P50 Expresses the Relative Affinities of Different Hemoglobins for Oxygen

The quantity P50, a measure of O2 concentration, is the partial pressure of O2 that half-saturates a given hemoglobin. Depending on the organism, P50 can vary widely, but in all instances it will exceed the Po2 of the peripheral tissues. For example, values of P50 for HbA and fetal HbF are 26 and 20 mm Hg, respectively. In the placenta, this difference enables HbF to extract oxygen from the HbA in the mother's blood. However, HbF is suboptimal postpartum since its high affinity for O2 dictates that it can deliver less O2 to the tissues.

The subunit composition of hemoglobin tetramers undergoes complex changes during development. The human fetus initially synthesizes a Z2£2 tetramer. By the end of the first trimester, Z and Y subunits have been replaced by a and £ subunits, forming HbF (a2Y2), the hemoglobin of late fetal life. While synthesis of P sub-units begins in the third trimester, P subunits do not completely replace Y subunits to yield adult HbA (a2P2) until some weeks postpartum (Figure 6-5).

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Diabetes 2

Diabetes 2

Diabetes is a disease that affects the way your body uses food. Normally, your body converts sugars, starches and other foods into a form of sugar called glucose. Your body uses glucose for fuel. The cells receive the glucose through the bloodstream. They then use insulin a hormone made by the pancreas to absorb the glucose, convert it into energy, and either use it or store it for later use. Learn more...

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