In this lecture, you’re going to learn about
the histological structure and function of
the testis. It’s a major organ in the male
reproductive system. In another lecture, I’m
going to talk about the accessory glands,
and also ducts that are involved with transporting
products from the testis, the spermatozoa.
At the end of this lecture, I’d like you
to be clearly understanding of what spermatogenesis
involves, the difference between spermatogenesis
and spermiogenesis. And you need to describe
the processes whereby spermatogonia go through
differentiation to finally become mature sperm.
It’s also important to understand the function
of two secreting cells, steroid-secreting
cells that produce hormones, and they are
the Leydig cell and also the Sertoli cell.
And it’s also important that you appreciate
the hormonal control of these secretory products
and the interaction of these hormones with
secretory products from the pituitary gland.
Like the ovary, the testis is responsible
for gametogenesis and also steroidogenesis.
The product from the testis is the male gamete
or the spermatozoa, and the secretion of androgens
of which testosterone is the major one. Sperm
maturation is going to involve the next tube
that these spermatozoa enter. And this is
the ductus they begin with, and that’s the
topic of another lecture. But the important
point to understand is that the testis produces
the spermatozoa. And then at this stage, they
are not motile and they acquire that when
they enter into the other ductus systems.
Let’s just have a look at a diagram that
illustrates the major organs of the male
reproductive system. And I’ve listed them on the left-hand
side of this particular slide. I want you
to concentrate first on the testis towards
the bottom of the diagram. It’s a round, green
colored structure illustrated there. You know spermatogenesis
cannot occur at normal body temperature.
For spermatogenesis to occur properly, the temperature
of the testis has to be lower than body temperature,
about two or three degrees lower. And because
of that, the testis is suspended in the scrotum
outside the body cavity. And a very unique blood
supply to the testis helps to cool the testis.
The testis is supplied by a branch straight
off the aorta, the testicular artery.
And on its way to the testis, it forms a very
coiled approach to the testis. And that coiled
approach is met by a series of veins called
the pampiniform plexus. These series of veins
is taking blood away from the testis. And this
very close association, the cooler blood coming
from the veins helps to cool the blood enter
into the testis. And that’s a major way
in which the testis is lowered in temperature
to two or three degrees below body temperature.
You can’t see evidence of those vessels here
because the diagram is not illustrating
them. Notice that illustrates a couple
of other important features. And one is that a
muscle called the cremaster muscle, branches
off, it’s a direct branch off from the internal
abdominal oblique muscle. And that can lift
or lower the testis. If it contracts, the
testis is raised. If it relaxes, the testis
is lowered. Also, the scrotum has a muscle,
the dartos muscle. And this can contract and relax.
And in cold temperatures, it will contract, and
the scrotum will become wrinkled and less
flaccid than it is really in a more relaxed
situation. Again, these are mechanisms to
avoid or control heat loss from the testis,
or heat gain.