What is the Tunica Vaginalis?

@Hawthorne - VivAnne's on the right track -- embryos don't start out female any more than they start out male. And yes, this stuff is quite useful for transgendered people or people who want to become transgendered, although it is in a limited capacity.

See, becoming transgendered involves alteration surgeries and hormone therapy. Hormones are in charge of everything during an embryo's development, but by the time you're an adult your bones and everything formed as male or female a long time ago.

That means no amount of hormone therapy is going to change male bone structure to female or vice versa, so transgendered male-to-female people will always be at least a bit recognizable as their original gender thanks to larger hands and squarer shoulders.

Hormone therapy might some day allow a transgendered woman's body to produce eggs to have children, though. That's still pretty impressive.

Back to the subject at hand...if the tunica vaginalis was formed improperly enough, could a person in theory be born with both a vagina and a penis?

@VivAnne - Whoa. So basically, human starts with no gender, then they're both genders, then they end up being one or the other? Weird, I never knew that.

I always heard that embryos started out female and then certain hormones make them male -- you know, like they talked about for the dinosaurs in Jurassic Park? Not that I first learned it there as far as humans go. My parents told me that embryos started female.

Your explanation actually makes a lot more sense. If embryos actually started out blank with "indifferent gonads" and switch to a gender by the time they're done developing, but have aspects of both genders at one point, that explains why some people are born with aspects of both genders and no technical gender of their own.

It's not because the "maleness" didn't take hold that well, it's because neither gender was "decided on". Hmm. This kind of information could be pretty useful for people who want to change their genders, couldn't it?

@TheGraham - It seems weird to have a word similar to "vagina" used to refer to a male body trait -- especially one in the testicles -- but there is a method to this madness.

Did you know that, up until about six weeks of age, human beings have no gender? A few weeks before the X or Y chromosomes initiate and "choose" a gender for the baby, the forming body grows sex organs called the "indifferent gonads" (not kidding, as funny as that sounds) which will eventually turn into either ovaries or testicles.

Even though the body hasn't determined a gender yet, the growing baby needs to develop before it can even become a fetus, so to save on time it grows internal sexual features to be both male and female. These are called the Mullerian and Wolffian ducts, respectively.

Anyway, at around six weeks of age the baby becomes one gender or the other, and in addition to the X or Y chromosomes it secretes a substance that inhibits the sexual organs of the opposite gender from developing. This makes the Mullerian ducts wither away if the baby is male, and the Wolffian ducts wither away if it turns out to be female.

What all of this means is that problems with the tunica vaginalis and testis are probably caused by the Mullerian ducts not disappearing entirely. Phew!

I clicked this article because I was curious what exactly the tunica vaginalis is; I assumed it had to do with female anatomy, and certainly didn't expect it to be a male body area inside the testicles!

That seems kind of backward, doesn't it? Do women have any genital traits with the word "testes" in them, then?