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Although there is wide anatomical variation, the length of the unaroused vagina of a woman of child-bearing age is approximately 6 to 7.5 cm (2.5 to 3 in) across the anterior wall (front), and 9 cm (3.5 in) long across the posterior wall (rear).
The vagina is a fibromuscular tubular tract that is a sex organ and has two main functions: (1) sexual intercourse and (2) childbirth. In humans, this passage leads from the opening of the vulva to the uterus, but the vaginal tract ends at the cervix .
The vaginal opening is much larger than the urethral opening. The inner mould of the vagina has a foldy texture which can create friction for the penis during intercourse. During arousal, the vagina gets moist to facilitate the entrance of the penis.
The vaginal opening is at the caudal end of the vulva, behind the opening of the urethra. The upper one-fourth of the vagina is separated from the rectum by the recto-uterine pouch. Above the vagina is the Mons pubis. The vagina, along with the inside of the vulva, is reddish pink in color, as are most healthy internal mucous membranes in mammals. A series of ridges produced by the folding of the wall of the outer third of the vagina is called the vaginal rugae. They are transverse epithelial ridges and they provide the vagina with increased surface area for extension and stretching.
Vaginal lubrication is provided by the Bartholin's glands near the vaginal opening and the cervix. The membrane of the vaginal wall also produces moisture, although it does not contain any glands. Before and during ovulation, the cervix's mucus glands secrete different variations of mucus, which provides an alkaline environment in the vaginal canal that is favorable to the survival of sperm.
The hymen is a membrane of tissue that surrounds or partially covers the external vaginal opening. The tissue may or may not be ruptured by vaginal penetration. It can also be ruptured by delivery, a pelvic examination, injury, or sports. The absence of a hymen may not indicate prior sexual activity. Similarly, its presence may not indicate a lack of prior sexual activity.
The Vagina and Arousal
The concentration of the nerve endings that lie close to the entrance of a woman's vagina (the lower third) can provide pleasurable sensation during sexual activity when stimulated in a way that the particular woman enjoys. However, the vagina as a whole has insufficient nerve endings for sexual stimulation and orgasm, which is considered to make the process of child birth significantly less painful. Ninety percent of the vaginal nerve endings are on the outer one-third of the vagina, near the opening, thus making this area much more sensitive to touch than the more interior two-thirds of the vagina.
Research has found that clitoral tissue extends considerably into the vulva and vagina. During sexual arousal, and particularly the stimulation of the clitoris, the walls of the vagina lubricate. This reduces friction that can be caused by various sexual activities. With arousal, the vagina lengthens rapidly, to an average of about 4 in. (10 cm), but can continue to lengthen in response to pressure. As the woman becomes fully aroused, the vagina tents (last ²) expands in length and width, while the cervix retracts. The walls of the vagina are composed of soft elastic folds of mucous membrane which stretch or contract (with support from pelvic muscles) to the size of the inserted penis or other object, stimulating the penis and helping to cause the male to experience orgasm and ejaculation, thus enabling fertilization.
An erogenous zone commonly referred to as the G-Spot (also known as the Gräfenberg Spot) is typically defined as being located at the anterior wall of the vagina, about five centimeters in from the entrance. Some women experience intense pleasure if the G-Spot is stimulated appropriately during sexual activity. A G-Spot orgasm may be responsible for female ejaculation, leading some doctors and researchers to believe that G-Spot pleasure comes from the Skene's glands, a female homologue of the prostate, rather than any particular spot on the vaginal wall. Other researchers consider the connection between the Skene's glands and the G-Spot to be weak. They contend that the Skene's glands do not appear to have receptors for touch stimulation, and that there is no direct evidence for their involvement. The G-Spot's existence, and existence as a distinct structure, is still under dispute, as its location can vary from woman to woman and appears to be nonexistent in some women.
The Vagina and Childbirth
The vagina provides the channel to deliver the infant from the uterus to its independent life outside the body of the mother. During birth, the elasticity of the vagina allows it to stretch to many times its normal diameter. The vagina is often typically referred to as the birth canal in the context of pregnancy and childbirth, though the term is, by definition, the area between the outside of the vagina and the fully dilated uterus.
90% of nerve endings are at the entrance to the vagina; the latter 2/3 is insensitive to touch, the G-spot, an erogenous zone found 5 cm from the vaginal entrance, is homologous to the prostate, stimulation of the clitoris causes vaginal walls to lubricate, easing penal penetration, or the many folds of the vagina allow it to stretch to accommodate a penis or to birth a baby