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.