the tissues. This is known as the Bohr effect. An increase in temperature also shifts the curve to the right, as does an increase in PCO2.
The oxygen-hemoglobin dissociation curve is important for understanding how oxygen is transported and released in the body, and how changes in physiological conditions can affect this process.
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