The vagina is a fibromuscular tube, 7.5 to 10cm in length, situated anterior to the rectum and anal canal and posterior to the bladder and urethra. It is parallel to the direction of the urethra; that is to say, it is directed upward and backward. It is the organ of copulation, for the deposition of semen in the female, and during parturition it serves as the exit from the uterus. The cervix projects into the vault of the vagina, and the vaginal recesses are formed around it. These recesses are known as the anterior, posterior, and lateral fornices (singular, fornix).
The vaginal wall consist of fascial, muscular, and mucous coats. The mucous coat is composed of stratified squamous epithelium with glycogen stored within its cells. Estrogen secretion during the menstrual cycle and pregnancy seems to cause an increase in glycogen stores and keratinization of the surface epithelium. The inner surface of mucous membrane is thrown into two longitudinal folds and transverse folds, or rugae. The circular and longitudinal smooth-muscle layers hypertrophy during pregnancy, and these layers, together with the rugae of the mucous coat and the interstitial elastic connective tissue, allow for extreme distensibility of the canal during parturition.
The vagina normally has a pH of between 4 and 6. This acidic environment impedes the growth of microorganisms and thus functions to prevent infection of the pelvic organs. The mucus that lubricates the vagina originates from the glands of the cervix. This mucus is acidified by the fermenting action of the vaginal bacteria, mainly lactobacilli, upon the glycogen from the vaginal epithelium. Striated muscle fibers form a ring-shaped sphincter around the introitus, or external orifice of the vagina. This opening may be partially occluded in the virgin by a fold of mucous membrane containing squamous epithelium with a thin connective tissue core called the hymen.
FIGURE 1-3. ILLUSTRATION OF FSH/LH/TESTOSTERONE
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FIGURE 1-4. ILLUSTRATION OF FSH/LH/-P/E
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