Question

A large proportion of oxygen is left unused in the human blood even after its uptakes by the body tissues. This $O _{2}$ :

• A. acts as a reserve during muscular exercise
• B. raises the $PCO_2$ of blood to $75 \,mm$ of $Hg$
• C. is enough to keep oxyhaemoglobin saturation at $96\%$
• D. helps in releasing more $O_2$ to the epithelial tissues

Answer 1

The Correct Option is A

The given question addresses the physiological aspect of oxygen utilization in the human blood. Let's analyze the concept step-by-step:

Concept Explanation: Oxygen is transported in the blood, primarily bound to hemoglobin in red blood cells, forming oxyhemoglobin. Not all the oxygen bound to hemoglobin is delivered to the tissues during normal resting conditions. A significant portion of this oxygen remains in the blood as a reserve.

Role of Oxygen Reserve: The oxygen that remains bound to hemoglobin after tissues have extracted their required amount serves as a reserve. During times of increased demand, such as during vigorous physical activities or muscular exercise, this reserve is crucial. It ensures that the body can meet the increased oxygen demands without immediate respiratory adjustments.

Why Other Options are Incorrect:

• $PCO_2 affecting blood pressure does not relate to oxygen reserve post tissue uptake.
• Oxyhemoglobin saturation at 96\% reflects a normal condition rather than surplus utilization strategy.
• The statement about releasing more O_2 to epithelial tissues does not directly explain the reserve concept.

Therefore, the correct option is that the oxygen acts as a reserve during muscular exercise, aiding in maintaining sufficient oxygen supply under physiological stress conditions.