The vagina is the fibromuscular tube of the female reproductive tract that leads to the exterior of the body. The wall of the vagina consists of three layers: a mucosa, a muscularis, and an aclventitia. The epithelium of the mucosa is nonkeratinized stratified squamous. It undergoes changes that correspond to the ovarian cycle. The amount of glycogen stored in the epithelial cells increases under the influence of estrogen, whereas the rate of desquamation increases under the influence of progesterone. The glycogen liberated from the desquamated cells is fermented by lactobacilli vaginalis, producing lactic acid that acidifies the vaginal surface and inhibits colonization by yeasts and potentially harmful bacteria.

The vagina has certain histologic similarities to the proximal portion of the alimentary canal but is distinguished by the following features: The epithelium does not keratinize, and except for the deepest layers, the cells appear to be empty in routine H&E sections; the mucosa contains neither glands nor a muscularis mucosae; the muscle is smooth and not well ordered. This should be contrasted with the oral cavity, pharynx, and upper part of the esophagus in which the muscle is striated. The more distal portion of the esophagus, which contains smooth muscle, can be distinguished easily from the vagina because it has a muscularis mucosae.

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