00:01
a later lecture. Well, so far, I’ve described the
process of spermatogenesis, the spermatogonial
phase and then the spermatogenic phase with
the spermatocytes going through their primary,
secondary divisions of meiosis, and then going
through a morphological change to produce
these late spermatids being then released
into the luminal space. And again, let me remind
you, that’s represented by the colored cells
in the diagram. Look now at the diagram and
you’ll see, down towards the bottom and in
the middle of the diagram, a yellow stained
or orange stained circular structure with a dark
orange stain in the middle. That represents
a Sertoli cell. These Sertoli cells are readily
identified in the wall of the seminiferous
epithelium. They sit up against the wall of
the tubule, but they are part of the epithelium.
01:07
They have a very pale nucleus. It’s often
shaped like a pyramid or triangular, but they
have a very prominent nucleolus, which is
represented in the diagram by that darker
orange round structure. And their cytoplasm is
very extensive. On the diagram, you can see
a grayish background that includes all the
spermatogenic cells that I’ve described
earlier. That’s the cytoplasm of the Sertoli
cell. It’s enormous, and they have a very
important job. They have many jobs in fact.
One job is to be the supporting cell of all
the developing spermatozoa. As the spermatocytes
go through their process of forming spermatozoa,
these Sertoli cells embrace them and give
them nutrition and support. And then when
the spermatids are released from the clutches
of these Sertoli cells, the Sertoli cells
then phagocytize a lot of debris around as
these cells go through that morphological
change to become mature or almost mature spermatozoa.
Another job they do is that they synthesize
and secrete a hormone called androgen binding
protein. This is secreted into the luminal
space of the seminiferous tubule. And it concentrates
testosterone that is secreted by the Leydig
cells in the interstitium. It concentrates
testosterone in the tubule almost 200 times
of concentration to which testosterone is
found in the blood. And that’s because the
process of spermatogenesis cannot occur with
that testosterone. Testosterone is needed
for spermatogenesis to proceed. So these Sertoli
cells are responsible for concentrating testosterone
in the environment of these spermatogenic
cells. The Sertoli cell also sits up against
another cell that lines that wall of the tubule
called the peritubular cell. This peritubular
cell is a little bit contractile. It helps
to move the contents along the length of the
seminiferous tubule. Well, in partnership
with the Sertoli cell, they create what we
call the blood-testis barrier. These spermatogenic
cells are going through stages of meiosis,
and therefore, they’re producing antigens
on their surface that we might recognize as
being foreign. When I say we, I mean males
have the immune system, and that immune system
might recognize these cells as being foreign
because of the different antigens expressed
on their surface. So the Sertoli cell in partnership
with the basal lamina and the connective tissue,
and also these peritubular cells around the
tubule create a barrier to prevent any immune
cell having access to these spermatogenic
cells. It’s a very important function.
04:40
It’s not so important in the ovary where the oocyte
is going through development. You know the ovary in
the granulosa cells in the developing follicle
in the ovary must have access to the blood
because those granulosa cells in the ovary
need various components they receive from
the blood. So there’s no blood-ovary barrier
or blood-follicular barrier in these developing
follicles. It doesn’t really matter anyway
because if the oocyte itself has a very thick
zona pellucida around it to protect it from
the possibility of any immune cells trying
to react against it. But here in the male,
it’s extremely important that this barrier
is maintained. I show you this slide to illustrate
two points. Firstly, what is dominant in this