In this talk on reproductive development, we will follow the structures
that form specific female internal genitalia and organs.
Typically, the chromosomes that are present in a person’s body
will kick start either male development if there are XY chromosomes present
or female development if XX chromosomes are present
or no specific male signals are released by the body.
So female development will happen in the absence of a Y chromosome
even if there are some other chromosomal abnormalities
that we’ll discuss later.
In an XX individual, the primitive sex cords
that have grown in from the genital ridge will regress
and there will instead be cortical cords that grow in from the epithelium
on the outside of the intermediate mesoderm.
These will associate with the primordial germ cells
that have migrated into the area
from the yolk sac a little bit earlier.
These will then break lose and the cortical cord cells
will associate with the primordial germ cells forming primordial follicles.
High levels of estrogen not only allow this set of circumstances to develop
but also, cause the Wolffian or mesonephric ducts to regress
but maintain the structures that are nearby, the paramesonephric ducts.
So near the ovary, the paramesonephric ducts open
and will be staying in close association with the ovary
even though they never actually invade the ovary.
They just associate with it nearby.
The paramesonephric ducts on the left and right
will come together to form the uterine body,
cervix, and the superior most portion of the vagina.
Small remnants of the disintegrating mesonephric duct
can sometimes be found nearby in the mature ovary
and these go by the excellent names of epoophoron and paraoophoron
and occasionally, can be seen flanking the uterine body
and are thereafter known as Gartner’s duct cysts or just Gartner’s cysts.
These are small remnants of the mesonephric duct
and are typically clinically unimportant
unless they develop problems that lead to cancer of those specific cells.
Now, we’ve mentioned that the paramesonephric ducts have come together
to form a common chamber that will be the body of the uterus.
These associate with the urogenital sinus
but instead of simply opening into the urogenital sinus,
something a little more complex happens.
Growths off of the urogenital sinus called sinovaginal bulbs
grow upward to meet the paramesonephric ducts, thicken
and actually form a solid plate of cells called the vaginal plate.
Now, overtime, the vaginal plate will develop a lumen
and connect the uterus, cervix, and vagina to the opening of the vestibule.
There will be a thin membrane there marking the location
of where the vaginal plate met the urogenital sinus
and that is going to be the hymen.
We can here see a sagittal view of the same process.
The paramesonephric ducts have fused to create the uterine body
which is associated with the urogenital sinus, the sinovaginal bulbs
and then, the vaginal plate enlarge
connecting the paramesonephric ducts to the vestibule.
As a lumen develops in the vaginal plate,
we’ll have a continuous chamber going from the vestibule,
into the vagina, to the uterus,
and thereafter, the oviducts.
However, the place where the vestibule and sinovaginal bulbs meet
is marked by the hymen.
Things that can go wrong in the process involve Turner syndrome
which is when only a single X chromosome is present
or if you have significant deletions or damage to an X chromosome,
Turner syndrome can still develop.
People with Turner syndrome typically are of short stature
and have a webbed neck,
sometimes extending from the base of the ears,
all the way out to the tips of the shoulders,
lymphedema, or swelling in the limbs,
a wide chest with widely spaced nipples, and amenorrhea,
failure to generate regular menstrual periods.
They typically have no intellectual disabilities
and the ovaries are often absent or sometimes,
regressed into a little fibrous cord
sometimes called streak ovaries.
Now, as the paramesonephric ducts fuse to create the uterine body
and then cervix, and proximal portion of the vagina,
a few problems can develop if they don’t fuse or don’t form properly.
If they stay separate, you can actually have a double uterus with a septum
running down the cervix and vagina.
So functionally, two separate openings of the vagina into the vestibule,
leading to two separate uterine cavities and two separate oviducts.
Less severe would be of no septum present in the vagina
but a clear separation of the uterus.
This can occur with completely separate uterine bodies
or a small common chamber with two uterine horns extending from it.
So here, and here, we have an example of a bicornate uterus.
One with a common chamber, one without.
Less severe is going to be the presence of a membranous septum
marking the place where the two mesonephric ducts came together
and instead of rupturing to create a single uterine cavity.
There’s only a small membrane separating the two halves of it.
These conditions may be completely unknown to the affected woman
until attempting to get pregnant.
At which point, there may be difficulties with implantation
and growth of the fetus in the womb.
If the paramesonephric ducts fail to form or form in a slightly atrophic way,
you can have a rudimentary horn of the paramesonephric duct
leading to a small and slightly kind of dwindled version
of the uterus on that side
but the ovary will likely be present.
It’s simply not able to shed eggs into the oviduct nearby.
Failure of a paramesonephric duct to form altogether
on one side results in uterine atresia.
Now, this can happen unilaterally or bilaterally.
In which case, the vagina will form from the sinovaginal bulbs
but it will not connect to a uterus.
Vaginal atresia itself can happen if even those sinovaginal bulbs fail to form
or the vaginal plate does not open up and create a lumen.
And occasionally, you can have vaginal atresia
with a completely normal uterus on the other side, just no canal in between.
Now, the place where the sinovaginal bulbs and vaginal plate
meet the urogenital sinus,
we have formation of the hymen.
Normally, the hymen will rupture over time, typically, around puberty.
But if the hymen either does not rupture or has a very small opening,
we can have incomplete perforation of the hymen,
this can be medium or very small.
We can have a septation of the hymen
where strips of tissue are covering the opening of the vagina.
There can be cribriform hymen where there are multiple small openings.
And there can be completely imperforate hymen
in which case, none of the secretions of the vagina, cervix,
and uterus are able to be released,
and this may need to be fixed surgically.
Okay, thank you for your attention and I’ll see you in our next talk.