The vagina resembles a deflated tube that's only 2 to 4 inches (5 to 10 centimeters) long and three-fourths of an inch (1.9 cm) wide [sources: Planned Parenthood; Harrison-Hohner]. However, the vagina is lined with ringed muscular ridges so that it can expand when necessary, such as during intercourse or childbirth. During sexual intercourse, for example, the vagina swells to approximately 4 to 8 inches (10 to 20 centimeters) in length and 2.5 inches in width [sources: Planned Parenthood; Harrison-Hohner].The vagina will only expand as much as it needs to in order to hold what's inside the vagina, be it a tampon or a baby. The vagina is curved and tilts forward, toward the belly, at an angle.
The inside of the vagina features lots of bumpy tissue called rugae. It's also full of bacteria and yeast, but unless the vagina is infected, that bacteria and yeast is healthy and necessary to maintain the vaginal ecosystem. The walls of the vagina are lined with membranes that maintain a steady level of moisture in the vagina, and at the opening of the vagina are Bartholin's glands, which release additional moisture when a woman becomes sexually aroused. The vagina's wrinkly and soft appearance belies those rings of muscle that are just below the surface. Maintaining these muscles through Kegel exercises, in which a woman squeezes as if she's cutting off the flow of urine, becomes more and more important as a woman ages or gives birth.
Although the vagina expands, the majority of the nerve endings in the vagina are located near the opening, and not near the end of the tube. That means that men's agony about the length of their penis is pretty meaningless, and it also means that when the baby crowns at the opening, can be the most painful.
About .4 to .8 inches (1 to 2 centimeters) inside the vagina, some women have a thin skin tissue that covers part of the vaginal opening. This tissue is known as the hymen, or the vaginal corona. Not every woman is born with a hymen, and the skin changes form throughout a woman's life due to hormonal changes, physical activity and sexual intercourse. Because the hymen is quite a complicated piece of skin, we'll return to its existence (or lack thereof) later on in the article.
Another controversial part of the vaginal anatomy is the G-spot, which is an area of sensitive tissue located on the front wall of the vagina, about one-third or one-half the way up the canal. This area has been linked with female sexual pleasure, though researchers are bitterly divided on whether it exists or not. We'll give this much-debated spot a little more discussion when we talk about the vagina's role in intercourse.
The vagina connects to the cervix, which has a miniscule opening. Essentially, only sperm can get through that opening, so women should relinquish the fear that a runaway tampon or condom is lost forever -- it will get stuck at the cervix.
That's essentially all the vagina is -- some muscles, bumpy tissue, bacteria, and maybe a hymen and a G-spot. And yet the vagina plays important roles in human reproduction and sexual pleasure. We'll explore the vagina's function in continuing the human species on the next page.