Structure of the uterus and vagina seen on an anterior coronal section.
Hey everyone! This is Nicole from Kenhub, and welcome to our tutorial on the uterus and the vagina. The uterus and vagina are both important parts of the female reproductive system – the former being the organ that nourishes fertilized ovum and the latter being the muscular tube through which a baby passes as well as menstrual flow. But before we get into that, we're going to spend some time describing some of the structural features of both – first the uterus then the vagina and the vulva.
So, let's just begin by setting up some expectations about what we're going to cover in this tutorial. And as indicated by the title in this tutorial, we're going to be focused on identifying different parts of the uterus and the vagina as well as the muscles that support them. As damage to the muscles during a surgical procedure can result in urological and rectal problems, it's important to understand how the structures of the uterus and the vagina and the muscles that support them interact with each other but also firstly it's important to have an idea about what the structures look like and where they are located.
So, in order to do that, we're going to focus on this particular coronal section of the pelvis with our uterus in its entirety up here, our uterine tubes or our fallopian tubes, and our ovaries over here and our vagina in coronal section over here. And, of course, we're located in the pelvis so we can see the bony sections of the pelvis highlighted at the margins of these images and we'll point these out a little bit more on the next slide. And as we pass through each structure, we're also going to have a brief chat about their function and so on, but some of these functions and aspects such as menstruation, labor and blood supply and so on will mostly be covered in other tutorials.
So as is the case when we're identifying elements in a single image, we're going to begin by starting with the bones or the osseous elements of the pelvis and reproductive system. And in this image on the left, we can see the iliac bone highlighted in green. And the uterus, as we can see, is clearly level with the iliac bone and, in general, the uterus is located within the pelvic cavity – the body cavity which is bounded by the bones of the pelvis. And on our right image here, we have a visual of the vagina which runs down from the iliac bone to the inferior pubic ramus. And the vagina can vary from around 8 to 10 centimeters in length although it can also vary on either end of the spectrum.
And the ischium cannot be seen as it lies posteriorly to the elements featured in these images but the ischial spines which are inward projections of the ischium around the pelvic rim are important as a landmark for labor as the descent of the fetal head is taken in relation to the spines.
And now we're back at our image of the uterus and the vagina and here we have highlighted the uterus in green. And the uterus or the womb is a long hollow organ in the female pelvis that is around about 8 centimeters long and, as we mentioned, it plays an important role in human reproduction as it’s the site of implantation and nourishment of the fertilized ovum. In this image, however, we're going to talk about the distinct anatomical regions of the uterus visible before moving on to discuss its relationship to neighboring anatomical structures.
So, in this image, we have the fundus of the uterus highlighted in green and, interestingly, the word fundus is a Latin word meaning "ground". And while it's not wrong to think of the fundus of the uterus as the base of the organ especially when examining the uterus by the vagina with a digital exam, the fundus actually lies above the cervix and vagina when a female is standing which we can see in this image. And the fundus is particularly significant when determining the growth rate of the fetus as its growth is determined by the height of the fundus. And though it's not really visible in this image, the corpus or the body of the uterus is the part of the uterus that lies between the fundus and the cervix which is down here. And the corpus is, of course, important to note as it is a major part of the uterus as it is the site of fertilization as well as the gestation of the fetus during pregnancy.
And now we're here at the cervix which is literally the neck of the uterus. And the cervix is the most inferior portion of the uterus lying subperitoneally and we can see it highlighted in green and sticking into the vagina on this slide. And the cervix can be defined as a narrow neck of tissue that connects the vagina with the uterus. The cervical canal which we can't see in this image is around about 2.5 centimeters long and has a lower portion which is referred to as the vaginal portion. The part of the vagina that's lying above the attachment of the vagina is known as the supravaginal portion which we can't really see here but if you can imagine the cervix running along here then we have the supravaginal portion of the cervix above the vagina – supra being Latin for "above" and the vaginal portion sticking out below.
It's also worth mentioning now the parametrium which is a type of fibrous tissue. And the parametrium separates the supravaginal portion of the cervix from the bladder which is anterior to the uterus although we can't see the parametrium or the bladder on this image.
And while we're here, we might as well talk about the orifices of the uterus which I'm going to do briefly by bringing in extra imaging over here. And we can see in this image, the uterus stretched out with the fundus up here, the body over here, the cervix down here and the vagina below it just here. And the uterus has two orifices – the internal orifice or the internal os and the external orifice or the external os. And the internal orifice is significant as it is the opening of the cervix into the corpus of the uterus while the external orifice is the opening of the cervix into the vagina. And as we mentioned before, the cervix has a cervical canal which is around about 2.5 centimeters long opening up into the vagina which is down here.
So now we've pointed out some of the structures of the uterus on our image, we'll now turn to discussing some of the anatomical relationships of the uterus. So, in this image, we have highlighted in green the uterine tubes. And the uterine tubes are tubular structures which arise from the posterolateral sides of the fundus of the uterus as we can see here on this image and they're more commonly known as fallopian tubes or salpinges for those of you in other parts of the world. And they provide an anatomical route between the ovaries and the uterus. And we'll talk about the process of fertilization in another tutorial a little bit more extensively but basically these tubes provide a passage through which ovum can pass.
The ovaries are ovum-producing organs and are both gonads and endocrine glands. They're located at the ovarian fossa, a region located beneath the external iliac artery and in front of the ureter and the internal iliac artery. And, of course, we can see the ovaries hanging out next to the uterine tubes just here. And as we were speaking of the ureters, we might as well point them out so they are here highlighted in green, and you can see these traveling behind the uterine tubes and the ovaries. And, of course, the ureters arise from the kidneys and carry urine to the bladder. And, as you can see, the ureter is initially located superficially to the external iliac vasculature – the elements of which we will discuss next.
So, the first element of the vasculature we're going to have a brief look at is the external iliac artery which is highlighted in green on the image here above the external iliac vein here and medial to the psoas major muscle over here. And, as we mentioned on the slide before, the ureters run superficial to the vessels and we can see it running along just here. And the external iliac artery is a branch of the common iliac artery which in turn comes off the abdominal aorta. And, as we mentioned before, the external iliac vein is located inferior to the external iliac artery and is superolateral to the ovary, and we can see it here in relation to our structures right now. And the external iliac vein is the continuation of the femoral vein inside the abdomen fusing with the internal iliac vein to form the common iliac vein which in turn terminates in the inferior vena cava.
So, a very important structure that's worth mentioning as we return to the full view of this image of the uterus and the vagina is the round ligament. And the round ligament is an important structure as it maintains the anteflexion of the uterus and attaches the anterior aspect of the uterus to the groin. And as we can see, the round ligament originates from either side of the uterus at the uterine horns which is where the uterine tubes enter the uterus and travels anteriorly to enter the deep inguinal ring and from here then enters the inguinal canal to finally attach to the labia majora.
So, as we mentioned before, the uterus sits in the pelvic cavity between the rectum and the bladder – the bladder being anterior to the uterus and the rectum being posterior to the uterus. And then a close up with our main image of the uterus in the vagina, we can see the rectum just behind the fundus of the uterus here while in our sagittal view below of the rectum, we have the corpus and the fundus of the uterus highlighted in green with our bladder anterior and our rectum posterior. And in the image below, we can also see the anteflexion of the uterus as the corpus and the fundus rest on top of the bladder.
And in this slide, we're going to take a look at another important ligament of the uterus which is the transverse cervical ligament also known as the cardinal ligament or Mackenrodt's ligament and this is here highlighted in green. And the transverse cervical ligament is considered an extension of the broad ligament which is not visible here but is a fold of peritoneum that connects the uterus, ovaries and fallopian tubes to the sides of the pelvic wall and connects the cervix to the fascia of the obturator internus muscle around about the level of the ischial spine.
The transverse cervical ligament is a fibrous band connecting the cervix to the lateral fornix of the vagina which we can see around here and, externally, the ligament is also continuous with the fibrous tissue that encapsulates the uterine artery and vein. But, for those of you who are wondering, this little cross-section here is actually the ureter, not the uterine artery, and it’s the ureter as it heads into the bladder which is anterior to this image so just make sure you make note of that. And, clinically, the transverse cervical ligament can get damaged during hysterectomies due to its proximity to the ureters.
And, of course, let's talk a little bit about the obturator internus muscle which originates in the obturator membrane and the ischiopubic membrane before exiting the pelvic cavity via the lesser sciatic foramen to insert on the greater trochanter of the femur. And the obturator internus muscle is a fairly major muscle of the hip contributing to the lateral rotation of the femur and femoral abduction when the hip is flexed. And, as we mentioned before, the transverse cervical ligament is connected to the fascia overlying the obturator internus.
So, thanks for sticking with me as we've made our way through the uterus and now we'll move on to talk about the parts of the vagina we can see in our main image of the uterus and the vagina.
So, the vagina is a muscular tube in the female genital system and it’s a tube that communicates the cervix of the uterus to the external genitalia and it's roughly about 8 to 10 centimeters long. And the vagina has multiple roles facilitating not only sexual intercourse but also menstruation and childbirth. And as we can see in this image, the vagina is located between the uterus and the vulva.
So now that we've pointed out the vagina, let's now take a look at the structures that are surrounding the vaginal canal. As you can see, the vagina is surrounded by both fat and several different muscles so we'll approach the structures closer to the uterus first before moving on to structures closer to the vulva in a medial to lateral approach. The tissues surrounding the vagina are referred to as the paracolpium. And as you can see, the paracolpium mostly consists of fat, connective tissue and vasculature.
And in this slide, we have the levator ani muscle highlighted in green. And the levator ani muscle has three components namely the puborectalis muscle, the pubococcygeus muscle and the iliococcygeus muscle and all of these are attached to various parts of the lesser pelvis. The levator ani is really a musculotendinous sheath that makes up the pelvic floor supporting the viscera of the pelvic cavity and the various structures that pass through it and they're also known as the pelvic floor muscles for those of you who are involved in childbirth or yoga classes or Pilates classes or any kind of anatomical work that relate to the core muscles. And the levator ani helps with urination and defecation as well as continence.
And as we can see in this image, in females, some of the levator ani's fibers wrap around the vagina – usually fibers of the pubococcygeus muscle – and this muscle is called the pubovaginalis muscle while other fibers terminate in the perineal body. And the muscle highlighted now in green is known as the deep transverse perineal muscle and this muscle lies in the perineum arising from the inferior rami of the ischium and inserting into its contralateral muscle on the other side, and its role is to fix the central tendon of the perineum also known as the perineal body and also to help the expulsion of the last drops of urine. And, in females, the deep perineal muscle is pierced by the vagina which we can see in this image. And in this image, we can also see the artery of the bulb of the vestibule crossing the deep transverse perineal muscle which is coming off the internal pudendal artery roughly around about here.
And now we're going to have a little bit of a chat about the vulva. And the vulva includes all the external female genital organs namely the mons pubis which is a mass of subcutaneous adipose tissue anterior to the pubic symphysis, the labia majora or the outer lips of the vagina, the labia minora or the inner lips of the vagina, and the clitoris. The vulva also includes the external openings of the urethra and the vagina – the former otherwise known as the urinary meatus and the latter otherwise known as the vaginal opening – and together these structures which open up between the labia minora are referred to as the vulval vestibule. And our highlighted green section on this image consists of the vestibule at the level of the vaginal opening which we can see here and the urinary meatus is anterior to this cross-section so we won't be able to see it.
Let's now move on to discussing the structures surrounding the vulval vestibule in the pelvic floor. So as we can see in this image, we have the vestibular bulbs highlighted in green and as we mentioned before, we have the artery of the vestibular bulb providing blood supply just here. And the vestibular bulbs also known as the clitoral bulbs are aggregations of erectile tissue and they are some of the parts that make up the internal part of the clitoris. The vestibular bulbs run along the lateral walls of the vestibule medial to the bulbospongiosus muscle and the clitoral crura and they corresponds to the bulb of the penis in a male.
And as we can see in the image, over the vestibular bulb, there's a little muscle covering it and this muscle is called the bulbospongiosus muscle. And the bulbospongiosus muscle is a superficial muscle that arises from the perineal body as well as the fascia of the bulb of the vestibule to insert in the corpus cavernosum of the clitoris. And it's innervated by the deep branch of the perineal nerve which is a branch of the pudendal nerve and its role is to close the vagina creating the feeling of orgasm and to contribute to clitoral erection. And it's important to note that in both men and women, the bulbospongiosus can help empty the urethral canal after urination.
So, it might be a little bit hard to see in this image but this is a really small arterial structure highlighted laterally to the bulbospongiosus muscle and this structure is known as the perineal artery, and I'll just point it out with my mouse as it’s a little bit tiny. And the perineal artery is a branch of the internal pudendal artery and it lies in the superficial perineal space between the bulbospongiosus and the ischiocavernosus muscle which is another muscle involved in maintaining female orgasm and which I'm pointing out with my arrow just here. And the perineal artery gives off both the transverse perineal arteries and the posterior labial arteries.
And the ischiocavernosus muscle which I mentioned on the previous slide arises from the inner surface of the ischial tuberosity and inserts into the crura of the clitoris which it also covers. And the function of the ischiocavernosus is to flex the anus and tense the vagina during orgasm as we briefly alluded to in the previous slide and for those of you who already know about these very intricate muscles, some of you will know that Kegel exercises can help tone the ischiocavernosus muscle. And down here on the lower image, we can see it running along the inner surface of the pelvis towards the clitoris.
So, in this image, I wanted to point out the clitoral crura which are literally the legs of the clitoris. And the clitoral crura are two erectile tissue structures that arise from the clitoral body which is anterior and medial to the crura not seen on this image. And from this clitoral body, the clitoral crura rise in a V-shape extending back around and lateral to the vestibular bulbs and the vagina. And during sexual arousal, the crura along with the corpus cavernosum which also make up the internal clitoris become engorged with blood and the crura are covered by ischiocavernosus muscle. And just to clarify what I said before, the external part of the clitoris that most people associate with external sexual arousal is called the clitoral body as we mentioned earlier or the glans. And in this image, we can't see it as it's anterior to the coronal section that is shown.
And, finally, the fascia covering all the tissues and the muscles that we've just mentioned is known as the perineal fascia which we can see highlighted in green. And the area that contains all of the tissues and muscles above is called the superficial perineal pouch.
And to finish this tutorial, I'd like to go over some clinical notes about the uterus and vagina. Firstly, I just want to bring up very briefly the role of the vagina as though the vagina appears to be a narrow tube, it’s a very, very flexible organ as during sexual arousal, the vagina can expand to around about 200% while during childbirth the vagina can expand to allow a 3-kilogram baby to pass through. And as its muscular tissue, it also provides pulsatile contractions to assist in the downward passage of the baby.
And I also just wanted to briefly chat about the pH of a vagina. A healthy vagina of a woman of childbearing age is acidic with a pH range of around 3.8 to 4.5 and it's primarily made up of lactobacillus species. The acidity which is maintained by the lactobacillus bacteria is provided by the production of lactic acid and hydrogen peroxide and the acidity also functions to retard and prevent growth of various strains of pathogenic microbes. And when this acidity is compromised, the number of lactobacillus bacteria is reduced, the pH rises, and infections are more likely to occur.
And, of course, when the vagina becomes infected, it can become inflamed in a condition called vaginitis. And vaginitis which we must remember is a general term for the inflammation of the vagina rather an infection itself can be very painful as it often results in itching, discharge and pain. And vaginitis can be caused by several afflictions some of which include bacterial vaginosis which is an excessive growth of one of the normal bacteria of the vaginal flora, vaginal candidiasis which is otherwise known as a yeast infection, and trichomoniasis, a parasite transmitted through sexual intercourse, as well as other sexually transmitted infections such as gonorrhea and chlamydia.
And I just wanted to talk briefly about cancer. So, there are two main types of cancers that can arise in the vagina and the uterus and these are cervical cancer and vaginal cancer. Cervical cancer which is cancer of the cervix arises from the human papilloma virus or HPV which is a commonly contracted sexually transmitted infection and various strains of these can currently be vaccinated against but as HPV is generally found in around about 80% of the population at any one time, early detection is also recommended. And a Pap smear, which is a routine examination, involves collecting cells from the outer part of the cervix with a tool called a speculum. And a Pap smear will identify epithelial changes which can be classified within the CIN system of cervical dysplasia and generally CIN refers cervical intraepithelial neoplasia.
Vaginal cancer is a rare condition that is related more to old age and its symptoms include abnormal vaginal bleeding or vaginal discharge. Vaginal prolapse is a condition that can occur as women get older where they have weakened pelvic muscles. It's characterized by a part of the vaginal canal protruding from the opening of the vagina.
And that concludes our tutorial on the uterus and the vagina for today. Thanks again for watching.
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