The vagina is part of the internal genitalia of the female reproductive system. The internal female sex organs form a pathway, the internal female genital tract, composed of the vagina, uterus, the paired uterine tubes and ovaries.
The vagina serves a multitude of functions. It facilitates menstruation, childbirth and sexual intercourse, as it is the copulatory organ in females. Additionally, it plays a significant role in human female sexuality and sexual pleasure.
This article will explore the gross and histologic anatomy of the vagina and its functions while also reviewing related clinical conditions.
|A copulatory organ of the female reproductive system
|Vaginal fornix (anterior/posterior/lateral parts), anterior and posterior walls of vagina, hymen, vaginal wall layers (mucosa [vaginal rugae → vaginal columns], lamina propria, muscular layer, adventitial layer)
|Vaginal and uterine arteries (branches of internal iliac artery)
Upper two thirds of vagina:
- Sympathetic efferent fibers from lumbar splanchnic nerves via uterovaginal plexus
- Parasympathetic efferent fibers from pelvic splanchnic nerves via uterovaginal plexus
- General visceral afferent (GVA) fibers carried via pelvic splanchnic nerves (S2-S4)
Lower third of vagina:
- Parasympathetic efferent fibers from pelvic splanchnic nerves (S2-S4)
- General somatic afferent (GSA) fibers carried via pudendal nerve (S2-S4)
|Acts as a birth canal, the outlet for the menstrual blood flow and a cavity for sexual intercourse.
- Gross anatomy
- Blood supply
- Clinical notes
The vagina is a distensible fibromuscular tube extending from the pelvic cavity (true pelvis) through the pelvic floor to the perineum. The cervix protrudes into its proximal end, which is enlarged and forms the vaginal fornix (vaginal vault). The vagina opens into the vaginal vestibule of the vulva (vaginal opening) at its distal end.
The vagina tilts posteriorly between the urethra and rectum, with the urethra bound to its anterior wall. If standing, the vaginal tube will point in a superoposterior direction to form a 45 degree angle with the uterus and an about 60 degree angle to the horizontal. However, the exact angle is variable depending on individual anatomy and with contents of the bladder and colon. Due to this tilting, the posterior wall of the vagina (8 to 10 centimeters (3 to 4 inches)) is longer than its anterior wall (7.5 centimeters (2.5 to 3 inches)).
Upper two thirds of vagina
Anatomically, the base of the bladder and the urethra is related to the anterior wall of the vagina, while, posteriorly, the vagina is related to the rectum.
Internally, the cervix protrudes into the proximal end of the vagina forming an enlarged recess between its lower margin and the vaginal wall. This blind-ended space is called vaginal fornix. There is a large posterior part of vaginal fornix, a smaller anterior part in addition to two small lateral parts.
Lower third of vagina
At the lower end of the vagina (lower third) are vaginal rugae, which allow for expansion of the luminal surface of the vaginal wall during childbirth. While the vagina itself does not have glands, it is lubricated by mucus from the cervical glands found above it, a process which is hormonally controlled. Upon sexual arousal, vaginal secretions can also come from the uterus, or a minuscule amount from the greater vestibular glands (of Bartholin). Engorgement of vaginal blood vessels during arousal also results in increased blood flow/pressure which causes fluid, known as vaginal transudate, to be pushed from the vasculature of the lamina propria onto the vaginal surface through transudation (i.e. escape of liquids via pores or breaks in the cell membranes);
Colloquially, the word 'vagina' is often incorrectly used to refer to the vulva. Anatomically, the vagina is the fibromuscular canal between the hymen and cervix, however in non-medical contexts (e.g. legally in court) it is considered to include the vulva (between the labia).
The vulva includes all of the external genital organs seen outside of the body, which include:
- the mons pubis (Latin for “pubic mound”)
- labia majora (outer lips)
- labia minora (inner lips)
- the external openings of the urethra and vagina.
At the vulva, the vaginal orifice (the introitus) may be partially covered by a membrane formed by inward folding mucosa known as the hymen. This is a thin mucosal structure found posterior to the urethra that [partially or completely] covers the entrance to the vagina. It is surrounded by the vaginal vestibule, which is exposed with spreading of the labia. The hymen stretches across the vaginal lumen and is normally incomplete to allow for passage of menstrual flow. It can be perforated during sexual intercourse, insertion of menstrual products, such as tampons, or during childbirth.
Hymenal caruncles are small firm reddish nodules located around the vaginal orifice in adult women; they are remnants of the hymen. The hymen is often crescent-shaped in preadolescent females, but many shapes are possible.
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The wall of the vagina is thin and distensible, consisting of four distinct layers (from outermost to innermost):
- an adventitial (fibrous) layer, providing additional strength and structural support to the vagina, merging with the bladder (anteriorly) and rectum (posteriorly),
- a muscular layer (made of smooth muscle), which has an inner circular and outer longitudinal layer,
- a layer of lamina propria which is rich in elastic fibers and does not contain any secretory glands,
- a mucosal layer composed of stratified squamous, non-keratinizing epithelium. This type of epithelial lining maintains the moisture of the vaginal canal and protects it from infection. While the vagina itself does not have any secretory glands, its surface is moistened by cervical secretions.
The vaginal mucosa is continuous with that of the uterus. Its inner surface presents two longitudinal ridges, one on the anterior and one on the posterior vaginal wall. These ridges are called the vaginal columns and form numerous transverse ridges, the vaginal rugae. The lower part of the anterior column of the vaginal rugae forms a prominent ridge in relation with the urethra, which is called the urethral carina of the vagina.
Vasculature of the vagina is primarily supplied by an arterial plexus derived by the vaginal artery and uterine artery, which area branches of the anterior division of the internal iliac artery. These two arteries anastomose to form azygos arteries of the vagina, which run longitudinally anterior and posterior to the vagina.
Abundant venous plexuses are situated in the muscular and mucosal layers of the vaginal wall, often colloquially referred to as the spongy layer of the vagina, hinting that the vaginal rugae can be regarded as a discrete layer of erectile tissue similar to the corpus spongiosum of the penis. These venous plexuses drain into the internal iliac veins.
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There is a higher concentration of nerve endings near the entrance of the vagina (lower third) that provides sexual pleasure when stimulated, and women may also derive pleasure from a feeling of closeness and fullness during sexual intercourse.
Autonomic efferent innervation to the upper two thirds of the vagina is supplied through the uterovaginal plexus containing both sympathetic and parasympathetic fibers. Sympathetic efferent fibers from the lumbar splanchnic nerves (lumbar outflow) travel first through the superior hypogastric plexus, and then through the bilateral hypogastric nerves to reach the inferior hypogastric plexuses, and finally the uterovaginal plexus.
Parasympathetic efferent fibers to the uterovaginal plexus originate from the pelvic splanchnic nerves (S2-S4) (sacral outflow).
Autonomic efferent innervation to the lower third of the vagina is carried through the pelvic splanchnic nerves (S2-S4).
Somatic sensation exists primarily in the distal one third of the vagina and is also carried by general somatic afferent fibers within the pudendal nerve to the sacral plexus.
Despite the scientific examinations of vaginal wall innervation showing no consistent or single areas with greater nerve ending densities, some women do have a greater density of nerve endings in the anterior vaginal wall that can lead to heightened sensitivity and pleasure when the anterior wall is stimulated. Therefore, it is in the anterior wall that the vaginal erogenous zone is located (commonly referred to as the ‘G-spot’ or Gräfenberg spot). In these examples, the outer third of the vagina near the opening will have more nerve endings, making it more sensitive to touch than the deeper and inner two-thirds of the vagina. Functionally, this is most likely the case so that childbirth will be significantly less painful, since increased nerve endings throughout would otherwise equate to more pain.
During sexual intercourse (coitus) and sexual arousal, the vagina will expand in both length and width. While the upper two-thirds of the vagina expands and lengthens, the uterus will rise into the greater pelvis, with the cervix being elevated above the vaginal floor. Semen is deposited in the vaginal fornix. Spermatozoa then travel to the external os of the cervix, traversing the cervical canal and uterine cavity to reach the ampulla of the uterine tube, where fertilization normally takes place.
During menstruation, the vagina allows passage and expulsion of the endometrium, which is shed on a monthly basis at the end of the follicular phase. Throughout the menstrual cycle, the epithelium will undergo subtle changes, where the rate of desquamation will be higher during the progesterone phase than during the estrogen phase.
During childbirth, the vagina expands to allow the baby to pass through and provides pulsatile contractions to assist the downward passage of the baby. A healthy vagina of a woman of childbearing age is acidic with a pH range of 3.8 to 4.5 due to the degradation of glycogen to lactic acid by enzymes secreted by the Döderlein's bacillus, which is part of the normal flora of the vagina. The acidity functions to retard and prevent growth of various strains of pathogenic microbes. An increased acidity can be caused by bacterial overgrowth, as in bacterial vaginosis, trichomoniasis, or the rupturing of membranes during pregnancy.
The ecosystem of a healthy vaginal microbiota consists majorly of the Lactobacillus species, but under stress or disturbances (hormonal or physical), changes can occur that upset the healthy balance of microorganisms that protect its host and result in undesirable outcomes, such as vaginosis or yeast infections.
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Common infections and diseases that can affect the vagina include candidal vulvovaginitis, vaginitis, vaginismus, sexually transmitted infections (STIs) or cancer.
Vaginitis is an inflammation of the vagina, and is attributed to several vaginal diseases.
Sexually transmitted infections
Sexually transmitted infections (STIs) or sexually transmitted diseases (STDs) are often caused by:
- human papillomavirus (HPV)
- genital herpes
It is therefore recommended by health care providers to appreciate safe sex practices (male or female condoms), while engaging in sexual activity to prevent transmittance of these STIs and STDs.
Cervicovaginal (PAP) smear
For women of childbearing age, it is recommended to receive cervical screens (Pap smear tests and HPV vaccines). Cervical cancer can be prevented if caught early enough through cervical screening or prophylactically by HPV vaccines. It is recommended for women to begin Pap smear tests starting around 21 years old until 65 years of age, with frequency varying from 3 to 5 years depending on age, genetics, or environmental factors. Vaginal cancer is a very rare condition that is related more to old age, and its symptoms include abnormal vaginal bleeding or vaginal discharge.
If there is a lump obstructing the vaginal opening, it is commonly due to a Bartholin’s cyst, which occurs when a greater vestibular gland (of Bartholin’s) is blocked and the gland becomes inflamed. Sometimes, bacterial infection can be associated, but the cysts are not sexually transmitted. Antibiotics are not generally needed, and treatment will depend on the severity of symptoms.
As women get older, or if there weakened pelvic muscles from trauma or childbirth, vaginal prolapse can occur. Vaginal prolapse, or vaginal vault prolapse, is characterized by a part of the vaginal canal protruding (prolapsing) from the opening of the vagina. In the case of a prolapse due to childbirth, the rectum, uterus, or bladder pushes on the vagina. Severe cases result in the vagina protruding out of the body.
Kegel exercises can be observed to strengthen the pelvic floor, and can help prevent or remedy vaginal prolapse.
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