What percentage of total CO2 is carried in the blood as bicarbonate?

The distribution of carbon dioxide (CO2) in the blood is an important aspect of respiratory physiology. In humans, a significant way that CO2 is transported from the tissues to the lungs is in the form of bicarbonate (HCO3−). The majority of CO2 in the blood—approximately 70%—is carried as bicarbonate ions.

This bicarbonate formation helps maintain the blood's pH balance through a buffering system and is crucial for transporting CO2, which is a byproduct of metabolic processes, from the body's tissues to the lungs for exhalation.

The conversion of CO2 to bicarbonate occurs primarily in red blood cells, facilitated by an enzyme called carbonic anhydrase, and allows for efficient transport and regulation of CO2 levels in the body. Understanding this process is essential for grasping how the body maintains homeostasis in relation to acid-base balance and gas exchange.

Recognizing that the correct answer reflects the physiological reality helps illustrate the integral role of bicarbonate in CO2 transport, while the other options do not accurately represent the prevalent method of CO2 carriage in the bloodstream.