Arterial supply to the intestines is provided by the superior and inferior mesenteric arteries (SMA and IMA respectively), both of which are direct branches of the aorta.The superior mesenteric artery supplies:
Small bowel
Ascending and proximal two-thirds of the transverse colonThe inferior mesenteric artery supplies:
Distal one-third of the transverse colon
Descending colon
Sigmoid colonOf note, the splenic flexure, or the junction between the transverse and descending colon, is supplied by the most distal portions of both the inferior mesenteric artery and superior mesenteric artery, and is thus referred to medically as a watershed area, or an area especially vulnerable to ischemia during periods of systemic hypoperfusion, such as in shock.Acute abdomen of the ischemic variety is usually due to:
A thromboembolism from the left side of the heart, such as may be generated during atrial fibrillation, occluding the SMA. Nonocclusive ischemia, such as that seen in hypotension secondary to heart failure, may also contribute, but usually results in a mucosal or mural infarct, as contrasted with the typically transmural infarct seen in thromboembolus of the SMA. Primary mesenteric vein thromboses may also cause ischemic acute abdomen, usually precipitated by hypercoagulable states such as polycythemia vera.Clinically, patients present with diffuse abdominal pain, bowel distention, and bloody diarrhea. On physical exam, bowel sounds will be absent. Laboratory tests reveal a neutrophilic leukocytosis, sometimes with a left shift, and increased serum amylase. Abdominal radiography will show many air-fluid levels, as well as widespread edema. Acute ischemic abdomen is a surgical emergency.
An acute abdomen refers to a sudden, severe abdominal pain. It is in many cases a medical emergency, requiring urgent and specific diagnosis. Several causes need immediate surgical treatment. Differential diagnosis
The differential diagnosis of acute abdomen includes:
Acute appendicitis
Acute peptic ulcer and its complications
Acute cholecystitis
Acute pancreatitis
Acute intestinal ischemia (see section below)
Acute diverticulitis
Ectopic pregnancy with tubal rupture
Ovarian torsion
Acute peritonitis (including hollow viscus perforation)
Acute ureteric colic
Bowel volvulus
Bowel obstruction
Acute pyelonephritis
Adrenal crisis
Biliary colic
Abdominal aortic aneurysm
Familial Mediterranean fever
Hemoperitoneum
Ruptured spleen
Kidney stone
Sickle cell anaemia
Carcinoid

Peritonitis
Acute abdomen is occasionally used synonymously with peritonitis. While this is not entirely incorrect, peritonitis is the more specific term, referring to inflammation of the peritoneum. It manifests on physical examination as rebound tenderness, or pain upon removal of pressure more than on application of pressure to the abdomen. Peritonitis may result from several of the above diseases, notably appendicitis and pancreatitis. While rebound tenderness is commonly associated with peritonitis, the most specific finding is rigidity. Ischemic acute abdomen
Vascular disorders are more likely to affect the small bowel than the large bowel.