What is the approximate intracellular pCO2 level in mmHg?

The intracellular pCO2 level typically reflects the metabolic activity occurring within cells and is generally higher than that found in systemic arterial blood due to the production of carbon dioxide during cellular respiration. The normal arterial pCO2 range is about 35-45 mmHg, and intracellular levels usually rise above this, as cells continuously produce CO2 as a byproduct of metabolism.

The choice of 45-50 mmHg aligns with the expected physiological response, particularly in metabolically active tissues. Cells produce CO2 through the Krebs cycle and other metabolic processes, leading to these increased internal levels. This elevation helps drive the diffusion of CO2 out of the cells into the bloodstream for transport to the lungs for exhalation.

Values lower than 45 mmHg, such as those suggested in the other options, would not accurately represent typical intracellular conditions, especially in highly active tissues where metabolism is robust and CO2 production is increased. Therefore, 45-50 mmHg reflects the range that can reasonably be expected in actively metabolizing cells.