The partial pressure of carbon dioxide is greatest in
The correct answer and explanation is :
The partial pressure of carbon dioxide (pCO₂) is greatest in the tissues of the body, particularly in metabolically active cells.
Explanation (300 words)
Partial pressure refers to the pressure exerted by a specific gas within a mixture of gases. In the human body, carbon dioxide (CO₂) is produced as a waste product of cellular respiration. Cells break down glucose and oxygen in the mitochondria to generate ATP, releasing CO₂ as a byproduct.
Since metabolism is constant, CO₂ accumulates in the tissues, leading to the highest partial pressure of CO₂ in body tissues. This creates a pressure gradient that allows CO₂ to diffuse from cells into the surrounding capillaries.
In contrast, the partial pressure of CO₂ is lower in arterial blood (around 40 mmHg) and even lower in the alveoli of the lungs (about 35-45 mmHg). This pressure difference facilitates the movement of CO₂ from the bloodstream into the lungs, where it is expelled during exhalation.
Thus, the order of CO₂ partial pressure from highest to lowest is:
- Tissues (highest, due to cellular respiration)
- Venous blood (after collecting CO₂ from tissues)
- Alveoli of the lungs (where CO₂ is exhaled)
- Atmosphere (lowest, since atmospheric CO₂ is very low, around 0.04%)
This efficient gas exchange process ensures that CO₂ does not accumulate dangerously in the body, maintaining homeostasis and proper pH balance.
