What is the life span of a red blood cell?

• A. About 120 days
• B. About 90 days
• C. About 60 days
• D. About 180 days

Answer: (A)

Red blood cells have a finite life because, once mature, they cannot repair themselves. They lack a nucleus and mitochondria, so they can’t synthesize new proteins or repair membrane damage. Over time their membranes become less flexible and surface markers change as they accumulate oxidative and mechanical damage. The spleen and other reticuloendothelial tissues then recognize and phagocytose these aged cells. In a healthy adult, this cycle results in an average lifespan of about 120 days (roughly four months).

Choosing the other timeframes would imply either overly rapid clearance or much slower turnover than what is typical. About 120 days best fits the normal rate of erythrocyte aging and removal.