Now we are starting our journey into the female body. The word vagina literally means sheath, which is a pretty good description of this organ. The vagina is a long, fairly thin tube of muscles and fibrous tissue, lined on the inside by mucous membranes. It accommodates the penis during intercourse and receives the ejaculated sperm. Additionally, it’s the passage through which babies are born (except for those which are born by Caesarean section) and it acts as a conduit for the discharge of the monthly menstrual fluids from the uterus.
The size of the vagina is very flexible: so much so that it can accommodate almost any size and shape of penis. It is about 10 cm long and forms a kind of H-shaped cavity inside, though during sexual intercourse it expands and molds itself around the penis. The vagina is actually quite an active organ, since it’s made up of an outer layer of circular muscles and an inner layer of longitudinal muscles. However, only the first third of the vagina has plenty of nerve endings, which leaves the inner two thirds fairly insensitive. This is yet another reason why “big penis” does not equal “big thrill” for most women.
Most of the muscles making up the vagina are smooth muscles, which means they are not under conscious control (similar to the muscles in your digestive system). However, a woman can contract the muscles around the vagina found in her pelvic floor: these are the pubococcygeus, or for short, PC muscles. These muscles can be trained and strengthened (see “Kegel exercises”), which increases the strength of a woman’s orgasms and improves the likelihood of her ejaculating during sex (more on that under “female ejaculation”).
The inside of the vagina is lined by a mucous membrane which secretes a sugar called glycogen. This provides energy for the normal, healthy bacteria of the vagina, which ferment the sugar and produce lactic acid as a by-product. This lactic acid results in the interior of the vagina being slightly acidic, which protects it from microbes, and also, rather oddly, sperm. (Semen therefore has to contain substances which neutralize the acidic environment of the vagina.) It is important that this natural balance of healthy bacteria is maintained inside the vagina, otherwise a woman may experience frequent infections such as Candida (also known as thrush).
As we mentioned before, the vagina opens externally into the vestibular area. During childhood a thin membrane called the hymen protects the entrance to the vagina. However, this membrane is perforated to allow menstrual fluids to flow through. An intact hymen has long been seen as a sign of virginity, but it actually has a tendency to rupture before a woman’s first intercourse during exercise or sporting activities. However, even if it’s still only partially in place it can make the first time of intercourse uncomfortable and produce a little bleeding for a young woman. Thankfully, as the obsession of the western civilization with women’s virginity has lessened, so has the importance of the hymen and the prevalence of the myths about the painfulness of having it broken by the penis during first intercourse. (Click on the images below to enlarge them. They show the remains of the hymen tissue around the vaginal opening.)
At the back end of the vagina lies the cervix, the narrow opening of the uterus into the vagina, situated in the front wall of the vagina. The vagina does not lead straight into the cervix; rather, the uterus sits next to the vagina at a right angle to the front and upwards from it. This arrangement leaves a little pouch at the end of the vagina called the fornix. The fornix is much less sensitive than the cervix. It absorbs the main thrusts during intercourse and forms a reservoir for the pool of sperm which is left behind in the vagina after a man has ejaculated. The location of the cervix means it is conveniently bathed in the pool of ejaculate if the woman is lying on her back after or during intercourse.
