Understanding The Uterus
How is the uterus formed?
So the first thing I want everybody to know when talking about the uterus is that developmentally, the uterus starts as two different buds inside the body. These buds elongate, fuse together, and the midline portion dissolves, leaving what we think of as the triangular shaped uterus. These buds compose the top one third of the vagina, the cervix, the uterus, and the fallopian tubes. I think this is important because you can have birth defects of your uterus, and understanding the uterine structure is really important to understand anything that can go wrong.
Uterine Abnormalities
So first of all, you can be born without a uterus and that's called Mullerian agenesis or Mayer-Rokitansky-Küster-Hauser (MRKH) and this is when you have complete absence of all of those Mullerian structures. Meaning, you have a blind vaginal pouch, the top one third of your vagina, the cervix, the uterus, and the fallopian tubes are all not there. Importantly, the ovaries are embryological origin, so anything that might interfere with the uterine development has nothing to do with the ovaries. So even in MRKH, you still have ovaries, you still go through the initial stages of puberty, which is all about ovarian activation and estrogen production. So, you have breast development, normal secondary sex characteristics, you just never get a period, that's called primary amenorrhea and that's really how you get diagnosed. You can also have a slew of other issues and many of these are actually not diagnosed until later in your reproductive years.
So you can have absence of an entire half, one whole bud doesn't develop, that's a unicornuate uterus, very often associated with unilateral kidney absence as well. You can have complete separate horns that never fuse and that's called the uterine didelphys. This can also be associated with a midline septum at the top third of the vagina and that is considered a longitudinal vaginal septum. When you have this, this is one of the only ones that might get diagnosed early because a pretty classic symptom is bleeding around a tampon. You're putting a tampon in, but it only goes to one side of that vaginal septum and one side of the uterus. The other uterus side and the open side is just still bleeding, and you can also have pain or difficulty with intercourse, or that septum could tear with intercourse.
Then you have bicornuate, which is partial fusion, partial reabsorption of the septum, so you have a classic heart shape with an indention at the top. Then have a uterine septum, which I have lots of content on, which is the most common and it's just failure of that last step, incomplete reabsorption of the midline septum. That is avascular and associated with miscarriage. Now that's the only one you really repair with the exception of taking out that vaginal septum and the other abnormalities of the uterus might cause more typically abnormal placentation, increased risk of placenta previa, preterm birth, preterm labor, growth restriction, abnormal presentation because the uterus is abnormally shaped, so the baby may not be head down, increasing the incidence that you might have a c- section. So, that's how the uterus is formed.
The Layers of the Uterus
Then the uterus has layers and this is also important in understanding the uterus. The inside part of the uterus is the endometrium. That is what we think of as what you're bleeding. It's what's growing, and it's responsive to estrogen and progesterone, prepares itself for implantation, and then sheds. The bulk of the uterus, most of the actual uterine structure is called the myometrium, and this is the muscular component of the uterus. This is what causes your cramps. This is what allows your uterus to expand when you get pregnant, and this is what allows you to have contractions when you go into labor. And then you have the outer portion of the uterus called the serosa, and this is actually silky smooth coating so that nothing sticks to the outside of the uterus.
Learn more about the uterus in the content below!
