The vagina (from Latin, literally "sheath" or "scabbard") is a fibromuscular tubular tract leading from the uterus to the exterior of the body in female placental mammals and marsupials, or to the cloaca in female birds, monotremes, and some reptiles. Female insects and other invertebrates also have a vagina, which is the terminal part of the oviduct. The Latinate plural (rarely used in English) is vaginae.
In common speech, the term "vagina" is often used to refer to the vulva or female genitals generally; strictly speaking, the vagina is a specific internal structure and the vulva is the exterior genitalia only.
Human anatomy
The human vagina is an elastic muscular canal that extends from the cervix to the vulva.[1] Although there is wide anatomical variation, the length of the unaroused vagina 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).[2] During sexual arousal the vagina expands in both length and width.[3] Its elasticity allows it to stretch during sexual intercourse and during birth to offspring.[4] The vagina connects the superficial vulva to the cervix of the deep uterus.
If the woman stands upright, the vaginal tube points in an upward-backward direction and forms an angle of slightly more than 45 degrees with the uterus. 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 rectouterine pouch. Above the vagina is Mons Veneris. The vagina, along with the inside of the vulva, is reddish pink in color, as with most healthy internal mucous membranes in mammals. A series of ridges produced by folding of the wall of the outer third of the female vagina is called vaginal rugae. They are transverse epithelial ridges and their function is to 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 secretes different variations of mucus, which provides a favorable alkaline environment in the vaginal canal to maximize the chance of survival for sperm.
The hymen is a thin membrane of connective tissue which is situated at the opening of the vagina. As with many female animals, the hymen covers the opening of the vagina from birth until it is ruptured during sexual or non-sexual activity. The tissue may be ruptured by vaginal penetration, a pelvic examination, injury, or certain types of activities, such as horseback riding or gymnastics. The absence of a hymen does not necessarily indicate prior sexual activity, as it is not always ruptured during sexual intercourse.[5] Similarly, the presence does not necessarily indicate a lack of prior sexual activity, as it is possible for light activity to not rupture it, or for it to be surgically restored.
Physiological functions of the vagina
The vagina has several biological functions.
Uterine secretions
The vagina provides a path for menstrual blood and tissue to leave the body. In industrial societies, tampons, menstrual cups and sanitary napkins may be used to absorb or capture these fluids.
Sexual activity
The concentration of the nerve endings that lie close to the entrance of a woman's vagina can provide pleasurable sensation during sexual activity, when stimulated in a way that the particular woman enjoys. During sexual arousal, and particularly the stimulation of the clitoris, the walls of the vagina self-lubricate. This reduces friction that can be caused as a result of various sexual activities. Research has found that portions of the clitoris extend into the vulva and vagina.[6]
With arousal, the vagina lengthens rapidly to an average of about 4 in.(8.5 cm), but can continue to lengthen in response to pressure.[7] As the woman becomes fully aroused, the vagina tents (last ²⁄₃ expands in length and width) while the cervix retracts.[8] The walls of the vagina are composed of soft elastic folds of mucous membrane skin which stretch or contract (with support from pelvic muscles) to the size of the inserted penis.
G-spot
An erogenous zone referred to commonly as the G-spot is 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.[9][10][11] Some researchers deny the existence of the G-spot.[12]
Childbirth
During childbirth, the vagina provides the channel to deliver the baby from the uterus to its independent life outside the body of the mother. During birth, the vagina is often referred to as the birth canal. The vagina is remarkably elastic and stretches to many times its normal diameter during vaginal birth.
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