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1. the musculomembranous partition separating the thoracic and abdominal cavities. On its sides it is attached to the six lower ribs, at its front to the sternum, and at its back to the spine. The esophagus, aorta, vena cava, and numerous nerves pass through the diaphragm. When relaxed it is convex, but it flattens as it contracts during inhalation, thereby enlarging the chest cavity and allowing for expansion of the lungs. See also respiration.
2. any separating membrane or structure.
3. a disk with one or more openings or with an adjustable opening, mounted in relation to a lens or source of radiation, by which part of the light or radiation may be excluded from the area.
contraceptive diaphragm a shallow dome-shaped disk used as a contraceptive, made of a soft plastic material such as latex. Its anterior lip fits behind the symphysis pubis and its posterior lip rests in the posterior fornix. It is used with a spermicide to prevent entrance of spermatozoa into the cervical os. See also contraception.
pelvic diaphragm the portion of the floor of the pelvis formed by the coccygeus muscles and the levator ani muscles, and their fascia.
polyarcuate diaphragm one showing abnormal scalloping of margins on radiographic visualization.
urogenital diaphragm a traditional but no longer valid concept that superior and inferior layers enclose the sphincter urethrae and deep transverse perineal muscles and together form a musculomembranous sheet that extends between the ischiopubic rami.
vaginal diaphragm contraceptive diaphragm.
a contraceptive device consisting of a hemisphere of thin rubber bonded to a flexible ring, inserted into the vagina together with spermicidal jelly or cream up to 2 hours before coitus. Fitted between the pubic symphysis and the posterior fornix of the vagina, the diaphragm cups the cervix in a pool of spermicide so that spermatozoa cannot enter the uterus, thus preventing conception. The rate of failure of the diaphragm method of contraception is approximately 2 unplanned pregnancies in 100 women using the method properly for 1 year. The principal advantage of the diaphragm is that it has no systemic effects. Diaphragms are manufactured in seven standard sizes from 55 to 100 mm in diameter. Kinds of diaphragms are arcing spring, coil spring, and flat spring. Also called (informal) diaphragm.