Vas Deferens, Accessory Glands and Urethra
Testis and Epididymis
This is a tutorial on male reproductive anatomy.
I'm going to talk you through some of the main structures relating to the male reproductive system, and we're going to begin with the testes, which are the primary sex organs of the males, so they're akin to the ovaries in the females, and the main functions of the testes are to produce sperm and to produce male hormone - so androgens, and the main one being testosterone.
In utero, the testes actually descend from the abdominal cavity via the inguinal canal, and they enter into the scrotum.
What we're going to do now is, I'm going to switch over to a diagram of the testes and we'll look at it in section, and we'll talk through some of the key structures to know about.
the testes are actually surrounded by a capsule, so this is formed by a layer of peritoneum, which is brought down with the testis when it descends from the abdomen, but this connection in between the abdomen and testis eventually gets broken, and it leaves the testis surrounded by its own separate capsule, so you can see that I've draw on in green this outer capsule.
And this is called the tunica vaginalis. And it has a parietal layer and a visceral layer. And then in blue you can see that I've draw on another layer, so this is the inner sac which encapsulates the testis, and this is called the tunica albuginea.
And as you can see here, the tunica albuginea actually forms these projections, which project into the testis and divide it up into lobules, so these projections from the tunica albuginea, are known as septa.
And the spaces that you have between each of these septa are called lobules, and then within each of these lobules, you've got this coiled tubular structure, so you've got the seminiferous tubules.
At the end of these coiled seminiferous tubules, you've actually got a straight tubule coming off.
You can see these straight tubules which I'm highlighting in yellow. And these straight tubules then all join together to meet this network of tubules, which is known as the rete testis.
in Latin, the word "rete" means "net", so you've got this sort of amalgamation of tubules forming this net-like structure. And then next in this series of tubules, coming off the rete testis, you’ve got the efferent ductules. And the efferent ductules connect to the epididymis.
Posteriorly on the testis you've got the epididymis, which you can see that I've outlined in purple.
What happens essentially is that you get these sperm cells which are secreted from the lining of the seminiferous tubules, and then they travel via this duct system which I've just described, to be stored in the epididymis. And it's in this location which they're stored until ejaculation.
Just coming back to the 3D model, you can see the epididymis here, sitting on the posterior and superior aspect of the testis, and its got three parts: it's got the head, it's got the body, and it's got a tail inferiorly.
Vas Deferens, Accessory Glands and Urethra
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.
There's a lot to talk about with the spermatic cord, and I'll do a separate tutorial on this.
As you can see here, the ductus deferens comes up and over the bladder, and then it passes posteriorly and medially behind it.
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.
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.
You can see this round structure sitting underneath the bladder.
This is the largest accessory gland of the male reproductive system, and it can be palpated through the rectum.
In a digital rectal examination, the posterior aspect of the prostate can be felt through the anterior wall of the rectum.
That's an important relationship to known about.
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.
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.
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.
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.
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".
The ejaculatory duct empties into this prostatic part of the urethra.
The urethra actually has four parts to it.
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".
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.
I've just switched over to another diagram, just to illustrate some of these parts of the urethra.
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.
I just wanted to show you another diagram to explain some features of the prostatic urethra.
We’re looking at the prostate gland here, and it's been opened up to show the prostatic urethra, running down its midline.
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.
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.
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.
Those are a couple of features to know about with regard to the prostatic urethra.
Next we're going to take a look at the basic anatomy of the penis.
The penis is a common outlet for the passage of both semen and urine, and it contains these venous sinuses, which can fill with blood and cause the penis to become erect.
Essentially you have three tubes which make up the penis, on either side of the penis, you've got two corpus, or corpora cavernosa, so you can see these on either side, and then the inferior aspect, if I rotate the model, you can see that there's this single central tube, which is known as the corpus spongiosum.
You’ve got two corpora cavernosa, and you've got one corpus spongiosum.
These three tubes make up the penis.
Let’s just take a look at the attachment of the corpora cavernosa.
If I rotate the model posteriorly, you can see that the two corpora cavernosa attach to the pelvis, and they attach on the ischial rami.
These proximal bits of the corpora cavernosa are known as the crura, which is Latin for "legs". "Crus" is singular.
Proximally they attach to the pelvis, and distally, if I rotate round, you can see that they come to form the end of the penis - the glans penis.
And then if we take a look at the corpus spongiosum, which runs down the middle on the under surface of the penis, you can see that it has this bulb, so this is the bulb of the penis, and it's here where the bulbo-urethral glands release their secretions.
The bulb is attached to the perineal membrane.
The proximal ends of these structures, so the crura of the corpora cavernosa and the bulb of the corpus spongiosum form the root of the penis. And the body of the penis is the, the free part of the penis formed by these three tubes.
The penis has certain ligaments which attach to its base, it has a suspensory ligament, and a fundiform ligament.
I've just switched over to a sagittal section of the male reproductive system, and I'll show you the suspensory ligament of the penis.
It’s just here, attaching to the base of the penis at one end, and at the other end, it attaches to the symphysis pubis.
The other ligament is the fundiform ligament of the penis, and this is more superficial, and it actually attaches above to the linea alba.
The linea alba is this midline of the anterior abdominal wall, where the abdominal muscles fuse centrally.
If I just zoom in a bit further, the fundiform ligament attaches superiorly to this linea alba, and then what it does is, it kind of goes around either side of the base of the penis, and it forms this sort of sling, by connecting inferiorly, underneath the penis.
That's an introduction to the male reproductive system. In the next tutorials, we'll take a look at the blood supply to some of these structures.