Melanin
Skin, hair, and the irises of your eyes all get their color from the pigment melanin, which is produced by specialized skin cells called melanocytes in the basal layer. Interestingly, the vulva has more melanocytes than many other body parts, yet it is the same skin tone as almost everywhere else (with the exception of palms and soles, which can be lighter). Medicine still can’t explain how your back has fewer melanocytes than your vulva but they end up the same or a very similar tone.
While melanin absorbs and reflects ultraviolet light and provides protection from the sun, melanocytes also respond to biological, physical, and chemical stimuli and are part of the immune system.
The Vestibule
The junction between the vagina and the vulva is the vestibule, and the urethra is located in the vestibule. Technically the vestibule is external, but the skin is similar to what you would find in the vagina: it’s mucosal skin, meaning there is very little keratin and the cells are filled with glycogen, a storage sugar. There is also no hair or sebum, so the tissue is primarily protected physically by the labia minora.
There are also two sets of specialized glands—the top pair are Skene’s glands, which are similar to the prostate in men (studies show that they secrete tiny amounts of prostate-specific antigen, or PSA). The Bartholin’s glands sit at the bottom on either side of the vestibule. They both may contribute a small amount of lubrication.
Anal Sphincters
The anus has two muscular rings called the internal and the external sphincter. The mucosa of the anus is highly innervated (full of nerves) because the tissue has to distinguish between solid and liquid stool as well as gas, in addition to coordinating the socially appropriate time for emptying. This rich network of nerves is why some people find anal sex very stimulating. It is also why hemorrhoids or fissures (small breaks in the skin) hurt so very much.
The internal sphincter is the most important in terms of stool continence. It is responsible for about 80 percent of fecal continence.
BOTTOM LINE
• The part of your body that touches your underwear is the vulva; anything inside is the vagina. The vestibule is in between.
• The clitoris is much larger than what you see and is the only organ that exists entirely for pleasure.
• There is no “normal” size for labia minora and labia majora.
• Labia minora, labia majora, and the mons contribute to both sexual pleasure and protection of the vagina opening.
• The pH of the vulvar skin is acidic, between 5.3 and 5.6.
CHAPTER 2
The Vagina
THE VAGINA IS A FIBROMUSCULAR TUBE that connects the vulva with the cervix. I realize this is the least sexy way to describe something that brings so much pleasure. Personally, I’d love to use a different term, as vagina means “sheath” in Latin, and I hate having female anatomy defined in terms of how it fits with a penis. Medically, the vagina starts at the hymen, so just inside the vestibule.
Why Do We Even Have a Hymen?
Evolutionary biologists have not been able to answer this question.
Some experts have postulated that a hymen may once have served to prove to a male mate that he wouldn’t be raising another man’s child, but there are several reasons why that seems improbable and ridiculously patriarchal. The hymen can tear from physical activity, and approximately 50 percent of teens who report sexual activity still have an intact hymen, meaning it is a highly unreliable “virginity indicator.” This “preserving purity” theory also implies that, evolutionarily speaking, only the first child has value, but for most of human history 30–50 percent of newborns did not survive their first year. It makes no sense to invest a supposedly precious biological resource for a sexual encounter that may not provide a child who lives—or even produce a child at all.
Another proposed theory is that the hymen evolved to make first sex painful so women would only have sex with a “bonded” male partner. However, it’s pretty clear that for the majority of women, their sexual debut is not painful enough that they are going to hold out for some hypothetical Mr. Right. If it hurt that much, we wouldn’t have so many teen pregnancies. Also, if the evolutionary goal was to keep the first sex disappointing enough that women wouldn’t bother to look elsewhere and hence stay with their “first man,” it seems counterproductive to have such an amazing organ as the clitoris be fully functional early in the reproductive years.
My theory is the hymen was at one point in human history a physical barrier for protection. Before puberty, the mucosa (skin) of the vagina is very sensitive to irritants. If a prepubertal girl gets even a small amount of dirt in her vagina, the dirt can cause a profuse inflammatory reaction. Estrogen, fat pads in the mons and labia majora, pubic hair, and labia minora—essentially all of the protective mechanisms for the lower vagina—don’t develop until puberty. So I believe the hymen was a prepuberty physical barrier against dirt and debris. As we evolved and began to walk upright, physically taking the vaginal opening farther away from dirt, the need for a physical barrier for the lower vagina lessened, and evolution became less invested in a rigid, physically protective hymen. This would explain why we now have so many variations in hymen shape: it is simply no longer biologically important.
In a fetus, the vagina starts as a solid tube. The cells from the inside gradually disappear—this proceeds from top (the cervix) to bottom. Any remnants that remain at the lower part of the vagina are the hymen, which can be a ring, crescent shaped, have holes, or even be absent altogether. Sometimes larger portions of cells are left behind, which can lead to a band of vaginal tissue that runs horizontally or vertically. This band is called a septum. A septum can be flimsy and break easily with a tampon or penetration during sex, but it can also be very thick; rarely, it can even obstruct the vagina. The presence of a septum should be considered for any teen who has not had a period by the age of sixteen, any women who is unable to insert a tampon, fingers, a penis, or have a speculum exam due to pain, and any woman who has a feeling of an obstruction with vaginal penetration.
Vagina: The Basics
The vagina is lined with specialized skin called mucosa. The mucosa is arranged in accordion-like folds or ridges called rugae—some women may perceive these as “bumps” or a roughness. The best visual for rugae is a king-sized fitted sheet on a queen-sized bed.
The mucosa sits atop a layer of smooth muscle, which is technically the outer wall of the vagina. Smooth muscle is a type of muscle not under voluntary control (your gut is also made of smooth muscle). While not all the functions of the vaginal smooth muscle are well known, it is believed it moves blood and vaginal discharge towards the vaginal opening. If the muscle contractions become uncoordinated or spasm excessively, this can cause pain. There is data that suggests that some women who have painful periods have more spasms or uncoordinated activity of their vaginal smooth muscle.
The rugae and smooth muscle allow the vagina to be collapsed at rest with the walls touching, keeping air out, and then to stretch for penetration or for a vaginal delivery. Everyone (okay, the patriarchy) seems very impressed with the ability of a penis to grow, but the few centimeters of change that a penis can muster up pales in comparison with the vagina’s ability to stretch.
The vaginal smooth muscle is surrounded by a network of blood vessels. The rich blood flow is one of the reasons the vagina typically heals well after injury.
Vaginal length can vary significantly. The back wall (closer to the rectum) is longer and can range from 5.1 to 14.4 cm, and the front wall ranges from 4.4 to 8.4 cm. Your body size and shape are not predictive of your vaginal length. The vagina gets wider as you move from the vaginal opening