Vagina

The vagina serves as a passage for the exit of menstrual flow, insertion of the penis during sexual intercourse, reception of semen, and is the birth canal.

Anatomy
The vagina is a canal that extends from the external vulva to the cervix. The vaginal walls can be easily distended but are normally 7.5 cm in length anteriorly and 9 cm long posteriorly. The upper portion of the vagina encircles the vaginal part of the uterine cervix. The vagina touches the empty bladder on the ventral and superior surface. Inferiorly the vagina adheres to the posterior wall of the urethra and opens adjacent to the labia minora. The vaginal lining has many transverse ridges, or folds.

Vaginal tissues receive blood supply from uterine arteries and sometimes branches of the internal iliac artery. Blood returns to the venous system through veins that empty into the internal iliac veins. Lymphatic drainage is via the external and internal iliac lymph nodes and superficial inguinal lymph nodes. The muscles of the pelvic floor provide important support to the vagina and uterus.

The vagina is moistened by primarily by mucous secretions from the cervix. Secretions from the vaginal epithelial cells containing glycogen and water also play a role.

Histology
The vaginal wall is made of three layers: a mucosa, muscular layer and an adventia. Vaginal epithelium is stratified squamous epithelium having a thickness of 15-200 microns. Intense keratinization like that seen in the stratified squamous epithelium of the skin is not seen, although some keratin is found in vaginal epithelium. Estrogen causes the epithelium to thicken, differentiate and accumulate glycogen. This glycogen is found within the vagina when the epithelial cells slough off. Vaginal bacteria metabolize the glycogen to lactic acid, causing the typically low pH of the vaginal environment. Loose connective tissue with many elastic fibers is found underneath the vaginal epithelium. A rich vascular supply is the source for vaginal moisture during sexual stimulation. Vaginal muscle is mostly smooth muscle oriented longitudinally. However, there are some circular bundles. The outer layer, the adventia, is made of dense connective tissue with many elastic fibers, extensive nervous supply and venous capillaries.

Vaginal Cycle
Cytologic examination of the cells exfoliated from the vagina yields information of clinical importance. In experimental animals, such as the rat, the exact stage of the estrous cycle can be determined by microscopic examination of vaginal smears. In humans, the ratio of different cell types and their morphology can be used to determine the hormonal status of the patient and can be useful in the early detection of cervical cancer. Vaginal smears can distinguish between the follicular phase and the luteal phase.

In post menopausal women, the vaginal epithelium becomes very thin, the blood supply to the vagina is reduced, and the cervical glands regress so that the vaginal wall can become weak, dry and itchy. Exogenous estrogen is often prescribed (oral, patch, or cream) to reverse the effects of estrogen withdrawal on the vaginal epithelium. In addition, vaginal moisturizers may be helpful, especially prior to sexual relations to compensate for lack of moisture.

Pathology
The vagina can become host to various infectious organisms including bacteria, fungi, protozoa and viral agents, most of which are sexually transmitted diseases. Treatment depends on the causitive agent.