What typically starts at 159 mmHg and decreases as oxygen detaches from hemoglobin?

The partial pressure of oxygen typically starts at 159 mmHg in dry air at sea level, where atmospheric pressure is at its standard atmospheric pressure. As oxygen is transported in the blood, it binds to hemoglobin in red blood cells. During this process, as tissues utilize oxygen for metabolism, the partial pressure of oxygen decreases. This reflects the reality that as oxygen is released from hemoglobin into the tissues, the concentration of oxygen in the blood lowers, leading to a decrease in its partial pressure. Thus, understanding the dynamics of partial pressure is crucial in physiology, especially in contexts involving gas exchange and transportation in the circulatory system.