What is the main function of red blood cells?

Red blood cells, also known as erythrocytes, primarily function to transport oxygen from the lungs to the body's tissues. This is made possible by the presence of hemoglobin, a protein within red blood cells that binds to oxygen molecules and carries them through the bloodstream. Once red blood cells deliver oxygen to the tissues, they also play a role in returning carbon dioxide, a waste product of metabolism, back to the lungs, where it can be exhaled. This gas exchange is crucial for cellular respiration and maintaining the body's overall metabolic processes.

The other options refer to different functions associated with other types of cells or physiological processes. For example, white blood cells are responsible for fighting infections, while the regulation of body temperature involves various systems, including blood flow to the skin and sweating, rather than a direct role of red blood cells.