Anatomy: Internal reproductive system

Now that we've covered all the details of external genital anatomy, it's time to move on to the inner plumbing.  The internal reproductive system consists of five main parts:

Aww, it's so pretty. Like some sort of pink squid.

The Vagina
Now we're talking about the literal vagina, NOT the common slang meaning of vagina, which usually refers to the vulva.  The vagina is basically a tube that connects the external vulva to the uterus.  In its relaxed state, the vagina is usually a few inches deep, but lengthens during arousal.  It also produces its own handy-dandy lubricants and stretches or contracts to accommodate an inserted penis or other object.  It functions as the birth canal, as well, as its extremely elastic nature allows it to stretch to many times its normal diameter.  The vagina also provides a path for menstrual fluid to leave the body.

The Cervix
If the vagina is like a drawbridge connecting the uterus to the vulva, then the cervix would be the porticullis - it's a seal or valve between the vagina and the uterus.  Most of the time, it's tightly closed, stretching open only during menstruation - which may the cause of some women's cramps, or at least part of it.  During childbirth, the cervix dilates to 10 cm wide, allowing enough space for spawning.

The cervix has two main parts - the side that faces the vagina, and the side that faces the uterus.  These are called the ectocervix and the endocervix, respectively.  The ectocervix (vagina side) is slight rounded and projects about 3 cm into the vaginal canal on average. The opening in the ectocervix is called the external os.    The endocervix (uterus side) is more canal-shaped, as it's basically the inside of the ectocervix, so it's sometimes referred to as the endocervical canal.  The opening in the endocervix is called the interal os.

The Uterus
The uterus is the major organ of female reproduction.  It's roughly pear-shaped and made up of muscle tissue, allowing it to contract during childbirth and menstruation. The uterus is lined with tissue called the endometrium, which grows thick and full of blood vessels during the menstrual cycle.  At the end of the cycle, if you're not pregnant, the endometrial lining will shed, exiting the body through the vagina with the help of small uterine contractions... so this is the bastard that's responsible for your periods.  During pregnancy, the endometrium becomes even thicker and more solid, forming the placenta that provides oxygen and nutrition to the develping embryo.  The uterus itself acts as physical protection for a developing embryo and, during the birth process, contracts to push the baby out.

Fallopian Tubes
The Fallopian tubes, also called the oviducts, are two tubes that lead from the uterus to the ovaries.  These tubes are lined with tiny cilia (wavy hair-like structures) that help the ova travel from the ovaries to the uterus during ovulation.

Above: Eleven doing an interpretive dance of cilia.

 Fertilization (sperm meets egg) usually occurs in the fallopian tube, with the fertilized egg continuing its journey to implant in the uterus, beginning pregnancy.

The Ovaries
The ovaries are a small pair of organs at the end of each Fallopian tube, and are responsible for the production of ova or eggs (singular = ovum).  The ovaries are also a source of estrogen and progesterone, two extremely important hormones related to puberty, menstruation, and pregnancy.

Since we're talking about hormones, I think next week's post will go into more detail about them, specifically how and why they cause puberty.  The week after that we'll go into the menstrual cycle, everyone's favorite monthly kick-in-the-crotch.