What is the primary function of red blood cells?

Red blood cells (RBCs), or erythrocytes, primarily function to transport oxygen from the lungs to the tissues throughout the body. This vital role is facilitated by hemoglobin, a protein within the red blood cells that binds to oxygen molecules. When blood flows through the lungs, red blood cells pick up oxygen and then carry it to the body’s cells, where it is used for metabolic processes, including the production of energy.

While red blood cells also play a minor role in transporting carbon dioxide from the tissues back to the lungs for exhalation, their primary purpose is the transport of oxygen. Other cell types and components of the immune system are responsible for fighting infections, and hormone production is generally not a function of red blood cells. Therefore, option C accurately describes the main function of red blood cells in human physiology.