Fetal Hemoglobin and Equilibrium

The double arrows in this equation indicate that the reaction can occur in both the forward and reverse directions and can reach chemical equilibrium. We encountered this term in Chapters 11 and 12, and we define it more carefully in the next section. 

A Hemoglobin is the oxygen-carrying protein in red blood cells. Oxygen binds to iron atoms, which are depicted here in white. 

For now, understand that the concentrations of the reactants and products in a reaction at equilibrium are described by the equilibrium constant, K. A large value of K means that the reaction lies far to the right at equilibrium—a high concentration of products and a low concentration of reactants. A small value of K means that the reaction lies far to the left at equilibrium— high concentration of reactants and a low concentration of products. In other words, the value of Tis a measure of how far a reaction proceeds— Ihe larger the value of K, the more the reaction proceeds toward the products. 

As blood flows out of the lungs and into muscles and organs where oxygen concentrations have been depleted (because muscles and organs use oxygen), the equilibrium shifts to the left— hemoglobin releases oxygen  

A fetus has its own circulatory system. The mother s blood never flows into the fetus s body, and the fetus cannot get any air in the womb. How, then, does the fetus get oxygen The answer lies in the properties of fetal hemoglobin (HbF), which is shghtly different from adult hemoglobin. Like adnlt hemoglobin, fetal hemoglobin is in equilibrium with oxygen  

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