Oxygen Transport in the Blood

Blood primarily transports oxygen bound to hemoglobin in RBCs, with a small percentage dissolved in the plasma due to its low solubility in the blood.

Hemoglobin, composed of four polypeptide chains containing iron-rich heme groups, can bind to four oxygen molecules.

As seen on the dissociation curve, the binding of oxygen to hemoglobin is greatly influenced by the partial pressure of oxygen or P_O2 .

As P_O2  increases, more oxygen binds to hemoglobin.

For this reason, the hemoglobin in oxygen-rich arterial blood is 98% saturated with oxygen.

Upon reaching the systemic capillaries, oxygen saturation decreases due to a low P_O2.

Several physiological factors influence the affinity of hemoglobin for oxygen.

As seen in this graph, a rise in cellular temperature decreases this affinity.

Additionally, the Bohr effect occurs when higher P_CO2 and elevated H ions  lower the blood pH, favoring oxygen unloading from hemoglobin.

Furthermore, RBCs produce 1,3-bisphosphoglycerate during glucose metabolism, which also increases the unloading of oxygen from hemoglobin.