Answer:
Low partial pressure of O2 in the tissues
Explanation:
Partial pressure of oxygen is the main factor that regulated binding and release of oxygen from the hemoglobin in RBCs. When the PO2 is high, hemoglobin binds with large amounts of O2 and is almost 100% saturated. On the other hand, hemoglobin is only partially saturated with oxygen at the lower partial pressure of oxygen. Therefore, the lower partial pressure of oxygen in tissue capillaries does not allow hemoglobin does to hold as much O2, and the dissolved O2 is unloaded via diffusion into tissue cells.
