At a PO2 of 100 mm Hg and normal temperature and pH, hemoglobin is _____percent saturated with oxygen.
The correct answer and explanation is :
At a PO₂ of 100 mm Hg, hemoglobin is approximately 98% saturated with oxygen.
Explanation:
Hemoglobin’s oxygen saturation is determined by the oxygen-hemoglobin dissociation curve, which describes how readily hemoglobin binds and releases oxygen under varying partial pressures of oxygen (PO₂). The curve has a characteristic sigmoidal (S-shaped) shape due to cooperative binding—when one oxygen molecule binds, hemoglobin’s affinity for additional oxygen molecules increases.
Key Factors at PO₂ of 100 mm Hg:
- Oxygen Binding in the Lungs:
- In normal physiological conditions, arterial blood has a PO₂ of about 100 mm Hg, which occurs in the pulmonary capillaries of the lungs.
- At this PO₂, hemoglobin is almost fully saturated, at around 98%. This means nearly all hemoglobin molecules are carrying the maximum four oxygen molecules.
- Oxygen Transport to Tissues:
- As blood circulates and reaches tissues, the PO₂ decreases. At 40 mm Hg (the typical PO₂ in resting tissues), hemoglobin saturation drops to about 75%, allowing oxygen release.
- In active tissues (e.g., exercising muscles), the PO₂ can drop below 20 mm Hg, facilitating even more oxygen unloading.
- Influence of Temperature, pH, and CO₂:
- The given conditions assume normal body temperature (37°C) and pH (7.4).
- A drop in pH or an increase in temperature shifts the curve rightward (Bohr effect), enhancing oxygen unloading to tissues.
- A higher pH or lower temperature shifts it leftward, making hemoglobin hold onto oxygen more tightly.
Thus, at a PO₂ of 100 mm Hg, hemoglobin is approximately 98% saturated, ensuring efficient oxygen delivery throughout the body.
Here’s an image illustrating the oxygen-hemoglobin dissociation curve and how saturation varies with PO₂.
