Does Your Body Really Replace Itself Every Seven Years?

red blood cell life cycle

This diagram shows the life cycle of red blood cells, which regenerate in our bodies about every 120 days. VectorMine/Shutterstock

As we’ve mentioned, cells in the body renew at varying rates. Just how long certain cells last depends on how much work they’re tasked with doing. Red blood cells, for example, have an average life span of about 120 days because of their arduous journey through the circulatory system, carting oxygen to tissues throughout the body.

Here are the life expectancies for other cells:

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  • Skin: The epidermis sees a fair amount of wear and tear, thanks to its role as the body’s outermost layer of protection. These skin cells rejuvenate every two to four weeks.
  • Hair: The body’s natural fuzz has a life span of about six years for women and three years for men.
  • Liver: The liver is the human body’s detoxifier, purifying a wide variety of contaminants from our systems. It’s aided in the process by a constant blood supply and remains largely immune to damage from these toxins by renewing itself with new cells every 150 to 500 days.
  • Stomach and intestines: Cells that line the surface of the stomach and intestines have a difficult, short life. Constantly battered by corrosives like stomach acids, they typically last only up to five days.
  • Bones: Cells in the skeletal system regenerate almost constantly, but the complete process takes a full 10 years. The renewal process slows down as we age, so our bones get thinner.

Despite all this regeneration and the fact that the average age of all our cells is about seven years, the truth is that we still get old and die because of mutations that appear in our DNA as our cells replicate over time. So if you think you’re going to live forever, you’ll will have to find the Fountain of Youth.

Still, there are cells that never leave us and may aid the aging process, or at least the body’s breakdown over time. While the eye’s cornea can regenerate itself in as little as one day, the lens and other areas don’t change. Similarly, neurons in the cerebral cortex — the brain’s outside layer that governs memory, thought, language, attention and consciousness — stay with us from birth to death. Because they aren’t replaced, the loss of these cells over time can cause maladies like dementia.

The good news is that other areas of the brain, like the olfactory bulb that helps us smell and the hippocampus that helps us learn, can and do rejuvenate.

So get out there and show off that big ol’ brain. It’s one asset that won’t last forever.

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Originally Published: Jun 6, 2014

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