Oxygen must be transported from outside the body to all the organs and tissues in the body. Oxygen is carried through the body by a protein called hemoglobin which binds oxygen in the lungs and carries it to the tissues. In the tissues, the hemoglobin releases the oxygen and returns to the lungs to repeat the cycle.

A chemical equilibrium [local] between the degree of oxygen saturation and the amount of oxygen in the air [local] is expressed in the amount of oxygenated and deoxygenated hemoglobin in the blood.

See jmol: Hemoglobin (Oxygenated Hemoglobin)

See jmol: Deoxyhemoglobin (Deoxygenated Hemoglobin)

In the absence of an oxygen molecule, the hemoglobin molecule is stabilized by third-party molecule. This allosteric control [local] is provided by 2,3- bis phosphoglycerate (BPG) and regulates the cooperative oxygen binding [local].