Video: Male urinary bladder

Hello, everyone! This is Joao from Kenhub, and welcome to another anatomy tutorial where, this time, we're going to be talking about the male urinary bladder. We will look at the structures and also organs found in the male pelvis paying then particular attention to those associated with the male urinary bladder. Now, of course, some of the structures found in the male pelvis differ in some ways to those found in the female pelvis due to the difference in the reproductive organs. So, what I will do is mainly focus here on this image that you see now on the screen. So, what you see here on this image, this is a coronal section of the urinary bladder – as you can see here – tilted slightly posteriorly and there are a few structures here that we’re going to be seeing and describing there found around this organ.

Let’s start off with this one that you see here highlighted in green, this is known as the peritoneum. So, before we start to describe several anatomical features of the urinary bladder, let’s have a look at the peritoneum which covers then part of the bladder – as you can also see here on this image. The peritoneum is a serous membrane that lines the peritoneal cavity. This membrane will be supporting and lining the organs of the abdomen and pelvis. Now, that we just covered the peritoneum, it is time to move on and describe the different structures of the bladder, the urinary bladder – the male urinary bladder – which you now see the first one highlighted in green. This is known as the body of the urinary bladder.

Now, the body is lined with transitional epithelium and this is a hollow pear-shaped part of the urinary bladder that holds the urine before it is voided. It is located between the fundus and the apex of the urinary bladder and the entire volume of the bladder varies but it can hold between 400 mL to 1000 mL. Now, the ureters will be opening here on the body of the bladder posteriorly and, when empty, the urinary bladder has a pyramidal shape.

Now, on the next slides, I would like to talk about several parts of the bladder including this one that you now see highlighted in green, which is known as the fundus. The fundus is basically the base of the bladder. It has the shape of an inverted triangle as you can see here. It faces posteroinferiorly and it is formed by the posterior wall of the bladder. The trigone as you can see here is found then on the fundus of the bladder and as you can see it is triangular in shape and faces posteriorly and it is lymphatically drained by the external iliac lymph nodes.

Next, we’re going to be highlighting this structure here which I just mentioned before, the trigone of the bladder, the urinary bladder. Now, this is a smooth, triangular part of the urinary bladder and as you can see in this illustration, the mucosa lining of the trigone is smooth and firmly attached to the underlying wall of the bladder like elsewhere in the bladder where the mucosa is folded and loosely attached to the wall. This triangular region is formed by the left and right ureteral orifices that are openings of the ureter into the bladder which you can see here. We’re also going to be covering them in a little bit more detail on the next slides. Once, the trigone of the urinary bladder is stretched to a certain degree, a signal is then sent to your brain that the bladder needs or your bladder needs to be emptied.

So, next slide, we’re going to be covering then the structures that I just mentioned before, the ureteral orifices. They are slit-like openings through which the ureters enter the bladder on the posterolateral angles of the trigone of the urinary bladder.

The next structure we’re going to be highlighting here on this image is known as the interureteral fold. This is a mucous membrane fold located between the two ureteral orifices that we talked about before, and this structure is also sometimes mentioned as the Mercier’s bar.

The next structure to be highlighted here on the image is known as the neck of the bladder. Now, the neck of the urinary bladder is the lowest portion of the bladder from which the urethra arises – as you can see here, this is the urethra. So, as you can see here from this illustration, the neck of the urinary bladder is the part of the urinary bladder where the urethra will begin.

Since we’re talking about this structure, it is time to move on and talk about then the urethra. Now, we’re looking at a longitudinal section here of the male urethra and, as you clearly see here, the urethra begins at the lowest part of the neck of the urinary bladder and, in men, the urethra is long, about 20 cm long. It passes through the deep perineal pouch and perineal membrane and immediately enters the root of the penis. 

Anatomically, the male urethra can be divided into 4 parts – the pre-prostatic urethra, the prostatic urethra, the membranous urethra and the spongy urethra. The initial part of the urethra is referred to as the pre-prostatic urethra or the intramural part of the urethra. It passes through the muscular neck of the bladder running from the internal urethral orifice to the point where the bladder meets the prostate. It's typically about 0.5 to 1.5 centimeters in length but this can vary depending on whether the bladder is filled with urine or empty. Surrounding the pre-prostatic urethra is the internal urethral sphincter which serves to assist in the control of continence of the bladder and also to prevent the backflow of semen into the bladder during ejaculation.

As we move distally along the urethra, we come to the prostatic urethra. This is a part of the urethra that passes through the prostate and is about 3-4 centimeters in length. It extends from the base of the bladder just below the pre-prostatic urethra to the membranous part of the urethra. There are a few features found on the posterior aspect of the prostatic urethra that I want to point out. The first of which is an elevation called the urethral crest. This elevation is where the prostatic ductules open up on either side bringing prostatic fluid into the urethral lumen. Just inferior to this, there is another rounded elevation called the seminal colliculus which is the point where the ejaculatory ducts open up into the prostatic urethra. The ejaculatory ducts carry sperm from the testes and fluid from the seminal vesicles into the urethra, therefore, this is the point where the urinary and reproductive tracts merge.

One last interesting feature of the prostatic urethra is the prostatic utricle. This feature is the homologue of the vagina and uterus in females and doesn’t develop in males during fetal life.

Now let's move on to the membranous part of the urethra which is the second shortest part of the urethra and connects the prostatic urethra to the spongy urethra. It's about 1 to 1.5 centimeters long and is surrounded by the external urethral sphincter which we can now see highlighted in green. This urethral sphincter plays an important role in voluntary control of urinary flow.

The largest and most distal part of the urethra is the spongy urethra which is approximately 15 centimeters long and runs within the corpus spongiosum. The spongy urethra ends as it opens to the outside environment through the external urethral orifice. There are some additional features associated with the spongy urethra that I'd like to bring your attention to. The first of which are the bulbourethral glands. These glands secrete fluid into the urethra acting as lubrication. There's also the ampulla of the urethra, which is located within the bulb of the penis and the navicular fossa which is located within the glans. Both of these structures are dilations within the spongy urethra.

On the next image, we’re going to be highlighting here this structure which is known as the internal urethral sphincter. At the very first part of the urethra, we can see the internal urethral sphincter. The internal urethral sphincter is comprised of smooth muscle that is located at the junction of the urethra and the urinary bladder. This muscle is innervated by the S2 to S4 nerves of the pelvic plexus and will be functioning to then constrict the internal urethra preventing then urine leakage and also prevents the reflux of semen on the urinary bladder during ejaculation.

The next structure we’re going to be highlighting here on this image – one that I pinpointed before – this is also a muscle known as the external urethral sphincter. So, at the membranous part, the urethra is then surrounded by skeletal muscle which is this one, the external urethral sphincter, and these muscles are responsible for controlling urination process – the urination process – and are innervated by the deep perineal branch of the pudendal nerve. And as I said before, they surround the membranous part of the urethra and have their origin at the ischiopubic ramus wrapping around the urethra as you can see here upon which they act.

Next structure I would like to highlight here on this section of the urinary bladder, this one is the prostate. And as we saw previously, the urethra is surrounded by the prostate at the prostatic part, and the prostate is located below the urinary bladder. This compound tubuloalveolar exocrine gland secretes an alkaline fluid that makes up 30% of the volume of the semen. Also worth mentioning here, this capsule which is known as the prostatic capsule. The prostate is surrounded by a capsule which is known as then – for lack of better name – the prostatic capsule. The capsule of the prostate is then comprised of smooth muscle fibers that are firmly attached to the prostate.

Next, we’re going to be highlighting here which is known as the seminal colliculus. The seminal colliculus seen here highlighted is the part of the prostatic urethra that refers to an elevation near the opening of the seminal vesicle.

Next highlight is this structure here which his known as the bulbourethral gland which just below the prostrate at the level of the deep perineal pouch we find then the bulbourethral gland. It is located in the urethrogenital diaphragm and it is a mucous exocrine gland found at the base of the penis. This gland, like the prostate, is a compound tubuloalveolar gland that secretes mucoprotein-rich fluid that makes up about 5% of the ejaculatory fluids.

The next structure we can highlight here is the spongy body of the penis. Known also as the corpus spongiosum or the spongy part of the penis, this is a cavernous body of the spongy tissue that surrounds the male urethra. This structure functions to prevent the occlusion of the urethra from being pinched during erection, thereby, allowing it to be a channel for ejaculatory fluid when ejaculation occurs as a result of the male orgasm.

The next structure we’re going to be highlighting now is known as the crus of the penis. The crura of the penis – plural – are attached to the inferior ramus of the pubis. Before the two crura meet, they form an enlargement known as the bulb of the corpus cavernosum. The merging of the crura forms then the corpus cavernosum which is expandable erectile tissue of the penis that fills up with blood during erection.

Moving on, we’re going to be highlighting now a muscle known as the bulbospongiosus muscle. The bulbospongiosus muscle arises from the perineal body and the median raphe of the corpus spongiosum. In the male pelvis, this muscle covers the bulb of the penis. It consists of two symmetrical parts uniting in front of the median raphe from the central tendinous part of the perineum. Now, this muscle contributes to ejaculation, erection of the penis, orgasm, as well as evacuation of the contents of the urethra. It is, as every muscle, innervated by a nerve but this time the perineal nerve will be innervating which is a branch of the pudendal nerve.

Next on our list, we’re going to be highlighting this membrane here, this is then the perineal membrane. Now, this is another structure that is indirectly related to the urinary bladder and this is then the perineal membrane which is a fascia found on the anterior inferior surface of the deep transverse perineal muscle. It is a thick, triangular fascia attached to the bony framework of the pubic arch and forms the superior border of the superficial perineal pouch and is continuous with the inferior part of the diaphragmatic part of the pelvic fascia. Now, the urethra vertically penetrates the perineal membrane as it escapes the pelvic cavity.

Another fascia I would like to highlight here, this time, it’s known as the deep perineal fascia. Now, the deep perineal fascia surrounds the muscle of the superficial perineal pouch. It attaches from the ischiopubic ramus to the deep suspensory ligament of the penis and is continuous with the deep fascia of the muscles of the abdominal wall. And another fascia here that we find on this image on this cross-section, this is the superficial perineal fascia. Now, the superficial perineal fascia is a thin aponeurosis that forms the anterior inferior border of the superficial perineal space.

Next structure we’re going to be highlighting is a muscle known as the ischiocavernosus muscle which originates from the ramus of the ischium and also the ramus of the pubis or pubic bone. The ischiocavernosus muscle functions to flex the anus and stabilize the erect penis by then compressing the crus of the penis and for that reason then delaying the return of blood through the veins. Located behind and inserting into the sides of the crus of the penis, this structure is innervated by the pudendal nerve.

Another muscle we can clearly highlight here, this is known as the levator ani muscle. Now, this is another important muscle for urination and the levator ani muscle forms a large part of the pelvic diaphragm which is basically the muscular floor of your pelvis. This muscle is found on either side of the pelvis. It originates from either side of the pelvic wall coursing medially and joining with its opposite counterpart. It is a thin funnel-shaped muscle extending from the pubis and obturator fascia to the anus and is made up of three parts namely the puborectalis muscle, the pubococcygeus muscle, and the iliococcygeus muscle.

But move on here to this image of the lateral view of the male pelvis, you can see now highlighted in green the levator ani muscle that we’re still talking about where you see that it has its origin on the posterior aspect of the superior pubic ramus and inserts in the, on the side of the rectum and the last two segments of the coccyx as you can see here. Now, the innervation of this muscle is then derived from the pudendal nerve and its branches as well as the S3 to S4 sacral spinal nerves. This muscle relaxes at the beginning of urination process and also defecation. For that reason, the levator ani is an important muscle or has an important role when it comes to preserving urinary and bowel continence.

The next muscle going back to this image of the coronal section, we’re seeing now another muscle highlighted which is known as the obturator internus. Now, seen here as part of the muscles of the male pelvis, it acts to facilitate lateral rotation, abduction, and adduction of the thigh. It has its origin in the inner surface of the obturator membrane as well as the rim of the pubis and ischium and will be inserting just above the trochanteric fossa. Now as for the innervation, this muscle is going to be innervated by the sacral plexus L5 to S1.

Still on this image, I would like to highlight these structures to show you what we’re looking at, this is the inferior pubic ramus, which is a thin and flat part of pubis or the pubic bone that merges with the inferior ramus of the ischium.

I would like to also include here a bit of blood vessels associated to the urinary bladder. Right now, we’re looking at a lateral view of the male pelvis with the highlighted structure which is the superior vesical artery. Now, the superior vesical artery is a paired terminal branch of the umbilical artery, and in our illustration, you can see one of the superior vesical arteries, specifically, the right superior vesical artery. Just to say that these paired arteries supply the upper and middle segments of the urinary bladder.

Speaking also of veins here, you can now see from the coronal section, the venous plexus of the urinary bladder. Now, all these structures highlighted in green, these are or these collectively are known as the venous plexus of the urinary bladder. Now, this plexus is found primarily on the inferior aspect of the urinary bladder. It drains into the hypogastric plexus via the vesical veins.

Now that you just completed this video tutorial, then it’s time for you to continue your learning experience by testing and also applying your knowledge. There are three ways you can do so here at Kenhub. The first one is by clicking on our “start training” button, the second one is by browsing through our related articles library, and the third one is by checking out our atlas.

Now, good luck everyone, and I will see you next time.