Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!gatech!hao!boulder!eddy From: eddy@boulder.Colorado.EDU (Sean Eddy) Newsgroups: sci.bio,sci.med Subject: Re: Models of biological aging Message-ID: <1357@sigi.Colorado.EDU> Date: Sun, 14-Jun-87 14:03:28 EDT Article-I.D.: sigi.1357 Posted: Sun Jun 14 14:03:28 1987 Date-Received: Sun, 21-Jun-87 01:11:19 EDT References: <622@unicus.UUCP> <1343@sigi.Colorado.EDU> <1756@ttrdc.UUCP> Sender: news@sigi.Colorado.EDU Reply-To: eddy@boulder.Colorado.EDU (Sean Eddy) Organization: University of Colorado, Boulder Lines: 40 Xref: mnetor sci.bio:443 sci.med:2442 In article <1756@ttrdc.UUCP> levy@ttrdc.UUCP (Daniel R. Levy) writes: >In article <1343@sigi.Colorado.EDU>, eddy@boulder.Colorado.EDU (Sean Eddy) writes: >< 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? Where DOES all the new skin come >from as the old skin cells constantly die and flake off, then? (At >least I was under the impression that skin cells do this. I also once read >an article [Scientific American?] which said, as best as I could understand >it, 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?) I've been thinking the same thing since I sort of blindly believed the stuff I read. It's close, though, and I might turn out to be right. A big example of massive cell division is erythropoiesis (the production of new blood cells). 3 million new red blood cells are put into circulation every second of an adult's life, on average. If you work this out for a 100 year life span, that's about 1x10E16 cells. 2 to the 50th is a tenth of that. But, if you give me 60 divisions, I have enough potential cells for a hundred lifetimes. I think then, that certain rapidly dividing cell populations (blood cells, intestinal epithelia, etc.) clearly must be approaching 50-60 cell divisions by the end of one's life, if not exceeding the limit as you suggest. It's probably important to note that in Hayflick's experiments, his embryo-derived cells never differentiate to epithelial cells. It's not an in vivo situation, by any means. - Sean Eddy - MCD Biology; U. of Colorado at Boulder; Boulder CO 80309 - eddy@boulder.colorado.EDU !{hao,nbires}!boulder!eddy - - Go Celtics!!