Oxygen - hemoglobin dissociation curve & Hemoglobin's affinity with oxygen - acidity

• The partial pressure of oxygen is a primary factor influencing the degree of saturation of hemoglobin. • The Po2 determines the number of oxygen molecules that can bind or dissociate from hemoglobin. • Blood in vessels coming from the lungs is very high in Po2 so saturation is high. • Oxygen binds to all available sites in hemoglobin and forms oxyhemoglobin. • Blood near skeletal muscle cells is very low in Po2 so saturation is low. • Oxygen bound to oxyhemoglobin detaches and is unloaded to the tissues. • Blood pH values affect oxyhemoglobin saturation. • Increased metabolic acids enhance dissociation of oxyhemoglobin and the unloading of oxygen. • For the same P02, the ability of hemoglobin to carry oxygen in acidic blood is decreased. This effect is called the Bohr effect. • Low blood pH increases the I unloading of 02 to actively metabolizing cells. • In contrast, elevated blood pH increases the affinity of 02 to hemoglobin thereby lowering the unloading of 02 to tissue cells.

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