‘The Vagina’
            
             The vagina is a thin walled-tube, 8 to 10 cm long. It lies between the
             bladder & the rectum & extends from the cervix to the body exterior. The
             urethra is embedded in its anterior wall. Often called the birth canal, the
             vagina provides a passageway for delivery of an infant & for menstrual
             flow. Since it receives the penis (& semen) during sexual intercourse, it is
             the female organ of copulation.
             The highly distensible wall of the vagina wall consists of three coats:
             An outer fibroelastic adventitia.
             A smooth muscularis.
             A mucosa marked by transverse ridges or rugae, which stimulate the
             penis during intercourse.
             The epithelium of the mucosa is a stratified squamous epithelium adapted
             to stand up to friction. Certain of the mucosal cells act as
             antigen-presenting cells & are thought the route of HIV transmission from
             an infected male to the female during intercourse. The vaginal mucosa
             has no glands; it is lubricated by the cervical mucous glands. Its epithelial
             cells release large amounts of glycogen, which is anaerobically metabolized
             to lactic acid by resident bacteria. Consequently, the pH of a woman’s
             vagina is normally quite acidic. This acidity helps keep the vagina healthy
             & free of infection, but it is also hostile to sperm. Although vaginal fluid of
             adult woman is acidic, it tends to be alkaline in adolescents, predisposing
             sexually active teenagers to sexually transmitted diseases.
             In virgins, the mucosa near the distal vaginal orifice forms an
             incomplete partition called the hymen. The hymen is very vascular & tends
             to bleed when it is ruptured during the first coitus (sexual intercourse).
             However, its durability varies. In some females, it is ruptured during a
             sports activity, tampon insertion, or pelvic examination. Occasionally, it is
             so though that it must be breach surgically if intercourse is to occur.
             The upper end of the vaginal canal lo...