Question: how long does it take for all the red blood cells in your body to be replaced?
Answer: Other cells are replaced at varying rates: Red blood cells have a lifespan of just 70–120 days. Intestinal cells turn over every 10 years or so — but the epithelial cells (exposed to the inside of the intestine) only last about 5 days, while the other intestinal cells last around 16 years.