In mammals , the vagina is the elastic, muscular part of the female genital tract. In humans, it extends from the vulva to the cervix. The outer vaginal opening is normally partly covered by a membrane called the hymen.
At the deep end, the cervix neck of the uterus bulges into the vagina. The vagina allows for sexual intercourse and birth. It also channels menstrual flow menses , which occurs in humans and closely related primates as part of the monthly menstrual cycle. Although research on the vagina is especially lacking for different animals, its location, structure and size are documented as varying among species. Female mammals usually have two external openings in the vulva, the urethral opening for the urinary tract and the vaginal opening for the genital tract.
This is different from male mammals, who usually have a single urethral opening for both urination and reproduction. The vaginal opening is much larger than the nearby urethral opening, and both are protected by the labia in humans.
In amphibians , birds , reptiles and monotremes , the cloaca is the single external opening for the gastrointestinal tract, the urinary, and reproductive tracts. To accommodate smoother penetration of the vagina during sexual intercourse or other sexual activity , vaginal moisture increases during sexual arousal in human females and other female mammals.
This increase in moisture provides vaginal lubrication , which reduces friction. The texture of the vaginal walls creates friction for the penis during sexual intercourse and stimulates it toward ejaculation , enabling fertilization.
Along with pleasure and bonding, women's sexual behavior with others which can include heterosexual or lesbian sexual activity can result in sexually transmitted infections STIs , the risk of which can be reduced by recommended safe sex practices.
Other health issues may also affect the human vagina. The vagina and vulva have evoked strong reactions in societies throughout history, including negative perceptions and language, cultural taboos , and their use as symbols for female sexuality , spirituality, or regeneration of life.
In common speech , the word vagina is often used to refer to the vulva or to the female genitals in general. By its dictionary and anatomical definitions, however, vagina refers exclusively to the specific internal structure, and understanding the distinction can improve knowledge of the female genitalia and aid in healthcare communication.
The term vagina is from Latin meaning "sheath" or " scabbard "; the plural of vagina is either vaginae , or vaginas. Using the term vagina to mean "vulva" can pose medical or legal confusion; for example, a person's interpretation of its location might not match another's interpretation of the location.
Because of this and because a better understanding of female genitalia can help combat sexual and psychological harm with regard to female development, researchers endorse correct terminology for the vulva. The human vagina is an elastic, muscular canal that extends from the vulva to the cervix. The urogenital triangle is the front triangle of the perineum and also consists of the urethral opening and associated parts of the external genitalia.
Near the upper vagina, the cervix protrudes into the vagina on its front surface at approximately a 90 degree angle. When not sexually aroused , the vagina is a collapsed tube, with the front and back walls placed together. The lateral walls, especially their middle area, are relatively more rigid. Because of this, the collapsed vagina has an H-shaped cross section. Supporting the vagina are its upper, middle, and lower third muscles and ligaments. The upper third are the levator ani muscles, and the transcervical, pubocervical , and sacrocervical ligaments.
The vaginal opening is at the posterior end of the vulval vestibule , behind the urethral opening. The opening to the vagina is normally obscured by the labia minora vaginal lips , but may be exposed after vaginal delivery. The hymen is a membrane of tissue that surrounds or partially covers the vaginal opening. Where it is broken, it may completely disappear or remnants known as carunculae myrtiformes may persist. Otherwise, being very elastic, it may return to its normal position. For these reasons, virginity cannot be definitively determined by examining the hymen.
The length of the vagina varies among women of child-bearing age. Because of the presence of the cervix in the front wall of the vagina, there is a difference in length between the front wall, approximately 7. If a woman stands upright, the vaginal canal points in an upward-backward direction and forms an angle of approximately 45 degrees with the uterus. The vaginal plate is the precursor to the vagina. As the plate grows, it significantly separates the cervix and the urogenital sinus; eventually, the central cells of the plate break down to form the vaginal lumen.
If the lumen does not form, or is incomplete, membranes known as vaginal septae can form across or around the tract, causing obstruction of the outflow tract later in life. During sexual differentiation , without testosterone , the urogenital sinus persists as the vestibule of the vagina.
The two urogenital folds of the genital tubercle form the labia minora , and the labioscrotal swellings enlarge to form the labia majora. There are conflicting views on the embryologic origin of the vagina. The vaginal wall from the lumen outwards consists firstly of a mucosa of stratified squamous epithelium that is not keratinized , with a lamina propria a thin layer of connective tissue underneath it. Secondly, there is a layer of smooth muscle with bundles of circular fibers internal to longitudinal fibers those that run lengthwise.
Lastly, is an outer layer of connective tissue called the adventitia. Some texts list four layers by counting the two sublayers of the mucosa epithelium and lamina propria separately. The smooth muscular layer within the vagina has a weak contractive force that can create some pressure in the lumen of the vagina; much stronger contractive force, such as during childbirth, comes from muscles in the pelvic floor that are attached to the adventitia around the vagina.
The lamina propria is rich in blood vessels and lymphatic channels. The muscular layer is composed of smooth muscle fibers, with an outer layer of longitudinal muscle, an inner layer of circular muscle, and oblique muscle fibers between. The outer layer, the adventitia, is a thin dense layer of connective tissue and it blends with loose connective tissue containing blood vessels, lymphatic vessels and nerve fibers that are between pelvic organs.
It forms folds transverse ridges or rugae , which are more prominent in the outer third of the vagina; their function is to provide the vagina with increased surface area for extension and stretching. The epithelium of the ectocervix the portion the uterine cervix extending into the vagina is an extension of, and shares a border with, the vaginal epithelium.
In these mid-layers of the epithelia, the cells begin to lose their mitochondria and other organelles. Under the influence of maternal estrogen, the vagina of a newborn is lined by thick stratified squamous epithelium or mucosa for two to four weeks after birth. Between then to puberty , the epithelium remains thin with only a few layers of cuboidal cells without glycogen.
Flattened squamous cells are more resistant to both abrasion and infection. The epidermis of the skin is relatively resistant to water because it contains high levels of lipids. The vaginal epithelium contains lower levels of lipids. This allows the passage of water and water-soluble substances through the tissue. Keratinization happens when the epithelium is exposed to the dry external atmosphere.
Blood is supplied to the vagina mainly via the vaginal artery , which emerges from a branch of the internal iliac artery or the uterine artery. Two main veins drain blood from the vagina, one on the left and one on the right. These form a network of smaller veins, the vaginal venous plexus , on the sides of the vagina, connecting with similar venous plexuses of the uterus , bladder , and rectum. These ultimately drain into the internal iliac veins. The nerve supply of the upper vagina is provided by the sympathetic and parasympathetic areas of the pelvic plexus.
The lower vagina is supplied by the pudendal nerve. Vaginal secretions are primarily from the uterus , cervix, and vaginal epithelium in addition to minuscule vaginal lubrication from the Bartholin's glands upon sexual arousal. The Bartholin's glands, located near the vaginal opening, were originally considered the primary source for vaginal lubrication, but further examination showed that they provide only a few drops of mucus. This initially forms as sweat-like droplets, and is caused by increased fluid pressure in the tissue of the vagina vasocongestion , resulting in the release of plasma as transudate from the capillaries through the vaginal epithelium.
Before and during ovulation , the mucus glands within the cervix secrete different variations of mucus, which provides an alkaline , fertile environment in the vaginal canal that is favorable to the survival of sperm. Nerve endings in the vagina can provide pleasurable sensations when the vagina is stimulated during sexual activity.
Women may derive pleasure from one part of the vagina, or from a feeling of closeness and fullness during vaginal penetration. Pleasure can be derived from the vagina in a variety of ways. In addition to penile penetration, pleasure can come from masturbation , fingering , oral sex cunnilingus , or specific sex positions such as the missionary position or the spoons sex position. Most women require direct stimulation of the clitoris to orgasm.
It is a sex organ of multiplanar structure containing an abundance of nerve endings, with a broad attachment to the pubic arch and extensive supporting tissue to the labia.
Research indicates that it forms a tissue cluster with the vagina. This tissue is perhaps more extensive in some women than in others, which may contribute to orgasms experienced vaginally. During sexual arousal, and particularly the stimulation of the clitoris, the walls of the vagina lubricate. This begins after ten to thirty seconds of sexual arousal, and increases in amount the longer the woman is aroused.
The vagina lengthens during the arousal, and can continue to lengthen in response to pressure; as the woman becomes fully aroused, the vagina expands in length and width, while the cervix retracts. An area in the vagina that may be an erogenous zone is the G-spot. It is typically defined as being located at the anterior wall of the vagina, a couple or few inches in from the entrance, and some women experience intense pleasure, and sometimes an orgasm, if this area is stimulated during sexual activity.
The vagina is the birth canal for the delivery of a baby. When labor a physiological process preceding delivery nears, several signs may occur, including vaginal discharge, and the rupture of membranes water breaking that can result in a gush of amniotic fluid  or an irregular or small stream of fluid from the vagina.
As the body prepares for childbirth, the cervix softens, thins , moves forward to face the front, and begins to open. This allows the fetus to settle or "drop" into the pelvis. While these symptoms are likelier to happen after labor has begun for women who have given birth before, they may happen ten to fourteen days before labor in women experiencing labor for the first time.
The fetus begins to lose the support of the cervix when contractions begin. Vaginal births are more common, but if there is a risk of complications a caesarean section C-section may be performed. The mucosa thickens and rugae return in approximately three weeks once the ovaries regain usual function and estrogen flow is restored.
The vaginal opening gapes and is relaxed, until it returns to its approximate pre-pregnant state six to eight weeks after delivery, known as the postpartum period ; however, the vagina will continue to be larger in size than it was previously. After giving birth, there is a phase of vaginal discharge called lochia that can vary significantly in the amount of loss and its duration but can go on for up to six weeks.
The vaginal flora is a complex ecosystem that changes throughout life, from birth to menopause. The vaginal microbiota resides in and on the outermost layer of the vaginal epithelium. The vaginal microbiome is dominated by Lactobacillus species.