So the next tube you can see in this series of tubes, connecting to the end of the epididymis,
is the vas deferens, or the ductus deferens, and this tube carries sperm from the epididymis
to the ejaculatory ducts, which I'll come on to show you in a moment.
But this tube, the vas deferens, is itself carried in the spermatic cord, and this spermatic
cord travels in the inguinal canal.
So there's a lot to talk about with the spermatic cord, and I'll do a separate tutorial on this.
So as you can see here, the ductus deferens comes up and over the bladder, and then it
passes posteriorly and medially behind it.
So I've just zoomed in a little closer, and you can see two other structures here, you
can see the seminal vesicles, and the prostate gland.
So the seminal vesicles lie either side of the ductus deferens, and these are responsible
for producing seminal fluid, which makes up sixty to seventy per cent of the total semen,
and this fluid contains things like proteins, amino acids, prostaglandins, fructose, and
several other things.
And where the ductus deferens terminates, is the prostate gland.
So you can see this round structure sitting underneath the bladder.
So this is the largest accessory gland of the male reproductive system, and it can be
palpated through the rectum.
So in a digital rectal examination, the posterior aspect of the prostate can be felt through
the anterior wall of the rectum.
So that's an important relationship to known about.
So in the male reproductive system, you've got three accessory glands: so you've the
two seminal vesicles which I just showed you, you've got the single prostate gland, and
you've got two bulbourethral glands, which I'll come on to talk about in a moment.
So what I'd like to do next is switch over to a cross sectional model to show you how
the ductus deferens joins with the prostate and the seminal vesicles to form the ejaculatory
ducts.
So now we've got this model of the bladder at the top, with the prostate underneath it
and posteriorly you've got the seminal vesicles and we've got a cross section so we can look
at the inside aspect of the prostate gland.
So it's not shown on here, but if we just imagine that we've got the ductus deferens
joining here, which I'm drawing on in green, you can see the seminal vesicle over here.
And where the seminal vesicle meets the ductus deferens at the prostate, you get this duct
within the prostate, called the ejaculatory duct, which I've just outlined in yellow.
So you can see another duct which runs through the prostate gland, and this is the urethra,
and because it runs through the prostate, it's called the "prostatic part of the urethra".
So the ejaculatory duct empties into this prostatic part of the urethra.
So the urethra actually has four parts to it.
So you can see the first part here, which is above the prostate, so this is called the
"preprostatic part", and then you've got the prostatic part, which I mentioned, and you've
got a "membranous part" and a "spongy part".
So remember that this is just the cross section, and you've only got one seminal vesicle and
one ejaculatory duct represented on this particular model, but you've got one on either side,
so you've got two ejaculatory ducts on either side.
So I've just switched over to another diagram, just to illustrate some of these parts of
the urethra.
So at the top you've got the, preprostatic part of the urethra, and at this point, you've
got the internal urethral sphincter, which surrounds this part of the, the preprostatic
urethra.
And the function of this internal urethral sphincter is to prevent the backflow of semen
into the bladder.
And then the next part is the prostatic urethra, which I mentioned before, and I've just draw
that on in blue.
And then you've got the membranous urethra, which is the part of the urethra which passes
through the deep perineal pouch, and it's surrounded by another sphincter, so you've
got the external urethral sphincter, which surrounds the membranous part.
And then remember I mentioned the bulbourethral glands, well these lie surrounded by the external
urethral sphincter, so they're these pea sized glands, which lie within the deep perineal
pouch, and they lie posteriorly and laterally to the membranous part of the urethra.
And then the final part of the urethra is the spongy part, which is surrounded by the
corpus spongiosum of the penis, which is the erectile tissue of the penis.
So I just wanted to show you another diagram to explain some features of the prostatic
urethra.
So we're looking at the prostate gland here, and it's been opened up to show the prostatic
urethra, running down its midline.
So you've actually got a fold of mucosa in the prostatic urethra, which runs down the
midline, and this fold, which sticks out to form this crest, is known as the urethral
crest.
And then on either side of the urethral crest, you've got something called the urethral sinus,
which is where the prostatic ducts drain into.
So you can see that I've drawn this enlargement of this fold, so the urethral crest forms
this circular enlargement, which is known as the seminal colliculus.
So as you can see there are three openings here.
This middle opening that you get is called the prostatic utricle, and it doesn't really
have any function, but it's this blind ending, small indentation.
And then on either side of the prostatic utricle, you've these other two openings, so these
are for the opening of the ejaculatory ducts.
So those are a couple of features to know about with regard to the prostatic urethra.