What term describes the unloading of O2 and loading of CO2 at the systemic capillaries?

The term that best describes the unloading of O2 and loading of CO2 at the systemic capillaries is systemic gas exchange. This process occurs in the tissues where oxygen, which has been delivered via the bloodstream, diffuses from the capillaries into the tissue cells to be used for cellular respiration. Concurrently, carbon dioxide, a waste product of cellular metabolism, moves from the tissues into the blood to be transported back to the lungs for expulsion.

In systemic gas exchange, oxygen concentration gradients facilitate the movement of oxygen from areas of higher concentration in the capillaries to lower concentration within the tissues. Simultaneously, carbon dioxide moves from the tissues, where its concentration is higher, into the bloodstream where the concentration is lower. This exchange is critical for maintaining cellular function and pH balance in the body, as the removal of CO2 prevents acidosis.

Other terms such as alveolar gas exchange refer specifically to the exchange of gases that occurs in the lungs between the alveoli and blood, while pulmonary gas exchange addresses the overall process of respiration in the lungs. Cellular respiration is recognized as the metabolic process in which nutrients are converted into energy in the presence of oxygen, but it does not specifically describe the gas exchange occurring at the capillary