What fraction of adult human cells are not replaced over a normal lifetime ?.

In summary, the fraction of adult human cells that are not replaced over a normal lifetime is a minority, with the brain and heart making up only 3% of body weight and the skeleton and muscles being replaced every decade and every 15 years, respectively. However, regeneration of heart cells does occur, albeit at a slower rate compared to other types of tissue. The lens of the eye and enamel on teeth are never replaced, and certain cells, like chondrocytes and osteocytes, have very low rates of turnover. Additionally, it is believed that podocytes are not replenished throughout an individual's lifetime.
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  • #2
B0b-A said:
What fraction of adult human cells are not replaced over a normal lifetime ?.

see ... http://en.wikipedia.org/wiki/Ship_of_Theseus / [ aka "Trigger's broom" ].

I'm guessing it's a minority : brain and heart only account for about 3% of body weight.[ skeleton is replaced every decade , but that's only 14% of body weight ]

[ muscles every 15 years ]
Why do you think the cells of the heart are not normally replaced? See this article:

http://en.wikipedia.org/wiki/Cardiac_muscle

Section 'Physiology', 'Regeneration of heart muscle cells'

Regeneration of the heart does occur, albeit more slowly compared to other types of tissue.
 
  • #3
SteamKing said:
Why do you think the cells of the heart are not normally replaced
My education on the subject was pre 2009 , when the orthodox-view was brain & heart do not regenerate.

SteamKing said:
Regeneration of the heart does occur, albeit more slowly compared to other types of tissue.

newscientist.com said:
A 25 year old turns over just 1 per cent of their heart cells ever year, and this figure decreases with age
So around half of the heart remains unchanged throughout adult life.
 
  • #4
If you're looking at this from the perspective of the ship of Theseus then it's not just cell lifespan you need to consider but the turnover of cell components. An individual cell will break down and rebuild/repair structures inside itself over time.
 
  • #5
The lens of your eye was almost fully formed prior to birth and no part is ever 'replaced', similarly to the enamel covering your teeth. Chondrocytes are nearly 'metabolically inert' (senescence) and have very low rates of turnover. Osteocytes can live 25 years or more.

Edit: I forgot to mention podocytes- while recent results show there are signaling pathways that can move podocytes into and out of the cell cycle, the prevailing view is that you are born with a full compliment and do not make any more throughout your lifetime.
 
Last edited:

1. What is the estimated fraction of adult human cells that are not replaced over a normal lifetime?

The estimated fraction of adult human cells that are not replaced over a normal lifetime is about 20-30%. This means that the majority of cells in our body, around 70-80%, are constantly being replaced throughout our lifetime.

2. Which cells in the human body are replaced and which are not?

Most cells in the human body are constantly being replaced, such as skin cells, blood cells, and cells in the digestive system. However, some cells, like neurons in the brain and muscle cells, are not replaced or are replaced very slowly.

3. How does the body replace old cells with new ones?

The body replaces old cells with new ones through a process called cell turnover. This involves the death of old cells and the production of new cells through cell division. Different cells have varying turnover rates, with some being replaced within days and others lasting for years.

4. Does the rate of cell replacement change with age?

Yes, the rate of cell replacement does change with age. As we get older, the rate of cell turnover slows down, leading to a decrease in the number of new cells being produced. This is one of the reasons why our bodies take longer to heal and recover as we age.

5. Can external factors affect the rate of cell replacement?

Yes, external factors such as diet, exercise, and exposure to toxins can affect the rate of cell replacement. A healthy lifestyle with a balanced diet and regular physical activity can help promote cell turnover, while factors like smoking and excessive alcohol consumption can slow it down. Exposure to toxins can also damage cells and hinder their ability to divide and replace themselves.

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