Here's why:
* Solubility: Oxygen is only slightly soluble in water (which plasma is mostly composed of). This means only a small amount of oxygen can dissolve in plasma at a given time.
* Pressure: The amount of oxygen that dissolves in plasma is directly proportional to the partial pressure of oxygen in the surrounding environment (like the air in the lungs).
* Partial Pressure: This is the pressure exerted by oxygen molecules in a mixture of gases.
Normal Values:
* Arterial blood: The normal pO2 in arterial blood is about 80-100 mmHg. This represents the oxygen that has been picked up by the blood from the lungs.
* Venous blood: The normal pO2 in venous blood is about 40 mmHg. This reflects the oxygen that has been used by the tissues.
Factors Affecting Oxygen Solubility:
* Temperature: Oxygen solubility decreases with increasing temperature.
* Salinity: Oxygen solubility decreases with increasing salinity.
Let me know if you have any other questions!
