Medical visualization of the lumen of the vaginal canal looking back towards the cervix. Far from being a smooth tube, the vagina contains many folds and ridges. During sexual intercourse the sperm that may be deposited within the vaginal canal will benefit from the pH buffering makeup of semen because the vaginal environment is acidic. The vagina also produces lubrication to make penetration less difficult during intercourse. The vaginal opening, seen in this view in the extreme foreground, tightens involuntarily as intercourse progresses.
The vagina is a fibromuscular elastic tubular tract (passage) which is a sex organ and mainly functions for the facilitation of sexual intercourse and childbirth. In mammals (especially primates), menstruation, which is the periodic discharge of blood and mucosal tissue (the endometrium) from the uterus and vagina, is another primary function of the vagina and usually signals fertility. The location and size of the vagina varies among species, and may vary in size within the same species. In humans, the vagina leads from the opening of the vulva to the uterus (womb), but the vaginal tract ends at the cervix.
Unlike mammalian males, who usually have only one genital orifice, mammalian females usually have two, the urethra and the vagina. The vaginal opening is much larger than the urethral opening, and both openings are protected by the labia. During sexual arousal, vaginal moisture increases (vaginal lubrication) to reduce friction and allow for smoother penetration of the vagina during sexual activity. In the absence or presence of sufficient vaginal lubrication, the vagina's inner mould has a foldy texture, which can create friction for the penis during sexual intercourse and stimulate it toward ejaculation, enabling fertilization.
The female reproductive tract may also be termed the vagina with regard to amphibians, birds, reptiles and monotremes, but is generally known among zoologists as the cloaca in these species and may additionally serve as intestinal and urinary tracts.
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