In this lecture, I’m going to describe the
accessory ducts and also the glands associated
with the male reproductive system. It’s
important at the end of this lecture that
you are able to identify each of the duct systems
and know what role they have in transporting
sperm from the testes to the penis. I want
you to understand and identify the different
sorts of accessory glands, the prostate, seminal
vesicle, and also their role in nourishing
and protecting the sperm after ejaculation.
You should all have a good understanding also
of the structure of the penis and how blood
flow going to the penis creates an erection.
These ducts are very important because they
store the mature spermatozoa. The glands add
secretions to the ejaculate to provide the
nourishment for those spermatozoa in the ejaculate.
And it’s important to understand the structure
of the penis as an organ of copulation in
the male, and also, the organ that delivers urine
outside the body. It contains the urethra.
And the urethra is a common conduit for delivering
not only urine but also the ejaculate.
This slide illustrates the major organs of the
male reproductive system. And I’ve listed those
organs on the left-hand side of the slide.
I’ve already described the testis in a separate
lecture. In this lecture, I’m going to
concentrate on the other structures listed.
Just look at the diagram and locate the testis.
It’s a green circular structure suspended
in the scrotum towards the base of the section
of the slide. The bluey stained or colored
component wrapping itself around, that posterior
aspect of the testis is the epididymis, the
ductus epididymis. And then that’s continuous
with a long tube you see running up around
the back of the bladder, that’s the vas or ductus
deferens. And that joins both the seminal
vesicle and the prostate gland which are the
two major accessory glands I’m going
to describe. And then, the delivery of both urine
and also spermatozoa from the vas deferens
is delivered into the urethra. You can see
the urethra initially coming from the bladder.
The urethra passes down through the prostate,
and then through a membranous component between
the prostate before it enters the penis. So
the urethra has both a prostatic component,
a membranous component, and also a penile
component. You can also see the ejaculatory
ducts coming from the seminal vesicle, passing
into the prostate gland. It’s important
to understand the relationships of all these
organs that I’ve just described, so that
when we go through these organs in more detail,
you’re aware of their relationship and the
interaction each has with each other. In this
slide, you can see an illustration of the
duct system that takes the spermatozoa away
from the testis. And I’ve listed each of
these ducts on the right-hand side and numbered
them because I’m going to refer to these
numbers to describe the duct system. Firstly,
look at the testis. I’ve already described
the testis in another lecture. But the testis
has a capsule around it called the tunica
albuginea. And that capsule divides the testis
into a number of lobules. And these testicular
lobules contain one to four long coiled tubes
we call seminiferous tubule. And each of these
tubules can be up to 50 centimeters long.
So this is its enormous length of epithelium
that is part of spermatogenic epithelium. This
tube was aligned by seminiferous epithelium,
which is the epithelium giving rise to the
spermatogenic cells or containing the spermatogenic
cells. And the final product of this epithelium
is to release spermatozoa into the lumen of
these tubules which then move their way towards
the mediastinum of the testis. Before they
get into the mediastinum of the testis, they
pass into straight tubules. You can see them
illustrated in the diagram and labelled 1 here.
Those straight tubules then carry the spermatozoa
along with fluid, into the mediastinum of the
testis, into channels referred to as the rete
testis, shown here labelled 2. And then, the fluid
and the spermatozoa travel from the mediastinum
into the epididymis via the efferent ducts.
These efferent ducts are about 12 to 20 of
them, they link the testis to the epididymis,
the ductus epididymis. When you look at the
epididymis, which is labelled 4 here, it’s
a very long coiled tube. It can range from
four to about six meters in length. It’s
the site where sperm are going to go through
their final maturation phase and become motile.
It’s also the site that they’re stored.
Now, that epididymis has a head, a body, and
a tail. The head is the component, the coil
part of the epididymis right up next to the
testis, joining the testis via these efferent
ducts. The body is in the bulk of the epididymis
passing around the posterior aspect of the
testis. And then it starts to one coil at
the tail region and it’s continuous then
with the vas deferens labelled here, 5. I want
you to keep in your minds a memory of this
particular picture, because I’m going to
refer now to all the different parts of the
epididymis, the vas deferens and even all the
duct systems coming out of the testis.
And I’m going to describe their histological
features or characteristics and their importance.
Now on the right-hand side, you can see a
histological section. This is taken right
near where the seminiferous tubules become
continuous with the straight tubule, number
1 in the diagram. You can see the seminiferous
tubule, the seminiferous epithelium is minimal.
It’s not as thick as you see in other parts
of the testis. It doesn’t contain a vast
number of spermatogenic cells because the
epithelium is changing as it moves from the
seminiferous tubule to the straight tubule.
In the straight tubule, it’s becoming cuboidal
or even columnar, there're a variety of shapes of
the epithelial cells, but generally speaking,
they adopt the cuboidal type of appearance.
And then the epithelium is maintained as we
pass through the rete testis shown here on
the right-hand section, and it’s equivalent
to this section area on the diagram number
2. These are just huge channels or spaces
that collect all the fluid containing the
spermatozoa from the seminiferous tubules.
And they have a cuboidal, sometimes an even
squamous epithelium. There is a little bit
of a variety in these tubes. It’s particularly
not that important, nor are the straight tubules
in terms of defining their histology and their
epithelial characteristics. The important
point is that they are channels that are going
to carry the spermatozoa from the testis up
towards the epididymis. And then the efferent
tubules look rather strange. They’re labelled
3 on the diagram, and they’re shown here
in the histological section. Have a look at
the epithelium. It’s rather an uneven surface,
an undulating or corrugated type lumen due
to the difference in the types of epithelial
cells here. Some are cuboidal, some are columnar.
It looks as though some are even pseudostratified.
It doesn’t matter too much. We tend to just
term this particular tube a pseudostratified
epithelium because really when you look at
a number of sections through these tubes, the bulk
of the epithelia illustrates a pseudostratified
appearance. They have, on their surface, cilia.
You can see some ciliated cells in this image.
And those cilia help to move the fluid along
and carry therefore the spermatozoa into the
epididymis. In the center of the lumen, you can
see some red stained components that represent
spermatozoa being transported along these
ducts, the efferent ducts. Now, we’re up
towards the epididymis. On the right-hand
side, you can see a section taken through
the testis and the epididymis. Testis is shown
here on the label, and then the epididymis
is shown on the far right label. In between
are the efferent ducts. Have a look at this
histological section, including the testis,
the efferent ducts, and the ductus epididymis.
And now, have a look at the figure. And just in
your own mind, draw a line where you think
the section passed when the histologist sliced
the section through the testis, the efferent
duct, and the epididymis to obtain the section
that you’re looking at here. It is important
sometimes in histology to be able to work out
the orientation of how sections were actually
taken through an organ. That’s just
a little exercise for you to do partly
of interest. Well, we now are looking at the
epididymis. Have a look at the two sections
shown here. Even though they are taken at
two different magnifications, there are a
few features I wish to point at. First of all,
the bulk of the cells are called principal cells.
They exhibit stereocilia, long extended
branching microvillus-like processes from
the apex of their cells. They’re important
to be able to absorb an enormous amount of
fluid from the contents, from the lumen of
the epididymis. Because the epididymis, one
function is to absorb all the fluid that moves
from the testis up into the epididymis duct,
the fluid that’s added by secretions from
the seminiferous tubule and by a secretion
from the cells in the ducts I’ve already
dealt with leading to the epididymis.
These stereocilia are then very important for that
absorptive role. In the center of the lumen
of each section through the epididymis shown
here, you can see spermatozoa, many, many,
many spermatozoa. The testis produces 300
million spermatozoa per day. Very different
to the ovary, whereby, only one oocyte is
ovulated every month. Huge contrast.
When you look at the epididymis, you can see smooth
muscle around the wall, just underneath the
lamina propria supporting the epithelium.
On the left-hand side, you don’t see a lot
of smooth muscles. On the right-hand side
where the smooth muscle is labeled, you do.
And that’s because, on the left-hand section,
you’re looking at a section through
the epididymis taken towards the head of the
epididymis, where really the prime role of
the epididymis here is absorption. And therefore,
you see a lot of stereocilia, as I’ve pointed
out, on the apex of many other principal cells.
Whereas, the section on the right contains
a lot of smooth muscles. And that smooth muscle
is important because, during ejaculation,
that muscle is going to contract and force
those spermatozoa along into the vas deferens
which also contracts to expel the spermatozoa
out through the penis during ejaculation.
So that muscle is very important and there
are lots of layers of muscle there. The other
thing you can’t notice really on this section,
but I’ll tell you about it anyway, is that
on the left-hand side, the epithelial cells
that are doing all the absorption, they are
very busy cells. They are tall. They are about
30 to 40 microns in height. Whereas, the ones
on the right-hand side where the prime role
is merely to move the spermatozoa into the
vas deferens during ejaculation, these epithelial
cells are half that size, half that height,
and they don’t exhibit as many stereocilia
on their surfaces. The vas deferens again
is very different. The ductus deferens or
vas deferens is a muscular tube. It has a
lot of smooth muscles wrapped around it. And
the layers of smooth muscle are orientated
in different directions, again, to ensure very
rapid force of all expulsion of the spermatozoa
in the lumen during ejaculation. The epithelium
also contains stereocilia, and sometimes the
epithelial forms this longitudinal fold, which
often might seem quite a characteristic structure
when you compare them with other ducts, and
not only in the male reproductive system,
but in other tubes of the body. Probably the
most distinguishing characteristic here though
is the very, very thick smooth muscle layers
around the wall. Here is a section through
the spermatic cord. The spermatic cord at
least contains a number of components.
On the left-hand side of this section, the tube
or the very small lumen and the thick muscular
wall is the vas deferens or ductus deferens.
Other structures you see here that dominate
are blood vessels, more towards the right-hand
edge of the section. Those blood vessels consist
of components or branches of the testicular
artery, and also, veins of the pampiniform
plexus. When I spoke about the testis in another
lecture, I explained that the testis has to
be maintained outside the body cavity. Spermatogenesis
only occurs if the temperature of the testis
is about two to three degrees below normal
body temperature. And that’s achieved because
the blood vessel supplying the testis, the
testicular artery, coils as it moves down towards
the testis, and it has a very intimate relationship
to the veins that drain the testis, the pampiniform
plexus of veins. And those veins carry cooler
blood back to the body, back to the heart.
And the relationship between the testicular
artery, being very coiled, and this pampiniform
plexus enables the blood to become to be cooled
by these veins as it passes down towards the
testis. That’s the primary role of this pampiniform
plexus. It’s the primary structural
specialization that cools the testis by cooling
the blood leading to the testis. You can’t
see it clearly on this slide, but if you look
very carefully around the vas deferens, the
rather red stained regions represent section
through the cremaster muscle. The cremaster
muscle lifts the testis or lowers the testis
in the scrotum. Scrotum also has a duct muscle
through it and that contracts or relaxes.
And this process of contracting or relaxing
creates the scrotum as being rather a tight
sac holding the testis or rather a loose flaccid sac,
and that’s designed to conserve heat loss
or create heat again in a cold temperature,
for instance, or heat retention in cold temperatures
that scrotum will contract and wrinkle to
maintain or at least reduce heat loss. So
you have this variety of mechanisms designed
to make sure the testis operates at a temperature
below body temperature. The accessory glands
consist mainly of the prostate gland and the
seminal vesicle, and they are the two glands
that I’m going to describe now. Let’s go
back to this diagram just to remind you
of where the seminal vesicle lies and where
the prostate lies. The seminal vesicle, you
can see in this diagram, lies just at the
posterior aspect of the bladder, at least
from the angle you’re looking at. And the
prostate gland is below the bladder. And just
refresh your memories about the ejaculatory
duct coming from the seminal vesicle into
the prostate to join the prostatic urethra.
And there, the secretion products from the
seminal vesicle and the prostate will pass
into the urethra during ejaculation and flash
the spermatozoa out that have been delivered
to the urethra by contraction of the vas deferens
and also the epididymis. Let’s now have a
look at this seminal vesicle in a bit
more detail. Here, you can see a number of different
features that are characteristic of the seminal
vesicle. It has got a fairly thick muscular wall.
And it has got a very, very folded mucosa.
You’ll see that more clearly on the right-hand
side section taken at high magnification.
This seminal vesicle forms a very long convoluted
sac, and it all connects to the ejaculatory
duct. And this sac, as I mentioned, is convoluted.
It’s very, very folded with lots of muscle
making up the wall. The epithelium secretes
fluid, and that fluid is rich in fructose
which is the major energy supply for the sperm.
Often, you see the seminal vesicle containing
lots of colloid type material in the lumen.
This reflects the fluid containing all
these fructose. The prostate gland is the largest
accessory gland. It secretes a watery slightly
alkaline fluid. It also secretes fibrinolysin which
liquefies the semen. Whereas, the seminal
vesicle secretes a yellowish, whitish solution
that’s rich in fructose. When you look at
the structure of the prostate gland, there
are separate units illustrated on the diagram.
Look closely at the urethra, and also, at the
ejaculatory duct coming into the prostatic
tissues. Around that area, immediately around
the urethra, is an area or a zone, if you
like, consisting of what’s labelled there
as mucosal glands. Then there is a middle
submucosal gland layer, and then an outer
peripheral or the main prostatic gland layer.
These three separate zones are quite significant
as I’ll explain to you in a moment.
The glandular tissue, even though they are restricted
within these three zones, three separate zones,
and the products are delivered via the ducts
into the urethra, the glandular tissue, if
you look at all through these zones,
is very similar. The epithelium is generally
described as being columnar, but there is
variation in the sort of arrangement of the
epithelium that you often see at various parts
of the prostatic gland. And these epithelial
surfaces can often become nodular, and that
creates a problem. If it occurs in the glandular
tissue immediately around the urethra, then
it can impinge on the lumen of the urethra,
and therefore, make urination a long slow
process. This increases as the males age.
There is another characteristic also of the
prostate, and that is the presence of prostatic
concretions called corpora amylaceas. These
build up again with age. They become calcified.
And again, if they build up in a zone immediately
around the urethra, then they can impinge
on the urethra, and therefore again, make
urination a long slow process. Now, these
cells also can become cancerous. Prostate
cancer is the most common cancer in males.
And it tends to occur in the outer peripheral
main prostatic glands. And there, the cancers
can develop and take over a lot of the mass
of that outer peripheral zone. And that can
be digitally palpated through a rectal examination.
But the problem is that when these cancers
grow within the prostate and maybe even start to
impinge on the urethra, and the male experiences
a long slow urination process, then it’s too late
because by that stage, the prostate cancer
has metastasized. It’s spread to other parts
of the body. The prostate gland secretes many
components of the seminal fluid. One is
prostate-specific antigen. It’s secreted
into the seminal fluid or into the secretions
of the prostate, but a bit of it also leaks
across into the blood stream. So it can be
detected in blood. And in normal individuals,
the levels are lessened about four nanograms
per mil. But in prostate cancers, the secretion
of this prostate-specific antigen can increase.
So, a blood test can reveal higher concentrations
of this prostate-specific antigen or PSA in
the blood. And that is an indication that
there are these cancerous cells present in
the prostate. So, males are encouraged over
a certain age to have a regular blood test
to detect the levels of this PSA.
Same as females, have a regular Pap smear to detect
the presence of cancer cells that may be exfoliated
from the cervix into the vagina. And similarly,
breasts can be scanned. The mammary gland
can be scanned for the presence of cancer
cells in the breast, because both the change
in the hormonal environment throughout the female
menstrual cycle and genetic predisposition
are risk factors for breast cancer. So there
are these different methods of scanning both
female and male reproductive organs to try
and detect these cancerous events. The penis
is the erectile organ of the male. It’s a
copulatory organ. And if you section through
the penis, you can see the erectile tissue.
The main erectile cylinders or tissues are
called the corpora cavernosa. They are really
just large spaces that engorge with blood,
and those large spaces are lined by endothelium,
the normal line you’d expect in blood vessels.
The urethra is within another tubular structure
called the corpus spongiosum. That doesn’t
become erectile tissue. It maintains the patency
of the urethra. So during ejaculation, erection
is maintained but also towards the lumen of the urethra
maintained open. If we now look at the erectile
process, in this diagram, you see pictures
or diagrams of the penis, the flaccid penis,
when it’s usually acting as part of the
urinary system, and then the erect penis when
it’s acting as part of the reproductive
system. And on the right-hand side, you see
a section through the penis, all be it rather
faint, just to point out the corpora cavernosas,
the erectile components of the penis that
become engorged with blood. And on the right-hand
section through the penis, you can see a very
faint outline of the male urethra enclosed
by the corpus spongiosum. Normally in the
flaccid penis, when blood comes down, it flows
a little bit into the corpora cavernosums
but it’s diverted mostly into the venous
system and returned back towards the heart.
Sphincters close down so that blood tends
to be diverted from the corpus carvenosums or at
least a lot of blood. Under sexual stimulation,
though, that sphincter can then open up. So more
blood is diverted into the corpora cavernosums,
and so the penis becomes erect, that area
becomes engorged with blood. And it becomes
engorged with blood because of the relaxation
of muscles, smooth muscle cells around the
vessels and the opening of that supply to
the corpora cavernosums. But at the same time,
the venous return out of the penis is restricted,
because the vein coming out of the penis through
the penile areas comes out at an oblique angle.
And so when the penis becomes erect, that vein
is closed off, and therefore, blood is not
then continually flowing through the penis,
hence, the erection. Here again is the corpus
cavernosums that is the erectile tissue, and
the corpus spongiosum is the area around the
urethra. Well, let’s now summarize what
I’ve covered in this lecture. It’s important
to understand that the epididymis is the location
for sperm to become mature. Sperms tend to
spend 10 to 12 days in the epididymis going
through this process, and they gain motility.
Then there's all duct system that leads the sperm
to the epididymis coming from the testis.
It’s important to understand those as well.
And then there’s a seminal vesicle that
secretes fructose, the main energy source
for the sperm, understand its structure.
It’s a tubular convoluted glandular tissue.
And then make sure you recall the importance
of the prostate gland, its secretory product,
and also the way in which the glands are arranged,
and therefore, the occurrence of conditions that
can restrict the flow of urine, and also the
conditions that can lead to cancerous lesions
in the prostate. And finally, recall the structure
of the penis, the erectile tissue, and the
process in which that erectile tissue becomes
engorged, and therefore, leads to erection
of the penis, so it become into the copulatory organ.
Well, thank you for listening to this lecture.
I hope you now know something about the duct
systems in the reproductive system of the
male, and also knowledge about the very important
accessory glands. And, of course, the structure
and function of the penis.
So thank you again for listening to this lecture.