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

[B0b-A]

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 ]

[ apparently average age of muscle cell is 15 years ]

 

[SteamKing]

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.

 

[B0b-A]

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.

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

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.

 

[Ryan_m_b]

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.

 

[Andy Resnick]

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.