Hello, everyone! This is Joao from Kenhub, and welcome to another anatomy tutorial where, right now, we’re going to be talking about the female pelvic viscera and perineum.
What I’m going to be doing on this tutorial is looking at this image that you see now popping on the screen, which is a parasagittal section of the female pelvis. We’re looking at it from the right view.
And what we’re going to do is describe all the structures that you can see here. There are a few organs here that we need to describe and also some boundaries and other structures that are somewhat related or found nearby these organs.
So there’s a lot to be covered here on this tutorial. I will be providing also a lot of information that you need in order to have some sort of solid background on all these structures and understanding what is going on on this important region of the body.
Now, sit back, relax, and enjoy this tutorial, and try to absorb as much information as you can.
The first thing that I’m going to be doing is describing an area here. I just said that we’re going to be covering the female pelvic viscera, which is “viscera” is a fancy word for “organ.” So we’re going to be describing these organs that you find here on the female pelvis. But also, another area that we’re going to be briefly mentioning here is the perineum.
And the perineum is generally defined as a segment between the anus and the genitalia, both in female and also males. And you can also see here on this image here where the anus is and also the female genitalia. So this is the area between the anus and the female genitalia, and the region of the body inferior to this structure here, which is known as the pelvic diaphragm.
There are a few structures related to the perineum that are worth mentioning here, some that we call deep boundaries of the perineum, and there is an anterior one which is defined as the pubic arch and the arcuate ligament of the pubis.
Posteriorly, we’re going to see the tip of the coccyx, which you can see here, this bone here, which will be also defining the deep posterior boundaries of the perineum. And on both sides, we’re going to see the inferior rami of the pubis, and the ischial tuberosity, and also the sacrotuberous ligament.
Superiorly, as I mentioned before, the deep boundaries of the perineum is going to be, then, the pelvic floor or the pelvic diaphragm, and also inferiorly, then, we’re going to be seeing, then, skin and fascia.
On this image, we’re going to be seeing some bony structures that we’re going to be briefly talking about them on this tutorial, including the inferior pubic ramus, the superior pubic ramus, and also the fifth lumbar vertebra.
And let’s start off by highlighting here what is seen or what is known as the inferior pubic ramus. And the inferior pubic ramus is a part of the pelvis. It is a relatively thin and flat part of the pubic bone. It projects laterally as you can see here. As you notice also, this is the midline of the body, and this is projecting laterally and downward from the medial end of the superior ramus.
This structure becomes narrower as it descends and joins, then, the inferior ramus of the ischium below the obturator foramen.
The next one that we’re going to be highlighting is then found superiorly, and we’re going to call it, then, the superior pubic ramus. The superior pubic ramus is a part of the pubic bone which forms a portion of the obturator foramen. This structure extends from the body of the pubic bone to the median plane where it articulates with the other superior pubic ramus on the opposite side.
Now, the next bone that we can see here, now highlighted, is known as the fifth lumbar vertebra, also commonly known as L5. And the fifth lumbar vertebra is, then, the largest, and the strongest, and also found on the lowest portion of the vertebral column. So you can also say that this is the lowest of the lumbar vertebrae.
As the last of the lumbar vertebrae, the L5 will bear 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 also strongest lumbar vertebrae, but it is also the most susceptible to stress-related injuries.
And as you can see here, L5 is located in the lumbar spine (lower back) inferior to this one that you only see a little bit, which is L4, and superior to, then, this bone here, which is known as the sacrum.
Now that we just covered the main bony structures here, just for a little bit of location and to see what is going on on here on this image, we’re now ready to move on to, then, a few muscles that are important to highlight here on this tutorial, especially the ischial cavernosus, the levator ani muscle, and the external anal sphincter.
We’re going to start, then, with the first one on the list that you now see here highlighted, and keep in mind that we’re now looking at the inferior or caudal view of the pelvis, where we can clearly see here the ischial cavernosus muscle, this muscle that we’re going to describe now for you.
Now, the ischial cavernosus is a muscle found just below the surface of the perineum, and in terms of origin points, it’s going to be originating from the ramus of the ischium.
The insertion of the ischial cavernosus will be, then, the corpus cavernosum of the clitoris, and this muscle will be innervated by the perineal nerve.
When it comes to the different actions or functions associated to this muscle, it will be compressing the crus of the clitoris and also forces blood in its sinuses into the distal part of the corpus cavernosum.
A bit of a fun fact, you have probably heard of Kegel exercises, which are also known as pelvic floor exercises, which can help tone the ischial cavernosus muscle.
The next muscle that we saw on that list that you now see here, highlighted in green, is known as the levator ani muscle. And we did not show you on the previous image where the ischial cavernosus is. This is where you can find the muscle on this particular image.
Now, continuing on with the information related to the levator ani, this muscle is a broad, thin muscle located on the sides of the pelvis. It forms the pelvic diaphragm together with another muscle known as the coccygeus muscle.
A bit on the origin points for the levator ani, it will be, then, the inner surface of the side of the lesser pelvis.
When it comes to its insertion point, it will be two points that we need to highlight here: the inner surface of the coccyx and also the anococcygeal ligament. These two structures will serve as an insertion point for the levator ani muscle. And you can see them a bit here on this image. This is where the insertion point for the levator ani will be happening.
The levator ani will be innervated by… or mostly innervated by the pudendal nerve, the perineal nerve, and also the inferior rectal nerve.
When it comes to the different functions or actions associated to the levator ani, you can see clearly on this image that this muscle is going to be supporting the organs or the viscera in the pelvic cavity. You can clearly see here how it’s serving as a support system for all these organs that sit above it.
The muscle will also be surrounding various structures that pass through it.
We’re now ready to move on to the next muscle here that you see highlighted, which is known as the external anal sphincter, and 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 measures about eight to 10 centimeters in length from its anterior to its posterior extremity and is about 2.5 centimeters opposite to the anus. So when defecation occurs, the sphincter muscle will retract.
An important fact to also add here to this list of facts that we just mentioned, that the external anal sphincter consists of two layers or two strata known as the superficial and deep layers.
We’re still continuing on to the different origins, insertion, and also innervations, and functions of the external anal sphincter. Now, we’re looking at the muscle from an inferior view or a caudal view of the pelvis, as we’ve seen with the ischial cavernosus.
Now, what you can see here, in terms of origin points, the anococcygeal raphe will serve as an origin point for the external anal sphincter, while it’s going to go and insert into the central tendon of the perineum.
The innervation of the external anal sphincter will be happening thanks to the branches from the fourth sacral and also twigs from the inferior rectal branch of the pudendal nerve.
In terms of functions or actions associated to this muscle, the action of this muscle, the external anal sphincter, is relatively peculiar. It is like other muscles, always in state of tonic contraction, and in the presence of no antagonistic muscle, it keeps the anal canal and orifice closed. So this is important to also add here to the list of functions.
Another thing that is worth mentioning is that it can 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 can help fix the central point of the perineum so that the bulbocavernosus may act from its fixed point.
Now that we covered these three main muscles that we find on this image, we’re now ready to move on and talk about the two blood vessels that we see here on this image, right here. Notice here, superiorly, you can see these two blood vessels. And we’re going to be talking about them.
These blood vessels include the common iliac artery and also a vein: the common iliac vein.
We’re going to start off here with the common iliac arteries. A word on these arteries that you’re now seeing from an anterior view of the open abdomen, you can clearly see here the common iliac arteries.
And the common iliac arteries are two large arteries, as you can see here, also on this image, that originate at the aortic bifurcation here. So you have here the abdominal aorta and this bifurcation, then, give origin to the common iliac arteries.
And this bifurcation happens at the level of the fourth lumbar vertebra.
These 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 muscles to their bifurcation at the pelvic rim in front of the sacroiliac joints.
The common iliac arteries will, then, bifurcate into two other important arteries known as the external iliac artery, which you can see here, and also the internal iliac artery.
Now, in this image of the female pelvis here, we’re highlighting what is known to be as the right common iliac artery. Remember that we’re looking at the female pelvis from the right view, and hence, the fact that we’re looking, then, specifically at the right common iliac artery.
And both the right and left common iliac arteries receive blood from the abdominal aorta and are distributed to the pelvis and the lower limb as the femoral artery on the corresponding… on their corresponding sides.
Just a little bit behind, we see another one that we’re highlighting, this time, a vein known as the right common iliac vein. And both right and left 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, and then they drain blood from the pelvis and lower limbs and drain, then, to the inferior vena cava, which then goes, takes all that deoxygenated blood back to your heart.
Now that we covered the two blood vessels that we see here on this image, it is time for us to cover a few tendons, ligaments, and fascia of the female pelvis and perineum that can be seen specifically here on this image. And the list includes the central tendon of the perineum, the proper ovarium ligament, the round ligament of the uterus, and also the visceral pelvic fascia.
We will start with the very first one here on our list, seen now highlighted in green, then, this is the central tendon of the perineum. And this central tendon of the perineum can also be called, sometimes, as the perineal body, is a pyramidal, fibromuscular mass in the midline of the perineum.
And in the female pelvis, as you can see here, it’s found between the vagina and also the anus, and about 1.25 centimeters in front of the anus, as you can see here.
The perineal body is essential for the integrity of the pelvic floor, particularly in females. It’s rupture during delivery leads to widening of the gap between the anterior free borders of the levator ani muscle on both sides, thus predisposing the person to prolapse of the uterus, the rectum, or even the urinary bladder.
At the central tendon of the perineum, there are a few muscles that will be converging here and also attaching to this point, and these include the external anal and urinary sphincters, the bulbospongiosus muscle, the superficial and deep transverse perineal muscles, and the anterior fibers of the levator ani.
We are now ready to move on to the next structure that you see here, highlighted in green. And this is known as the proper ovarian ligament, or simply called the ovarian ligament.
This ligament is comprised of muscular and fibrous tissue. It extends from the uterine extremity of the ovary to the lateral aspect of the uterus—just below the point where the uterine tube and uterus meet.
This ligament runs in the broad ligament of the uterus, which is a fold of peritoneum rather than a fibrous ligament. To be more specific, it is located in the parametrium, and the proper ovarian ligament connects the ovary to the lateral surface of the uterus.
Next structure we’re going to be highlighting here is also known as a ligament. This is known as the round ligament of the uterus. And this ligament originates at the uterine horns, in the parametrium, and the round ligament leaves the pelvis via the deep inguinal ring, passes through the inguinal canal, and continues on to the labia majora, where its fibers then spread and mix with the tissue of the mons pubis.
This ligament has a roll, and the main function of the round ligament is maintaining the anteversion of the uterus, a position where the fundus of the uterus leans ventrally during pregnancy.
Normally, the cardinal ligament is what supports the uterine angle, and when the uterus grows during pregnancy, the round ligaments can stretch, causing, then, pain.
The round ligament of the uterus is supplied by the artery of the round ligament, otherwise known as Sampson’s artery.
We’re going to move on to another structure that we’re now highlighting, which is known as the visceral pelvic fascia, and this is—as you probably know, a fascia is a structure of connective tissue that surrounds muscles, groups of muscles, blood vessels, and nerves, binding some of these structures together, while permitting others to, then, slide smoothly over each other—and the visceral pelvic fascia is attached to the diaphragmatic part of the pelvic fascia and has been subdivided according to the viscera to which it is related to.
We will be quickly listing the divisions of the visceral pelvic fascia here. So the anterior part is known as the vesical layer. It forms the anterior and lateral ligaments of the bladder, while the middle part, the transverse cervical ligament, is perforated by the cervix.
Finally, we’re going to be finding the posterior part, which is known as the rectal layer, which passes to the side of the rectum, forms a loose sheath for the rectum, but is firmly attached around the anal canal.
We’re going to be highlighting this structure now that you see. This is a serous membrane known as the peritoneum. And as I mentioned, this is a serous membrane that forms the lining of the abdominal cavity.
The peritoneum will be supporting the abdominal organs and also serves as a conduit for blood vessels, lymph vessels, and also nerves that belong to these organs specifically.
We are now ready to move on to the next set of structures that are known as anatomical spaces. We’re going to be covering two, specifically the rectouterine pouch and also the vesicouterine pouch.
Let’s start with the very first one here on the list that you see here, highlighted in green. This is, then, known as the rectourterine pouch. And the rectouterine pouch is the extension of the peritoneal cavity between the rectum and the posterior wall of the uterus in the female human body.
As it is the furthest-most point of the abdominopelvic cavity in women, it is a site where infection and fluids typical collect.
The next one that we’re going to be highlighting here, that if you remember from the previous list, yes, this is the vesicouterine pouch or excavation. This is a second, but a-bit-shallower-than-the-previous-one-that-we-saw pouch that forms from the peritoneum over the uterus and bladder, as you can clearly see here on this image. The uterus is found here and then the bladder. And you notice clearly here, highlighted, the vesicouterine pouch.
Now, this pouch is close to the anterior fornix of the vagina, as you can also see here. This is where you can find the vagina, just below the uterus.
We are now ready to move on to the next set of structures, now, related to the different components of the digestive system that we can see here on this image. So we’re going to be talking about the sigmoid colon, the sigmoid mesocolon, and the taenia coli, and also the rectum.
We’re going to start off with the very first one here on our list, now seen highlighted in green. This is known as the sigmoid colon. And the sigmoid colon or pelvic colon is a part of the large intestine that is closest to the rectum and anus. This structure forms a loop that averages about 40 centimeters in length and normally lies within the pelvis, but due to its freedom of movement, it’s liable to be displaced into the abdominal cavity.
This 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. It, then, curves on itself and turns toward the left to reach the middle line at the level of the third piece of the sacrum where it bends downward and ends in the rectum.
Now, there are certain structures that you can find behind the sigmoid colon, and those include the external iliac vessels, left piriformis muscle, and left sacral plexus of nerves.
In front of it, we’re going to find that it is separated from the uterus by coils of the small intestine.
The sigmoid colon is going to be also innervated by the inferior mesenteric ganglia and sacral nerve.
This sigmoid colon also has a function worth mentioning here on this tutorial. Well, the function of this structure is to expel solid and gaseous waste from the gastrointestinal tract. The curving path it takes towards the anus allows it to store gas in the superior arched portion, enabling the colon to expel gas without excreting feces simultaneously.
We’re now ready to move on to the next structure that I’m now highlighting in green. This is known as the sigmoid mesocolon. And the sigmoid mesocolon is a fold of peritoneum that attaches to the sigmoid colon that we just talked about on the previous slide to, then, the pelvic wall, and one of the four mesenteries of 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.
So this is enough information about this structure. We’re ready to move on to this new highlight here. This is the taenia coli.
The taenia coli (plural) are three separate longitudinal ribbons of smooth muscle on the outside of the sigmoid colon. They are visible and can be seen just below the serosa and fibrosa layers, and the bends can converge at the root of the vermiform appendix.
The taenia coli contract lengthwise to produce what is known to be as the haustra, which are the bulges that you find on the colon—these bulges that you can clearly see here on the coli. This is what we call haustra.
Ready for the next one, a bit further down, we’re highlighting now one structure that we already mentioned, known as 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 or the end of the sigmoid colon, just at the level of the third sacral vertebra.
The rectum terminates at the level of the anal rectal ring, the level of the puborectalis sling.
The rectum also has an important role worth mentioning, and this structure acts as a temporary storage site for feces. As the rectal walls expand due to the materials filling it within, stretch receptors from the nervous system located in the rectal walls stimulates the desire to defecate.
If this urge is not acted upon, the material in the rectum is often returned to the colon where more water is absorbed from the feces. If defecation is delayed for a prolonged period, constipation and hardened feces may result then.
We’re now done covering the different components of the digestive system to now move on to the different components of the urinary system that we can see here on this image, and we can clearly see the ureters and also the urinary bladder.
Now, let’s start with the very first one that you see on the list. We’re looking again at an anterior view of the open abdomen so I can show you here the next structures that we’re going to be talking about. If you can see here on both sides, these are the ureters.
And the ureters are tubes made of smooth muscle fibers that propel your urine from the kidneys to the urinary bladder. In the adult, the ureters are usually 25 to 30 centimeters and about three to four millimeters in diameter.
The ureters, as you can clearly see here on this image, they arise from the pelvis of each kidney, which is found right about here on both sides, as you can see, and then they descend on top of the psoas major muscle and reach the brim of the pelvis. The psoas major muscle should be hidden a bit here, but you can see how the ureters, then, reach the pelvis here.
Here, they cross in front of the common iliac arteries, which can also be seen clearly here, the two common iliac arteries. They, then, pass down along the sides of the pelvis and finally curve forward and enter the bladder from its left and right sides, which you can also see here.
Now, we’re looking at a female pelvis where you can see the uterus here and the bladder, and you notice here the connection, then, with the ureters and the bladder and on each side.
In females, the ureters pass through the mesometrium and under the uterine arteries on the way to the urinary bladder.
An effective phrase for remembering this anatomical relationship is water (ureters) under the bridge (uterine arteries or vas deferens – if we’re talking about males).
Now, back to this image here, now, we’re looking at the right ureter, but just to add that 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 to this organ here that we just talked about. This is known as the urinary bladder, a hollow, muscular, and elastic organ. The bladder will be sitting or found here, as you can clearly see here on this image, on the pelvic floor.
Then, urine will be entering the bladder via the ureters, as we’ve seen before, and exits via, then, another structure known as the urethra.
It’s quite difficult to give an exact measurement for the volume of the human bladder, but different sources mention that we’re looking at between 500 to 1,000 milliliters.
On this tutorial, I would like to also give a word on the innervation of the urinary bladder. The bladder receives motor innervation from sympathetic fibers, most of which arise from the hypogastric plexuses and nerves, and also parasympathetic fibers which come from the pelvic splanchnic nerves and the inferior hypogastric plexus.
For the urine to exit the bladder, both autonomically controlled internal sphincter and the voluntarily controlled external sphincter must be opened.
Problems with these muscles can lead, then, to incontinence.
There’s also a role that we need to talk about related to the urinary bladder. This organ is going to collect urine that is excreted from the kidneys before disposal by urination.
We’re now done covering the different components of the urinary system to, then, move on to the different components of the reproductive system that we can see here on the female pelvis. We’re going to be talking about the labium majus, the labium minus, the vagina, the uterus, and the fallopian tube or tubes.
We’re going to start off with the very first one here on our list that we’re now highlighting. This is known as… singular as labium majus. Plural would be, then, labia majora. And there are two prominent longitudinal cutaneous folds consisting mostly of skin and adipose or fatty tissue that extend downward and backward from the mons pubis to the perineum.
Now, the outer surface is covered with skin and pubic hair and contains sweat glands and also the inner surface will be, then, free from hair and covered by mucus membrane.
In terms of the arteries that we’re going to be talking about related to this structure, to the labia majora, we’re going to be seeing, then, the deep external pudendal artery. And in terms of nerves, we’re going to be seeing the perineal branches of the posterior femoral cutaneous nerve.
There is also a function associated to the labia majora. So when standing or with closed legs, they usually entirely or partially cover the moist and sensitive inner surfaces of the vulva, which indirectly protects the vagina and urethra, much like the lips protect the mouth.
We’re now moving on to this one, this structure that you see now, highlighted in green, which is known as the labium minus, for plural would be, then, labia minora. There are two flaps of skin on either side of the vaginal opening that contain connective tissue but no fat, and they’re located between the labia majora.
In the front, each lip will divide into two parts, the upper part of each lip passes above the clitoris to meet the upper part of the other lip, forming a fold which overhangs the glans clitoridis. This fold is named the preputium clitoridis.
The lower part passes beneath the glans clitoridis and becomes united with its lowest surface, forming with the inner lip of the opposite side the frenulum clitoridis.
Now, the labia minora also will have an artery that is related to it, and this is the deep external pudendal artery.
And also an associated nerve which will be, then, the perineal branches of the posterior femoral cutaneous nerve.
And as we mentioned for the labia majora, there is also a function associated to the labia minora, and the main function of the labia minora is to lubricate the skin around the genitals and provide bactericidal secretions to help protect against infections.
We’re now ready to move on to the next structure that you see here, highlighted. I briefly mentioned on the previous slide. This is known as, then, the vagina. This is a muscular tube that extends upwards and slightly backwards from the vaginal opening to reach the uterus, as you can see here. Here is the uterus.
The vaginal canal sits between the bladder at the front and the rectum at the back as you can clearly see here on this image: the rectum and the bladder.
The mucus lining of the vagina constantly sheds its top layer of skin cells. This is a natural self-cleansing mechanism.
The vagina is surrounded and supported by pelvic muscles.
There is also a group of blood vessels that are associated to this structure, and they include the uterine artery, the vaginal artery, the uterovaginal venous plexus, the vaginal veins. So these are the group of blood vessels that will be supplying the vagina.
There is also a group of nerves worth mentioning. Sympathetic nerves will be, then, the lumbar splanchnic plexus. The parasympathetic will be the pelvic splanchnic plexus.
There is also a role or function associated to this structure. It will receive the penis during sexual intercourse and also provides a path for the menstrual blood and tissue to leave the body.
We’re going to move on to the next structure that you see here, highlighted, that I briefly mentioned before. This is known as the uterus. And the uterus is a major female hormone responsive reproductive sex organ.
One end, the cervix opens into the vagina while the other is connected to the fallopian tubes. And you can clearly see here on this image, this end here, the cervix will be then connecting to the vagina, while the upper portion is, then, connected to the fallopian tubes.
The uterus is located inside the pelvis immediately dorsal to the urinary bladder, as you can see here clearly on this image, and also ventral to the rectum.
The human uterus is pear-shaped and about 7.6 centimeters long, 4.5 centimeters broad (side to side), and three centimeters thick. The uterus can be divided anatomically into four segments: the fundus, the corpus, the cervix, and the internal os or the internal orifice of the uterus.
There are also arteries that are associated to or blood vessels that are associated to the uterus, and these include the ovarian artery, the uterine artery, and the uterine veins.
Some nerves that will be innervating the uterus include T11 to T12, the hypogastric plexus, the ovarian plexus, and S2 to S4.
There are also different roles associated to the uterus, and the uterus is essential in sexual response by directing blood flow to the pelvis and to the external genitalia, including the ovaries, vagina, labia, and clitoris.
The reproductive function of the uterus is to accept a fertilized ovum from the fallopian tube, which happened to be the next structures that we’re going to be highlighting here. The next structure—we only see one here, but you would expect, then, the left one—this is the fallopian tube, more specifically the right fallopian tube.
The fallopian tubes or oviducts are two narrow, hollow tubes that lead from either side of the top of the uterus, spreading outward and downward towards the ovaries.
There are few arteries that are associated to the fallopian tubes, including the tubal branches of the ovarian artery and the tubal branch of the uterine artery.
There’s also a main role here or a function associated to the fallopian tubes, and these tubes receive the ovum at ovulation and conducts it to the uterus where a fertilized egg may implant.