abdomen

The abdomen is the portion of the trunk between the diaphragm and the pelvis. It houses the abdominal cavity, which contains most of the digestive organs, portions of the urinary system, and various glands. The peritoneal cavity is a potential space within the abdomen lined by a serous membrane called the peritoneum; many organs are intraperitoneal, while others are retroperitoneal.

The abdominal wall consists of skin, fascia, and muscle layers, including the external oblique, internal oblique, transversus abdominis, and rectus abdominis. The space can be described in four quadrants or nine regions. Major organs include the stomach, small and large intestines, liver, gallbladder, pancreas, and spleen. The kidneys and adrenal glands are primarily retroperitoneal, while the bladder and, in females, reproductive organs extend into the lower abdomen or pelvis. The peritoneal cavity contains a small amount of fluid that lubricates surfaces.

Vascular supply and innervation: Blood is supplied by the celiac trunk, and the superior and inferior mesenteric arteries, with venous drainage into the portal system. Innervation includes lower thoracic and first lumbar nerves, as well as autonomic fibers. The abdominal viscera perform digestion, absorption of nutrients, and formation of waste; the abdominal wall muscles contribute to posture, protect internal organs, and aid respiration and coughing.

Clinical relevance: Abdominal pain prompts evaluation for conditions such as appendicitis, gastritis, pancreatitis, hepatitis, obstruction, hernias, or aneurysm. Imaging techniques such as ultrasound, computed tomography, and magnetic resonance imaging aid diagnosis. Developmentally, the organs arise from the foregut, midgut, and hindgut and are partitioned by peritoneal and retroperitoneal relationships.