abdomen

In vertebrates, the part of the body below the thorax, containing the digestive organs; in insects and other arthropods, it is the hind part of the body. In mammals, the abdomen is separated from the thorax by the diaphragm, a sheet of muscular tissue; in arthropods, commonly by a narrow constriction. In mammals, the female reproductive organs are in the abdomen. In insects and spiders, it is characterized by the absence of limbs.

In humans, the abdomen is enclosed by the lower ribs and the muscles of the belly, and supported by the pelvis. The whole abdominal cavity is lined by a membrane called the peritoneum.

The abdomen is tightly packed with a number of organs that are involved in the nutrition of the body. These are kept in their relative positions by the muscles of the abdominal wall and the bands of the visceral peritoneum. If there is a gap in the muscles of the abdominal wall, part of the contents of the abdomen may protrude, giving rise to a hernia, or rupture. The stomach is situated in the upper part of the abdomen, with the liver in front and the kidneys, pancreas, and spleen behind. From the stomach the intestines, with a total length of about 10 m/33 ft, lead to the anus. The organs occupying the pelvic cavity, the lower part of the abdomen, are the intestines, rectum, and bladder in the male and the intestines, rectum, bladder, uterus, and ovaries in the female.