- (Narrator) They'll actually make these sperm, though
the sperm production.
It's not just simply a, here's one step-done.
There's several different steps that must be required.
You must go through mitosis and meiosis
of cells inside the seminiferous tubules.
So what's the purpose. Why?
Well, we need to produce a large number of sperm.
But the sperm must have half the number of chromosomes.
The key thing here is this half number
because the sperm are going to cause an
individual with an egg. That's the idea of reproduction.
If you take half of the chromosomes in the sperm,
half in the egg.
Once you combine, you end up with a full set of chromosomes.
So that's why it's so important to have half the number.
If a sperm or egg ever started
with a full set of chromosomes.
If there was fertilization.
Well, that offspring would have three
or four sets of chromosomes.
Way above the normal amount.
So to end up with a normal amount, the diploid,
you want to have half the chromosomes to start,
or called haploid.
What you start with is a cell called spermatogonia.
The figure 2n means it has the full set of chromosomes,
two copies.
From the spermatogonia you go to the primary spermatocytes,
secondary spermatocyte, spermatid, sperm.
You can see that you go from the 2n,
both sets of chromosomes, to 1n.
Half.
Any cell that's not going to be
actually be produced into a sperm
is called a sertoli cell.
It's meant to help support, nourish.
So here you can see, top left,
we have a cross-section through a teste.
You can see that they bring out that seminiferous tubule
Kind of enlarge it comes out.
Cut it in half, you can see what the
large scene in the bottom left looks like,
the cross-section.
But in the top-right, that's an
artist rendition of what the wall of
a seminiferous tubule would look like.
Because see how they go from the cells from along the wall.
They divide and divide and divide.
Until eventually, they look like immature sperm.
You're going through mitosis first, then meiosis.
So you divide from one to two, two divides into four.
So the idea of this meiosis, is taking one cell
and eventually creating four from it.
Four cells that are haploid.
Four cells that half the amount of chromosomes.
And all that material is going
to be stored in each individual sperm.
As you can see in the bottom right,
the artists rendition of a sperm.
You have the head units, which contains the chromosomes
you have a mid-section,
which is all energy, on the contrary,
and you have a tail which helps with movement.
Now we've gone through the production of sperm, in general.
Let's talk about testosterone,
the major hormone of the male reproductive system.
Testosterone is produced by the
interstitial cells of the testes.
"Inter" or in between means these interstitial cells
are between the seminiferous tubules.
Testosterone is going to help control the growth,
the functionality,
of all male reproductive tissues.
It causes the secondary sexual characteristics to develop.
It stimulates more aggressive behavior
in males than females.
It helps to stimulate sexual behaviors.
So most things you attribute to male sexuality
is because of testosterone.
But it also deals with the rate of sperm formation.
So its talking about how fast are sperm produced.
Is it efficient or is it inefficient?
Is there too much or too little testosterone?
But testosterone itself has to be regulated.
It must be kept in a proper amount.
So you have these hormones called GnRH.
The full name is gonadotropin-releasing hormone.
But the abbreviation is just fine.
These things come from the hypothalmus,
it's up in your brain.
You also have LH, it comes from pituitary glands.
You have FSH, coming from the pituitary gland as well.
Both LH, luteinizing hormone and
FSH, follicle-stimulating hormone
come from the anterior pituitary
and deal with testosterone production.
But if you notice,
only LH can stimulate testerone production.
FSH, actually helps with the helper cells,
the sertoli cells.
And then we have this hormone called inhibin.
I'm willing to bet you can probably
figure out what inhibin does.
Yeah, inhibin inhibits.
It inhibits the secretion of FSH.
So by reducing FSH production,
you also reduce overall production of testosterone.
So here's the same thing, just more in a visual form.
We start with the hypothalmus, producing that GnRH,
which then we can get luteinizing hormone, or LH,
FSH, follicle-stimulating produced.
They come down the testes and
in their own ways help to trigger testosterone production.
While testosterone production helps with sperm production.
Well you can see all these dotted lines,
or dashed lines going back up.
Those are all negative feedback.
Too much of any one of these steps,
goes back up and triggers that
you stop producing the hormone.
So enough testosterone tells LH to stop producing.
Enough inhibin will help stop the production of FSH.
So it's all about this negative feedback.
It's like, hey we've got enough.
Slow down. Back off.
You don't want too much.