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From: Peter Armstrong <>
Subject: Re: [trivvies] smoking
Date: Fri, 14 Mar 2003 21:37:00 +0000
References: <00d901c2e4c3$37e67140$0100007f@qjtmb> <000201c2ea37$7974e500$5c3ae4d4@brittlestar>


> Dr Peter will correct me if I'm wrong, but I think this must be another
> developmental hiccup

Almost entirely correct, Lizzie, the only correction is that you got
endoderma nad ectoderm the wrong way round...
> ... ectoderm (inside bits ... mostly the linings of your innards)

Ectoderm are the outside bits

> and endoderm (outside bits ... the outside of your skin ... and all
> nervous tissue, which isn't as odd as it sounds)

And endoderm are the inside bits.

What follows is so beautifully descriptive your words should be taken up
in a documentary script!

> First it makes as if to roll itself up with the skinside inside, but just
> does a quick nip and tuck to form a channel down the middle (where the brain
> and spinal column will be ... and then it rolls up in the other direction
> leaving the skinside outside and the linings inside and in between the
> mesoderm cells disperse to points where they can make themselves useful
> making bone and muscle and connective tissue that knits it all together.
>
> This second tube will remain open at both ends throughout life, the brain
> controlling them with varying degrees of success. <grin> A number of useful
> organs develop along the route. (This is a very simplified expalantion and
> Dr Peter will tell me if I've got it all wrong.)

> 1. So I suppose it's not suprising that sometimes a few cells end up with
> the wrong instructions. Maybe Dr Peter can tell us. Did some of Emma's
> abdominal lining cells lose the plot and think they were in a lung?

No, cells were left behind during the origami, cells that were destined
to become lung tissue, and the genes "switched on" within them kept them
on that pre-ordained course. The term "ectopic" is used... healthy
correctly developing tissue, but just in the wrong place.
Neil's

> 2. Does something like this happen in edometriosis where some women have
> womb lining cells in their abdominal cavity which react to hormones and
> cause misery and discomfort?

No again. Endometriosis is thought to arise because the womb lining
(endometrium) sheds cells that migrate backwards through the Fallopian
tubes to the abdomen. The ovaries are in the abdomen and drop the egg(s)
each month into the opening of the F. tubes. So the route is open for
endometrial cells to go in the other direction. But yes the cells are
then under hormonal influence.

> 3. Are these stray pieces of tissue more likely to become cancerous ... or
> is it that we only hear about the ones that cause trouble?

Yes they are. Any tissue that is not correctly placed can undergo
malignant change. The other well-known example is when a boy enters
puberty with an undescended testicle. Cancer is then a huge risk. That
is why surgery is performed early (before the age of 5) to put the
testicle where it ought to be.

> It's still a miracle though, isn't it? ... Lizzie

Yes indeed it is that so many of us have all our bits in the right
place. All the more reason to treat them kindly to reduce the risk of
disease developing.

Peter A.

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