Red Blood Cells

Higher circulating red blood cell counts significantly improve the body's capacity to transport oxygen to tissues. Carbon monoxide binding to red blood cells impairs their oxygen-carrying function. Altitude exposure triggers increased red blood cell production as the body's primary adaptive response. The body produces 2.4 million red blood cells every second in the bone marrow of long bones. Red blood cells survive between 100 and 120 days once in circulation. Each red blood cell contains approximately 270 million hemoglobin molecules. Red blood cells lack a nucleus and therefore cannot be infected by viruses. Red blood cells complete a full circulatory circuit — from lungs through the body and back — in approximately one minute. Red blood cells rely exclusively on glucose for fuel and cannot use ketones. Red blood cells have binding sites that can be occupied by either oxygen or carbon monoxide. Red blood cells constitute roughly 70% of all cells in the human body, totaling 20–30 trillion.