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Structure of the vagina, uterus, fallopian tubes and ovaries.
Hello everyone! This is Nicole from Kenhub, and welcome to our tutorial on the uterus and the ovaries. In this tutorial, we will be looking at these structures you can see on this particular image which is a coronal view of the vagina, uterus, uterine tubes, and ovaries stretched out. And these organs that you're looking at are the internal organs of the female reproductive tract, and we'll have a look at their structure and function as well as their supporting structures. And along the way, we'll also talk about any clinically relevant information in regards to these structures.
So, first, let's just begin with a little bit of an introduction to the function of the female reproductive system. And the female reproductive system is responsible for several functions. The first of which is producing the eggs necessary for reproduction which we'll talk a little bit more about later. It's also responsible for facilitating or creating the environment in which reproduction can occur and, finally, it's also responsible for producing the female sex hormones that maintain the reproductive cycle and play a direct or indirect role elsewhere in the body.
So, in this slide, we're going to have a look at the structures of the female reproductive tract in detail. And the first internal structure we will look at is the vagina which is highlighted in green on this slide. And the vagina is also known as the birth canal as the baby passes from the uterus through this passage during labor. And the vagina is a particularly multitasking organ as it has multiple roles and these roles include the facilitation of menstruation, childbirth and sexual intercourse. The vagina also plays a significant role in human female sexuality and sexual pleasure. Structurally, the vagina is a fibromuscular tube roughly 8 to 10 centimeters long across the posterior wall and about 7.5 centimeters across the anterior wall.
And, now, we're going to zoom in a little bit to get a closer look at our vagina. And as you can see here, part of the structure superior to the vagina in this image known as the uterus protrudes into the vagina. And to come back to our structures and their relationships to one another, the recess that is formed between the cervix and the vaginal wall is known as the vaginal fornix. And although this fornix is continuous, it is sometimes divided into an anterior fornix, posterior fornix and lateral fornix.
And now let's move on to our uterus. And the uterus also known as the womb also has several functions. The most important of which include its role as a host for the development of a fetus during gestation. The uterus also provides vaginal and uterine secretions and the last sperm to pass through the uterine or fallopian tubes in order to fertilize an egg. The uterus is about 8 centimeters long and can be divided into three main parts – the cervix which we mentioned on the slide before, the isthmus, and the corpus or the body. And the fundus is also an important part of the uterus which we'll talk a little bit about after the first three.
And let's now take a closer look at the parts of the uterus in more detail. And the first part of the uterus I want to look at is the cervix. And the cervix which is otherwise considered the neck or the narrowing of the vagina extends from the isthmus of the uterus which is around about here to the external os or the external orifice which is down here. And the cervix is around about 2.5 centimeters long and plays an important role in fertilization and childbirth. And another thing that's important to note about the cervix is that while some of it protrudes into the vagina, some of it does not. We talked a little bit about this earlier one in one of the earliest slides and the portion that projects into the vagina is called the vaginal portion while the portion that does not project into the vagina the vagina is called the supravaginal portion – "supra" being the Latin word for above.
And the cervix has two orifices or openings which are important to note – the internal orifice opening into the isthmus of the uterus which is the connection between the cervix and the body of the uterus and the external orifice opening into the vagina. And the canal between these two openings is referred to as the cervical canal. And, of course, down below we have the vagina as pointed out by this arrow.
A brief clinical note to make while we're here. So, cervical cancer is a common cancer associated with human papilloma virus or HPV. As HPV is a common sexually transmitted disease, its presence as well as the presence of the epithelial changes that cervical cancer can elicit can be detected with regular Pap smears. And the Pap smear involves opening the vagina with a speculum and collecting cells from the cervix in order to look for any precancerous or cancerous changes.
And let's now take a look at the next part of the uterus. And the second part of the uterus is known as the isthmus which you can see highlighted in green in this image. And the isthmus is a narrowing of the uterus that's around about 1 centimeter long connecting the cervix and the corpus of the uterus.
The third part of the uterus is referred to as the body though it's also known as the corpus. And as we can see, the body has a triangular-shaped lumen which houses not only the site for fertilization but also the fetus during gestation. The fundus as we mentioned earlier is also an important part of the uterus and though it's up top in this image, it's considered the base of the uterus. And the fundus is often measured in pregnancy to determine growth rates of the fetus.
So now we've examined the macroscopic anatomy of the uterus, we're going to move on to talk about its microscopic anatomy. And microscopically, the uterus is known to have three layers – the endometrium, the mucosa of the uterus; the myometrium, the smooth muscle layer of the uterus; and the perimetrium, the outer serous layer covering the uterus. We'll now have a brief look at each of these in detail.
The endometrium is the innermost layer of the three layers of the uterus and is also referred to as the uterine mucous membrane. The endometrium is lined with simple columnar epithelium and contains numerous tubular glands as well as a lamina propria. Histologically, the endometrium is divided into two layers – a functional layer and a basal layer. And both of these layers are important to note as the functional layer is the layer of blood that is shared in the process of menstruation when the uterus does not get fertilized during a female's monthly cycle and the functional layer regenerates from the basal layer after each shedding.
The myometrium is comprised of a complex of three smooth muscle layers. And the first layer that we're going to talk about is the subvascular layer which is a thin layer of smooth muscle that participates in the sealing of the uterine tubes and the separation of the endometrium during the menstrual cycle. The second layer of the myometrium is the vascular layer which is a strong layer of muscle that is well-perfused running around the uterus like a net and the vascular layer plays a major role during labor. The supravascular layer which is our last layer on our smooth layers of the myometrium is a thin sheet of crossing muscle fibers stabilizing the uterine wall. And the myometrium is a continuation of the muscle layers of the uterine tubes and the vagina.
The perimetrium or serosa is our outer layer of the uterus and is made up of mesothelium and a thin layer of loose connective tissue and it's continuous with the peritoneum in the pelvic and abdominal cavities.
So, now, we're going to briefly talk about the orientation of the uterus as it's quite important in clinical practice with regards to palpation as well as some clinical conditions and, in this image, which is a sagittal section of the pelvis, we can see our favorite organs. So, of course, our uterus is here, our bladder here, our rectum here and our vagina stretching out down here. And, of course note, that the uterus and vagina are located in between the bladder and the rectum with the body and the fundus of the uterus lying on top of the bladder. And I wanted to point out just a couple of features about the direction of the uterus mainly that in 90% of women, the uterus is both in anteflexion and anteversion.
Now, both of these refer to the forward tipping of the body of the uterus but I just wanted to point out the difference mainly that anteflexion refers to the long axis of the uterus and the cervix while the anteversion refers to the long axis of the cervix and the vagina. And I'm just going to draw a couple of lines on the slide here. So, here, we have the axis of the cervix and the uterus – so anteflexion - and as you can see anteflexion refers to the forward tipping of the uterus over the cervix. While now we have the axis of the cervix and the vagina or anteversion and we can see here that the cervix is tipping forward over the vagina. And in 10% of cases, the uterus can be retroverted while occasionally the uterus is in other positions.
So, now, let's move on to talk about the fallopian tubes or the uterine tubes as I think it's referred to in some other tutorials or the salpinges or the oviduct, as they're also sometimes called. And the fallopian tubes are important structures in the female reproductive tract providing a site for fertilization as well as providing passage for the transport of the ovum or egg from the ovaries to the body of the uterus. They're also the main connection between the uterine and peritoneal cavities. The two fallopian tubes are about 10 centimeters long and projects superolaterally from the body of the uterus at the uterine horns as we can see in this image. And the fallopian tubes consist of four main parts which I'll point out to you as we list them – the intramural part, the isthmus, ampulla, and the infundibulum.
So, now, of course, we're going to look at our parts of the fallopian tubes in detail and the first part we're going to look at is the intramural part, sometimes also called the interstitial part. And this part of the fallopian tube is located within the myometrium of the uterus and it's roughly about 1 centimeter long and 0.7 millimeters wide.
And the next part of the fallopian tube we're going to look at is the isthmus. And the isthmus is a lateral continuation of the intramural part and, as we can see, it's a rounded muscular part of the fallopian tube and is also the narrowest part of the tubes that's around about 3 centimeters long and between 1 and 5 millimeters wide.
The third part of the tube is referred to as the ampulla and, as we can see, it is the longest and widest part of the fallopian tube with a diameter of 1 centimeter at its widest point. And the ampulla is around about 5 centimeters long which is roughly over half the length of the tube and also has a thin wall, a folded luminal surface, which is usually the site of fertilization.
And the last part of the fallopian tube that we're going to discuss is the infundibulum. And the infundibulum which is the most distal part of the fallopian tube is funnel-shaped opening into the peritoneal cavity at the abdominal ostium. And this finger-like mucosal projections which we can see attached to the distal end of the infundibulum are what we would refer to as fimbriae. And, of course, let's zoom in a little and have a closer look at these fimbriae. And these finger-like projections of which they're roughly 25 are basically like little fingers that drape over the ovary and help gather the ovum from the ovaries and into the fallopian tubes. And the fimbriae are 1 millimeter wide while the longest of the fimbriae – the ovarian fimbria – attaches to the superior aspect of each ovary.
And just to go back to our proximal part of our fallopian tube, an important thing to remember about the fallopian tubes is that they connect the uterine cavity to the peritoneal cavity. And the point where the fallopian tubes open into the uterine cavity is called the uterine opening of the oviduct or the fallopian tube. And as we can see, the proximal part of the opening forms the utero-tubal junction.
So before we move on to look at some other structures, I'd like to mention a few clinical points about the fallopian tubes. So, the most common pathology affecting the tubes is salpingitis, which is inflammation of the fallopian tubes. And salpingitis is usually the result of a bacterial infection such as gonorrhea or chlamydia. Salpingitis is a fairly serious condition as without treatment, it can result in infertility. And common symptoms which are often related to the bacterial infection include fever, pain, lower back pain, and nausea and vomiting; however, it can also be asymptomatic.
With regards to birth control, ligation or tying of the fallopian tubes is an effective surgical method. Ligation of the fallopian tubes prevents fertilization of the oocytes – the immature egg – which then degenerates and becomes absorbed. An ectopic tubal pregnancy occurs when a fertilized ovum implants in the mucosa of the fallopian tubes which can occur if the fallopian tubes are obstructed. And it's best if ectopic tubal pregnancies are detected early as if not, they can result in the rupture of the fallopian tube and commonly an emergency surgery.
So now let's move on and have a look at the ovaries. And the ovaries are a bilateral pair of flattened egg-shaped discs which themselves are egg-producing organs as well as endocrine glands analogous to the testes in a man. In women, however, this structure is found in the pelvic cavity on either side of the uterus which we can see in this image. In order to understand the function of the ovaries, we have to look at the microscopic anatomy and it is important to note that the ovarian follicles are the basic units of the ovaries. And if you follow my mouse here, you can just see one in the highlighted image, this small dark cavity here, though it's more correctly called a Graafian follicle, which we'll talk about in the next slide. But, essentially, a follicle is a cyst-like sac in the ovary that embeds an oocyte which is an immature ovum or egg cell.
The oocytes mature in the follicles and once they have finished their maturation process, they become what we would now refer to as an ovum. And the ova which is the plural form of ovum are released by the follicles into the fallopian tubes in order to be fertilized. The ovaries released these egg cells every 3 to 4 weeks in the average adult female and are shed by the body in the process of menstruation.
So, now, that we've spoken briefly about the ovary as a structure, let's now have a look at some structures that may be found within the ovaries. And the first structure we will look at is this structure here highlighted in green which I pointed out on the last slide – the tertiary follicle. And, as I mentioned before, the follicles develop through different stages during the menstrual cycle and when the follicle is fully matured, it's referred to as a tertiary follicle. It's also sometimes called a Graafian follicle named after the first man to describe their development. And during the process of ovulation, usually only one follicle fully develops, the other follicles degenerating in a process called atresia.
After the oocyte is released into the fallopian tube, the follicle or the remaining sac now empty of an egg develops into a structure called the corpus luteum. "Corpus luteum" is the Latin term for yellow body and as we could see on the previous slide when it wasn’t highlighted it is a yellowish color. The main secretion of the corpus luteum is to develop and maintain pregnancy by secreting the hormone progesterone and progesterone helps to prepare the endometrium for implantation of the embryo. If the oocyte is not fertilized, however, the corpus luteum will begin to degenerate after 12 to 14 days. Now, after about 2 months, the corpus luteum forms a whitish scar which is referred to as the corpus albicans and the corpus albicans which is made up of collagen laid down by fibroblasts persists as a scar on the ovary for several months before being absorbed. And on this image, we can point out the corpus luteum which is now yellow again and the corpus albicans highlighted in green.
And before we move on to look at some more structures in the female reproductive system, let's talk a bit about some clinical points on the ovaries. So, pain arising from the ovaries is often perceived in the periumbilical region which is located around the umbilicus or belly button. And periumbilical pain is important to note as this can be mistaken for appendicular pain since painful sensation from the vermiform appendix can also be felt here. However, those good students of you who remembered the migratory pain that's associated with appendicitis will recognize that the absence of migratory pain from the umbilicus to the right lower quadrant would be a pretty key differentiation between appendicitis and ovarian pathologies.
A frequently encountered pathology of the ovary is the presence of benign cystic lesions. And benign cystic lesions can originate from ruptured or whole follicles, be singular or multiple in occurrence. Polycystic ovarian syndrome or PCOS, however, is a common endocrine condition where immature follicles within the ovaries increase or grow bigger resulting in pain or hormonal changes such as increased hair growth or acne. The exact causes of polycystic ovarian syndrome are still unknown though it usually occurs within women of reproductive age and can result in long term complications such as heart disease and type 2 diabetes. And other symptoms of PCOS include irregular menstrual cycles and reduced fertility.
So, now, let's move on to look at some of the supporting structures of the uterus and ovaries. And the first structure we will look at is the uterosacral ligament. And as we can see in this image, this ligament arises from the body of the uterus and then attaches to the sacrum. And this ligament helps to hold the uterus in place.
The next structure we will look at is the ovarian ligament. And the ovarian ligament is a fibrous ligament that connects the ovary to the lateral surface of the uterus and we can see in this image how the medial aspect of the ovary is connecting to the uterine horn. And now let us take a look at the suspensory ligament of the ovary and as we can see, it extends out from the ovary to the wall of the pelvis. And the suspensory ligament is a fold of peritoneum which some people considered to be part of another ligament, the broad ligament.
So since we're bringing up the broad ligament, let's have a closer look at it. And highlighted green in this image is the wide fold of peritoneum referred to as the broad ligament as well as part of the fallopian tube on the right side here. And the broad ligament connects the side of the uterus to the walls of the pelvis as well as the floor of the pelvis. And the broad ligament contains numerous structures such as the ovaries, fallopian tubes and ovarian vessels and it is usually separated into three components – the mesometrium, the mesosalpinx, and the mesovarium.
And let's have a brief look at the mesometrium. And as we can see, the mesometrium which is essentially the mesentery of the broad ligament makes up the majority of the broad ligament and extends from the body of the uterus to the ovarian ligament. The mesosalpinx is the superior part of the broad ligament and is attached to the ovarian ligament medially, the fallopian tube superiorly and the suspensory ligament laterally. And the third and smallest part of the broad ligament is the mesovarium. And the mesovarium is actually is a transverse extension of the broad ligament inferoposteriorly suspending the ovary and it lies between the mesometrium and the mesosalpinx and encloses the ovarian ligament.
And, of course, while we're here, let's take a look at some of the structures that are located within the broad ligament, and the first structure that we will look at is the ovarian artery. And though on this side we're only showing one, the other one is reflected in the mesometrium on the contralateral side. And the ovarian arteries directly branch from the abdominal aorta cross their respective ureters and then travel within their respective suspensory ligaments of the ovary before entering the mesovarium part of the broad ligament and giving off branches to the ovaries. And the ovarian arteries are the corresponding arteries to the testicular arteries in males.
And, of course, we can't forget to talk about the ovarian vein which is highlighted in green in this image and both the ovarian veins drain the ovaries before traveling through the suspensory ligament and the right ovarian vein then joins the inferior vena cava while the left ovarian vein joins the left renal vein.
Another structure that is found within the broad ligament is the ureter. And the ureter arises from the renal pelvis of the kidney before it descends retroperitoneally in the abdominal cavity. And in the pelvic cavity, it travels in the broad ligament before it enters the bladder.
The next structure we will look at is the epoophoron. And the epoophoron is a remnant of the mesonephric duct, which is an embryological structure that regresses in females but differentiates into many reproductive organs in the male. Specifically, the epoophoron is the equivalent of the male epididymis but does not really have a function in females, and the epoophoron is found bilaterally.
And, finally, the last structure I'd like to talk about is the vesicular appendage of the epoophoron which is a remnant of the mesonephric duct. Specifically, it's a remnant of the cranial part of the duct and the vesicular appendage is found bilaterally and is a small pedunculated cyst that usually has no function. And we can see it in this image hanging down like a piece of fruit as its pedunculated description describes.
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