**Differences of Small & Large Intestines. **Blood Supply Of
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It supplies 2nd part duodenum till distal third transverse colon. It arises from abdominal aorta & runs downward & behind neck of pancreas then pass in front of 3rd part of duodenum. a) Inferior pancreaticoduodenal artery : It passes as along 3rd part of duodenum . It supplies pancreas & adjoining part of duodenum. b) jejunal & ileal branches : 12 to 15 in number . c) ileocolic artery: It gives rise to a superior branch & inferior branch. The inferior branch gives rise to anterior & posterior cecal arteries. d) Right colic artery: .It passes to right to supply ascending colon & divides into ascending &descending branches. e) Middle colic artery: .It runs to supply transverse colon. .It divides into RT & LT branches. It arises from abdominal aorta about 3.8 cm above its bifurcation It supplies distal 1/3 of transverse colon till upper part of rectum. It runs downward & crosses LT common iliac artery. Here, it becomes superior rectal artery a) left colic artery: . runs upward & to left . supplies distal third of transverse colon, left colic flexure & upper part of descending colon. .It divides into ascending & descending branches. b) sigmoid arteries : 2 or 3 in number & supply descending & sigmoid colon. c)superior rectal artery: .It is a continuation of inferior mesenteric artery as it crosses LT common iliac artery. It descends into pelvis behind rectum. .The artery supplies upper half of rectum & anastomoses with middle rectal & inferior rectal arteries. It is an anastomosis of colic arteries around concave margin of large intestine forms a single arterial trunk. This begins at ileocecal junction & it ends with superior rectal artery. The venous blood from greater part of G.I.T. & accessory organs drains to liver by portal venous system. The proximal tributaries drain directly into portal vein. But the veins forming distal tributaries correspond to branches of celiac artery , superior &inferior mesenteric arteries. It drains blood from abdominal parts of GIT (lower third of esophagus to halfway down rectum) . It also drains blood from spleen, pancreas & gallbladder. The portal vein is about 5 cm long . It formed behind neck of pancreas by union of superior mesenteric & splenic veins . It ascends to right, behind 1st part of duodenum . It then runs upward to porta hepatis, where it divides into right & left terminal branches. It leaves hilum of spleen & passes to behind tail & body of pancreas . It unites with superior mesenteric vein behind neck of pancreas to form portal vein . It receives : short gastric, left gastroepiploic, inferior mesenteric and pancreatic veins. It ascends on posterior abdominal wall & joins splenic vein behind body of pancreas . It receives: superior rectal veins, sigmoid veins & left colic vein. These veins either drain gallbladder directly into the portal vein. : It ascends in root of mesentery of small intestine. It passes in front of 3rd part of duodenum joins splenic vein behind neck of pancreas . It receives: the jejunal, ileal, ileocolic, right colic, middle colic, inferior pancreaticoduodenal and right gastroepiploic veins. It drains left portion of lesser curvature of stomach & distal part of esophagus. It opens directly into portal vein. It drains right portion of lesser curvature of stomach and drains directly into portal vein..