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14 multiple-choice questions and 5 flashcards on Gastrointestinal System, about 8% of the USMLE Step 1 bank. Every one carries a written rationale.
Gastrointestinal System is one of 10 chapters in CoStudy's USMLE Step 1 — Medical Licensing bank, and it holds 14 of the bank's 172 multiple-choice questions — roughly 8% of the total. That proportion is not arbitrary: chapters follow the certifying body's published exam outline, and the number of questions in each is set by that domain's published weight, so the share of your practice time this chapter takes matches the share of the real exam it accounts for.
Studying by chapter is worth doing once you have a diagnostic score. A single overall percentage tells you whether you are close; it does not tell you which domain is dragging. Working a weak chapter in isolation, and re-testing it in isolation, is the fastest way to move a score that has stalled — and it is why the mock exams in CoStudy report by domain rather than as one number.
7 questions drawn from this chapter, with the full rationale shown — the controlling principle behind the right answer, and why each wrong option tempts and fails.
Which finding is most specific for diagnosing acute appendicitis?
Answer: B — Right-lower-quadrant pain that migrates from periumbilical region, with rebound tenderness at McBurney's point
Classic appendicitis: visceral periumbilical pain (early) → somatic RLQ pain (after peritoneal irritation), with rebound tenderness, guarding, and elevated WBC. (D) suggests duodenal ulcer.
The primary site of bilirubin conjugation is the:
Answer: C — Hepatocyte — UDP-glucuronosyltransferase conjugates indirect bilirubin into water-soluble direct bilirubin for biliary excretion
C) Hepatic UGT1A1 activity. A/B/D) Each is a different metabolic site.
Acute pancreatitis is most often caused by:
Answer: A — Gallstones and alcohol
GET SMASHED mnemonic for causes — but Gallstones and Ethanol top the list, accounting for ~80% in the developed world. Diagnosis: epigastric pain + elevated lipase (+/- imaging).
A 28-year-old man presents with episodic abdominal pain, non-bloody diarrhea, and a perianal fistula. Colonoscopy shows skip lesions with cobblestoning in the terminal ileum. Biopsy would MOST likely show:
Answer: D — Transmural inflammation with noncaseating granulomas
D) Correct: Crohn's disease shows transmural inflammation, skip lesions, and noncaseating granulomas — fistulas reflect transmural involvement. A) Crypt abscesses confined to mucosa describe ulcerative colitis — off-by-one IBD trap. C) Caseating granulomas + AFB = intestinal TB (can mimic Crohn's). B) Signet ring cells = diffuse gastric cancer. E) Flask-shaped ulcers + trophozoites = amebiasis (Entamoeba histolytica).
Where is intrinsic factor produced?
Answer: D — Parietal cells of the stomach
Parietal cells produce both gastric acid (HCl) AND intrinsic factor. IF binds vitamin B12 in the duodenum, enabling absorption in the terminal ileum. Pernicious anemia = autoimmune destruction of parietal cells → B12 deficiency.
A 50-year-old man with cirrhosis presents with hematemesis. Endoscopy reveals bleeding esophageal varices. Which medication reduces the risk of rebleeding by decreasing portal pressure?
Answer: A — Propranolol
A) Correct: nonselective beta-blockers (propranolol, nadolol) reduce portal pressure by decreasing cardiac output (β1) AND causing splanchnic vasoconstriction via unopposed α (β2 blockade) — both effects required. B) Metoprolol is β1-selective; lacks the splanchnic vasoconstriction — off-by-one beta-blocker trap. C) Atenolol is β1-selective. D) Esmolol is ultra-short-acting β1-selective IV agent. E) Carvedilol is nonselective AND alpha-blocking, BUT the option falsely describes it as β1-only.
A 40-year-old woman is found to have multiple polyps on screening colonoscopy. Family history reveals her father and paternal aunt had colon cancer in their 40s. Genetic testing reveals a mutation in the APC gene. Which is the MOST appropriate management?
Answer: D — Prophylactic total colectomy
D) Correct: familial adenomatous polyposis (APC mutation) results in 100% lifetime risk of colorectal cancer; prophylactic colectomy is standard. A) Standard average-risk screening is inappropriate — undertreatment. B) Surveillance alone with hundreds of polyps cannot reliably prevent cancer. C) Aspirin reduces polyp burden but doesn't replace colectomy. E) Sulindac and other NSAIDs/COX-2 inhibitors regress polyps but are adjunctive, not definitive.
4 cards from the 5 in this chapter.
Liver function tests pattern (hepatocellular)?
AST/ALT > ALP. Hepatitis pattern.
Hepatitis B serology: anti-HBs?
Immunity (prior infection or vaccination).
LFT pattern (cholestatic)?
ALP > AST/ALT. GGT also elevated. Biliary obstruction pattern.
Hepatitis B serology: HBsAg + HBeAg?
Active infection, high infectivity.
These are a sample. The full Gastrointestinal System chapter runs 19 items with per-chapter progress tracking, on the web and in the iOS app.
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