Which gas is primarily exchanged in systemic gas exchange?

In systemic gas exchange, the primary function occurs at the level of the tissues, where oxygen is delivered to cells and carbon dioxide is removed from them. Carbon dioxide is produced as a byproduct of cellular metabolism, specifically from processes such as cellular respiration. The concentration of carbon dioxide is typically higher in the tissues compared to the blood, which drives its diffusion from the tissues into the bloodstream.

This gas exchange is crucial for maintaining the acid-base balance in the body and ensuring that cells continue to function efficiently. While oxygen is also involved in this exchange process, its primary function is to enter the cells rather than being expelled. Therefore, carbon dioxide is predominantly the gas that is exchanged in systemic circulation, reflecting the metabolic processes occurring throughout the body's tissues.