peritoneum(redirected from Celomic epithelium)
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peritoneum(pĕrətənē`əm), multilayered membrane which lines the abdominal cavity, and supports and covers the organs within it. The part of the membrane that lines the abdominal cavity is called the parietal peritoneum. The portion that covers the internal organs, or viscera, is known as the visceral peritoneum and forms the outer layer (serosa) of most of the intestinal tract. The supportive peritoneum forms a double sheet of greatly modified membrane called the mesentery. This tissues hold the organs of the digestive tract in position and convey nerves, blood vessels, and lymphatic ducts to the viscera. The space between the visceral and parietal membranes contains a watery fluid that permits the abdominal organs to slide freely against the abdominal wall. A ruptured appendix can lead to inflammation of the peritoneum, a condition known as peritonitis.
a thin, semitransparent membrane with a smooth, shiny surface that lines the interior wall of the abdominal cavity and covers the organs inside it in vertebrate animals and humans.
In the normal state, the cavity between the parietal and visceral peritoneums is filled with serous fluid, which facilitates the shifting of organs in relation to each other and the abdominal wall. The total area of the peritoneum in an adult human is approximately 1.6-2.04 sq m (16,000-20,400 sq cm), and its thickness is 0.7-1.1 mm. The outer layer of the peritoneum is formed of mesothelium, and its base is composed of fibrous connective tissue. The peritoneum that covers internal organs (visceral peritoneum) is compactly knitted with them; the peritoneum covering the abdominal wall (parietal peritoneum) is united with underlying parts by an interlayer of loose connective tissue or subperitoneal fatty tissue. The diaphragmatic peritoneum lacks such an interlayer. The peritoneum is abundantly supplied with blood and lymph vessels and nerves.
Covering the wall of the abdominal cavity and the organs inside it, the peritoneum forms a system of slitlike spaces— the peritoneal cavity, which is completely closed in men and which communicates with the external environment through the opening of the Fallopian tube in women. Going from organ to organ and from organ to the wall of the abdominal cavity, the peritoneum forms ligaments, mesenteries, omenta, pouches, pits, and folds. Internal organs may penetrate through depressions in the transperitoneal space, forming hernias. Internal organs may be covered with peritoneum on all sides (intraperitoneally), on three sides (mesoperitoneally), or on only one side (extraperitoneally). Depending on the disposition of blood and lymph vessels, sections of peritoneum that primarily absorb or secrete serous fluid are distinguished; this conditions the circulation of fluid in the peritoneal cavity. In some sections of the peritoneum (on the diaphragm, in the pelvic cavity, and other sections) are located special apparatus, so-called pipes of the peritoneum, which assure especially intensive absorption of fluids. Of diseases of the peritoneum, the most dangerous is its inflammation—peritonitis.
IU. I. DENISOV-NIKOL’SKII