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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urogenital diaphragm a traditional but no longer valid concept that superior and inferior layers enclose the sphincter urethrae and deep transverse perineal muscles and together form a musculomembranous sheet that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.