The vagina is an important organ of the female reproductive tract. It has multiple roles within the female reproductive system, such as receiving the penis and ejaculate during sexual intercourse, expanding to provide a channel for delivery of a newborn in childbirth, and serving as a canal for menstrual fluid and tissue to leave the body. In this article, we will examine the anatomy of the vagina – its structure, innervation, vascular and lymphatic supply.
The vagina is related to many organs in the pelvic region – anteriorly to the bladder and urethra, posteriosuperiorly to the rectouterine pouch, rectum and anal canal, and laterally to the ureters and levator ani muscle.
The vagina is a fibromuscular tube with anterior and posterior walls which are normally collapsed and in contact with one another. The shape of the vagina is more like an H lying on the side in the transverse plane, and at the upper end, the vagina surrounds the cervix, creating two domes (fornices or vaults) – an anterior and a (deeper) posterior one. The posterior fornix is important as it acts as a natural reservoir for semen after intravaginal ejaculation, and the semen retained in the fornix liquefies in the next 20-30 minutes, allowing for easier penetration through the cervical canal.
The vagina is composed of four histological layers (internal to external):
The arterial supply to the vagina is via the uterine and vaginal arteries, both branches of the internal iliac artery. Venous return is by the vaginal venous plexus, which drains into the internal iliac veins via the uterine vein. Lymphatic drainage is divided into three sections - superior (drains to external iliac nodes), middle (drains to internal iliac nodes) and inferior (drains to superficial inguinal lymph nodes).
Innervation of the vagina is predominantly from the autonomic nervous system. Parasympathetic and sympathetic nerves arise from the uterovaginal nerve plexus (in turn a subsidiary of the inferior hypogastric plexus). Only the inferior 1/5 of the vagina receives somatic innervation. This is via a branch of the pudendal nerve, the deep perineal nerve.
A vaginal fistula is an open communication between the vagina and one of the adjacent pelvic organs. It typically occurs as a result of prolonged labour (where a Caesarean section is not available). As the fetus gradually progresses down the vaginal wall, it exerts pressure – obstructing the blood supply and causing tissue necrosis. There are three main types of vaginal fistulae – vesicovaginal (abnormal communication with the bladder, where urine enters the vagina), urethrovaginal (abnormal communication with the urethra, where urine only enters the vagina during urination) and rectovaginal (abnormal communication with the rectum).
The shape of the human vagina is not round like a tunnel, but more like a sideways “H” in the transverse plane. At its upper end, the vagina surrounds and encompasses the cervix in two domes; the anterior fornix and the deeper posterior fornix. The posterior fornix plays an important role in holding and preserving the semen after intravaginal ejaculation, as its unique structure allows for the semen to liquefy after 20-30 minutes and facilitates permeation through the cervical canal.
The vagina is composed of four distinct histological layers - from innermost to outermost they are: the stratified squamous epithelium, the elastic lamina propria, a fibromuscular layer, and the adventitia - in order of increasing strength and durability. The epithelium layer provides protection and lubrication, while the lamina propria contains the larger veins of the vagina. The fibromuscular layer is composed of two layers of smooth muscle, an inner circular and an outer longitudinal layer, that together strengthen and support the walls of the vagina. Lastly, the fibrous adventitia layer binds the vagina to surrounding structures.
Vascular supply and lymphatics to the vagina are derived from the uterine and internal iliac vessels. Arterial supply is provided by the uterine and vaginal arteries, while venous return is accomplished by the vaginal venous plexus and the uterine vein. The three sections of the vagina each have their own lymphatic drainage pattern: the superior section drains to the external iliac nodes, the middle section drains to the internal iliac nodes, and the inferior section drains to the superficial inguinal lymph nodes. The iliac and pudendal nerves provide the majority of innervation to the vagina, while parasympathetic and sympathetic nerve fibers are sourced from the uterovaginal nerve plexus.
Vaginal (obstetric) fistulae are abnormal pathways or connections between the vagina and one of the adjacent pelvic organs. This type of fistula is normally caused by prolonged labour, in which the fetus slowly progresses down the vaginal wall and exerts pressure, leading to an obstruction in the blood supply and resulting in tissue necrosis. There are three main types of vaginal fistulae: vesicovaginal, which is an abnormal communication with the bladder and allows for urine to enter the vagina; urethrovaginal, where urine only enters the vagina during urination; and rectovaginal, with an abnormal communication to the rectum that allows for faecal matter to enter the vagina.
The vagina is a component of the female reproductive system and its primary activities are sexual intercourse and childbirth. During sexual intercourse, the walls of the vagina become lubricated, providing a comfortable and pleasurable experience. During childbirth, the vagina serves as the birth canal for the baby. During menstruation, the lining of the uterus is shed as menstrual fluid or blood, which is expelled through the vagina.
