Red Blood Cells Live Only 120 Days and Are Produced at 2 Million Per Second
Adult human red blood cells (erythrocytes) have a lifespan of only 100–120 days before being broken down in the spleen and liver. To compensate, the bone marrow produces approximately 2 million new red blood cells every second — about 200 billion per day. Remarkably, mature red blood cells contain no nucleus or mitochondria, which maximises their space for haemoglobin. A single red blood cell carries around 270 million haemoglobin molecules, each able to transport 4 oxygen atoms.