What role does hemoglobin play in the circulatory system?

Hemoglobin's primary role in the circulatory system is to carry oxygen from the lungs to the body's tissues. Found within red blood cells, hemoglobin binds to oxygen molecules when blood passes through the lungs, where oxygen concentration is high. It then transports this oxygen-rich blood throughout the body, releasing oxygen where it is needed for cellular respiration, a critical process that provides energy to cells.

While hemoglobin does play a secondary role in carbon dioxide transport—it helps carry some carbon dioxide back to the lungs for exhalation—its fundamental and most crucial function is oxygen transport. This is essential for maintaining the overall metabolic processes of the body. Other processes like digestion or fighting infections are attributed to different systems and components within the body, not hemoglobin.