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Structure of the penis

Structure of the penis seen from the inferior view.

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Learning reproductive anatomy is just plain awkward sometimes. Nobody enjoys it. For instance, you're sitting there in your lecture theatre with a whole lot of male anatomy staring back at you from the projector screen and it's not pretty, but we just sit there pretending it's all totally normal. But, really, behind all the statue-like faces – the guys are sitting there, uncomfortably shuffling around in their seats, internally freaking out at the idea of the dissected man parts in front of them cut into pieces all in the name of anatomy and the ladies are equally uneasy making sure to fixate their eyes either on the screen ahead or bury their heads deep into their notepads. Anything to avoid making eye contact with any guy right now. Totally awkward to say the least.

Similarly, if you're watching this video right now in your college library, I imagined you've made sure to strategically place yourself somewhere where no one can see this currently displayed on your screen. Of course, any normal person would understand that you're just studying anatomy, but admit it, you're still terrified to get caught in the act! It’s so embarrassing.

Well awkward or not, it's time to tackle this topic head-on – no pun intended - as we discuss the structure of the penis.

The penis is part of the male reproductive and urinary systems and is the largest part of the external male genitalia. It’s located on the external anterior surface of the male pelvis slightly below the level of the pubic symphysis. When speaking about the various aspects of the penis, it is important to keep in mind that its correct anatomical position is when it is erect, therefore, the surface that is facing anterior when the penis is flaccid is in fact the dorsal side of the penis.

To get a good understanding of the structure of the penis, we're going to be looking at the following: the orientation, the parts of the penis, its fascial coverings, and its associated muscles; and for the guys whose thoughts have completely run away with them, I'm going to take a moment to mention what we won't be talking about today. We’re not going to be talking about how big is really big. We’re not going to tell you if you're nasty rash, funky smell, or gunky stuff is normal or not, and we're not going to discuss what you can and can't do with your penis. We will, however, briefly talk about when your penis quite literally takes a turn for the worst, but more about that later.

As we look at the various structures that make up the penis, we're going to be doing so from several different views. This will help to give a well-rounded understanding of how the structures are all related to one another. In this image, we're looking at the penis from an inferior view to see how it makes a part of the perineum, specifically, the urogenital triangle. Making up the two anterolateral borders of the urogenital triangle are the structures highlighted in green, and these are the ischiopubic rami.

We can see several other familiar structures in this view posterior to the urogenital triangle. Highlighted now is the levator ani muscle. This muscle marks the boundary between the pelvis and the perineum which is the area that we're looking at now. The structure that we can see highlighted now is the external anal sphincter which is a muscle under voluntary control surrounding the anus itself. And lastly in this view, we can now see the gluteus maximus muscle posterior to the levator ani.

This image allows us to see a longitudinal section of the entire length of the penis while this image is a midsagittal section and allows us to see the right or the left half of the penis again along its full length.

So the penis is made up of three main parts – the root, the body, and the glans penis. The root of the penis is the proximal portion of the penis and it lies in the perineum, specifically, the urogenital triangle. It consists of three structures – a single bulb and two crura, one on either side of the median bulb. In the longitudinal section of the bulb, we can see a luminous structure running through the bulb and this is called the urethra. Also of note in these images is that all of these structures that make up the root of the penis – the bulb and both crura – continue distally into the body of the penis.

The body of the penis, therefore, will be made up of three parts as well and these are three masses of erectile tissue. What we can see highlighted in this image is the corpus spongiosum or the spongious body of the penis. The corpus spongiosum is the distal continuation of the bulb at the penis and is the anterior portion of the penis. Through both the bulb and the corpus spongiosum runs the spongy urethra which we can see in this longitudinal section of the penis just here.

The other two components of the body of the penis are the paired corpora cavernosa or the cavernous bodies of the penis. These are distal continuations of the crura of the penis, one on either side, and these form the dorsal aspects of the penis. In this midsagittal section, we can see the cavernous body of the penis highlighted in green and you can imagine if this penis were in the anatomical position – that is erect – the corpus cavernosa would be on the dorsal aspect of the erect penis.

Now what we see highlighted is the corpus spongiosum. We can see the spongy urethra running through it and, at the most distal end of the corpus spongiosum, there's an expanded part called the glans penis, which we'll look at next.

So, here we are looking at the third part of the penis – the glans penis – and in both images, the glans penis is the structure highlighted in green. Especially in this longitudinal section, we can see how it is in fact the distal expansion of the corpus spongiosum as it wraps over the corpora cavernosa here.

In this image, we can see the very distal portion of the glans penis highlighted and the reason we cannot see the entire glans penis in this image is because most of it is covered with foreskin. Foreskin is a double layer of skin and connective tissue which extends from the neck of the glans to just beyond the tip of the penis. In both the foreskin and the glans penis, there is an opening. Specifically, the opening of the glans penis is called the external urethral orifice. This opening at the distal most end of the urethra allows both urine and semen to exit the body.

In addition to skin overlying the penis, there are a couple of different fascial layers or coverings and, beginning from deep and moving superficially, we have the tunica albuginea – the deep fascia of the penis – otherwise called Bucks fascia; the superficial fascia of the penis, otherwise, called Dartos fascia; and skin.

In this image, the tunica albuginea surrounding the corpora cavernosa and the corpus spongiosum is highlighted and each of the three erectile bodies of the penis are individually covered by this fibrous tissue. Moving superficially, this image shows the deep fascia of the penis also called Buck’s fascia. This fascia surrounds all three erectile bodies together and some dorsal neurovascular structures run between the tunica albuginea and this Buck’s fascia.

As well as surrounding all three erectile bodies, the deep fascia of the penis also runs between the cavernous bodies and the spongious body forming the highlighted structure we can see in this image, and this is called the intercavernous part of the deep fascia.

In this image, a cut portion of the superficial fascia of the penis is highlighted and this layer which is the most superficial of the three fascial coverings also surrounds all three erectile bodies together. Some vessels enter the base of the penis and run longitudinally within the Dartos fascia forming a rich anastomotic network inside it.

So we're going to now take a look again at the root of the penis where we'll find some associated muscles. And there are three paired muscles in the superficial perineal pouch of the urogenital triangle and they are the bulbospongiosus, the ischiocavernosus, and the superficial transverse perineal. So, let's get to them!

So covering the bulb of the penis are the bulbospongiosus muscles. This is a paired muscle that originates from either side of the bulb and makes its opposite muscle in a midline raphe. It covers the bulb and inserts on the corpus spongiosum. This muscle helps to compress the bulb of the penis and force blood into an erect penis.

Covering the crura of the penis are the ischiocavernosus muscles and these muscles originate from the inferior internal surface of the ischiopubic ramus and the ischial tuberosity and they insert on the crura of the penis. These muscles help erections by increasing blood flow into the penis and preventing outflow of blood.

The final pair of muscles in the superficial perineal pouch are the superficial transverse perineal muscles and there's a lot to this name, but all parts should make sense. So, superficial and perineal are used because they're located in the superficial perineal pouch, transverse is used because the fibers run transversely, and muscle, well, because they’re muscles. These muscles run transversely anterior to the anus from each ischial tuberosity to the perineal body.

On either side of the perineal body, there are two triangular spaces created by the muscles we just identified and through those spaces, we can see a membrane called the perineal membrane. And this membrane is a sheet of fibrous tissue that separates the deep perineal pouch from the superficial perineal pouch.

So now that we've explored the anatomy of the penis, let's finish up by exploring one major penile disorder that we see in clinical practice.

So, Peyronie's disease is a relatively common and generally incurable disorder which involves the formation of fibrous plaques around the cavernous bodies of the penis and these plaques are effectively lesions of scar tissue which build up due to inflammation of the tunica albuginea. This is most often experienced by men aged 40 and above, however, it can occur in younger individuals also, albeit, pretty rarely.

Peyronie's disease most often results in abnormal curvature of the penis when erect, reduced length or circumference of the penis, and even erectile dysfunction in severe cases, and it also may cause significant pain especially during sexual intercourse, however, this is not always the case, and obviously it can have psychological or psychosexual implications also.

The cause of Peyronie's disease is not particularly well understood but it is believed to be related to trauma sustained by the penis during intercourse or physical activity. Many patients, however, are unable to pinpoint injury to a specific time or an event and it's believed that some sufferers of this disorder may be genetically predisposed to connective tissue disorders, therefore, making them more susceptible to this condition.

Effective treatment options for this disorder are unfortunately limited despite a variable range of interventions available and these include a host of medications, surgery as well as a type of physical therapy known as penile traction therapy. But, again, unfortunately, none of these are known to have a consistently positive success rate.

So that brings us to the end of our tutorial. Before I let you go, we'll have a quick review of what we looked at today.

So we began by looking at parts of the penis including the root, the body, and the glans penis. The root of the penis consists of one median bulb and two lateral crura. In the body of the penis, we saw the distal continuation of the bulb which is the corpus spongiosum and the distal continuations of the crura which are the corpora cavernosa. We then looked at the glans penis as the distal expansion of the corpus spongiosum.

Next, we talked about the fascial coverings of the penis. So from deep to superficial, we looked at the tunica albuginea, deep fascia of the penis or Buck’s fascia, the superficial fascia of the penis or Dartos fascia, and, finally, the skin including the distal double-layered foreskin.

Next up were three paired muscles associated with the penis – the bulbospongiosus overlying the bulb of the penis, the ischiocavernosus overlying the crura of the penis, and the superficial transverse perineal muscle. And seen within the triangles created by the muscles is the perineal membrane which divides the two perineal pouches.

Finally, we looked at a clinical correlate regarding Peyronie's disease which involves the build-up of scar tissue in the tunica albuginea of the penis leading to abnormal curvature, pain, and even erectile dysfunction.

So that brings us to the end of our tutorial on the structure of the penis. Feel free to leave your secret reproductive anatomy hiding place now and return to the real world. Thanks for watching! Ciao!

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