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From: craig@think.uucp (Craig Stanfill)
Newsgroups: sci.bio,sci.med,comp.ai,sci.misc
Subject: Re: Models of biological aging
Message-ID: <5491@think.UUCP>
Date: Wed, 17-Jun-87 09:34:44 EDT
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Posted: Wed Jun 17 09:34:44 1987
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Xref: mnetor sci.bio:453 sci.med:2457 comp.ai:555 sci.misc:359

> Hayflick limit: In actual practice, it is not thought that any
> human cell approaches 50 divisions during the human lifetime.

***

> Is this true even for skin cells? ....that intestinal cells continually
> regenerate and get sloughed off during the normal digestive process.
> That's a lot of cell division, or am I mistaken?)

***

> 2^50 is a very large number, if every cell had two progeny (which of course
> they don't) - but the rate of proliferation is impressive. In fifty
> divisions two cells would produce something like 10,000 lbs of tissue. Thus
> a little proliferation goes a long way.

***

If I am correctly informed, in the skin, intestines, and other areas of
the body which are constantly renewed, there is a thin layer of rapidly
reproducing cells, covered by a layer of non-reproducing but living
cells, followed by a layer of dead cells.  In essence, after each
division one daughter will cease to divide and one will continue to
divide.  Thus, the number of rapidly reproducing cells stays more or
less constant, and the production of new tissue is steady.  Of course,
sometimes the mechanism (whatever that may be) malfunctions, producing
tumors of various sorts.