Internal Anatomy 1: Featuring the Uterus and Associated Organs

External body structures can be incredibly complicated: organs often have more features than we expect, and sometimes body parts are made up of hidden organs we don’t often think about. Of course, even while complicated on the outside, bodies become even more convoluted under the skin, which houses hundreds of structures with their own idiosyncrasies and relationships.

This post ventures into those unseen places and attempts to dissect the way that a body’s internal organs interact with and affect the organs that we see externally. I will mainly focus on the uterus – an organ that connects to the vagina (an internal organ that becomes external at the vaginal opening of the vulva). I also discuss the ovaries and the fallopian tubes and their influence on the uterus.

It was difficult for me to begin this post because I could not find a succinct phrase to describe my topic. The diagrams I include depict what most people refer to as “internal female anatomy.” However, not everyone who has a uterus is a woman, and not everyone who lacks one is a man. Trans women may not have a uterus and ovaries, but this doesn’t make them any less female – nor does a trans woman’s lack of uterus and ovaries make her any more male. Cis women who have had ovarian cancer or a hysterectomy may lack a uterus or ovaries or both, but that doesn’t take away their femaleness, either. Some people identify as genderqueer (meaning that they don’t identify as either male or female), and the presence or absence of a uterus in their bodies doesn’t really mean anything in terms of gender. People will continue being the gender they identify with, regardless of the organs that their bodies contain. Gender is not defined by anatomy.

How then, should I refer to this post’s topic? I briefly considered calling it “internal anatomy often associated with vulvas,” but it doesn’t quite sound right. For one, it’s wordy. For another, it seems (at least to me) to support the belief that somehow uteruses and vulvas are meant to be paired with one another; that the two depend on each other. This assumption is, of course, inaccurate. There are trans men who have penises but still have a uterus and ovaries. There are trans women who have vulvas who do not have a uterus or ovaries. There are intersex people who might have a penis and a vagina/vulva. Perhaps the phrase “internal anatomy often associated with vaginas” would be more accurate, as the uterus connects to the vagina, but again, this seems to pigeonhole both trans men and women, as well as cis women who had had some of their internal sexual organs surgically removed for health reasons.

When you get down to it, really, the truth is simple: some people have uteruses, ovaries, and fallopian tubes. Some people don’t. The presence or absence of these organs doesn’t say anything about the person’s identity, be it gender, sexuality, or personality. The fact that a person has a uterus tells us about as much about their personal identity as the fact that they have a lung or a bladder. Organs are organs, and they perform certain functions, but they do not reveal any secrets about a person, be it their favorite movie or the look of their external genitalia. Thus, I refer to my diagrams in this post as simply “internal anatomy,” and I call the organs by their names; I do not gender them.

I imagine that this might be confusing for some people, as we grow up in a world that often insists that anatomy does, in fact, define gender (the common usage of the phrase “female internal anatomy” being just one example). However, I want to challenge these normative assumptions by using non-normative gender neutral language in this blog. I hope that the absence of this familiar, gendered language will challenge the commonplace assumption that anatomy defines gender and vice versa.

Internal Anatomy: The Big Picture

The diagram below depicts a cross-section of a body that contains a uterus and ovaries that pair with an external vulva. As mentioned above, not all bodies look like this and uteruses do not always pair with vulvas, but I wanted to include some external genitalia, and, as I discuss menstruation in this post, it seemed fitting that said genitalia would include a vagina and other organs associated with the vulva.

The body depicted here also has a bladder, a pubic bone, and a rectum, which is part of the large intestine. Externally, it has a clitoris (this could also be included in the internal section), a urethra, a vaginal opening, and two sets of labia. In the diagram, I have colored in different sections so that they may be more easily differentiated. As I have already discussed some of the anatomy in this diagram in a previous post, I will not summarize their form and function again here.

Internal Anatomy Vulva

Pubic Bone – working from front to back, the pubic bone is the first internal structure in this body that can play a part in a human’s sexual experience. Although not an organ, and not technically sexual either, because it entirely circles the pelvis, the pubic bone becomes part of a person’s internal sexual anatomy. The legs of the clitoris actually attach to part of the pubic bone called the pubic arch (please note: not all of the pubic bone is depicted in the diagram – otherwise, it would hide many of the other organs from view). If a person is using an internal condom as a form of birth control or to protect against STIs, the condom’s inner ring is kept in place by a ring that fits behind the pubic bone.

Bladder – the bladder’s main purpose is to store urine until a person can eliminate it from their body (i.e. find a toilet or a secluded public area). You might also notice that the bladder is situated fairly close to both the vagina and the uterus. It’s worth noting that penetrative sex can induce the feeling of needing to pee if the bladder is close to full because said penetrative object might push the vaginal walls into the bladder. (A sensation of needing to pee during penetration might also come from the urethral sponge being stimulated – we’ll get to that soon). The bladder’s location below the uterus also contributes to the fact that pregnant people often need to pee a lot more than people who are not pregnant. The uterus expands significantly during pregnancy, which compresses all nearby organs. The bladder, being very close to the uterus, gets significantly squished.

Urethra & Urethral Sponge – you might remember from my summary of the clitoris that the urethral sponge is a layer of erectile tissue that lines the entirety of the urethra (the tube that connects the bladder to the urethral opening in the vulva – yes, we often refer to the urethral opening as simply the urethra). If you’re somewhat aware of current sexuality research, you’ve probably heard of the G-spot (named after a German gynecologist named Ernst Gräfenberg. I won’t pretend that he discovered the G-spot, because there were probably a lot of people before him exploring their bodies and their pleasure spots, but he was the first person to name said spot, and he named it after himself). You’re also probably somewhat aware that no one really knows if there’s a G-spot or not, and that people keep arguing about whether or not it exists, and how it does or does not contribute to orgasm.

I bring this up because, if you ask Deborah Sundahl, a pretty prominent second-wave feminist and definite believer in the G-spot (she has a book on it), she will tell you that the G-spot is, in fact, the urethral sponge. Sundahl actually refers to the urethral sponge as the “female prostate,” although this isn’t entirely accurate. Some of the glands inside the urethral sponge are similar to some of the glands in the prostate, but they are not the same. In general, the medical and scientific community seems to have decided that the urethral sponge is not analogous to a prostate (a structure most often found in people with penises). That being said, stimulating the urethral sponge can be extremely pleasurable for some people and can result in what is often called a “G-spot orgasm.” Or, if you want to be less exact about it, a vaginal orgasm.

I want to be clear here: not all orgasms that originate in the vagina (or at least feel like they originate in the vagina) are caused by stimulation of the urethral sponge. And not all people like this type of stimulation. Some people complain that they experience a burning sensation when their urethral sponge is stimulated, and some people can’t shake the feeling that they have to pee. But some people do respond to this type of stimulation, and it can cause very strong orgasms in these people. Hence all the hype about the G-spot. The authors of the comprehensive Guide to Getting It On have suggested that there might not be an exact “G-spot,” per se, but rather a “G-spot area” whose stimulation some people respond to quite positively and others do not. So, to solve this G-spot mystery, we might say that all people with a urethral sponge have an area which can be stimulated (the G-spot area), but not all people will enjoy that stimulation.

If you’re curious as to whether you or your partner(s) enjoys G-spot area stimulation, you can find said area by inserting one or two fingers an inch or two into the vagina and making a “come hither” motion against the vaginal wall (note: this should be toward the urethra, and thus toward the navel). If neither you nor your partner(s) have a vagina, and you’re still curious about what this stimulation might feel like, you can ask a friend who has one, if they’re the kind of friend who won’t mind being asked.

Vagina – in my post on the vulva, I included a short description of the vaginal opening, which is where the vagina either ends or begins, depending on your world perspective. The vagina itself in a hollow tube, the tube itself being defined by the four tissue layers, blood vessels, and nerve endings forming the vaginal wall. The vagina is an incredibly dynamic organ. When the body it belongs to is not aroused, the walls cave in on themselves, touching each other. But when a person becomes aroused, the vagina expands; the part closer to the uterus balloons out and the part closer to the vaginal opening narrows.

The vagina is the canal through which many babies travel when they are born and a key player in conception. The vaginal walls also secrete plasma, which allows the vagina to stay moist. Vaginas can also make their own farts (commonly referred to as “queefs”) if air gets trapped inside of them, usually as a result of sexual activity. Queefs often sound just like farts, but tend to be louder and wetter. They don’t really smell, and they’re completely normal – they’re just kind of goofy sounding. Unlike anal farts, it’s difficult to hold them in and most will escape the vagina by accident. Some people feel embarrassed when and if they queef, but the only thing to do about them is laugh because they’re just another funny sound that bodies make.

If you learned about sex by watching porn, it’s highly likely that you think the vagina is the ultimate sex organ: the place where all orgasms will originate if they are rammed hard enough with a penetrative object, be it a penis, a dildo, a lollypop, stalk of celery, or a high-heeled shoe. This is an unfortunate side-effect of most* pornography being targeted at people with penises. Because the truth is, if you’re looking for an organ that will provide pleasure to a body, you should really concentrate on the clitoris.

Here’s the deal: when you compare these two organs, the clitoris has many many many more nerve endings that respond to touch than the vagina. In fact, the clitoris has more nerve endings than any other sexual organ in a human’s body (yes, that includes the penis). So if you’re trying to give someone with a clitoris and a vagina an orgasm, whether it’s yourself or a partner, you are more likely to have success if you concentrate on the clitoris. That being said, vaginal orgasms are also possible to achieve, but they are often also more difficult to reach. And they rarely happen with the steady hammering that so many porn flicks are so fond of depicting. I will discuss exactly how one might have a vaginal orgasm (and a clitoral orgasm, for that matter) in a later post.

*not all porn is made for people with penises! And not all porn insists that penetrative hammering is the only way to induce orgasm! There’s really good porn out there, but it’s hard to find (especially for free). If you’re interested in pornography that isn’t just your run-of-the-mill wham, bam, thank you ma’am, I recommend checking out Tristan Taormino’s feminist porn, as well as Erica Lust‘s “XConfessions“.

Cervix – the cervix is a dome that both connects and separates the vagina from the uterus. If my diagram was in three dimensions, it would more accurately be able to show the cervix as resting over the opening to the uterus, rather than seeming to be that opening. The cervix itself has a small dimple in its center that serves as a door into and out of the uterus; that dimple is called the os.

As the vagina is usually three to four inches long, a penis or other object (a dildo, for example) might sometimes hit the cervix during penetrative sex. Some people will find this pleasurable; others will find it painful. The problem of pain might be dealt with by switching positions so that the penetrative object avoids the cervix (which, you might have noticed, reaches down quite a bit into the vagina) and instead enters the fornix, which is just a fancy name for the vagina as it continues up past the cervix. Although my diagram does not show it, the fornix exists both in front, behind and to the sides of the cervix.

Uterus – the uterus is perhaps best known as a baby incubator. It is the organ that houses and nourishes an embryo as it develops into a fetus and then into a baby. It has three distinct layers: the endometrium, the myometrium, and the perimetrium, which I will discuss later.

As depicted in the diagram, most uteruses point slightly toward the navel, but some are the opposite, and tilt toward the navel. This is called, fittingly, a tipped uterus. About 30% of uteruses are at least somewhat tipped in this backwards direction. Having a tipped uterus isn’t a huge deal, but it can change the way that a person interacts with and feels about their uterus. The tipped uterus might cause a person to feel menstrual cramps in their back, or to even have diarrhea during their period due to cramps. Penetrative sex in certain positions can also be more uncomfortable, especially positions that involve “rear entry” into the vagina (i.e. in positions like “doggy-style”).

Fallopian Tubes – the fallopian tubes connect a person’s ovaries to their uterus and create a pathway that guides an egg (either fertilized or unfertilized) to the uterus. Although this diagram, being a cross-section of a person’s body, only shows one fallopian tube, most people have two of them, as well as two ovaries.

Ovariesa person’s ovaries are responsible for housing their body’s sex cells, also referred to as gametes, ova (singular ovum), oocyte, or eggs. Ovaries don’t actually house the individual sex cells, but rather a host of follicles that might one day mature and expel a developed egg that may or may not be fertilized in the fallopian tubes. If a follicle does expel an egg, the follicle turns into a structure called the corpus luteum, which secretes a hormone called progesterone. Progesterone is the hormone responsible for maintaining the endometrial layer of the uterus.

Rectumthe anus opens up into the rectum, which lies at the end of the large intestine. The rectum can also be a key player in sexual activity. Although there are sometimes cultural stigmas and taboos surrounding the anus and rectum in sexual play, the anus has a variety of very sensitive nerve endings which can deliver great pleasure. If partners are partaking in penetrative anal sex, a person might insert fingers, a penis, or another penetrative object into the rectum. If a person has a prostate, the rectum is the best way to reach the organ and apply pressure there (more on this in the next post). A penetrative object might also be able to stimulate the portions of the clitoris that are located closer to a person’s back, such as the perineal sponge or even the clitoral crura. If someone inserts something into their rectum during penetrative vaginal sex, the person penetrating the vagina will be able to feel the object in their partner’s anus, which can make the vagina feel tighter and more textured.

Focus on the Uterus and Ovaries

 Having overviewed all the different structures that can be in one body and interact with each other, I want to focus more on one very important organ: the uterus. My above summary was a bit short due to the fact that the uterus does so much that it deserves its own sub-section and diagram. So I gave it one.

Uterus

The above depicts a sketch of a generic uterus. As always, my diagram is incredibly rudimentary, but this one is perhaps more so than usual. The uterus, first of all, does not look like a bull, but rather like an upside-down pear that rests in the body’s lower abdomen. Most uteruses are about the size of a person’s fist. I’ve always been amazed at how such a small organ can 1) grow a five-to-eleven-pound baby inside of it, and 2) can produce so much blood.

I’m not going to discuss conception or pregnancy in this post, but I will cover the blood part a little later. But in order to understand the blood part, you also have to know what part of the uterus produces said blood, and what its purpose is, and how it is expelled from the uterus. And in order to explain that, I need to cover a few components of the uterus, as well as the adjoining fallopian tubes and ovaries.

First off, the uterus is composed of three layers, each serving its own purpose. First is the perimetrium, which encloses the uterus and keeps it safe. You might think of it as the skin of the uterus, which protects the muscles and blood vessels underneath. Speaking of muscles and blood vessels, the second layer is the myometrium, the muscular layer of the uterus. The myometrium is the main player in both menstrual cramps and the birthing process: when it is time to expel anything from the uterus, it contracts. You can imagine the kind of power it can produce if you think about just how much force it must take to push a baby through a person’s cervix and vagina, neither of which, although stretchy, is all that wide.

The third, innermost layer of the uterus is the endometrium (also known as the uterine lining), which supplies nutrients to a fertilized egg. The endometrium has two parts. The first part is the basal layer, which lies up against the myometrium. It does not change and never leaves the uterus. In contrast, the second layer, called the functional layer, changes dramatically over the course of a month. During the first fourteen days after a person menstruates, the functional layer grows on top of the basal layer, forming a mass of glands and blood vessels that can provide a fertilized egg with the nutrients it needs to grow into a baby. Eventually, the functional layer reaches optimum thickness for egg implantation, and it stops growing. These two layers then stay static for about two more weeks, until menstruation occurs (more details to follow), when the uterus expels the functional layer of the endometrium. The basal layer stays put.

The ovaries and connecting fallopian tubes also play a key role in the functions of the uterus. The ovaries, as mentioned previously, store and expel eggs. Once a month, one ovary expels one egg into a fallopian tube (it’s a common myth that people alternate ovaries – in fact, which ovary expels an egg each month is completely random); the fallopian tube then helps transport the egg into the uterus. Each tube has little cilia that create a current that pushes the egg along. You’ll notice that the uterus is not, in fact, attached to the fallopian tubes. Rather, the tubes seem to barely grasp the ovaries with finger-like extensions called fimbriae. The ovaries, in fact, are not connected to the fallopian tubes, and each month a matured egg makes a perilous jump from an ovary into its tube. The egg doesn’t always make it. Sometimes an unfertilized egg gets lost in the abyss of a person’s body or, in very rare cases, an ectopic pregnancy occurs, and a fetus may begin to develop in the abdominal body cavity. (Note: ectopic pregnancy refers to any pregnancy in which an egg implants into something other than the uterine lining; pregnancies in the abdominal cavity are just one type of ectopic pregnancy. Again, they are extremely rare).

If the egg makes it into the fallopian tube and there happens to be a few sperm nearby, it might become fertilized. This usually happens in the first curve of the tube, called the ampulla. Post-fertilization, the egg continues down into the uterus, where it might implant into the functional layer of the endometrium. But if the egg is not fertilized and/or it doesn’t implant, then the endometrium dissolves, and menstruation occurs.

Menstruation

Menstruation, colloquially referred to as having a period (being on the rag, Aunt Flo paying a visit), is the process of the uterus expelling the endometrial lining when a pregnancy does not occur. It’s a process that, although we only visually witness the end result, takes almost a month to prepare and between three days to a week to execute (on average). So although we, as humans, usually only think about menstruation a few days out of the month (depending on whether you menstruate or not and whether you study it or not and whether your partner(s) menstruate or not), bodies that have uteruses are undergoing processes related to menstruation all the time.

Before I start explaining the intricate dance of hormones, organs, and gametes that result in menstruation, I want to mention an essay by Emily Martin titled, “Medical Metaphors of Women’s Bodies: Menstruation and Menopause.”

In it, she notes that many medical texts, when they mention menstruation, use language that connotes it as wasteful or shameful: a failure of the body to produce a living being. Paragraphs explaining menstruation will describe it as a “disintegration” or “loss” of “endometrial debris” going through a process of “necrosis (death of tissue).” In one instance, she points to a text that states, “When fertilization fails to occur, the endometrium is shed…That is why it used to be taught that ‘menstruation is the uterus crying for lack of a baby’” (emphasis mine). This type of language, Martin argues, turns menstruation from a natural and common bodily process into a shameful failure to perform the essential bodily (and, in extension, societal) function of production. She notes, “Perhaps one reason the negative image of failed production is attached to menstruation is precisely that women are in some sinister sense out of control when they menstruate. They are not reproducing, not continuing the species, not preparing to stay at home with the baby, not providing a safe, warm womb to nurture a man’s sperm.”

When writing about menstruation, as Martin points out, it’s easy to make it sound like a waste, like a bad thing. This language is probably also fueled (in my opinion) from the fact that periods are difficult. They can be painful, they’re usually messy, people who have them have to either line their underwear with something to prevent staining or insert something into their vagina to catch the blood. Periods can be a hassle. But I don’t want to fall into the trap that Martin identifies in her essay: I don’t want to describe menstruation as a waste or a failure. Menstruation is a normal, healthy process that many bodies with uteruses undergo about once a month, and they are nothing to be ashamed of. In fact, as a sexually active person, I welcome my period when it comes, because it means I’m not pregnant, and I know that I’m not at all ready to take on the responsibility of caring for a tiny, helpless human being. Martin addresses this fact in her essay, suggesting that medical texts would make periods sound a lot more normal and less shameful if they described it as a process of monthly renewal of the endometrium, not a result of a lack of cellular implantation. She suggests that textbooks might begin describing the process thus: “A drop in the formerly high levels of progesterone and estrogen create the appropriate environment for reducing the excess layers of endometrial tissue…As a part of the renewal of the remaining endometrium, the capillaries begin to reopen, contributing some blood and serous fluid to the volume of endometrial material already beginning to flow” (emphasis mine). She concludes, “I can see no reason why the menstrual blood itself could not be seen as the desired ‘product’ of the female cycle, except when the woman intends to become pregnant.” This is the type of message I also hope to convey: menstruation is not a waste, but rather production of bodily fluids that the uterus eventually releases. (Note how similar this description now becomes to people who produce sperm: ejaculate is a result of the body producing something that it later releases).

The menstrual cycle is a result of a few hormonal interactions that cause changes in the ovaries and the uterus. Many hormones interact with each other and other organs during this process, but for the sake of simplicity I focus on just a few of them. If you’re interested in all the hormones that are involved in human reproduction and where they come from, I recommend the Wikipedia page on the menstrual cycle.

Menstrual Cycle

The Menstrual Cycle: The Ovarian Phase

As the above diagram suggests, there are two “phases” associated with the menstrual cycle, and they’re related (they also have their own separate sub-phases). The first is the ovarian phase, which consists of the follicular phase and the luteal phase. During the follicular phase, various hormones act on dormant cells in the ovary called granulosa cells. First, a hormone called follicle-stimulating hormone (FSH) wakes up a number of granulosa cells, which are all housed (along with the oocyte/egg) in a structure called a primordial follicle. People with ovaries have thousands and thousands of primordial follicles, but only a few hundred wake up and do something during a given month. When FSH interacts with the granulosa cells, they wake up and begin to divide and multiply within the primordial follicle. If the granulosa cells respond well, the primordial follicle will eventually become a secondary follicle full of lots of granulosa cells. And then, eventually, the follicle might become a Graafian follicle, which will either die or ovulate. It’s important to note that even though many primordial follicles become Graafian follicles over just a span of two weeks, only one actually ovulates. Ovulation occurs when the basement membrane of the Graafian follicle breaks open and expels a matured oocyte into the fallopian tube (hopefully). The granulosa cells go with it, forming a protective cloud around the egg.

The luteal phase lasts for the two weeks following ovulation. The Graafian follicle, having done its job of nurturing and expelling an oocyte, turns into a body known as the corpus luteum, which has only one purpose: to secrete progesterone. And it does this for the two weeks of its existence, up until it dissolves back into the body.

The Menstrual Cycle: The Uterine Phase

According to most anatomy textbooks, the uterine phases starts with menstruation (although it really could “start” anywhere – I doubt that the body has a day it considers the “beginning” of any phase), probably because that’s also the first day of the follicular phase. I will go out of order with my diagram, and begin with the proliferative phase of the uterine phase. As the diagram shows, the endometrium grows in thickness during this phase – at the same time, the follicles in a person’s ovaries continue to develop.

After the proliferative phase comes the secretory phase which begins the day after ovulation. Although the name of this phase suggests that the endometrium is secreting something, this word actually refers to the corpus luteum, which at that point is secreting progesterone. Progesterone is the hormone that maintains the endometrium, basically keeping it in place in case an egg happens to become fertilized and needs a place where it can implant.

The corpus luteum is not an immortal body, and it disintegrates after about two weeks. When this happens, the uterus enters the menstrual phase, in which it sheds the endometrium. Uterine contractions expel the functional layer from the uterus, which results in a period. In many people, the menstrual phase will last between three to seven days, although this phase will be shorter in some people and longer in others. The length of a person’s menstrual phase will also depend on whether or not they are taking a hormonal form of birth control, have an IUD, or take any medication that may affect their menstrual cycle. The length of a menstrual cycle, by the way, also varies. Most textbooks will describe the cycle as being 28 days because it looks nice on a diagram, but this will vary from person to person, and even from month to month in the same person. Although most people generally have a cycle that completes itself within 21 to 35 days, other people will fall outside of this spectrum, and that’s normal. However, if you suspect that your cycle is too short or too long (for example, if you only have a period every six months and you’re not on any medications that may cause this to happen), it’s best to consult a doctor.

That’s the basics of menstruation, as regulated by the uterus, ovaries, and all the hormones that they create and that act upon them. Next post, I’ll be covering another type of internal anatomy: this time showing how the testis and the prostate gland work together to create semen, and how this process is connected to the penis and ejaculation. In the meantime, feel free to email me at postivelysexed@gmail.com with questions and comments, or leave a comment down below!

References

Joannides, Paul. Guide to Getting It On. Oregon: Goofy Foot Press, 2009.

Martin, Emily. “Medical Metaphors of Women’s Bodies: Menstruation and Menopause,” in Writing on the Body: Female Embodiment and Feminist Theory. Eds. Katie Conboy, Nadia Medina, and Sarah Stanbury. New York: Columbia University Press, 1997. 15-41.

Roach, Mary. Bonk: The Curious Coupling of Science and Sex. New York: W. W. Norton & Co., 2008.

Sundahl, Deborah. Female Ejaculation and the G-Spot. Alameda: Hunter House Publishers, 2003.

Wikipedia: Uterus, Endometrium

**One of my biggest sources for today’s blog were my compilation of lecture notes from an anatomy class that I took in college. Unfortunately, these do not exist on the public internet, and I cannot link to them. The professors who delivered these lectures were Daniel Lieberman and Peter Ellison.

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