The vagina is a distensible muscular tube, approximately 9cm long. It extends upwards and backwards from the vestibule of the external genitalia, to the cervix.
In this article we will look at the functions and structure of the vagina and consider some common clinical presentations. We will also be covering the vascular and lymphatic supply of the vagina, as well as its innervation.
Functions of the Vagina
The vagina has several biological functions:
- During sexual intercourse, the vagina receives the penis and ejaculate, assisting its transport to the uterus.
- Expands to provide a channel delivery of a newborn from the uterus to the outside world during childbirth.
- It serves as a canal for menstrual fluid and tissue to leave the body.
The vagina is closely related to many of the other visceral structures in the pelvic region.
- Anterior to the vagina is the bladder and urethra.
- Posterior to the vagina is the rectum and anus.
- Laterally located are the ureter and uterine artery.
Clinical Relevance: Vaginal (Obstetric) Fistulae
A vaginal fistula usually occurs as a result of a long and traumatic childbirth, where a caesarian section is not available. It is seen as a disease of poverty.
As the foetus slowly progresses down the vaginal wall, it cuts off the blood supply, and necrosis results. A fistula occurs when there is an open communication between the vagina and one of the adjacent pelvic organs.
There are three main types of vaginal fistulae:
- Vesicovaginal – Between the vagina and the bladder. Urine enters the vagina constantly.
- Urethrovaginal – Between the vagina and the urethra. Urine only enters the vagina during urination.
- Rectovaginal – Between the vagina the rectum. Fecal matter can enter the vagina in this type of fistula.
It is composed of 4 layers (internal to external)
Stratified squamous epithelium lining: This layer provides protection, and is lubricated by cervical mucus – the vagina does not contain any glands. Oestrogen stimulates the epithelial cells to secrete glycogen.The glycogen is digested by Lactobacillus vaginalis inhabiting the vagina to produce lactic acid and maintain a low vaginal pH of ~4.5. This prevents infection by other organisms.
- Elastic lamina propria: A dense connective tissue layer which projects papillae into the overlying epithelium. The larger veins are located here.
(Note that together, the lamina propria and epithelium comprise the vaginal mucosa)
- Fibromuscular layer: Comprising 2 layers of smooth muscle; an inner circular, and an outer longitudinal layer.
- Adventitia: A fibrous layer, which provides additional strength to the vagina, whilst also binding it to surrounding structures.
Clinical Relevance: Vaginal Infections
Low oestrogen levels, for example during pregnancy and with diabetes, and/or a reduction in lactobacilli, as seen with antibiotic treatment, can disrupt the natural vaginal flora. This may lead to overgrowth and infections such as candidiasis (thrush) and bacterial vaginosis.
Vascular Supply and Lymphatics
Blood is supplied to the vagina by the uterine and vaginal arteries, both branches of the internal iliac artery.
Venous return is achieved by the vaginal venous plexus, which drains into the internal iliac veins, via the uterine vein.
Lymphatic drainage is via the iliac and superficial inguinal lymph nodes.
The parasympathetic and sympathetic nerves supplying the vagina are derived from the uterovaginal nerve plexus. The uterovaginal plexus lies in the base of the broad ligament either side of the supravaginal part of the cervix.
The inferior fibres from the uterovaginal plexus supply the superior part of the vagina. These are derived from the inferior hypogastic plexus and the pelvic splanchnic nerves.
The inferior part of the vagina is innervated by a branch of the pudendal nerve called the deep perineal nerve.