The pancreaticoduodenal arcade bridges celiac and SMA. Superior pancreaticoduodenal (gastroduodenal → celiac) ↔ inferior pancreaticoduodenal (SMA). Celiac occlusion → SMA back-fills via inferior → superior pancreaticoduodenal → gastroduodenal → hepatic and splenic. This is the #1 most-tested abdominal anastomosis on Step 1.

The marginal artery of Drummond is a continuous arcade along the inner colonic margin connecting middle colic (SMA) with left colic and sigmoid arteries (IMA). Griffith's point (splenic flexure) and Sudeck's point (rectosigmoid) are watershed danger zones where the marginal artery is most tenuous. IMA ligation during aortic aneurysm repair → sigmoid ischemia if the marginal artery is inadequate.

Leriche syndrome: atherosclerotic occlusion of the distal aorta at the bifurcation. Classic triad: bilateral leg claudication, impotence, absent femoral pulses. Collateral: internal thoracic → superior epigastric ↔ inferior epigastric (from external iliac) → femoral. This epigastric axis is the main rescue route keeping the legs perfused.

Greater curvature of the stomach has a dual supply via the gastroepiploic arcade: right gastroepiploic (from gastroduodenal/celiac) and left gastroepiploic (from splenic). After splenectomy, the right gastroepiploic takes over greater curvature perfusion. Short gastric arteries supply the fundus — most vulnerable region when the splenic artery is occluded.

The embryological gut divisions define arterial supply, venous drainage, lymphatics, autonomic innervation, and referred pain patterns. Foregut (esophagus → duodenum at ligament of Treitz) = celiac trunk; pain referred to epigastrium. Midgut (ligament of Treitz → proximal 2/3 of transverse colon) = SMA; pain referred to periumbilical region. Hindgut (distal 1/3 transverse colon → upper rectum) = IMA; pain referred to hypogastrium/suprapubic. The splenic flexure marks the midgut–hindgut transition = SMA–IMA watershed.

Both connect SMA and IMA territories, but they are anatomically distinct. The marginal artery of Drummond is a continuous peripheral arcade along the inner colonic border from cecum to rectosigmoid. The Arc of Riolan (meandering mesenteric artery) is a short, central, variable anastomosis running directly between the middle colic (SMA) and left colic (IMA) in the transverse mesocolon. The Arc of Riolan enlarges and becomes visible on CT/angiography as a tortuous central vessel when either SMA or IMA is critically stenosed. Ligation of an enlarged Arc of Riolan during sigmoid resection in an SMA-stenosed patient → catastrophic small bowel ischemia.

The corona mortis is the anastomosis between the pubic branch of the inferior epigastric artery (external iliac territory) and the pubic branch of the obturator artery (internal iliac territory), crossing the superior pubic ramus. It is present in ~70% of people. It is surgically dangerous during pelvic fracture fixation, inguinal/femoral hernia repair, and pubic symphysis surgery — inadvertent ligation or laceration causes brisk hemorrhage that is difficult to control given its deep pelvic location. It earns its name: "crown of death."

The liver receives ~70% of its blood flow and ~50% of its oxygen from the portal vein, independent of the hepatic artery. When the hepatic artery occludes, portal venous flow maintains viability. The kidneys, by contrast, have segmental arteries that are functional end arteries with no dual supply — occlusion causes permanent wedge infarcts. Clinically: hepatic artery aneurysm, celiac occlusion, or accidental hepatic artery ligation is often survivable; renal artery embolism causes permanent infarction. This hepatic dual supply concept is also why TIPS (creating a portohepatic shunt) can reduce hepatic parenchymal oxygenation.

TIPS creates an artificial stented channel between a portal vein branch and a hepatic vein within the liver parenchyma, bypassing the high-resistance hepatic sinusoids. This directly decompresses the portal system → reduces variceal pressure and ascites. Because portal blood now bypasses the liver's detoxification (urea cycle, first-pass metabolism), ammonia and gut-derived toxins accumulate → hepatic encephalopathy is the main complication. TIPS is an artificial application of the same portosystemic shunting that occurs spontaneously at the four natural anastomotic sites in portal hypertension.

The posterior wall of the first part of the duodenum (duodenal bulb) is directly related to the gastroduodenal artery (GDA), a branch of the common hepatic artery from the celiac trunk. A penetrating posterior duodenal ulcer (typically H. pylori-related) erodes into the GDA, causing massive upper GI hemorrhage — one of the most feared peptic ulcer complications. The anterior duodenal ulcer, by contrast, perforates into the peritoneal cavity (peritonitis), not into a vessel. This anatomical relationship is a Step 1 classic.