# What is the reason for certain parts of the body not regenerating properly over time? **URL:** \ **Category:** Factual Questions\ **Created:** [February 7, 2005, 1:12am UTC](https://boards.straightdope.com/t/what-is-the-reason-for-certain-parts-of-the-body-not-regenerating-properly-over-time/288730 "2005-02-07T01:12:03Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![Lobsang](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lobsang/32/4067_2.png) [@Lobsang](https://boards.straightdope.com/u/Lobsang)\ **Post date:** [February 7, 2005, 1:12am UTC](https://boards.straightdope.com/t/what-is-the-reason-for-certain-parts-of-the-body-not-regenerating-properly-over-time/288730/1 "2005-02-07T01:12:03Z")
I know that our bodies have a mechanism for replacing dead cells with live ones. And that numerous parts of the body ‘grow back’ if removed. So why do so many poor fellow men lose hair (in an ugly manner too)? why have I lost all nasal hair? Why does eyesight and hearing deteriorate? Why, with the amazing ability of cells to replicate and replace old with new, do we grow old and die? ---
**Author:** ![Reeder](https://avatars.discourse-cdn.com/v4/letter/r/c6cbf5/32.png) [@Reeder](https://boards.straightdope.com/u/Reeder)\ **Post date:** [February 7, 2005, 1:27am UTC](https://boards.straightdope.com/t/what-is-the-reason-for-certain-parts-of-the-body-not-regenerating-properly-over-time/288730/2 "2005-02-07T01:27:04Z")
> [@](#): > > And that numerous parts of the body ‘grow back’ if removed. Other than the nails…what lost body parts do humans have that grow back? ---
**Author:** ![Lobsang](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lobsang/32/4067_2.png) [@Lobsang](https://boards.straightdope.com/u/Lobsang)\ **Post date:** [February 7, 2005, 1:40am UTC](https://boards.straightdope.com/t/what-is-the-reason-for-certain-parts-of-the-body-not-regenerating-properly-over-time/288730/3 "2005-02-07T01:40:15Z")
> [@Reeder](#): > > Other than the nails…what lost body parts do humans have that grow back? Most of the adult human body is only a few years old. The whole lot is regrown cells from what we eat. By ‘lost body parts’ I mean the cells that die or get taken away by small injuries such as cuts and grazes on the skin. I realize that losing a whole arm does not result in an arm growing back. ---
**Author:** ![Smeghead](https://avatars.discourse-cdn.com/v4/letter/s/f1d935/32.png) [@Smeghead](https://boards.straightdope.com/u/Smeghead)\ **Post date:** [February 7, 2005, 4:51am UTC](https://boards.straightdope.com/t/what-is-the-reason-for-certain-parts-of-the-body-not-regenerating-properly-over-time/288730/4 "2005-02-07T04:51:50Z")
There’s a huge difference between cells dividing to replace dying cells and the regeneration of a whole limb or organ. The latter would require coordination between a whole lot of cells from a whole lot of cell types. Say you lose an arm. Or even just a finger. You’d have to regenerate bone, nerves, blood vessels, muscle, connective tissue, skin, etc, etc. That’s hugely different than having some epithelial cells in your gut lining constantly sloughing off and replenishing. Our healing system is designed to just close up any gaps as quickly as possible. ---
**Author:** ![Ms2001](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ms2001/32/18463_2.png) [@Ms2001](https://boards.straightdope.com/u/Ms2001)\ **Post date:** [February 7, 2005, 12:30pm UTC](https://boards.straightdope.com/t/what-is-the-reason-for-certain-parts-of-the-body-not-regenerating-properly-over-time/288730/5 "2005-02-07T12:30:04Z")
> [@Reeder](#): > > Other than the nails…what lost body parts do humans have that grow back? The [liver](http://journalism.berkeley.edu/projects/transplants/liver.html) can grow back: > [@](#): > > The first living donor liver transplant, in which a portion of the donor’s liver is transplanted, was performed in 1989. In 2000, 385 living donor liver transplants were performed. The number jumped to 518 in 2001 and fell back down to 358 in 2002. > > The liver’s ability to regenerate itself also makes it an ideal organ for a living donation. For the donor, the liver grows back and regains full function. > > This is probably because most of the other organs of the body are made up of specialized sub-organs to some extent, says Dr. Nicholas Jabbour, a liver transplant surgeon at the University of Southern California. Consider the kidney. It is divided into glomeruli, which are basically kidney units, and the sum of them will perform the functions of the kidney, he says. > > The liver, on the other hand, is made up of many cells each of which does everything the liver does, Jabbour says. Hepatocyte and Kupffer cells are the liver’s principal cell types and both can regenerate. ---
**Author:** ![One\_And\_Only\_Wanderers](https://avatars.discourse-cdn.com/v4/letter/o/838e76/32.png) [@One\_And\_Only\_Wanderers](https://boards.straightdope.com/u/One_And_Only_Wanderers)\ **Post date:** [February 7, 2005, 12:38pm UTC](https://boards.straightdope.com/t/what-is-the-reason-for-certain-parts-of-the-body-not-regenerating-properly-over-time/288730/6 "2005-02-07T12:38:18Z")
> [@Lobsang](#): > > I know that our bodies have a mechanism for replacing dead cells with live ones. And that numerous parts of the body ‘grow back’ if removed. > > So why do so many poor fellow men lose hair (in an ugly manner too)? why have I lost all nasal hair? Why does eyesight and hearing deteriorate? Why, with the amazing ability of cells to replicate and replace old with new, do we grow old and die? [This article is a pretty good discussion on the topic](http://www.findarticles.com/p/articles/mi_m1374/is_1_62/ai_82013457) I found it an interesting read anyway.