## Why option 1 (correct answer) is right The structure marked **B** is the Superior Mesenteric Artery (SMA), which arises from the ventral aorta at the L1 vertebral level. It supplies the midgut — specifically from the distal duodenum (beyond the ampulla of Vater, which marks the foregut–midgut junction) through the proximal two-thirds of the transverse colon. The clinical presentation of postprandial pain and vomiting following spinal surgery is classic for SMA syndrome, where rapid weight loss or postoperative changes allow the duodenum to be compressed between the aorta posteriorly and the SMA anteriorly. This compression occurs at the 3rd part of duodenum, which is within the SMA's vascular territory. (Gray's Anatomy 42e Ch 60; Bailey & Love 28e) ## Why each distractor is wrong - **Option 0**: Incorrect because it extends SMA territory to include the pylorus (a foregut structure supplied by the celiac trunk) and fails to specify the distal duodenum as the true proximal limit. - **Option 2**: Incorrect because it claims SMA arises from the dorsal aorta (it arises from the ventral aorta) and incorrectly includes the pylorus as the proximal limit; also ends at the splenic flexure rather than the proximal 2/3 of transverse colon. - **Option 3**: Incorrect because it misidentifies SMA as supplying hindgut structures; the IMA (marked **C**) supplies the hindgut from the distal 1/3 of transverse colon to the rectum. **High-Yield:** SMA syndrome occurs when rapid weight loss or spinal surgery allows compression of the 3rd part of duodenum between the aorta and SMA — the watershed zone at the splenic flexure (Griffith point) is most vulnerable to ischemic colitis in low-flow states. [cite: Gray's Anatomy 42e Ch 60; Bailey & Love 28e]
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