Hello, everyone! This is Joao from Kenhub, and welcome to another anatomy tutorial where, today, we’re going to be talking about the male pelvic viscera and perineum.
So what I’m going to be doing is basically looking at this image that you see now popping on your screen, which is a parasagittal section of the male pelvis and perineum as well, and we’re looking at it from a right view, as you can see.
And what we’re going to be doing on this tutorial is basically describing the different structures that you see here, different bones, different ligaments, some muscles, and the organs, the viscera that we find here.
Now, sit back, relax, because this is going to be a tutorial where we’re going to be dealing with all the important details that you need to know about these structures. So I’m going to provide you with enough information so you can have some solid background on these structures.
And before I do so, I would like to describe what is the perineum. And the perineum is generally defined as the segments between the anus and the genitalia and the region of the body inferior to the pelvic diaphragm, which you see here and a little bit cut here. So this is the pelvic diaphragm. So the perineum should be around this area, right about here.
There are some deep boundaries of the perineum that are worth noting here. There’s one anteriorly, which is known as the pubic arch, and the arcuate ligament of the pubis will be defining the anterior boundaries of the perineum.
Also, posteriorly, we’re going to be finding the tip of the coccyx, defining the deep or the posterior, deep boundaries of the perineum, which you can also see here on this image. This should be the coccyx right about here.
And on both sides, we’re going to be seeing, then, the inferior rami of the pubis and ischial tuberosity and also the sacrotuberous ligament.
Defining the deep boundaries on a superior level, we’re going to be seeing, then, the pelvic floor, like I mentioned before, and inferiorly, then, you’re going to be finding skin and fascia.
We’re going to start off with this structure that you see here. We just removed some of the fascia, some of the bones here as well. We just cut a little bit more into the bone as you can see here. We removed some of the peritoneum, some of the fascia, and also the bones here, the pelvic bones, were removed to highlight this structure here, which is known as the pubic symphysis. And you’re going to be looking at this image throughout this… this tutorial, so it’s worth highlighting here the pubic symphysis, which is an important midline cartilaginous joint uniting the superior rami of the left and right pubic bones.
This structure is located anterior to the urinary bladder and superior to the external genitalia, as you can clearly see here on this image. This is the urinary bladder, and this is, of course, the male genitalia.
The main motions associated to the pubic symphysis include the superior and inferior glide, some superior and inferior glide happening, and also separation and compression.
If we were to also mention a function or a role associated to the pubic symphysis, the functions of this joint are to absorb shock during walking.
We’re now moving forward to this image again, where I’m putting back all the structures that I removed on the previous image, and I can also show you here that the pubic symphysis should be around here. And notice some of the pelvic bones that we’re going to be talking about.
But we’re highlighting now a structure, a bony structure, worth highlighting here on this tutorial so we can understand what is happening here on this image. And this structure that we’re highlighting is known as the fifth lumbar vertebra, also known as L5.
This one is the largest, strongest, and lowest of the lumbar vertebrae. And as the last of the lumbar vertebrae, L5 bears more body weight than any of the other 23 vertebrae that sit on top of it in the vertebral column. For that reason, L5 is the largest and strongest lumbar vertebrae but is also the one that is most susceptible to stress-related injuries.
As I mentioned, L5 is located in the lumbar spine, on the lower back, inferior to this structure that you just see a little bit here. This is L4, then, and superior to this bone here, which is known as the sacrum.
We’re going to move forward and to start talking about the different muscles or some of the muscles that you can see here on this image. We’re going to be talking about the levator ani, the rectus abdominis. We’re also going to talk about the external anal sphincter.
Let’s start off with the very first one here on the list, now highlighted in green. This is known as the levator ani muscle. And here on this image, there is a cut here of the muscle (so keep that in mind) because it should go all the way to cover this area here.
The levator ani is a broad, thin muscle that is located on the side of the pelvis, as you can see here on this image. And it forms the pelvic diaphragm with another muscle known as the coccygeus muscle.
A little bit on the origin and insertions of the levator ani, in terms of origin, this muscle is going to be originating from the inner surface of the side of the lesser pelvis.
Then, goes to insert in the inner surface of the coccyx and also a ligament, the anal coccygeal ligament.
Also a word on the innervation of the levator ani, and the levator ani muscle is going to be mostly innervated by the pudendal nerve, the perineal nerve, and the inferior rectal nerve.
In terms of the different functions that this muscle will be performing in your body, the levator ani supports the viscera in the pelvic cavity, as you can clearly see here, that this muscle is serving as a support system for the viscera or the organs that are found above it. And it also surrounds the various structures that pass through it.
Now, we’re going to highlight this muscle here, just to briefly talk about it and also understand what is happening here on this parasagittal section of the male pelvis. This is known as the rectus abdominis muscle. And of course, you cannot see the entire muscle here, but we just want to add some important information about this structure so you can always add to your notes. But I do recommend you go to our atlas here at Kenhub or watch other videos where we can go into a little bit more detail on the rectus abdominis.
But the rectus abdominis muscle is a paired muscle that runs vertically on each side of the anterior wall of the abdomen. There are two parallel muscles that are separated by a midline band of connective tissue that we call linea alba or also known as white line.
In terms of the origin points for the rectus abdominis, we’re going to see that this muscle originates from the pubic symphysis, the pubic crest, and also the pubic tubercle. This muscle, then, goes and inserts all the way to the xiphoid process, and the costal cartilages of the fifth to seventh ribs.
The rectus abdominis is going to be innervated, then, by the thoracoabdominal nerves.
We’re going to move on to this muscle that you see now, highlighted in green, and we’re just showing you the inferior view of the pelvis where you can see this muscle a bit better. This is known as the external anal sphincter.
The external anal sphincter is a flat plane of muscular fibers, elliptical in shape, and intimately adherent to the integument surrounding the margin of the anus.
It measure about eight to 10 centimeters in length from its anterior to posterior extremities and is about 2.5 centimeters opposite to the anus.
It consists of two strata as well, or two layers, known as the superficial and deep layers.
There’s also an origin and insertion that we would like to mention here on this tutorial. The origin point for the external anal sphincter is going to be, then, the anococcygeal raphe, and then the muscle is going to insert on the central tendon of the perineum, which is a structure that we’re going to be covering here on this tutorial, so keep that in mind.
In terms of the innervation of the external anal sphincter, a branch from the fourth sacral and also twigs from the inferior rectal branch of the pudendal nerve will be, then, innervating the external anal sphincter.
There are some roles or actions associated to the external anal sphincter, and now, you can see the muscle highlighted on the parasagittal section of the male pelvis.
This muscle, like other muscles, is always in a state of tonic contraction, and in the presence of no antagonistic muscle, it keeps the anal canal and orifice closed. But it can also be put into a condition of greater contraction voluntarily, so it can more firmly occlude the anal aperture.
And due to its fixed point at the coccyx, it helps fixing the central point of the perineum, so that the bulbocavernosus may act from this fixed point.
We are now ready to move on to another set of structures that we’re going to be seeing here on this parasagittal section, the blood vessels. And there are two that you can see here superiorly that we’re going to be discussing, and these are the common iliac artery and also the common iliac vein.
And before we distinguish those two structures there on that particular image, I would like to show you this image here, which is the anterior view of the abdomen if we were to cut it open and then expose a few structures that you find more posteriorly, like the kidneys you see here and these blood vessels that are quite important for what we’re going to be talking about next.
You have here the aorta, the abdominal aorta, and also here, you notice the inferior vena cava.
Now, a word on the common iliac arteries, these arteries are two large arteries that originate from this bifurcation right here, happening on the abdominal aorta, which is known as, then, the aortic bifurcation at the level of the fourth lumbar vertebra.
These common iliac arteries are about four centimeters long in adults and more than a centimeter in diameter.
The arteries run inferolaterally along the medial border of the psoas muscle to the bifurcation at the pelvic rim in front of the sacroiliac joints. These arteries are going to, then, bifurcate again into the external iliac artery, as you can see here—so these are the external iliac arteries—and then the internal iliac arteries.
I’m still using this image to talk about, here, these structures that we’re going to talk about later on, which will be, then, the bifurcation of the inferior vena cava. These will, then, result into the common iliac veins, which we will be seeing also on that image.
But before we talk about them, let’s go back to this image where I’m highlighting now, in green, the right common iliac artery, yes, because we’re looking at this from this image particularly from a right view. So we’re seeing, then, the right common iliac artery.
And both the left one and also the right common iliac artery will receive blood from the abdominal aorta, if you remember from the previous slide, and are distributed to the pelvis and lower limb as the femoral artery on the corresponding side.
We’re moving on to highlight this one here on the back. This is a vein, the right common iliac vein. Both the left and right common iliac veins are formed by the external and internal iliac veins. The left and right common iliac veins come together in the abdomen at the level of the fifth lumbar vertebra.
They, then, drain blood from the pelvis and lower limbs and drain back to the inferior vena cava, if you remember from the previous slides, where, then, the blood goes, the deoxygenated blood goes all the way back to your heart.
Let’s move on now to a next set of structures that we see here on this beautiful image, and we’re going to look at, then, the tendons, ligaments, and fascia that we can find here, including these two: the central tendon of the perineum and also the visceral pelvic fascia.
Now, we’re going to start off with the very first one here on our list that you see now, highlighted in green, this is known as the central tendon of the perineum, which we can also call it the perineal body. And this is a pyramidal fibromuscular mass in the middle line of the perineum, and in males, it is found both between the bulb of the penis and the anus, as you can clearly see here on this image.
There’s a function or role associated to the central tendon of the perineum, and the perineal body is essential for the integrity of the pelvic floor.
There are also a list of muscles that converge and also attached to this structure, including the external anal and urinary sphincters, the bulbospongiousus muscle, the superficial and deep transverse perineal muscles, and the interior fibers of the levator ani.
Second on that list that we looked at previously, now, we’re highlighting, then, the visceral pelvic fascia. And as you remember, a fascia is a structure of connective tissue that surrounds muscles, group of muscles, blood vessels, and also nerves binding some of these structures together while permitting others to slide smoothly over each other.
The visceral pelvic fascia is attached to the diaphragmatic part of the pelvic fascia and has been subdivided in accordance with the viscera to which is related to, and we’re going to, then, split it up into three different parts.
The anterior part, which is known as the vesical layer, forms the anterior and lateral ligaments of the bladder. There is also a middle part, which is, then, the transverse cervical ligament, perforated by, then, the cervix. And then there is a posterior part, known as the rectal layer that passes through the side of the rectum, forms a loose sheath for the rectum but is firmly attached around the anal canal.
There’s also an important structure worth highlighting on this… this particular image, which is known as the peritoneum. And the peritoneum is a serous membrane that forms the lining of the abdominal cavity.
The peritoneum also has its functions or roles. It mainly supports the abdominal organs and also serves as a conduit for their blood vessels, lymph vessels, and also nerves.
There are some anatomical spaces that we’re going to covering, now, you see this one, highlighted in green. This is the rectovesical pouch, as you can clearly see here, highlighted in green. And also, as the name indicates, in the male pelvis, the rectovesical pouch is a double folding of peritoneum between the rectum and the bladder, as you can see here. So this is the rectum, and as I mentioned before, this is the bladder.
We’re now ready to move on to the next set of structures. Now, we’re going to be talking about some of the components of the digestive system that we can see here on this image. We’re going to be talking about the sigmoid colon, the sigmoid mesocolon, the taenia coli, and the rectum.
Starting off with the very first one here on the list, that you see now highlighted, this is, then, the sigmoid colon. The sigmoid colon, or also called sometimes as the pelvic colon, is part of the large intestine that is closest to the rectum and anus. It forms a loop that averages about 40 centimeters in length and normally lies within the pelvis, but on the account of its freedom of movement, it is liable to be displaced into the abdominal cavity.
The sigmoid colon begins at the superior aperture of the lesser pelvis, where it is continuous with the iliac colon and passes transversely across the front of the sacrum to the right side of the pelvis. Then curves on itself and turns toward the left to reach the middle line at the level of the third piece of the sacrum, which you can see here—this bone that I just mentioned before. And here, it will bend downward and ends into, then, this structure here, known as the rectum.
Behind the sigmoid colon, we’re going to find a few structures, including the external iliac vessels, the left piriformis muscle, and the left sacral plexus of nerves. I would like to also add a word on the innervation of the sigmoid colon and the inferior mesenteric ganglia and also the sacral nerve will be innervating the sigmoid colon.
There’s also a role or a function associated to this structure, and its function is to expel solid and gaseous waste from the gastrointestinal tract. The curving path that it takes towards the anus allows it to store gas in the superior arched portion, enabling, then, the colon to expel gas without excreting feces simultaneously.
We are ready now to move on to the next structure that we’re highlighting. This is known as the sigmoid mesocolon. And the sigmoid mesocolon is a fold of peritoneum that attaches to the previous structure that we talked about, the sigmoid colon, to the pelvic wall and one of the four mesenteries in the abdominal cavity.
The sigmoid and superior rectal vessels run between the layers of the sigmoid mesocolon, and the left ureter descends into the pelvis behind its apex.
We’re done with the sigmoid mesocolon to move on to this structure here, known as the taenia coli, seen here highlighted. The taenia coli are three separate longitudinal ribbons of smooth muscle on the outside of the sigmoid colon, as you can clearly see here. They are visible and can be seen just below the serosa or fibrosa layers. The bands converge at the root of the vermiform appendix.
The taenia coli contract lengthwise to, then, produce these structures here, these bulges in the colon, which are known as the haustra.
We’re now going to move a bit further down, here to this highlight. We’re highlighting the rectum. And the rectum is the final straight portion of the large intestine. The human rectum is about 12 centimeters long and begins at the rectosigmoid junction, the end of the sigmoid colon, at the level of the third sacral vertebra. The rectum terminates at the level of the anorectal ring.
This structure will also have a function or a role that we would like to highlight here on this tutorial. The rectum acts as a temporary storage site for feces. As the rectal walls expand due to the materials filling it from within, stretch receptors from the nervous system, located in the rectal walls, stimulate, then, the desire to defecate.
If the urge is not acted upon, then what happens is that the material in the rectum is often returned to the colon where more water is going to be absorbed from the feces, and if defecation is delayed from a prolonged period, then what happens is, then, constipation and hardened feces.
And now that we just covered a bit of the rectum, we’re going to move on to another set of structures, now components of the urinary system that we find here on this structure, on this image. And we can list two, mainly, the ureters and also the urinary bladder.
We’re going to start off with this image here, so I can show you these structures. Notice here these two long structures that we’re going to be covering. These are the ureters. They are tubes made of smooth muscle fibers that will propel urine from the kidneys that you see here on this image to, then, the urinary bladder that you find here.
In the adult, the ureters are usually 25 to 30 centimeters long and three to four millimeters in diameter.
And if we look at this image here, the ureters arise from these areas here at the kidneys, known as the pelvis of each kidney. Then, they descend on top of these muscles here, of the psoas major muscles. They are found behind all these structures to reach, then, the rim of the pelvis.
Here, they are crossing in front of the common iliac vessels. They, then, pass along the sides of the pelvis and finally curve forwards and enter the bladder as you can see here. So it’s they’re entering the bladder from its left and also we’re looking at the subject’s perspective, so from its left and also from its right sides at the back of the bladder.
We’re now moving on to this image here that I can show you, then, the right ureter to be more specific. We’re now back to the parasagittal section of the male pelvis where we can highlight the right… a bit of the right ureter, that portion that will be entering the urinary bladder, just at the back of the urinary bladder. And these structures will also be innervated. The ureters are richly innervated by nerves that travel alongside the blood vessels.
The primary sensation to the ureters is provided by nerves that come from T12 to L2 segments of the spinal cord.
We’re now ready to move on and highlight this structure here, this organ, now that you see here, just a portion highlighted because this should be all under the pelvic fascia and also the peritoneum. This is, then, the urinary bladder. This is a hollow, muscular, and elastic organ.
The bladder sits on the pelvic floor, as I also showed you before. We just cut a bit of the pelvic floor here to expose a little bit more the urinary bladder and another two structures that we’re going to be talking about later on on this tutorial, but just to show you that it sits on the pelvic floor.
Urine will be entering the bladder via the ureters and then exits it via the urethra. It’s almost impossible to give an exact measurement for the volume of the human bladder, but different sources mention from 500 to 1,000 milliliters.
There’s also some innervation associated to the urinary bladder that I would like to talk about. The bladder receives motor innervation from both sympathetic fibers, most of which arise from the hyposgastric plexuses and nerves.
And also parasympathetic fibers which come from the pelvic splanchnic nerves and the inferior hypogastric plexus.
For urine to exit the bladder, both the autonomically controlled internal sphincter muscle and also the voluntarily controlled external sphincter muscle must be open. And problems with these muscles will lead, then, to what is known to be (you probably heard about this) incontinence.
Now, there is also a role or a function that we need to highlight here, associated to the urinary bladder. All the urinary bladder is an organ that collects urine that is excreted by the kidneys before disposal when you urinate.
We’re now ready to move on to a next set of structures, the last set of structure that we’re going to be covering on this tutorial. Now, we’re going to be dealing with components of the reproductive system.
We’re going to be talking about the seminal vesicles, the vas deferens, and the prostate.
We’re going to start off with the very first one here on the list that you see here highlighted. This is the right seminal vesicle. There is also a left one, but we’re looking now at the right view, and therefore, at the right seminal vesicle.
The seminal vesicle’s also known as vesicular glands. They are a pair of simple tubular glands posteroinferior to the urinary bladder, as you can clearly see here on this image. Each vesicle consists of a single tube, folded and coiled on itself with occasional diverticula in its wall.
Each vesicle spans approximately five centimeters, but if we were to uncoil and unfold totally, we would be seeing around 10 centimeters in length.
Both the right and left seminal vesicles are, then, supplied by a few arteries, including the inferior vesicle artery and the middle rectal artery.
There’s also a role or a function associated to these vesicles that we need to highlight here. These vesicles are going to produce a substance that causes the semen to become sticky or jelly-like after ejaculation.
We’re moving on to the next structure that you see here, highlighted in green. This is known as the right vas deferens. Sometimes, they are also referred to as ductus deferens, and there are two, and each tube is about 30 centimeters long and three to five millimeters in diameter. These are muscular or surrounded by smooth muscle.
Now, when it comes to blood supply, the vas deferens is supplied by an artery which follows a similar path, which is known as the artery of the vas deferens. This artery normally arises from the vesicle artery, a branch of the internal iliac artery.
As for a function or role associated to these structures, they transport sperm from the epididymis to the ejaculatory ducts in anticipation of ejaculation.
We’re going to move on to this structure, now, that you see here under the bladder. This is known as the prostate. The prostate is a compound tubuloalveolar exocrine gland of the male reproductive system.
A healthy human prostate is usually said to be slightly larger than a walnut. The weight of a normal prostate in adult males is about 11 grams, usually ranging between seven and 16 grams, surrounds the urethra a- just below the urinary bladder, as you can also see here on this image, and can be felt during rectal exam.
The prostate also contains smooth muscle fibers that help expel semen during ejaculation.
There is also some blood supply or blood vessels here that we’re going to associate to the prostate. Now, the blood vessels include, then, the internal pudendal artery, the inferior vesical artery, the middle rectal artery, and the prostatic venous plexus.
And this prostatic venous plexus is connected to the vesical venous plexus. It receives blood and empties it into the internal iliac vein.
Now, there is also innervation for the prostate, and the prostate is going to be innervated by the inferior hypogastric nerve plexus.
Now, the role associated or the function associated to the prostate is that this structure will secrete fluid that nourishes and protects the sperm. During ejaculation, the prostate squeezes this fluid into the urethra, and it is expelled with sperm as, then, semen.