What is the main function of erythrocytes in the body?

Erythrocytes, also known as red blood cells, have the primary function of transporting oxygen from the lungs to the tissues throughout the body. They contain hemoglobin, a protein that binds oxygen efficiently in the lungs and releases it in the tissues where it is needed for cellular respiration and energy production. This oxygen transport is essential for maintaining the metabolic processes of cells and overall homeostasis within the body.

While erythrocytes do also play a minor role in the transport of carbon dioxide back to the lungs, their main physiological purpose is the delivery of oxygen. The other choices do not accurately represent the primary role of erythrocytes. Cofactors for enzyme function pertain to different biochemical contexts and are not the function of red blood cells, while regulating blood pressure is mediated by various mechanisms including blood vessel constriction and dilation, rather than erythrocytes themselves.