[ExI] biology question please

[Giovanni Santostasi]

Spike,
sperm is produced by germ cell that are (from wiki)
Within the seminiferous
tubules<http://en.wikipedia.org/wiki/Seminiferous_tubules>

   - Here, germ cells <http://en.wikipedia.org/wiki/Germ_cells> develop
   into spermatogonia <http://en.wikipedia.org/wiki/Spermatogonia>,
   spermatocytes <http://en.wikipedia.org/wiki/Spermatocytes>,
spermatids<http://en.wikipedia.org/wiki/Spermatids>
    and spermatozoon <http://en.wikipedia.org/wiki/Spermatozoon> through
   the process of spermatogenesis. The gametes contain DNA for fertilization
   of an ovum[6] <http://en.wikipedia.org/wiki/Testicle#cite_note-5>


   - Sertoli cells <http://en.wikipedia.org/wiki/Sertoli_cells> - the true
   epithelium of the seminiferous epithelium, critical for the support of germ
   cell development into spermatozoa. Sertoli cells secrete
inhibin<http://en.wikipedia.org/wiki/Inhibin>
   .[7] <http://en.wikipedia.org/wiki/Testicle#cite_note-6>


   - Peritubular myoid cells
<http://en.wikipedia.org/wiki/Myoid_cells> surround
   the seminiferous
tubules.[8]<http://en.wikipedia.org/wiki/Testicle#cite_note-7>


Giovanni


On Fri, Jun 22, 2012 at 2:11 PM, Adrian Tymes <atymes at gmail.com> wrote:

> 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.
>
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