Roughly how long does a human red blood cell circulate before the body removes it?
- About 12 days
- About 40 days
- About 120 days
- About 2 years
Why C? And why not the others?
Correct answer: C. About 120 days
A red blood cell survives roughly 120 days, and the reason it cannot last longer is built into its design: to cram in maximum hemoglobin, it ejects its nucleus before entering the bloodstream, leaving it unable to repair itself or make new proteins. As the aging cell stiffens, it can no longer squeeze through the spleen's narrow slit-like passages, where waiting macrophages engulf and recycle it, salvaging the iron. The guess of about 12 days is tempting because it is close to the lifespan of platelets, which last only days. Forty days sounds like a safe middle figure but undershoots badly, and two years wildly overestimates a cell with no repair machinery.
Source: NIH PMC: How Do Red Blood Cells Die? (Front. Physiol., PMC8006275)