What function do erythrocytes serve in the blood?

Erythrocytes, commonly known as red blood cells, play a critical role in the circulatory system primarily by transporting oxygen from the lungs to the tissues and carbon dioxide from the tissues back to the lungs. Their structure is uniquely suited for this function; they contain hemoglobin, a protein that binds oxygen efficiently. This allows red blood cells to effectively pick up oxygen during their journey through the lungs and release it as they enter tissues that require it for cellular metabolism.

In addition to oxygen transport, erythrocytes also facilitate the removal of carbon dioxide, which is a waste product of cellular respiration. As the red blood cells circulate back to the lungs, they release carbon dioxide to be expelled from the body during exhalation. This dual function of transporting gases is vital for maintaining pH balance and supporting overall metabolic processes.

Other options like immune response regulation and infection-fighting are primarily functions of leukocytes, or white blood cells, not erythrocytes. Blood clotting is mainly the responsibility of platelets. Thus, the primary and correct function of erythrocytes in blood is accurately represented by their role in the transport of oxygen and carbon dioxide.