What role does Hemoglobin (Hgb) play in the body?

Hemoglobin plays a crucial role in the body primarily by carrying oxygen from the lungs to the tissues and organs and facilitating the transport of carbon dioxide back from the tissues to the lungs for exhalation. This function is vital for maintaining the necessary oxygen levels for cellular metabolism and overall physiological function. The structure of hemoglobin, which consists of iron-containing heme groups, allows it to bind with oxygen in the high-oxygen environment of the lungs and release it in the lower-oxygen environment of body tissues. Additionally, it helps to buffer the blood and assist in carbon dioxide transport, making it essential for respiratory and metabolic processes.

In contrast, the other options describe functions that are not directly associated with hemoglobin. Regulating blood pressure is managed by other systems, primarily involving the heart, blood vessels, and kidneys. Catalyzing metabolic reactions is a role performed by enzymes. Fighting infection is primarily the responsibility of the immune system, with white blood cells and antibodies playing key roles. Thus, while all these processes are critical to bodily function, none directly pertain to the specific role of hemoglobin.