![]() ![]() This is called positive cooperativity.Īround 60mmHg, the vast majority of the hemoglobin subunits have bound oxygen, so the curve starts to level off. So binding that 4th O2 molecule is much easier than binding that first O2 molecule. In practical terms, this sigmoidal shape means that hemoglobin has an increasing affinity for O2 as the number of bound O2 molecules goes up. ![]() So for example, at a partial pressure of 25mmHg, hemoglobin proteins might be 50% saturated, called P50 and at a partial pressure of 100mmHg, they might be 98% saturated, meaning most are fully saturated.Īnd when these points are plotted, the curve takes on a sigmoidal shape. The main factor that influences oxygen saturation is the partial pressure of oxygen in the blood, measured in millimeters of mercury (mm Hg). Now it turns out that hemoglobin absorbs different wavelengths of light as it gets more and more oxygenated.Ī technique called pulse oximetry uses this property of hemoglobin to figure out the average oxygen saturation across millions of hemoglobin proteins. But each hemoglobin isn’t always 100% saturated or bound by oxygen.Ī hemoglobin molecule might have no oxygen bound, and be 0% saturated, called deoxyhemoglobin, and it will take on a tense state shape, or T-state or it might have one oxygen bound and three open spots, meaning that particular protein would be 25% saturated or two filled spots and two open spots-50% or 3 spots filled and one spot open-75%, or all spots filled and 100% saturated.Īll of these states - where oxygen is bound to hemoglobin - are called oxyhemoglobin, changing to its relaxed state, or R-state with each O2 molecule that binds.Īnd since there are millions of hemoglobin molecules in a single cell and millions of red blood cells, the hemoglobin saturation of oxygen is the average saturation among all of these proteins. So each hemoglobin protein can bind 4 molecules of oxygen. Hemoglobin is the main protein within red blood cells, and it’s made of four globin subunits, each containing a heme group capable of binding one molecule of O2. The oxygen-hemoglobin dissociation curve shows how the hemoglobin saturation with oxygen (SO2,), is related to the partial pressure of oxygen in the blood (PO2). ![]()
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