[ExI] biology question please

[Adrian Tymes]

On Fri, Jun 22, 2012 at 9:12 AM, spike <spike66 at att.net> wrote:
> 2.       The stem cells get to the damage site by some means.
>
> 3.       It must be they are carried there by the blood.

Unless they are already present, but if they are always present
near any part of the body, then they are also present near and
probably in the blood too.

> 4.       So there must be stem cells in the blood stream always.  So far so
> good?

Not necessarily.  Stem cells could be released upon event, such as
a signal that part of the body is damaged.  (Unless they are always
present anyway, per above.)

> 6.       Like any other cell, sperm must come from stem cells.
>
> 7.       I would assume one particular stem cell becomes one particular
> sperm cell.
>
> 8.       The stem cells must get to the testes from the bloodstream.

I think, but I am not sure, that the testes has its own internal stem cell
supply.  They divide, and some of them become sperm while others
divide (some of those becoming sperm, and so on).  No bloodstream
necessary...

> 12.   Some fraction of these would make their way to the testes, and create
> sperm cells with the donor’s DNA.

...which breaks this.

I know this is not the case for a woman's egg cells, all of which are
present when the girl is born.