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[L. abdomen, belly]
The portion of the trunk between the thorax and the pelvis. The abdomen and the pelvis form the abdominopelvic cavity. The abdomen is bounded superiorly by the thoracic diaphragm and inferiorly by the pelvic brim. The anterolateral abdominal wall is formed by the flat abdominal musculature. The abdomen contains the stomach, the inferiormost part of the esophagus, the small and large intestines, liver, gallbladder, and spleen. The parietal peritoneum lines the abdominal cavity. The visceral peritoneum envelop the organs within the abdominal cavity. The kidneys, adrenal glands, ureters, prostate, seminal vesicles, and greater vascular structures (such as the abdominal aorta and inferior vena cava) are located external to the peritoneum (extraperitoneal); those lying posteriorly are retroperitoneal.
abdominal (ab-dom′ĭ-năl)
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, adj.
SEE: abdominal quadrants for illus

Visual examination of the abdomen is best done while the patient is supine with the knees slightly bent. In a healthy person the abdomen is oval, with elevations and depressions corresponding to the abdominal muscles, umbilicus, and, to some degree, the forms of underlying viscera. Relative to chest size, the abdomen is larger in children than in adults; it is more rotund and broader inferiorly in males than in females.

Disease can alter the shape of the abdomen. A general, symmetrical enlargement may result from ascites; a partial and irregular enlargement may result from tumors, from hypertrophy of organs such as the liver or spleen, or from intestinal distention caused by gas. Retraction of the abdomen may occur in extreme emaciation and in several forms of cerebral disease.

The respiratory movements of the abdominal walls and the movements of the thorax are inversely proportional: when the movements of the one increase, the movements of the other decrease. Thus, abdominal movements increase in pleurisy, pneumonia, and pericarditis but decrease in peritonitis and abdominal pain.

The superficial abdominal veins are sometimes visibly enlarged, indicating an obstruction of blood flow in either the portal system (as in cirrhosis) or the inferior vena cava.

Listening to sounds produced in abdominal organs provides useful diagnostic information. Absent or diminished bowel sounds may indicate paralytic ileus or peritonitis. High-pitched tinkling sounds are associated with intestinal obstruction. Bruits may indicate atherosclerosis or an abdominal aortic aneurysm. During pregnancy, auscultation enables identification and evaluation of the fetal heart rate and vascular sounds from the placenta.

For the practitioner to obtain the greatest amount of information, the patient should be supine with the head slightly raised and knees slightly flexed. Percussion should be carried out systematically over the anterior surface of the abdomen. A combination of audible or tactile sensation will be perceived by the examiner according to underlying structures (such as gaseous distended organs versus solid organs).

The abdomen may be palpated with fingertips, the whole hand, or both hands; pressure may be slight or heavy, continuous or intermittent. The head is supported to relax the abdominal wall. On occasion, the patient may be examined in a standing position, e.g., palpation of groin hernias may not be feasible in the supine position.

Palpation is helpful in detecting the size, consistency, and position of viscera; the existence of tumors and swellings; and whether the tumors change position with respiration or are movable. It is necessary to ascertain whether there is tenderness in any portion of the abdominal cavity, whether pain is increased or relieved by firm pressure, and whether pain is accentuated by sudden release of firm pressure, i.e., rebound tenderness.

An arterial impulse, if one exists, is systolic and expansive. A thrill accompanying a bruit may occasionally be palpated. The surface of a tumor is usually firm and smooth but may be nodular. Inflammatory masses are typically firm and reproducibly tender. Effusion of blood into tissues, e.g., hematoma, may produce a palpable mass.

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