00:00
or heat gain. Now let’s look at the testis
in more detail. Let’s look at its histological
structure. Well, here are two images of the
testis. The one on the left hand side is a
histological section taken through the testis.
The one on the right is a diagram I’m
going to refer to, to explain some of the internal
structures of the testis that you don’t
really see clearly in a histological section.
The outside of the testis, like any other
or most other organs anyway in the body, has
a capsule, a very thick dense connective tissue,
collagenous capsule on the outside, called
the tunica albuginea. It’s highly innervated
with sensory nerve fibers. And septa, from
that connective tissue capsule, penetrate
into the testis and divide into a series of
lobules which I’ll describe in a moment.
01:03
Within that capsule are a number of blood
vessels. It’s called the tunica vasculosa.
01:09
And these blood vessels penetrate into the testis
because the testis is an important endocrine
gland. If you look down at the smaller section
of tissues shown, that’s part of the
ductus epididymis. And I point that out too because that’s
the destination of the spermatozoa when they’re
produced in the testis. That’s the site or
the location whereby the sperm will achieve
final maturity, that will become motile. Have
a look at the diagram now. I’ve labelled
the mediastinum. Most organs have what we
call a mediastinum or a hilum where blood
vessels enter and leave, or ducts or tubes
enter or leave. You don’t often see it in
section to the testis such as the one on the
left-hand side because often, you just can’t
section through that part of the testis. It’s
orientated differently. In the diagram, focus
your attention on the lower part of the diagram,
the very dark green colored component.
02:21
It represents the capsule around the testis,
the tunica albuginea that I've pointed out on
the histological section. Remember, it’s
collagenous, highly sensitive. Well, as I
also pointed out, and you can see on the diagram,
septa go into the testis. And those septa
divide the testis into a number of lobules. There
is up to 250 or even 300 of these separate
lobules within the testis created by this
connective tissue penetrating into the testis.
03:01
Within those lobules, there are very coiled
tubes called seminiferous tubules. They begin
in the mediastinum and they extend that in
a very cold manner to the periphery of the
testis, turn around and come back again. So
they’re blind-ended tubes. They’re about
50 centimeters long, and there are about one
to four of those in each lobule. So you can
do the mathematics to work out how long this
tube is going to be, these seminiferous tubules
when they all join together because that represents
the tube that is going to produce spermatozoa.
03:53
That tube, that seminiferous tubule, is lined
by a very special epithelium. It’s called
the seminiferous epithelium. And those epithelial
cells are the ones that undergo differentiation
to produce sperm. And that’s what we are going
to examine in the next part of this lecture.
04:16
First of all, just note on the diagram that
these tubes enter the mediastinum. They all
come together on colorless in structures we
call the rete testis. And then the spermatozoa
pass from the rete testis in the mediastinum
of the testis. They pass out of the testis
through efferent ducts or the ductus efferentes
or ductuli efferentes depending on whether
you’re talking about singular or plural.
And then, they then pass into the epididymis
that I pointed out earlier, and that becomes
continuous with the ductus deferens. All those
tubular structures I’m going to talk about
in a later lecture, but I think it’s very
important to point out their associated with
the testis at this stage. Let’s look at