Image Caption : 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 tube, about 10 cm long, that extends from the cervix of the uterus to the outside. It is located between the rectum and the urinary bladder. Because the vagina is tilted posteriorly as it ascends and the cervix is tilted anteriorly, the cervix projects into the vagina at nearly a right angle. The vagina serves as a passageway for menstrual flow, receives the erect penis during intercourse, and is the birth canal during childbirth.
The external genitalia are the accessory structures of the female reproductive system that are external to the vagina. They are also referred to as the vulva or pudendum. The external genitalia include the labia majora, mons pubis, labia minora, clitoris, and glands within the vestibule.
The clitoris is an erectile organ, similar to the male penis, that responds to sexual stimulation. Posterior to the clitoris, the urethra, vagina, paraurethral glands and greater vestibular glands open into the vestibule.
In mammals, the vagina is a muscular and tubular part of the female genital tract, which in humans extends from the vulva to the cervix. The outer vaginal opening may be partly covered by a membrane called the hymen. At the deep end, the cervix (neck of the uterus) bulges into the vagina. The vagina allows for sexual intercourse and childbirth, and channels menstrual flow, which occurs periodically as part of the menstrual cycle.
The vagina has been studied in humans more than it has been in other animals. Its location and structure varies among species, and may vary in size within the same species. Unlike mammalian males, who usually have the external urethral opening as the only opening for urination and reproduction, mammalian females usually have the urethral opening for urination and the vaginal opening for the genital tract. The vaginal opening is much larger than the nearby urethral opening, and both are protected by the labia in humans. In amphibians, birds, reptiles and monotremes, the cloaca is the single external opening for the gastrointestinal tract and the urinary and reproductive tracts.
To accommodate smoother penetration of the vagina during sexual intercourse or other sexual activity, vaginal moisture increases during sexual arousal in human females and also in other female mammals. This increase in moisture is vaginal lubrication, which reduces friction. The texture of the vaginal walls creates friction for the penis during sexual intercourse and stimulates it toward ejaculation, enabling fertilization. Along with pleasure and bonding, women's sexual behavior with others (which can include heterosexual or lesbian sexual activity) can result in sexually transmitted infections (STIs), the risk of which can be reduced by recommended safe sex practices. Other disorders may also affect the human vagina.
The vagina and vulva have evoked strong reactions in societies throughout history, including negative perceptions and language, cultural taboos, and their use as symbols for female sexuality, spirituality, or regeneration of life. In common speech, the word vagina is often used to refer to the vulva or to the female genitals in general. By its dictionary and anatomical definitions, however, vagina refers exclusively to the specific internal structure, and understanding the distinction can improve knowledge of the female genitalia and aid in health care communication.
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