Abdomens

The abdomen is the region of the trunk between the thorax and the pelvis. It contains most digestive organs as well as parts of the urinary and circulatory systems, and is bounded above by the diaphragm and below by the pelvic brim. The abdominal cavity is lined by the peritoneum and is divided into the peritoneal cavity and the retroperitoneal space behind it.

Anatomy: The abdomen houses organs from the foregut, midgut, and hindgut. The stomach, liver, gallbladder, and pancreas lie in the upper abdomen; the small intestine fills the central region, and the large intestine frames the periphery. The spleen sits in the left upper quadrant. The kidneys and parts of the ureters are retroperitoneal. The peritoneal cavity contains the greater and lesser sacs; many organs are intraperitoneal and connected by mesenteries.

Abdominal wall and vessels: The wall contains layers of muscle including the external and internal obliques, transversus abdominis, and rectus abdominis, with fascia and skin outside. Blood supply comes from the celiac trunk, superior mesenteric, and inferior mesenteric arteries, with venous drainage to the portal system. Innervation involves somatic nerves from thoracic and lumbar levels and autonomic fibers from the vagus and splanchnic nerves.

Function and clinical relevance: The abdomen supports digestion, absorption, and excretion, and its muscles contribute to posture, core stability, and expiration. Clinically, abdominal pain ranges from benign to life-threatening conditions such as appendicitis, cholecystitis, or bowel obstruction. Other common issues include hernias, ascites, pancreatitis, liver disease, and inflammatory bowel disease. Imaging commonly uses ultrasound or computed tomography to diagnose abdominal disorders.