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USMLE Step 1 High‐Yield Gastrointestinal Topics

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Gastroenterology

High Yield USMLE Step 1 Notes

Welcome to the Gastroenterology High-Yield Notes for Step 1.

These are the most commonly tested topics on the exam—ideal for quick review in your last 2 weeks before the exam, when you’re short on time, or when you’re just starting out and want to focus on what is high yield. Created and peer-reviewed by physicians who scored 260+ on Step 1 in a Q&A style to reinforce active learning.

How to use this file

Read the question ➔ cover the answer ➔ self-quiz before revealing.
Review the NOTES ➔ they include high-yield details you don’t want to miss.
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Congenital & Pediatric GIT

1. A newborn begins choking, coughing, and vomiting immediately after the first feeding. A nasogastric tube is inserted but coils in the upper esophagus on X-ray. What is the most likely diagnosis?
➔ Tracheoesophageal fistula with esophageal atresia

Note: The failure to pass a nasogastric tube into the stomach is due to associated esophageal atresia

2. A newborn presents with respiratory distress shortly after birth. Chest X-ray reveals bowel loops in the left thoracic cavity with mediastinal shift. What is the most likely diagnosis
➔ Congenital diaphragmatic hernia (Occurs due to failure of pleuroperitoneal membrane fusion allows abdominal contents to herniate into the thorax, typically on the left side, impairing lung development)

Note: Leads to pulmonary hypoplasia and neonatal respiratory distress

3. A full-term newborn is delivered with loops of bowel protruding from the abdomen to the right of the umbilicus. The bowel is uncovered and exposed to air. What is the most likely diagnosis?
➔ Gastroschisis (Bowel herniation + usually right of umbilicus + no covering sac (not covered by peritoneum or amnion → think Gastroschisis)

Note: VS Omphalocele:
○ Midline herniation of abdominal contents through the umbilical ring
○ Covered by peritoneum and amnion (sac visible)
○ Frequently associated with congenital anomalies (e.g., Down syndrome)

4. A 4-week-old firstborn male presents with projectile, nonbilious vomiting. Exam reveals a firm, olive-shaped mass in the epigastric area and visible gastric peristalsis. Labs show metabolic alkalosis. What is the most likely diagnosis?
➔ Hypertrophic pyloric stenosis (occurs due to concentric hypertrophy of pyloric sphincter)

Note: Nonbilious projectile vomiting leads to
○ Loss of Hcl → leading to hypochloremia and alkalosis
○ Volume depletion→ which causes RAAS activation → leading to hypokalemia
○ Final metabolic disturbance is hypokalemic, hypochloremic metabolic alkalosis → this concept is asked about much in acid base disturbances and arrows questions
Note: First born males and exposure to macrolides (erythromycin) ↑ risk.

5. A 3-day-old newborn presents with bilious vomiting and abdominal distension. An abdominal X-ray shows a “double bubble” sign. Surgical exploration confirms duodenal atresia. Which embryological region is affected?
➔ Foregut (As it develops into the pharynx → to proximal duodenum, It is supplied by Celiac artery)

Note:
○ Midgut: develops into the distal duodenum → to proximal 2/3 transverse colon; supplied by SMA
○ Hindgut: develops into the distal 1/3 transverse colon → to upper anal canal; supplied by IMA

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6. A newborn with Down syndrome develops bilious vomiting within hours of birth. Abdominal X-ray shows a “double bubble” sign. What is the most likely diagnosis?
➔ Duodenal atresia (Newborn + bilious vomiting + “double bubble” → think duodenal atresia, it occurs due to failure of recanalization of the duodenum)

Note: Duodenal atresia is strongly associated with Down syndrome
Note: Double bubble sign can also be seen in annular pancreas
Note: VS Jejunal atresia → which shows ‘’Triple bubble sign’’ – occurs due to mesenteric vessel disruption → ischemic necrosis of fetal intestine → leading to segmental resorption).
Note: VS Hypertrophic pyloric stenosis → which causes nonbilious vomiting VS the bilious vomiting of duodenal atresia

7. A 2-month-old male presents with a groin swelling that enlarges when crying and extends into the scrotum. What is the most likely diagnosis?
➔ Indirect inguinal hernia (It is a congenital hernia that occurs due to a patent processus vaginalis following the inguinal canal into the scrotum)

Indirect Inguinal Hernia	Direct Inguinal Hernia
– Protrudes through Deep inguinal ring → to superficial inguinal ring → then to groin – It is lateral to inferior epigastric vessels – Caused by failure of processus vaginalis to close – Covered by all three layers of spermatic fascia	– Protrude through Hesselbach triangle – It is medial to inferior epigastric and lateral to rectus abdominis – Caused by acquired weakness of transversalis fascia mostly in older men. – Covered only by external spermatic fascia

Indirect Inguinal Hernia

Direct Inguinal Hernia

– Protrudes through Deep inguinal ring → to superficial inguinal ring → then to groin

– It is lateral to inferior epigastric vessels

– Caused by failure of processus vaginalis to close

– Covered by all three layers of spermatic fascia

– Protrude through Hesselbach triangle

– It is medial to inferior epigastric and lateral to rectus abdominis

– Caused by acquired weakness of transversalis fascia mostly in older men.

– Covered only by external spermatic fascia

Note: VS Umbilical hernia is a congenital defect due to incomplete closure of the umbilical ring. It is covered by skin and subcutaneous tissue and typically resolves spontaneously within the first few years of life.

8. A 3-day-old infant presents with bilious vomiting. Imaging shows bowel loops clumped on the right side and a corkscrew duodenum on upper GI series. What is the most likely diagnosis?
➔ Midgut volvulus (Occurs due to twisting of the midgut around its mesentery, it is predisposed by midgut malrotation)

Note: Midgut malrotation
○ Occurs when small bowel clumped on the right side
○ Associated with Ladd bands: fibrous bands compressing the duodenum
Note: Midgut volvulus shows Corkscrew appearance on upper GI series (common in neonates).
Note: VS Sigmoid volvulus which affects elderly and shows Coffee bean sign on X-ray.

9. A 1-year-old boy presents with intermittent severe abdominal pain and is drawing his legs to his chest. He has dark, currant jelly stools and a sausage-shaped mass is felt in the abdomen. What is the most likely diagnosis?
➔ Intussusception (Occurs due to telescoping of bowel, most commonly at the ileocecal junction)

Note: Risk factors in children include:
○ Recent viral infections or rotavirus vaccine as they both leads to Peyer patch hypertrophy
○ Meckel diverticulum and small bowel wall hematoma (IgA vasculitis)
○ They all act as a lead point for Intussusception in children
Note: In adults lead points for Intussusception include intra luminal masses or tumors
Note: Associated with Ladd bands: fibrous bands compressing the duodenum
Note: Shows Target sign on ultrasound or CT
Note: Air enema is diagnostic and therapeutic

10. A 5-year-old boy is brought to the clinic due to episodes of painless rectal bleeding over the past week. Physical examination reveals conjunctival pallor. A fecal occult blood test is positive. What is the next step in diagnosis?
➔ 99mTc-pertechnetate scan (Symptoms suggestive of Meckel diverticulum, a true diverticulum due to persistent vitelline duct → the scan detects ectopic gastric mucosa found in Meckel diverticulum).

Note: Meckel diverticulum is the most common cause of rectal bleeding in children
Note: True diverticulum = Involves all gut wall layers.
○ Example: Meckel diverticulum (remnant of vitelline duct)
○ Meckel diverticulum may contain ectopic gastric or pancreatic tissue → bleeding (hematochezia/melena).
Note: VS False diverticulum (Pseudodiverticulum) = Involves outpouching of mucosa/submucosa only.

11. A premature, formula-fed newborn develops abdominal distension and lethargy. Abdominal X-ray reveals lucent areas within the bowel wall. What is the most likely diagnosis?
➔ Necrotizing enterocolitis (It is Intestinal necrosis that → leads to perforation of intestine→ leading to pneumatosis intestinalis/pneumoperitoneum/ portal venous gas)

Note: (Premature infant + hospitalized + has vomiting or distension→ think Necrotizing enterocolitis)
Note: The lucent areas within the bowel wall indicates pneumatosis intestinalis
Note: Affects premature, formula-fed infant

12. A 3-week-old infant is brought in for evaluation of persistent jaundice. Physical exam shows hepatomegaly and scleral icterus. Labs reveal elevated direct (conjugated) bilirubin. Urine is dark and stools are pale. What is the next step in diagnosis?
➔ Abdominal ultrasound (To assess gallbladder anatomy; hypoplasia or absence suggests biliary atresia).

Note: Biliary atresia
○ Persistent jaundice >2 weeks + pale stools + dark urine + hepatomegaly → think biliary atresia.
○ Occurs due to progressive fibro-obliteration of extrahepatic bile ducts.

13. Newborn presents with failure to pass meconium, tight anal sphincter and explosive expulsion of feces on digital exam. What is the cause of the patient’s symptoms?
➔ Hirschsprung disease (a disease caused by failed neural crest cell migration → leads to lack Auerbach and Meissner plexuses in the distal colon and rectum)

Note: Normally
○ Submucosal plexus (Meissner) → located in submucosa
○ Myenteric plexus (Auerbach) → located in muscularis externa
Note: Gut wall layers (from inside → out)
○ Mucosa: Epithelium + Lamina propria + Muscularis mucosa
○ Submucosa: Contains Meissner (submucosal) plexus → controls secretion
○ Muscularis externa: Contains Auerbach (myenteric) plexus → controls motility
○ Serosa (if intraperitoneal) or Adventitia (if retroperitoneal)

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Upper GIT System

14. A 45-year-old man presents with burning chest pain that worsens after meals and when lying flat. He reports sour-tasting fluid in his throat at night. What is the mechanism?
➔ Decreased lower esophageal sphincter (LES) tone (GERD occurs due to transient or chronic relaxation of the LES, allowing gastric acid to reflux into the esophagus)

Note: Heartburn, regurgitation, and worsening when supine or after meals → think GERD
Note: Chronic GERD can lead esophagitis, strictures and Barrett esophagus

15. A 70 year old patient presents with chronic heartburn that has been recurring for 7 years undergoes endoscopy, showing Barrett esophagus. What type of cellular change is seen?
➔ Intestinal Metaplasia (Occurs due to replacement of nonkeratinized stratified squamous epithelium with intestinal/nonciliated columnar epithelium → this is intestinal metaplasia).

Note: Leads to increased risk of esophageal adenocarcinoma (Lower 1/3 of esophagus).

16. A 28-year-old pregnant woman in her second trimester complains of frequent heartburn and occasional constipation. What is the cause of these symptoms?
➔ Progesterone-mediated smooth muscle relaxation

Note: Progesterone ↓ lower esophageal sphincter (LES) tone → leading to gastroesophageal reflux (heartburn
Note: Progesterone also slows intestinal motility → causing constipation

17. A 45-year-old man presents with dysphagia to solids and liquids. A barium swallow reveals a narrowing at the distal esophagus, creating a tapering, pointed shape resembling a bird’s beak. What is the most likely diagnosis?
➔ Achalasia (Occurs due to loss of inhibitory neurons in the myenteric plexus, leading to failure of LES relaxation.)

Note: In achalasia: dysphagia starts with solids and liquids in the same time VS Mechanical obstruction (e.g., cancer): dysphagia starts with solids and progresses to liquids
Note: Esophageal manometry is the gold standard for diagnosis
Note: Achalasia causes:
○ Idiopathic (most common)
○ Pseudoachalasia: Can be caused by Chagas disease (Trypanosoma cruzi) or esophageal malignancies.

18. A 50-year-old woman presents with chest pain and dysphagia, relieved by nitrates. A barium swallow shows a “corkscrew” appearance of the esophagus. What is the most likely diagnosis?
➔ Diffuse Esophageal Spasm (Occurs due to uncoordinated esophageal contractions causing chest pain and dysphagia.

Note: Barium Swallow shows “Corkscrew” esophagus.
Note: It causes Angina-like chest pain that is relieved by Nitrates.

High Yield Manometry findings:

Disorder	LES Tone	Peristalsis	Key Features	Imaging Findings
Achalasia	↑ (Impaired relaxation)	Absent	Dysphagia to solids & liquids	Bird’s beak on barium swallow
Diffuse Esophageal Spasm (DES)	Normal or intermittent relaxation	Premature, simultaneous contractions	Intermittent chest pain & dysphagia	Corkscrew esophagus on barium swallow
Scleroderma Esophageal Dysmotility	↓ (Hypotensive)	Absent in lower 2/3	GERD symptoms, systemic sclerosis	Dilated esophagus on imaging

19. A 30-year-old male with a history of atopic dermatitis presents with difficulty swallowing. Endoscopy shows rings and linear furrows in the esophagus. Biopsy reveals eosinophilic infiltration. What is the most likely diagnosis?
➔ Eosinophilic Esophagitis (It is caused by Eosinophilic infiltration of the esophagus, often seen in atopic patients.)

Note: Endoscopy shows Rings and linear furrows.
Note: It is associated with atopic conditions (e.g., asthma, eczema).

20. A patient with HIV presents with dysphagia, odynophagia, and substernal pain. What’s the next step in diagnosis?
➔ Esophagogastroduodenoscopy with biopsy (HIV or IV drug use + dysphagia → suspect infectious esophagitis; confirmed with EGD and biopsy).

Note: White plaques on EGD → Candida → treat with Fluconazole.
– Microscopy: Yeast with pseudohyphae invading squamous epithelium.
Note: Small, punched-out ulcers on EGD → HSV → treat with Acyclovir.
– Microscopy: Multinucleated giant cells, eosinophilic intranuclear inclusions.
Note: Large, linear ulcers on EGD → CMV → treat with Ganciclovir.
– Microscopy: Enlarged cells with intranuclear and cytoplasmic inclusions.

21. A 45-year-old man presents with severe chest pain and subcutaneous emphysema after a bout of violent retching. What is the most likely diagnosis?
➔ Boerhaave Syndrome (Occurs due to transmural esophageal rupture, often after forceful vomiting → leads to severe chest pain, subcutaneous emphysema, and crepitus)

Note: In Boerhaave Syndrome there is transmural esophageal rupture VS Mallory-Weiss syndrome; which causes only mucosal +/- submucosal partial thickness longitudinal lacerations after severe episodes vomiting that ends with a bloody one

22. A 55-year-old woman presents with difficulty swallowing, fatigue, and pallor. Lab results show iron deficiency anemia. Esophagram reveals esophageal webs. What is the most likely diagnosis?
➔ Plummer-Vinson Syndrome (Dysphagia + iron deficiency anemia + esophageal webs → think Plummer-Vinson Syndrome)

Note: Plummer-Vinson Syndrome increases risk of esophageal squamous cell carcinoma (in the upper 2/3 of the esophagus).

23. A 70-year-old man presents with progressive difficulty swallowing, especially with solids. His wife notes he often coughs after eating and has foul-smelling breath. What is the most likely diagnosis?
➔ Zenker diverticulum (A pharyngoesophageal false diverticulum caused by herniation of mucosa/submucosa through Killian triangle—between the cricopharyngeus and thyropharyngeus muscles).

Note: Zenker diverticulum presents with dysphagia, halitosis, regurgitation, and aspiration.
Note: Other example of false diverticulum include Colonic diverticula (common in the sigmoid colon of elderly patients, often asymptomatic or may cause painless bleeding or diverticulitis)

24. A 50-year-old man presents with epigastric pain that worsens after meals and is associated with weight loss. He has a history of regular NSAID use. What is the most likely diagnosis?
➔ Gastric Ulcer (Associated with pain that increases with meals, typically caused by H. pylori or NSAID use).

Note: NSAIDs → Causes ↓prostaglandin and mucosal blood flow → leading to erosion of the gastric mucosa
Note: Complications include
○ Gastric ulcer in the Lesser curvature → leads to bleeding from the left gastric artery.
○ Gastric ulcers have a higher risk of cancer than duodenal ulcers → so gastric ulcer margins should always be biopsied to rule out malignancy.

25. A 30-year-old man presents with epigastric pain that worsens between meals and improves with food.Urea breath test is positive. Endoscopy reveals erythematous mucosa in the antrum. What is the most likely pathogen?
➔ Helicobacter pylori

Note:
○ H.pylori is oxidase, catalase, and urease positive leading to → ↑ Ammonia → ↑ pH → this enables survival of organisms.
○ Bacterial attachment + cytotoxin release (e.g., cagA) → leads to ↓somatostatin and bicarbonate → leads to mucosal barrier disruption → leads to epithelial damage

26. A 40-year-old man with recurrent abdominal pain reports that his pain improves after eating, and he has gained some weight. He is also positive for H. pylori. What is the most likely diagnosis?
➔ Duodenal Ulcer (Associated with pain that decreases with meals, often caused by H. pylori)

Note: Complications include
○ Posterior duodenal ulcer can cause bleeding from the gastroduodenal artery.
○ Anterior duodenal ulcers are more prone to rupture → leading to air under the diaphragm.
○ Perforation is suggested by sudden severe pain followed by → signs of peritonitis (e.g., guarding, rebound tenderness) + air under the diaphragm on imaging

27. A 58-year-old man in the ICU after a traumatic brain injury develops hematemesis. Endoscopy reveals multiple shallow gastric ulcers. What is the most likely cause?
➔ Cushing ulcer (Cushing ulcers are gastric ulcers associated with increased intracranial pressure, which leads to → increased vagal stimulation → leads to increased ACh release → causes increased gastric acid secretion)

Note: Differentiate from Curling ulcer, which occurs after burns and is due to mucosal ischemia

28. A 58-year-old woman presents with fatigue, glossitis, and paresthesia. Labs reveal macrocytic anemia and anti-parietal cell antibodies. What is most likely deficient in this patient?
➔ Intrinsic factor (Secreted by parietal cells, It is necessary for vit B12 absorption).

Note: Autoimmune destruction of IF or parietal cells → leads to Pernicious anemia → leading to vit B12 deficiency.
Note: Parietal cells → secrete HCl (acidic environment) & Intrinsic Factor (for vit B12 absorption).
Note: Other causes of vit B12 deficiency include:
○ Malabsorption disorders (e.g., Crohn’s disease and Pancreatic insufficiency)
○ Gastric surgery (e.g., gastrectomy → loss of IF-secreting cells)
○ Chronic metformin or alcohol use
○ Strict vegan diet (due to lack of dietary B12)

29. A 67-year-old man with osteoarthritis presents to the ER with hypotension (BP 90/60 mmHg) and severe epigastric pain. He has been on chronic NSAID therapy. Endoscopy reveals a ruptured gastric ulcer on the lesser curvature of the stomach. Which vessel is ruptured?
➔ Left gastric artery (When a gastric ulcer perforates, it can erode into adjacent blood vessels, leading to significant bleeding. The specific artery involved depends on the ulcer’s location.).

Note: Celiac trunk branches include common hepatic, splenic, left gastric arteries
Note: Blood supply of stomach (Ulcers perforated in those areas can lead to bleeding from its supplying artery):
○ Lesser curvature → Supplied by left & right gastric arteries
○ Greater curvature → Supplied by left & right gastroepiploic arteries
○ Fundus → Supplied by short gastric branches from splenic artery

30. A 62-year-old woman presents with early satiety and unintentional weight loss. Endoscopy reveals diffuse thickening of the stomach wall. Biopsy shows mucin-filled cells with nuclei pushed to the periphery. What is the cause of the patient’s symptoms?
➔ Diffuse-type gastric adenocarcinoma (Mucin-filled cells with nuclei pushed to the periphery indicates Signet Ring Cells which are characteristic for Diffuse-type gastric adenocarcinoma)

Note: Occurs due to loss of E-cadherin function.
Note: Associated with leather-like stomach wall.

31. A 70-year-old man presents with iron deficiency anemia, weight loss, and intermittent epigastric pain. Endoscopy reveals a gastric ulcer with raised margins located on the lesser curvature of the stomach. What is the diagnosis?
➔ Intestinal-type gastric cancer (Ulcer with raised margins located on the lesser curvature of the stomach is characteristic)

Note: Notable signs for gastric cancer (intestinal and diffuse types):
○ Virchow node: Left supraclavicular metastasis.
○ Krukenberg tumor: Bilateral ovarian metastasis (signet ring cells).
○ Sister Mary Joseph nodule: Periumbilical metastasis.
○ Blumer shelf: Rectouterine pouch metastasis (palpable mass).

32. A 36-year-old woman experiences right upper quadrant pain and nausea after eating a fatty meal. Ultrasound shows gallstones without signs of cholecystitis. Which hormone is most responsible for triggering her pain?
➔ Cholecystokinin (CCK) (As it stimulates gallbladder contraction, causing stone to obstruct cystic duct → leading to biliary colic).

Note: CCK deficiency can lead to → biliary stasis → leading to gallstone formation.
Note: CCK (secreted from I cells – in duodenum/jejunum):
○ ↑ Pancreatic enzymes, gallbladder contraction
○ Relaxes sphincter of Oddi

33. A 60-year-old man presents with new-onset diabetes, steatorrhea, and gallstones. Imaging reveals a pancreatic mass. Labs show decreased insulin, secretin, and CCK levels.
Which hormone is most likely secreted by this tumor?
➔ Somatostatin (Symptoms indicate somatostatinoma which leads to ↓ insulin → leading to Diabetes ,↓ secretin → leading to steatorrhea,↓ CCK → leading to gallstones).

Note: Somatostatin (secreted from D cells – GI/pancreas):
○ ↓ All GI hormones, insulin, glucagon.

34. A 45-year-old man presents with multiple recurrent duodenal and jejunal ulcers unresponsive to PPIs. Imaging shows a pancreatic mass. Labs reveal hypercalcemia and elevated gastrin levels that further increase after secretin administration. What is the diagnosis?
➔ Zollinger-Ellison syndrome, Gastrinoma (Recurrent or jejunal ulcers + elevated gastrin levels + after secretin administration + pancreatic mass → indicates the presence of a gastrin-secreting tumor.)

Note: Associated with MEN1: pituitary, pancreatic, parathyroid tumors.
Note: Gastrin (secreted from G cells – antrum):
○ ↑ Gastric acid & motility
Note: Secretin (secreted from S cells – duodenum):
○ ↑ Pancreatic HCO₃⁻, bile secretion
○ ↓ Gastric acid

35. A 50-year-old woman presents with chronic watery diarrhea, hypokalemia, and a pancreatic mass. What is the most likely diagnosis?
➔ VIPoma (Watery Diarrhea + hypokalemia + achlorhydria → think VIPoma (WDHA syndrome))

Note: VIP (secreted from enteric neurons):
○ ↑ Water/electrolyte secretion, relaxes sphincters.
Note: Treated with Octreotide

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Lower GIT System

36. A 72-year-old woman presents with a bulge below the inguinal ligament, just lateral to the pubic tubercle. What structure lies immediately lateral to the herniated area?
➔ Femoral vein (Femoral hernias occur below the inguinal ligament and protrude through the femoral canal, which lies medial to the femoral vein within the femoral sheath)

Note: Femoral region anatomy; From lateral to medial: (NAVEL)
○ Nerve (femoral nerve)
○ Artery (femoral artery)
○ Vein (femoral vein)
○ Empty space
○ Lymphatics (in femoral canal → potential hernia site)

37. A 6-year-old child with diarrhea is given plain water but continues to show signs of dehydration. However, improvement is seen after administering a glucose-containing oral rehydration solution. What is the transporter responsible for this therapeutic effect?
➔ SGLT1 ( It is a Sodium-glucose cotransporter facilitates absorption of water with glucose and Na⁺).

Note: Oral rehydration therapy relies on Na⁺ and glucose co-transport to drive water absorption.
Note: If water is given alone → causes poor absorption;so solutions must include glucose + electrolytes.

38. A researcher studies carbohydrate absorption in enterocytes. She notes that glucose and galactose use one transporter, while fructose uses another. Which transporter is specific for fructose uptake into enterocytes?
➔ GLUT5 (Allows facilitated diffusion of fructose across apical membrane.)

Note: Carbohydrate transporters
○ SGLT1: Allows glucose/galactose uptake with Na⁺ (active transport)
○ GLUT5: Allows fructose uptake (facilitated diffusion)
○ GLUT2: Allows basolateral transport of monosaccharides into blood
○ GLUT2: presents in pancreatic β-cells, where it plays a key role in glucose sensing and insulin release.

39. A 34-year-old woman presents with chronic diarrhea, bloating, fatigue, and a pruritic, vesicular rash on her elbows. Her duodenal biopsy shows villous atrophy, crypt hyperplasia, and lymphocytic infiltration. What is the most likely diagnosis?
➔ Celiac Disease

Note: Autoimmune reaction to gluten → leads to damages small intestinal mucos
Note: Duodenal biopsy shows villous atrophy + crypt hyperplasia + intraepithelial lymphocytes
Note: Associated with iron deficiency anemia and dermatitis herpetiformis (IgA deposition in dermal papillae)

40. A 55-year-old man presents with weight loss, diarrhea, arthralgia, and memory difficulties. His biopsy reveals PAS-positive foamy macrophages in the lamina propria. What is the most likely diagnosis?
➔ Whipple Disease (Diarrhea + cardiac symptoms + arthralgias + neurologic symptoms → think Whipple Disease.

Note: Caused by Tropheryma whipplei (intracellular Gram-positive actinomycete).
Note: PAS + foamy macrophages is seen in the lamina propria.

41. A 30-year-old patient reports bloating, abdominal cramps, and watery diarrhea after consuming dairy products. What is the best test to confirm the diagnosis?
➔ Lactose hydrogen breath test (Symptoms suggestive of Lactase deficiency → resulting in undigested lactose fermented by colonic bacteria → leading to formation of gas & osmotic diarrhea)

Note: Can occur secondary to gastroenteritis.
Note: In the absence of lactase → lactose (milk sugar) is not digested → gut bacteria ferment lactose down → leading to lactose conversion into:
Short-chain fatty acids (SCFAs) → leading to ↓ Stool pH
Gases like hydrogen (H₂) → +ve hydrogen breath test

42. A 30-year-old man returns from a coastal trip with profuse, watery diarrhea. He denies abdominal pain or fever. Stool appears pale and cloudy. He is lethargic and hypotensive. What is the cause of his symptoms?
➔ Vibrio cholerae

Note: Source is contaminated water/seafood.
Note: Can be complicated to severe dehydration, electrolyte loss → leading to shock.
Note: VS Other travel related watery diarrhea include
○ Enterotoxigenic E. coli (ETEC) → produces Heat-labile (↑ cAMP) and heat-stable (↑ cGMP) toxins
○ Giardia lamblia → foul-smelling, fatty stools, especially from untreated water
○ Norovirus →common on cruise ships, highly contagious, causes vomiting and watery diarrhea

43. A 25-year-old tourist develops watery diarrhea two days after arriving in Mexico. He has no fever or blood in the stool. He reports eating from street vendors. What is the most likely pathogen?
➔ Enterotoxigenic Escherichia coli (Also known as Traveler’s diarrhea)

Note: Toxins produced:
○ Heat-labile toxin → which ↑ cAMP.
○ Heat-stable toxin → which ↑ cGMP.
Note: Prevention: Avoid raw produce and untreated water while traveling.

44. A 58-year-old woman presents with watery diarrhea and abdominal pain after a recent course of antibiotics for a urinary tract infection. What is the most likely diagnosis?
➔ Clostridium difficile

Note: Risk factors include antibiotics (esp. clindamycin, fluoroquinolones), PPIs and hospitalization.
Note: Treated with oral vancomycin or fidaxomicin, depending on severity
Note: Can be complicated into toxic megacolon

45. A 28-year-old hiker develops foul-smelling, greasy diarrhea and bloating after drinking from a mountain stream. He denies fever or blood in the stool. What is the most likely cause of his symptoms?
➔ Giardia lamblia (It can lead to malabsorption.)

46. A 36-year-old man with untreated HIV presents with chronic, profuse watery diarrhea. He reports significant weight loss and weakness. Stool exam shows acid-fast oocysts. What is the most likely cause?
➔ Cryptosporidium (Can cause chronic diarrhea in HIV )

47. A 1-year-old child presents in winter with vomiting and profuse watery diarrhea. He attends daycare and is showing signs of dehydration. What is the most likely cause?
➔Rotavirus (Can cause Severe dehydration in children)

48. An adult passenger on a cruise ship develops acute-onset vomiting and watery diarrhea. Several others on board have similar symptoms. What is the most likely cause?
➔ Norovirus (Usually Self-limited, lasts 2–3 days.)

49. A 5-year-old child presents with bloody diarrhea, fever, and abdominal cramping. Stool culture reveals Shigella species. The child develops renal failure and thrombocytopenia. What is the most likely complication?
➔ Hemolytic-Uremic Syndrome ( Shigella produces Shiga toxin → causes endothelial damage → leading to hemolytic anemia + renal failure + thrombocytopenia → diagnostic of HUS)

Note: Transmission is Fecal-oral and has low infectious dose (ID50)
Note: HUS can also be caused by EHEC (O157:H7) which is transmitted in undercooked beef.

50. A 10-year-old develops fever, abdominal pain, and bloody diarrhea after eating undercooked eggs. Stool culture grows a gram-negative rod. What is the most likely organism?
➔ Salmonella (non-typhi) (inflammatory diarrhea + Undercooked poultry/eggs → think Salmonella,non-typhi)

Note: Can be complicated by Reactive arthritis, especially in HLA-B27+ individuals.

51. A 16-year-old recent traveler presents with prolonged fever, abdominal pain, and a faint salmon-colored rash on the abdomen. He initially had constipation, but now has diarrhea. What is the most likely organism?
➔ Salmonella typhi (Rose spots on abdomen + stepwise fever + constipation then diarrhea → think Salmonella typhi)

Note: Can be complicated into intestinal perforation

52. A 32-year-old man presents with bloody diarrhea, fever, and crampy abdominal pain after traveling to a rural area and consuming undercooked chicken. What is the diagnosis?
➔ Campylobacter jejuni

Note: May be complicated by Guillain-Barré syndrome or Reactive arthritis

53. A 7-year-old boy presents with fever, right lower quadrant abdominal pain, and diarrhea. Surgical exploration showed no inflamed appendix. His symptoms began shortly after eating pork. What is the diagnosis?
➔ Mesenteric lymphadenitis (Due to Yersinia enterocolitica, differentiate from appendicitis by the presence of inflammatory diarrhea)

54. A 30-year-old man who recently returned from India presents with several days of bloody diarrhea and new-onset right upper quadrant abdominal pain. Imaging reveals a liver abscess. What is the most likely organism?
➔ Entamoeba histolytica (Recent travel + bloody diarrhoea + liver abscess or colon ulcers → think Entamoeba histolytica)

Note: Entamoeba histolytica has prolonged course with mild fever VS bacterial causes of diarrhea which has high fever and short course
Note: Transmitted by contaminated water/food; fecal-oral route.
Note: Key feature: Flask-shaped ulcers in the colon

55. A 20-year-old man presents with fever, vomiting and abdominal pain that started around the umbilicus and later localized to the right lower quadrant. What is the diagnosis?
➔ Acute appendicitis (The mechanism is obstruction of the appendiceal lumen by fecalith, or lymphoid hyperplasia leading to inflammation of the appendix)

Note: Periumbilical pain is caused by visceral pain via T8–T10 afferents.
Note: RLQ (McBurney’s point) pain is caused by somatic pain from parietal peritoneum irritation.
Note: McBurney’s point lies 1/3 the distance from the right ASIS to the umbilicus.

56. A 75-year-old man is hospitalized after a collision. He arrives in hypovolemic shock and receives multiple blood transfusions. Two days later, he develops abdominal pain and bloody stool. CT imaging shows mucosal edema and thumbprinting of the colon. Which regions of the colon are mostly affected by ischemia?
➔ Splenic flexure and rectosigmoid junction (These regions are most susceptible to ischemia as they are regions between two arterial supplies → they are called Watershed areas)

Note: Bloody diarrhoea + post surgery or hypotension → think Ischemic colitis
Note: Watershed areas:
○ Splenic flexure: between SMA and IMA
○ Rectosigmoid junction: between IMA and superior rectal artery

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Watershed regions of colon

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57. A 68-year-old man with atrial fibrillation presents with sudden-onset severe abdominal pain. Physical exam shows a soft, non-tender abdomen. Labs reveal elevated lactate. What is the most likely diagnosis?
➔ Acute mesenteric ischemia (AF or irregular rhythm + periumbilical or epigastric pain out of proportion to exam + blood in stool → think acute mesenteric ischemia)

Note: Elevated lactate and metabolic acidosis are key lab findings
Note: VS Chronic Mesenteric Ischemia (“intestinal angina”):
○ Caused by Atherosclerosis
○ Symptoms include chronic postprandial pain, food aversion, weight loss

58. A 75-year-old man with end-stage renal disease presents with episodic painless GI bleeding. Colonoscopy is inconclusive. What is the next diagnostic step?
➔ Angiography (Used to identify bleeding from angiodysplasia, a vascular malformation common in the elderly and patients with ESRD, vWD, or aortic stenosis).

Note: GI Bleeding Classification
○ Upper GI Bleed: Above the ligament of Treitz → Hematemesis/Melena
○ Lower GI Bleed: Below the ligament of Treitz → Hematochezia.

59. A 28-year-old woman presents with recurrent abdominal pain that improves after defecation and is associated with changes in stool frequency and consistency. What is the diagnosis?
➔ Irritable Bowel Syndrome (IBS) (Chronic abdominal pain + change in stool frequency/form + relief with defecation for >3 months → are diagnostic for IBS)

60. A 25-year-old patient presents with chronic diarrhea, weight loss, and abdominal pain. Colonoscopy reveals skip lesions, cobblestone mucosa, and rectal sparing. What is the diagnosis?
➔ Crohn Disease (Findings are classic for Crohn due to its patchy, transmural inflammation that can affect any part of the GIT with characteristic skip lesions and rectal sparing)

61. A 30-year-old patient presents with bloody diarrhea. Colonoscopy shows continuous colonic lesions starting from the rectum. What is the diagnosis?
➔Ulcerative Colitis (The hallmark features for Ulcerative Colitis are continuous mucosal inflammation confined to the colon, always involving the rectum.)

Crohn Disease	Ulcerative Colitis
Skip lesions throughout GIT with rectal sparing; cobblestone mucosa; creeping fat	Continuous colonic lesions with rectum involved
Transmural inflammation – Fissures, strictures and fistulas	Only mucosa/submucosa involved- superficial/deep ulcers
Noncaseating granulomas on microscopy	Crypt abscesses and ulcers on microscopy
Bowel wall thickening “string sign” on small bowel follow-through	Loss of haustra leading to “lead pipe” appearance on imaging.
Notable complications include Calcium oxalate kidney stone→ as Calcium binds to fat in the stool while oxalate gets absorbed and reaches kidney	Notable complications include: – Toxic Megacolon – Associated with 1° sclerosing cholangitis (MPO ANCA/p-ANCA).

62. A 52-year-old patient undergoes colonoscopy revealing an adenomatous polyp. Molecular testing shows an APC mutation and KRAS activation. What is the next key molecular event leading to carcinoma formation?
➔ Loss of TP53 (This tumor suppressor loss allows malignant transformation of the adenoma).

Note: Colorectal Cancer Pathogenesis – Chromosomal Instability Pathway:-
○ Normal Colon: Healthy epithelium + APC gene intact.
○ APC mutation → leads to ↑ proliferation, ↓ adhesion
○ KRAS mutation → leads to Polyp (growth)
○ TP53 loss → leads to Carcinoma (invasion/malignancy)
Note: Aspirin is protective as it inhibits COX-mediated inflammation, which can slow polyp progression and reduce colorectal cancer risk

63. A 17-year-old male is found to have hundreds of colonic polyps on colonoscopy. Genetic testing reveals a mutation in the APC gene. What is the recommended next step in management?
➔ Prophylactic colectomy (Symptoms suggestive of Familial Adenomatous Polyposis (FAP) due to APC mutation, with near 100% risk of colorectal cancer if untreated → Prophylactic colectomy should be performed)

Note: Other syndromes:
○ Gardner Syndrome: FAP + osteomas, dental abnormalities and soft tissue tumors
○ Turcot Syndrome: FAP + CNS tumors (e.g., medulloblastoma)
○ Juvenile Polyposis Syndrome: Numerous hamartomatous polyps in young children (<5 years)

64. A 19-year-old female presents with a history of intermittent abdominal pain and melena. Physical examination reveals dark blue to brown macules on her lips and buccal mucosa. Endoscopy shows multiple hamartomatous polyps in the small intestine. What is the most likely diagnosis?
➔ Peutz-Jeghers Syndrome (Hamartomatous polyps + mucocutaneous pigmentation strongly suggest → Peutz-Jeghers)

Note: Other syndromes:
○ Lynch Syndrome (HNPCC): Occurs due to MMR gene mutations → leads to microsatellite instability; associated with colorectal, endometrial, ovarian, and skin cancers

65. A 65-year-old man undergoes a screening colonoscopy, which reveals a large colonic polyp with villous histology. What is the most likely clinical significance of this finding?
➔ Increased risk of colorectal cancer

Note: High-risk Polyp include:
○ Adenomatous polyps: Villous type has higher risk of malignancy than Tubular
○ Serrated polyps: CpG methylation + BRAF mutation → precursor to Colorectal cancer.

66. A 65-year-old male presents with fatigue, weight loss and microcytic anemia. He denies any overt bleeding. What is the next best step in management?
➔ Colonoscopy (Age >50 + anemia or bowel habit changes → suspect colorectal cancer → do colonoscopy)

Note:
○ Most common location: Rectosigmoid > Ascending > Descending colon
○ Apple core lesion will be seen on barium enema X-ray
○ CEA is a tumor marker used for monitoring, not for screening

Feature	Right-Sided CRC (Ascending Colon)	Left-Sided CRC (Descending Colon)
Growth Pattern	Exophytic mass	Infiltrating mass
Symptoms	Occult bleeding → leads to Iron deficiency anemia, weight loss	Colicky pain, hematochezia, obstruction
Lumen Size	Larger lumen → causes Late obstruction	Smaller lumen → causes early obstruction

67. A 70-year-old male presents with fever, fatigue, and a heart murmur. Blood cultures grow Streptococcus gallolyticus, and he is diagnosed with bacteremia and endocarditis. What is the next best step in management?
➔ Colonoscopy (S. gallolyticus bacteremia/endocarditis is associated with an increased risk of underlying colorectal cancer).

Note: Colorectal cancer disrupts the mucosal barrier, allowing S. gallolyticus to enter the bloodstream and seed heart → valves leading to endocarditis
Note: Colonoscopy is indicated to rule out colorectal malignancy

68. A 47-year-old man with no significant medical history comes for a routine checkup. He has no family history of cancer. What is the appropriate next step regarding screening?
➔ Colonoscopy (In patients with average risk of CRC and no family history → Start screening at age 45, repeat every 10 years)

Note: Screening
○ First-degree relative with CRC → Start screening at age 40 or 10 years before the relative’s diagnosis
○ High-Risk Conditions (e.g., Lynch syndrome, FAP, IBD, personal history of CRC or polyps) → Screen earlier & more frequently
○ Colonoscopy is the gold standard screening method

69. A 50-year-old man with chronic constipation has 2 weeks of anal pain and bright red blood on toilet tissue after bowel movements. Pain improves with sitz baths. What is the most likely diagnosis?
➔ Anal fissure (tear below the dentate line causing painful defecation and bleeding)

Note: Mostly occurs at the posterior midline.
Note: Initial treatment includes stool softeners, sitz baths, topical analgesics, and vasodilators.
Note: VS External hemorrhoids: located below the dentate line; can be painful, especially if thrombosed; may cause swelling and visible bluish perianal lump.

70. A patient presents with rectal pain and a tender perianal mass. It lies below the dentate line. What is the most likely diagnosis?
➔ External hemorrhoid, (Somatic innervation from pudendal nerve below the dentate line makes them very painful, especially if thrombosed).

Note: VS Internal haemorrhoids
○ Lies above the pectinate/dentate line.
○ It has visceral innervation → makes it not painful.

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Liver, Biliary, and Pancreatic Systems

71. 25-year-old takes high doses of acetaminophen for headache. Develops RUQ pain and elevated AST/ALT. Which liver zone is most affected?
➔ Zone III (lies centrilobular/pericentral) (It is the 1st zone to be affected by ischemia and metabolic toxins)

Note: Hepatic lobules are the functional unit of liver and consists of:
○ Central vein in the center
○ Portal triads (portal vein, hepatic artery, bile ducts) on the edges
Note: Hepatic lobules organization (arranged from outside to inside):
○ Zone I: periportal, Zone II: intermediate, Zone III: pericentral.

72. A trauma patient is brought to the ER with ongoing intra-abdominal bleeding. During laparotomy, compression of the hepatoduodenal ligament between the thumb and index finger stops the bleeding. What structure is most likely involved?
➔ Proper hepatic artery (The Pringle maneuver includes clamping or compressing the hepatoduodenal ligament leading to temporarily occludes the portal triad to control bleeding from liver sources)

Note: Hepatoduodenal contains the portal triad: proper hepatic artery, portal vein and common bile duct
Note: Hepatoduodenal ligament is part of the lesser omentum connecting the liver to the duodenum

73. A 34-year-old woman in late pregnancy presents with abdominal pain, ascites, and hepatomegaly. Imaging shows absent hepatic vein flow. What is the most likely diagnosis?
➔ Budd-Chiari Syndrome (Caused by hepatic venous outflow obstruction → leads to↑ sinusoidal pressure → congestive liver disease)

Note: Caused by hypercoagulability (e.g., pregnancy, HCC, polycythemia vera) or compression

74. A 6-year-old boy is brought in with vomiting, lethargy, and confusion 3 days after recovering from influenza. His parents gave him aspirin during his illness. Labs show elevated liver enzymes and hypoglycemia. What is the most likely diagnosis?
➔ Reye Syndrome (Viral illness + aspirin use + encephalopathy → think Reye Syndrome).

Note: Occurs due to ↓ β-oxidation in mitochondria.
Note: Findings:
○ Microvesicular fatty liver, hypoglycemia.
○ Vomiting, hepatomegaly, encephalopathy and coma.
Note: Prevention; avoid aspirin in children except in Kawasaki disease.

75. A 28-year-old woman presents with nausea and vomiting 6 hours after intentionally ingesting 20 acetaminophen tablets. Labs show AST and ALT >1000 U/L. What is the most appropriate next step in management?
➔ Administer N-acetylcysteine (NAC) (Excess acetaminophen → leads to ↑ NAPQI → which causes glutathione depletion → leading to centrilobular hepatic necrosis, treated with NAC which replenishes glutathione)

Note: Lab findings: AST & ALT (>1000 U/L) and ↑ PT/INR.
Note: Risk Factors for glutathione depletion include:
○ Chronic alcohol use → leads to ↑ CYP2E1 → leads to ↑ NAPQI → causes glutathione depletion.
○ Fasting/malnutrition → leads to ↓ glutathione reserves.

76. A 28-year-old non-smoker presents with shortness of breath and elevated liver enzymes. Imaging reveals panacinar emphysema, and liver biopsy shows PAS-positive globules. What is the most likely diagnosis?
➔ α₁-Antitrypsin Deficiency (Young + emphysema without smoking + liver disease → think α₁-Antitrypsin Deficiency)

Note: Mechanism:
○ Misfolded α₁-antitrypsin (AAT) accumulates in hepatocytes → leading to Cirrhosis
○ ↓ AAT → causes uninhibited neutrophil elastase → leading to panacinar emphysema (esp. lower lobes)

77. A 17-year-old boy presents with tremors, personality changes, and hepatomegaly. Slit-lamp exam shows golden-brown rings around the cornea. What’s the most likely diagnosis?
➔ Wilson disease (caused by ATP7B mutation → which causes ↓ copper excretion → leading to copper buildup)

Note: Neuropsychiatric Symptoms + signs of liver injury → think Wilson disease
Note: Copper accumulates in organs:
○ Liver → leading to hepatitis, cirrhosis
○ CNS →leading to parkinsonism, psych changes
○ Eyes → leading to Kayser-Fleischer rings
○ Kidneys → leading to Fanconi syndrome (glucosuria, phosphaturia, bicarbonaturia and proteinuria)
Note: Diagnosed by ↓ ceruloplasmin and ↑ urinary coppe
Note: Treated with Penicillamine, Zinc

78. A 52-year-old man presents with fatigue, arthralgia, darkening of the skin, and newly diagnosed diabetes mellitus. Labs show elevated liver enzymes and increased serum iron studies. What is the most likely diagnosis?
➔ Hereditary Hemochromatosis (Cirrhosis + diabetes + skin pigmentation → think bronze diabetes → Hereditary Hemochromatosis).

Note: Caused by HFE gene mutation → causes ↑ intestinal iron absorption → leading to iron overload.
Note: Labs show ↑ Ferritin, ↑ Serum iron, ↓ TIBC, ↑ Transferrin saturation.
Note: Liver biopsy: Prussian blue stain shows iron deposits.
Note: Treatment includes Phlebotomy (first-line), iron chelators if needed.

79. A 50-year-old man with a history of alcohol use presents with fatigue. Labs show AST 160, ALT 65. What is the pattern of liver injury?
➔ Alcoholic hepatitis (when AST > ALT, typically 2:1 ratio → think alcoholic hepatitis)

Note: VS Cholestatic pattern of injury → will lead to ↑ ALP & ↑ GGT.
○ ALP is also elevated in bone disease, elevated GGT helps differentiate cholestatic pattern of injury from bone disease.
Note: VS Severe hepatocellular (Drug-induced, ischemic, autoimmune, or acute hepatitis) → will lead to Aminotransferases being >1000 U/L.

80. A 48-year-old man with chronic alcohol use undergoes imaging that reveals a shrunken, nodular liver and signs of ascites. What is the most likely diagnosis?
➔ Alcoholic cirrhosis (Chronic alcohol use can lead to irreversible fibrosis → cirrhosis → causing portal hypertension and liver failure)

Note: Other alcoholic liver injuries include;
○ Hepatic Steatosis → which leads to macrovesicular fat in hepatocytes; It is reversible with abstinence.

81. A 52-year-old man with a long history of heavy alcohol use presents with right upper quadrant pain and malaise. Labs show AST 180, ALT 70, and elevated GGT. What histological finding is expected to be seen?
➔ Swollen hepatocytes, neutrophilic infiltrate, Mallory bodies (This is the characteristic histological findings associated with Alcoholic hepatitis which is suggested by history and AST > ALT (2:1)).

Note: VS Non-alcoholic fatty liver disease which shows Fatty infiltration of hepatocytes → Cellular ballooning and necrosis.

82. A 55-year-old man with a history of alcohol use disorder presents with abdominal distension, breast enlargement and red lesions on his chest. Physical exam shows gynecomastia and multiple spider angiomas. What is the cause of these findings?
➔ Decreased estrogen metabolism (Symptoms suggestive of Cirrhosis → leading to Decreased estrogen metabolism → leading to gynecomastia, spider angioma and palmar erythema)

83. A 52-year-old man with a history of alcohol use and recent pancreatitis presents with fever, diffuse abdominal pain, abdominal tenderness, and ascites. Paracentesis reveals neutrophil count >250/mm³. What is the most likely diagnosis?
➔ Spontaneous bacterial peritonitis (SBP) (Occurs as a result of bacterial translocation from the intestinal lumen → to mesenteric lymph nodes→ to bloodstream → to ascitic fluid)

Note: The most common causing organism is E.coli
Note: Diagnosed by paracentesis which shows → neutrophils >250/mm³
Note: Treated by Cefotaxime

84. Cirrhotic patient with recurrent variceal bleeds undergoes TIPS. A few days later, he becomes confused. What is the underlying cause?
➔ Hepatic encephalopathy (TIPS is making a shunt from portal vein to hepatic vein → leads ↓ ammonia clearance)

Note: Ascetic patient + Confusion, asterixis (flapping tremor) → think Hepatic encephalopathy
Note: TIPS makes blood bypass the liver to systemic circulation →leads to ↓ portal pressure → leads to relief of portal hypertension.
Note: Treatment:
○ Lactulose → Non-absorbable disaccharide that traps ammonia in the colon as NH4+
○ Rifaximin → Non-absorbable antibiotic that reduces ammonia-producing gut bacteria
Note: Common sites of anastomoses in portal HTN:

Site of Anastomosis	Portal Drainage	Systemic drainage
Esophageal varices	Left gastric vein	Esophageal vein
Caput medusae	Paraumbilical veins	Small epigastric veins of anterior abdominal wall
Anorectal varices	Superior rectal vein	Middle & inferior rectal veins

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85. A 58-year-old man with cirrhosis presents with confusion and flapping tremors. He recently had an upper GI bleed. What is the initial treatment?
➔ Start lactulose (Cirrhosis + confusion + asterixis → think Hepatic Encephalopathy caused by ↓ ammonia clearance → leading to CNS toxicity)

- Note: liver normally detoxifies ammonia (NH₃) by converting it to urea
- Note: In cirrhosis there is impaired ammonia clearance
- Note: Common triggers include GI bleeding, infections, electrolyte imbalances, TIPS, altered mental status and coma which lead to build up of ammonia
- Note: Treatment includes;
  ○ First-line → Lactulose (acidifies colon → traps ammonia as NH₄⁺)
  ○ Second-line → Rifaximin (kills ammonia-producing gut bacteria)

86. A 60-year-old man with chronic hepatitis B presents with unintentional weight loss and right upper quadrant discomfort. Labs reveal elevated AFP. What is the most likely diagnosis?
➔ Hepatocellular carcinoma (HCC)

Note: HCC tends to spread hematogenously.

Liver Tumor	Features
Hepatic Hemangioma	Most common benign liver tumors, it has high risk of hemorrhage (NEVER perform biopsy).
Hepatic Adenoma	Associated with OCP use, may rupture in pregnancy.
Hepatocellular Carcinoma (HCC)	↑ AFP, has hematogenous spread.
Angiosarcoma	Angiosarcoma, exposure to vinyl chloride is a risk factor

87. Neonate presents with extensive jaundice, high pitched crying and hypotonia. Total bilirubin of 35 mg/dl; direct bilirubin is 0.5mg/dl. What is the diagnosis?
➔ Kernicterus (occurs due to accumulation of unconjugated/indirect bilirubin in the basal ganglia and brainstem nuclei as it is liposoluble)

Note: Unconjugated bilirubin (indirect) is → water insoluble, doesn’t appear in urine.
Note: Causes include:
○ Hemolysis.
○ Gilbert (Occurs due to mild UDP-glucuronosyltransferase deficiency; Jaundice is precipitated by stressors).
○ Crigler-Najjar (Occurs due to absent UDP-glucuronosyltransferase).
○ Physiologic (newborn).
Note: Bilirubin metabolism pathway:

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88. A 32-year-old man is found to have jaundice during a routine checkup. He feels well. Labs show elevated direct (conjugated) bilirubin and normal LFTs. Liver biopsy reveals dense pigment in hepatocytes. What is the most likely diagnosis?
➔ Dubin-Johnson syndrome (Occurs due to defective hepatic excretion of conjugated bilirubin; liver appears dark due to impaired excretion of epinephrine metabolites).

Note: Conjugated bilirubin is water soluble → causes dark urine + acholic stools.
Note: VS Rotor syndrome: Similar to Dubin-Johnson but without dark liver.
Note: Other causes of direct hyperbilirubinemia include Obstruction (stones, tumors), Primary Biliary Cholangitis and Primary Sclerosing Cholangitis (PSC).

89. A 19-year-old male experiences intermittent jaundice during periods of stress or fasting. His total bilirubin is mildly elevated with normal liver enzymes and no signs of hemolysis. What is the likely diagnosis?
➔ Gilbert syndrome (Caused by mild deficiency of UDP-glucuronosyltransferase, leading to elevated unconjugated bilirubin, especially during stress, illness, or fasting).

Note: VS Crigler-Najjar syndrome, which involves a complete or near-complete deficiency of the same enzyme and presents with more severe jaundice

90. A 35-year-old man with a history of ulcerative colitis presents with fatigue, pruritus, and right upper quadrant discomfort. Labs show cholestatic liver enzyme elevation. MRCP reveals beading of intra- and extrahepatic bile ducts. What is the most likely diagnosis?
➔ Primary Sclerosing Cholangitis (Male patient with UC + signs of biliary obstruction → think Primary Sclerosing Cholangitis)

Note: ERCP/MRCP shows “Beading” due to strictures and dilations of bile ducts
Note: Biopsy shows “Onion skin” periductal fibrosis
Note: It shows positive p-ANCA
Note: It increases the risk of developing cholangiocarcinoma

91. A 35-year-old woman presents with fatigue, generalized itching, dry eyes, and dry mouth. Liver biopsy shows lymphocytic infiltrates in portal tracts with loss of bile ducts. What’s the next step in treatment?
➔ Ursodeoxycholic acid (Middle aged woman + signs of biliary obstruction(itching, jaundice) → think primary biliary cholangitis → treated with Ursodeoxycholic acid as it increases bile flow).

Note: Associated with +ve serum antimitochondrial antibody.
Note: Biopsy shows lymphocytic infiltrate + granulomas.

92. A 42-year-old obese woman presents with a 2-hour episode of colicky RUQ pain without fever, leukocytosis, or abnormal liver function tests. Ultrasound shows gallstones. What is the cause of the abdominal pain?
➔ Biliary colic (Suggested by postprandial pain <6 hours without fever or leukocytosis)

Note: Risk factors include (4F) Fat, Female, Fertile, Forty
Note: Cholesterol stones → Caused by ↑ cholesterol, ↓ bile salts, and gallbladder stasis.
Note: Other type of stones is pigment stones:-
○ Black stones caused by hemolysis.
○ Brown stones caused by Infection.

93. A 45-year-old woman with obesity presents with right upper quadrant pain radiating to her right shoulder, fever, and nausea. On exam, she has inspiratory arrest when the RUQ is palpated. What is the most likely diagnosis?
➔ Acute Cholecystitis (Cholecystitis Suggested by persistent pain >6 hours with fever and leukocytosis)

Note: Pain with inspiration on RUQ palpation → indicates Murphy’s sign → think Acute Cholecystitis.
Note: Caused mostly by impacted gallstone in cystic duct → leading to inflammation
Note: In Acute Cholecystitis pain is radiating to right shoulder due to phrenic nerve irritation

94. A 65-year-old man presents with fever, jaundice, and right upper quadrant pain. He is hypotensive and confused on examination. Labs show elevated bilirubin and alkaline phosphatase. What is the most likely diagnosis?
➔ Acute cholangitis (Which presents with Charcot triad: fever + jaundice + RUQ pain if hypotension + altered mental status is present it is called Reynolds pentad )

Note: It is caused by ascending bacterial infection due to biliary obstruction (e.g., gallstones, strictures, tumors)
Note: Common pathogens include E. coli, Klebsiella, Enterococcus
Note: Requires urgent biliary drainage and antibiotics

95. A 60-year-old woman is found to have a calcified gallbladder wall on abdominal X-ray during evaluation for vague abdominal discomfort. She has a long-standing history of gallstones but no acute symptoms. What is the most appropriate next step?
➔ Prophylactic cholecystectomy (Calcified gallbladder indicates Porcelain gallbladder which is a precancerous condition → Prophylactic surgery is recommended due to cancer risk)

96. A 78-year-old woman with a history of cholelithiasis presents with nausea, vomiting, and abdominal pain. An X-ray shows pneumobilia, small bowel obstruction, and a gallstone in the ileocaecal junction. What is the most likely diagnosis?
➔ Gallstone ileus (occurs due to a fistula between the gallbladder and GI tract, allowing a gallstone to obstruct the small bowel.)

Note: Associated with a triad of pneumobilia, small bowel obstruction, and gallstone in the ileocaecal junction imaging.

97. A 47-year-old man with a history of alcohol use disorder presents with severe epigastric pain radiating to the back. Serum lipase is elevated. Which enzyme is responsible for activating pancreatic digestive enzymes in the small intestine?
➔ Enterokinase (Enteropeptidase) (It converts trypsinogen to trypsin, which activates other proenzymes).

Note: Pancreas → secretes Amylase (breaks carbs), lipase (breaks fats) and proteases as trypsinogen (breaks proteins).
Note: Enterokinase (from duodenal brush border) activates trypsinogen → into trypsin → which activates other enzymes.
Note:
○ Trypsin is a pancreatic enzyme that digests proteins in the small intestine.
○ VS Pepsin is a gastric enzyme that digests proteins in the stomach
Note: Fecal elastase (a form of protease) is decreased in chronic pancreatitis and serves as a diagnostic marker of exocrine insufficiency.
Note: Pancreatitis occurs due to premature enzyme activation within pancreas → leading to autodigestion.

98. A 47-year-old man with a history of alcohol use presents with severe epigastric pain radiating to the back. His serum lipase is elevated to more than three times the upper limit of normal. What is the diagnosis?
➔ Acute pancreatitis (2 of the following: epigastric pain radiating to the back, serum amylase/lipase >3x upper limit of normal, characteristic imaging findings is diagnostic of pancreatitis).

Note: Risk factors for pancreatitis: Alcohol use, gallstones, hypertriglyceridemia, certain drugs (e.g., azathioprine, thiazides), ERCP and trauma
Note: Complications include:-
○ Pseudocyst (lined by granulation tissue)
○ Hypocalcemia due to saponification ((fatty acids released from necrotic fat bind calcium to form soaps)
Note: Serum amylase/lipase >3x upper limit of normal in acute pancreatitis VS In chronic pancreatitis where amylase and lipase levels are not always elevated.

99. A 52-year-old man with a history of chronic alcohol use presents with chronic epigastric pain and greasy, foul-smelling stools. Imaging shows pancreatic calcifications. What is the most likely diagnosis?
➔ Chronic pancreatitis (Chronic inflammation leads to irreversible damage, causing exocrine insufficiency and fat malabsorption. Pancreatic calcifications are a classic finding)

Note: Most commonly caused by chronic alcohol use, also seen with CF and obstructive disease
Note: Serum amylase/lipase may be normal or only mildly elevated

100. A 65-year-old man presents with epigastric pain radiating to his back, unexplained weight loss, and painless jaundice. On examination, a palpable gallbladder is noted. What is the most likely diagnosis?
➔ Pancreatic adenocarcinoma

- Note: CA 19-9 is a tumor marker for Pancreatic adenocarcinoma but it’s non specific.
- Note: Pancreatic adenocarcinoma is associated with
  ○ Courvoisier sign: Painless jaundice and a palpable gallbladder suggest obstructive jaundice due to a tumor.
  ○ Trousseau syndrome: Migratory thrombophlebitis, which may be seen in pancreatic cancer.

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GI Pharmacology

101. A patient being treated for acid reflux develops gynecomastia and decreased libido. Which class of medication is most likely responsible?
➔ H₂ blockers (especially cimetidine)

Note: Mechanism is reversible H₂ receptor blockade in parietal cells → leading to ↓ gastric acid (H⁺) secretion.
Note: Adverse effects (notably cimetidine):
○ Antiandrogenic effects: gynecomastia, impotence, ↓ libido.
○ CYP450 inhibition → leading to multiple drug interactions.
○ Note that the most tested interaction is that Cimetidine inhibits metabolism of theophylline, increasing risk of theophylline toxicity

102. A 68-year-old man is admitted to the ICU for sepsis and is started on stress ulcer prophylaxis. One week later, he develops watery diarrhea, and stool testing confirms Clostridium difficile infection. Which medication is the contributor to these findings?
➔ Proton pump inhibitors (PPIs)

Note: Mechanism: Irreversible inhibition of H⁺/K⁺ ATPase (active transport) in parietal cells → profound reduction in gastric acid secretion
Note: Used for peptic ulcer, gastritis, GERD, Zollinger-Ellison syndrome, H. pylori therapy, and stress ulcer prophylaxis.
Note: Adverse effects:
○ ↑ Risk of C. difficile infection due to decreased gastric acidity
○ Acute interstitial nephritis
○ Vitamin B12 malabsorption
○ ↓ Mg²⁺ and Ca²⁺ absorption → leads to ↑ fracture risk

103. A 56-year-old man with chronic gastritis presents with constipation, proximal muscle weakness, and low phosphate levels. He has been self-medicating with an OTC antacid. Which drug is the likely cause?
➔ Aluminum hydroxide

Antacid	Side Effects
Aluminum hydroxide	Constipation, Hypophosphatemia, Osteodystrophy, Proximal muscle weakness, Seizures (CHOPS)
Calcium carbonate	Hypercalcemia (milk-alkali syndrome), rebound acid ↑
Magnesium hydroxide	Diarrhea, hyporeflexia, hypotension, cardiac arrest

104. A 58-year-old woman with diabetes and gastroparesis is started on a medication that enhances gastric motility. Two weeks later, she develops involuntary facial movements and hand tremors. What medication is responsible?
➔ Metoclopramide (D₂ receptor antagonist)(Causes Extrapyramidal symptoms as an adverse effect).

Note: Used for gastroparesis, antiemetic, persistent GERD
Note: Contraindicated in Parkinson’s disease, small bowel obstruction

105. A 45-year-old man undergoing chemotherapy is given medication to prevent nausea. Shortly after infusion, he develops a headache and is found to have a prolonged QT interval on ECG. Which medication is responsible?
➔ Ondansetron (5-HT₃ antagonist used as an antiemetic)

Note: Used for chemotherapy and post-operative induced nausea/vomiting
Note: Adverse effects include QT prolongation, serotonin syndrome, headache
Note: VS Aprepitant (Substance P antagonist, NK₁ receptor blocker)
○ Also used for chemotherapy-induced nausea/vomiting

106. A 35-year-old man with acute diarrhea is prescribed a medication that slows gut motility by acting on μ-opioid receptors, without crossing the blood-brain barrier. He later reports constipation as a side effect. What is the most likely medication?
➔ Loperamide (μ-opioid receptor agonist)(It has poor CNS penetration → So it is non-addictive)

Note: Mechanism: slows gut motility
Note: Adverse effects: constipation

107. A 62-year-old man with chronic constipation is started on a laxative that acts by drawing water into the colon through osmotic retention. Which laxative is being used?
➔ Lactulose

Note: Osmotic laxatives (Magnesium hydroxide, Lactulose, PEG,Magnesium citrate)
○ Draw water into the intestinal lumen via osmosis
Note: Bulk-forming laxatives (Psyllium, Methylcellulose)
○ They are soluble fiber that draws water → leading to ↑ peristalsis

108. A 68-year-old woman with long-standing constipation begins using a laxative. Months later, colonoscopy reveals dark pigmentation of the colonic mucosa. Which laxative is she most likely using?
➔ Senna

Note: Stimulant laxatives (Senna, Bisacodyl)
○ Causes enteric nerve stimulation → leading to colonic contraction
○ Can cause melanosis coli (which is pigmentation in intestines)
Note: Emollient laxatives (Docusate)
○ Incorporates water & fat into stool
Note: All laxative can cause diarrhea and bloating as an adverse effect

109. A 60-year-old man with metastatic carcinoid tumor presents with flushing, diarrhea, and wheezing. He is started on a medication that inhibits secretion of serotonin and various GI hormones. What is the most likely treatment?
➔ Octreotide (Octreotide is a somatostatin analog that reduces secretion of serotonin, gastrin, VIP, and other hormones)

Note: Uses include Carcinoid syndrome, VIPoma, acromegaly, glucagonoma, esophageal variceal bleeding

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Disclaimer

Version 1.0 May 2025. No part of this document may be reproduced or distributed without written permission. For personal study only. Medical information herein is for educational purposes and does not constitute clinical advice. Always confirm with current guidelines and your institution’s policies.

Prefer a narrative review instead of Q&A style? Scroll down to the section below for high-yield concepts in paragraph format (they cover the same concepts).

Narrative Format

High-Yield Gastrointestinal Topics

Ace the USMLE Step 1 with this high-yield review of gastrointestinal notes. Covers key topics, mnemonics, and study tips to boost your GI score.

Embryology
○ Liver Anatomy
○ Portosystemic anastomoses in portal hypertension
○ Intestinal Atresia
○ Hypertrophic pyloric stenosis
○ Midgut malrotation and Volvulus
○ Intussusception
○ Necrotising enterocolitis
○ Hemorrhoids
○ GI Hormones
○ GI secretions
○ Carbohydrate absorption
Bilirubin Metabolism and Jaundice
High Yield Pathology
○ Esophageal disorders
Gastrointestinal pathologies
○ Colorectal Cancer (CRC)
Hepatobiliary and pancreatic pathologies
GI Pharmacology
○ Acid Reducing Agents
○ Antacids
○ Ulcer Protective Agents
○ Motility & Antiemetic Agents
○ Laxatives
○ Other GI Agents

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Embryology

GIT regions and blood supply

Foregut: pharynx to proximal duodenum; Celiac artery
Midgut: Distal duodenum to proximal 2/3 of transverse colon; SMA
Hindgut: Distal 1/3 of transverse colon to upper portion of anal canal; IMA

Branches of celiac trunk and blood supply of stomach

Common hepatic, splenic, and left gastric.
Blood supply along the lesser curvature: Lt/Rt Gastric
Blood supply along the greater curvature: Lt/Rt Gastroepiploic
Blood supply along fundus: Short gastric branches of splenic artery

Clinical correlation for test day: Elderly male with prolonged NSAID use for OA presenting in a decompensated state with BP 90/60 mmHg, severe epigastric pain. Endoscopy shows a ruptured gastric ulcer on the lesser curvature of the stomach. Which vessel is most likely ruptured?

The answer is Left gastric artery

Layers of the gut wall from inside to outside

Mucosa: epithelium, lamina propria, muscularis mucosa
Submucosa: submucosal nerve plexus (Meissner), secretes fluid
Muscularis externa: myenteric nerve plexus (Auerbach), motility
Serosa (when intraperitoneal), adventitia (when retroperitoneal)

Clinical correlation for test day: Newborn with congenital megacolon, failure to pass meconium, tight anal sphincter and explosive expulsion of feces on digital exam. This pathology is characterized by absence of ganglion cells in which layers of colon

Answer: Hirschsprung disease is characterized by lack of ganglion cells/enteric nervous plexuses (Auerbach and Meissner plexuses in submucosa and muscularis externa respectively of distal segment of colon (failed neural crest cell migration).

Watershed regions of colon

Most susceptible to colonic ischemia due to dual blood supply from distal arterial branches.
Splenic Flexure: SMA and IMA
Rectosigmoid junction: IMA and superior rectal artery

Clinical correlation: Elderly patient involved in road traffic accident presenting to ED with shock. Multiple transfusions given to stabilize vitals. On day 2, gross blood is noted in his stool and imaging shows a thumbprint sign due to mucosal edema/ hemorrhage. Acute Ischemic colitis of which location is predominantly responsible for this patient’s symptoms

Answer: Watershed areas- splenic flexure and rectosigmoid junction

Liver Anatomy

Hepatic Lobules are the functional unit of liver with

Central vein in the center
Portal triads (portal vein, hepatic artery, bile ducts) on the edges
Zones I: periportal, II: intermediate, III: pericentral (from outside to inside)

Clinical correlation for exam day: Which zone of the liver is first affected by ischemia and is most sensitive to metabolic toxins.

The answer is Zone III-pericentral/Centrilobular

Portosystemic anastomoses in portal hypertension

	Portal Drainage	Systemic Drainage
Esophageal varices	Left gastric vein	esophageal
Caput medusae	Paraumbilical veins	small epigastric veins of the anterior abdominal wall.
Anorectal varices	Superior rectal vein	middle and inferior rectal

Clinical correlation for exam day: Patient with decompensated cirrhosis and repeated variceal bleeding despite ligation undergoes TIPS (shunt between Portal vein and hepatic vein) procedure to relieve the portal hypertension. This patient is now at risk of which complication?

TIPS induced hepatic encephalopathy due to ↓ clearance of ammonia from shunting.

Abdominal wall defects

Gastroschisis: Extrusion of bowel contents to the right of the umbilicus and importantly the contents are not covered by peritoneum or amnion.
Omhalocele: Midline herniation of abdominal contents, covered by sac (peritoneum and amnion). Omphalocele is associated with congenital anomalies like Down syndrome.

Tracheoesophageal fistula

Neonates with choking, drooling, and vomiting after first feeding
Due to associated esophageal atresia there is failure to pass a nasogastric tube into the stomach.

Intestinal Atresia

Duodenal atresia (failure to recanalize)→Double bubble sign
Associated with Down syndrome.
Bilious emesis.
Note: Double bubble sign can also be seen in annular pancreas
Jejunal atresia→Triple bubble sign
(Mesenteric vessel disruption→ ischemic necrosis of fetal intestine→segmental resorption).

Hypertrophic pyloric stenosis

Infants (~around 4 weeks old) with

Palpable olive-shaped mass in epigastric region
Visible peristaltic waves
Nonbilious projectile vomiting leading to hypokalemic, hypochloremic metabolic alkalosis. (Loss of Hcl leading to hypochloremia and acidosis; Volume depletion→RAAS activation → Hypokalemia)
First born males and exposure to macrolides (erythromycin) ↑ risk .

Midgut malrotation and Volvulus

Midgut Malrotation:
– Small intestine clumped up on the right side
– ↑ risk of midgut Volvulus
– Ladd bands (Fibrous peritoneal bands attaching the cecum to the retroperitoneum are a common pathological finding in midgut malrotation and volvulus)
Volvulus: Twisting of bowel around its mesentery
– Midgut volvulus in younger age group; corkscrew duodenum on upper GI series
– Sigmoid volvulus in elderly: Coffee Bean sign on X-ray

Intussusception

Telescoping of proximal bowel segment into distal segment (ileocecal junction MC location)

Currant jelly dark stool, bilious emesis
Sausage shaped mass on palpation
Target sign on USG/CT
Intermittent, severe abdominal pain during which patient may draw their legs to chest to ease the pain
Management usually involves air enema

Necrotising enterocolitis

Affects premature, formula fed infants
Feed intolerance, lethargy and abdominal distension
Intestinal necrosis →Perforation of intestine→ pneumatosis intestinalis/ pneumoperitoneum/ portal venous gas.

Hemorrhoids

Internal hemorrhoids
Above the pectinate/dentate line;
Visceral innervation →Not painful.
External hemorrhoids
Below the pectinate line/dentate line;
Somatic innervation →Very painful (especially if thrombosed).

Hernia

Indirect Inguinal Hernia	Direct Inguinal Hernia
– Deep inguinal ring → superficial inguinal ring → groin – Lateral to inferior epigastric vessels – Caused by failure of processus vaginalis to close – Covered by all three layers of spermatic fascia	– Protrude through Hesselbach triangle – Medial to inferior epigastric and lateral to rectus abdominis – Older men with acquired weakness of transversalis fascia. – Covered only by external spermatic fascia

● Femoral hernia is more common in females and arises below the inguinal ligament and below/ lateral to the pubic tubercle. Compared to inguinal hernia (most common overall), femoral hernias are more susceptible for incarceration or strangulation.

GI Hormones

Vasoactive intestinal peptide(VIP)
↑ Intestinal secretion of water, electrolytes
Relaxing the intestinal smooth muscle sphincters.
VIPoma is a pancreatic tumor associated with Watery Diarrhea, hypokalemia, achlorhydria i.e. WDHA syndrome.
CCK is secreted by I cells
↑ pancreatic secretion
Gallbladder contraction in response to fatty meals
Relaxes the sphincter of Oddi.
Secretin is secreted by S cells
↑ pancreatic HCO3- and bile secretion
↓ gastric acid secretion.
Gastrin secreted by G cells
↑ gastric H+ secretion
↑ gastric motility.
Somatostatin secreted by D cells
↓ secretion of various GI hormones.

– Clinical correlation for exam day: 45M presenting with refractory peptic ulcers across Duodenum and Jejunum, unresponsive to PPI. Imaging reveals a pancreatic mass. Serum Hypercalcemia is noted in labs. Gastrin levels rise after secretin stimulation test. What is the diagnosis?
Zollinger-Ellison syndrome/ Gastrinoma (Note: Associated with MEN1 syndrome- Pituitary, pancreatic, parathyroid tumors).

– A patient with RUQ pain, N/V after fatty meals. USG shows multiple gallbladder stones. Which hormone is responsible for the pain described?
Answer is CCK- triggers contraction of gallbladder, forcing stone into cystic duct leading to biliary colic.

GI secretions

Parietal cells of the stomach secrete Intrinsic factor (facilitate B12 uptake) and HCL. Pernicious anemia has autoantibodies against IF or parietal cells therefore manifests as B12 deficiency and chronic gastritis.
Chief cells of the stomach secrete pepsin to aid with protein digestion.
Pancreatic secretions
Amylase, lipase and trypsinogen are secreted by pancreas. Trypsinogen is activated to trypsin by brush border enterokinase which activates other proenzymes. Autoactivation of these enzymes in pancreatitis.

Carbohydrate absorption

Enterocytes take up glucose/galactose via SGLT1 (Na+ dependent active transport); fructose via GLUT5 (facilitated diffusion). Further transport from enterocytes to blood is done by GLUT 2.
Glucose + Sodium cotransport in the small intestine is the basis of Oral Rehydration Therapy.
(Simply giving plain water in dehydration is ineffective because water alone isn’t absorbed efficiently without Na⁺ and glucose)

Bilirubin Metabolism and Jaundice

Heme is metabolized to Bilirubin
Unconjugated/Indirect bilirubin is water insoluble.
Conjugated/Direct bilirubin is water soluble (dark urine and acholic stools).

Conjugated (direct) hyperbilirubinemia	Unconjugated (indirect) hyperbilirubinemia
– Biliary tract obstruction like gallstone/malignancy – Biliary tract disease like PBC/PSC – Excretion defect: Dubin-Johnson syndrome (Grossly dark liver due to impaired excretion of epinephrine metabolites), Rotor syndrome (Normal liver color)	– Hemolysis – Physiologic (Newborns): ↓ activity of UDP-glucuronosyltransferase (Bilirubin peaks at <15 mg/dL so values higher than 15 should prompt a search for pathological cause) – Crigler-Najjar: Absent UDP-glucuronosyltransferase – Gilbert syndrome: Mild UDP-glucuronosyltransferase deficiency; jaundice precipitated by stressors

Clinical correlation for exam day: Neonate with total bilirubin of 35 mg/dl; direct bilirubin is 0.5mg/dl. Examination finds extensive jaundice, high pitched crying, hypotonia. What would be the diagnosis?

Answer: Kernicterus due to high unconjugated/indirect bilirubin(Liposoluble therefore can deposit in the basal ganglia and brainstem nuclei)

Biliary Atresia

Fibro-obliterative destruction of bile ducts→cholestasis and persistent jaundice after 2 weeks of life.
↑ Conjugated/direct bilirubin: Direct bilirubin is water soluble therefore dark urine with pale stools and hepatomegaly.
Next step for diagnosis is Abdominal Ultrasound (Hypoplasia or absence of gallbladder)

High Yield Pathology

Esophageal disorders

Achalasia

Pathophysiology: Failure of LES relaxation due to loss of inhibitory neurons (NO, VIP) in myenteric plexus.
Clinical Features:
Dysphagia to both solids and liquids.
Barium swallow: Dilated esophagus with distal stenosis → “Bird Beak” sign.
Causes:
Idiopathic
Pseudoachalasia- Chagas disease (Trypanosoma cruzi) or extraesophageal malignancies.

Barrett Esophagus

Definition: Replacement of nonkeratinized stratified squamous epithelium with intestinal/nonciliated columnar epithelium (intestinal metaplasia).
Clinical Significance:
Increased risk of esophageal adenocarcinoma (Lower 1/3 of esophagus).
Progressive dysphagia: Solids → Liquids.

Clinical Correlation: A patient with chronic heartburn for 7 years undergoes endoscopy, showing Barrett esophagus. What type of cellular change is seen? Answer: Intestinal Metaplasia.

Other Esophageal Pathologies
Diffuse Esophageal Spasm	– Corkscrew esophagus on Barium swallow – Dysphagia with angina-like chest pain (also relieved by nitrates) – Spontaneous uncoordinated contractions of the esophagus
Eosinophilic Esophagitis	– Atopic patient – Rings and linear furrows on esophageal endoscopy – Eosinophilic infiltration
Boerhaave Syndrome (transmural)	– Subcutaneous Emphysema (Crepitus) after violent retching
Mallory-Weiss Syndrome	– Mucosal/submucosal partial thickness longitudinal lacerations after severe vomiting – Hematemesis
Plummer-Vinson Syndrome	– Dysphagia + Iron deficiency Anemia + Esophageal webs – Increased risk of esophageal squamous cell carcinoma (Upper 2/3rd of esophagus)
– Cytomegalovirus (CMV) – Herpes simplex virus (HSV)	– Linear esophageal ulcers in immunocompromised patients – Punched-out esophageal ulcers

High Yield Manometry Findings
Disorder	LES Tone	Peristalsis	Key Features	Imaging Findings
Achalasia	↑ (Impaired relaxation)	Absent	Dysphagia to solids & liquids	Bird’s beak on barium swallow
Diffuse Esophageal Spasm (DES)	Normal or intermittent relaxation	Premature, simultaneous contractions	Intermittent chest pain & dysphagia	Corkscrew esophagus on barium swallow
Scleroderma Esophageal Dysmotility	↓ (Hypotensive)	Absent in lower 2/3	GERD symptoms, systemic sclerosis	Dilated esophagus on imaging

Gastrointestinal pathologies

Gastric Ulcers & Duodenal Ulcers

Gastric ulcer: ↑ Pain with meals (weight loss), due to H. pylori (75%) or NSAIDs.
Duodenal ulcer: ↓ Pain with meals (weight gain), almost always H. pylori (95%).
Risk of carcinoma: Gastric ulcer >Duodenal ulcer
Therefore always biopsy margins of gastric ulcer to rule out malignancy
Complications
Gastric ulcer (Lesser curvature) → Bleeding from left gastric artery.
Posterior duodenal ulcer → Bleeding from gastroduodenal artery.
Anterior duodenal ulcer → More prone to rupture (air under diaphragm).
Hypovolemia→ mucosal ischemia→ Curling ulcer
Brain injury→ vagal stimulation→ ↑ Ach→ ↑ H+production→ Cushing ulcer
NSAID→ ↓Prostaglandin and mucosal blood flow→ erosion of the gastric mucosa
-H. pylori (Oxidase, catalase, Urease positive)→ ↑ Ammonia→ ↑pH→ enables survival of organism
-Bacterial attachment & cytotoxin release (e.g., cagA), ↓somatostatin and bicarbonate → mucosal barrier disruption → epithelial damage
-H. Pylori also increases the risk of MALT lymphoma

Gastric Cancer

Intestinal: Commonly located on lesser curvature and looks like an ulcer with raised margins
Diffuse: Grossly thick and leather like stomach wall with biopsy showing signet ring cells (mucin filled cells with peripherally pushed nuclei); loss of E- cadherin.

Notable Signs

Leser-Trélat sign: Sudden onset of multiple seborrheic keratosis
Virchow node: Left supraclavicular node metastasis from stomach.
Krukenberg tumor: B/L metastasis to ovaries(signet ring cells on ovarian biopsy).
Sister Mary Joseph nodule: subcutaneous periumbilical metastasis.
Blumer shelf: Metastasis to rectouterine pouch (pouch of Douglas) with palpable mass on digital rectal exam.

Pathogen	Type	Key Features	Transmission/Source	Complications
Vibrio cholerae	Watery	Rice-water diarrhea, no fever, noninvasive	Contaminated water/seafood	Severe dehydration
ETEC (Traveler’s diarrhea)	Watery	Heat-labile (cAMP) & heat-stable (cGMP) toxins	Contaminated food/water	Dehydration
C. difficile	Watery → Inflammatory	Pseudomembranous colitis, antibiotic use (clindamycin)	Nosocomial, altered gut flora	Toxic megacolon
Giardia lamblia	Watery	Foul-smelling, fatty diarrhea, bloating	Contaminated water (campers)	Malabsorption
Cryptosporidium	Watery	Severe in immunocompromised (AIDS)	Waterborne (oocysts)	Chronic diarrhea in HIV
Rotavirus	Watery	Winter outbreaks, infants & young children	Fecal-oral	Severe dehydration in children
Norovirus	Watery	Cruise ships, daycare outbreaks	Fecal-oral	Self-limited
Shigella	Inflammatory	Bloody diarrhea, HUS (Shiga toxin)	Fecal-oral (low ID50)	Hemolytic-uremic syndrome (HUS)
EHEC (O157:H7)	Inflammatory	Undercooked beef, Shiga-like toxin, NO fever	Contaminated food	HUS (↓ platelets, AKI, anemia)
Salmonella (non-typhi)	Inflammatory	Poultry, eggs, turtles, fever	Undercooked poultry/eggs	Reactive arthritis
Salmonella typhi	Inflammatory	Typhoid fever: rose spots, fever, constipation → diarrhea	Fecal-oral, chronic carriers	Intestinal perforation
Campylobacter jejuni	Inflammatory	Bloody diarrhea, comma-shaped, GBS association	Contaminated poultry/water	Guillain-Barré syndrome, reactive arthritis
Yersinia enterocolitica	Inflammatory	Mimics appendicitis, pseudoappendicitis	Pet feces, contaminated milk/pork	Mesenteric adenitis
Entamoeba histolytica	Inflammatory	Flask-shaped ulcers, liver abscess	Contaminated water	Liver abscess (RUQ pain)

Celiac Disease (Gluten-Sensitive Enteropathy)

Pathophysiology: Autoimmune-mediated intolerance to gliadin in gluten → villous atrophy & malabsorption.
Histology (VIC):
•Villous atrophy
•Intraepithelial lymphocytosis
•Crypt hyperplasia
Genetics: HLA-DQ2, HLA-DQ8.
Dermatologic Association: Dermatitis herpetiformis (pruritic, grouped vesicles).
Serology:
• IgA anti-tissue transglutaminase (IgA tTG) (IgG-based tests more useful in IgA-deficient patients)
• Anti-endomysial antibodies
• Anti-deamidated gliadin peptide antibodies
Clinical Features: Diarrhea, steatorrhea, malabsorption (loss of fat-soluble vitamins A, D, E, K).
Complications: ↑ Risk of T-cell lymphoma.
D-Xylose Test:
• Abnormal in Celiac disease (↓ mucosal absorption).
• Normal in pancreatic insufficiency (pancreatic enzymes not required for xylose absorption).

Whipple Disease

Tropheryma whipplei (intracellular Gram ⊕ actinomycete).
Histology: PAS⊕ foamy macrophages in intestinal lamina propria.
Classic Triad:
• Cardiac symptoms
• Arthralgias
• Neurologic symptoms
• Other Features: Steatorrhea, malabsorption, weight loss (GIT manifestations are late findings)

Lactose Intolerance

Pathophysiology: Lactase enzyme deficiency → Undigested lactose ferments in colon → osmotic diarrhea & bloating.
(Can occur secondary to gastroenteritis)
Clinical Features: Flatulence, diarrhea, cramping after dairy consumption (e.g., milk, cheese).
Diagnosis:
• Lactose hydrogen breath test⊕ (↑ H₂ due to bacterial fermentation).
• ↓ Stool pH (fermentation of lactose to short-chain fatty acids).
• Normal intestinal mucosa

Acute Abdominal Pain – Key Differentiation

Right Lower Quadrant (RLQ) Pain → Think appendicitis.
Left Lower Quadrant (LLQ) Pain (elderly patient) → Think diverticulitis.

Appendicitis

Pathophysiology: Obstruction of appendiceal lumen (fecalith, lymphoid hyperplasia).
Pain Progression:
○ Periumbilical pain → Stimulated visceral afferent fibers (T8-T10).
○ Pain localizes to RLQ (McBurney’s point: 1/3 the distance from right ASIS to umbilicus) → Parietal peritoneal irritation.

Irritable bowel syndrome

Recurrent abdominal pain associated with:
○ Defecation (relief or worsening)
○ Change in stool frequency/consistency.

Crohn Disease	Ulcerative Colitis
Skip lesions throughout GIT with rectal sparing; cobblestone mucosa; creeping fat	Continuous colonic lesions with rectum involved
Transmural inflammation – Fissures, strictures, and fistulas	Only mucosa/submucosa involved – superficial/deep ulcers
Noncaseating granulomas on microscopy	Crypt abscesses and ulcers on microscopy
Bowel wall thickening “string sign” on small bowel follow-through	Loss of haustra leading to “lead pipe” appearance on imaging.
Notable complications: Calcium oxalate kidney stone: Calcium binds to fat in the stool while oxalate gets absorbed and reaches kidney	– Toxic Megacolon – Associated with 1° sclerosing cholangitis (MPO ANCA/p-ANCA).

Diverticular Diseases

1) True Diverticula (All gut wall layers involved)

Example: Meckel diverticulum (persistence of vitelline duct).
Contains: Heterotopic gastric or pancreatic tissue → Hematochezia/melena in children.
Diagnosis: 99mTc-pertechnetate scan (Meckel scan) (detects ectopic gastric mucosa).

2) False Diverticula (Pseudodiverticula) (Only mucosa/submucosa outpouch)

Examples:
Zenker diverticulum → Above UES, Killian triangle (between cricopharyngeus and thyropharyngeus), presents with dysphagia and halitosis.
Colonic diverticula → Most common in sigmoid colon.

Clinical correlation: 5 y.o. boy presenting with blood in stool and pallor. Which investigation is useful to evaluate for Meckel diverticulum. Answer is 99mTc-pertechnetate scan (aka Meckel scan) for uptake by heterotopic gastric mucosa.

Mesenteric Ischemia

Acute Mesenteric Ischemia
• Cause: Arterial embolism/thrombosis (SMA occlusion).
• Symptoms: Severe abdominal pain out of proportion to exam, currant jelly stools.
Chronic Mesenteric Ischemia (“Intestinal Angina”)
• Cause: Atherosclerosis of mesenteric arteries → ↓ blood flow postprandial.
• Symptoms: Postprandial epigastric pain → Food aversion, weight loss.

Vascular GI Disorders

Angiodysplasia

Pathology: Tortuous dilation of mucosal/submucosal vessels → GI bleeding.

Associations:

End-stage renal disease (ESRD)
Von Willebrand disease (vWD)
Aortic stenosis

Diagnosis: Angiography.

GI Bleeding Classification
Upper GI Bleed (UGIB): Above the ligament of Treitz → Hematemesis/Melena.
Lower GI Bleed (LGIB): Below the ligament of Treitz → Hematochezia.

Polyposis Syndromes: Important Points
Familial adenomatous polyposis (FAP): APC tumor suppressor gene mutation leading to numerous pancolonic polyps after puberty, necessitating prophylactic colectomy. Gardner syndrome: FAP + Osteomas Turcot syndrome: FAP + CNS tumors Peutz-Jeghers syndrome: Numerous hamartomas throughout GI tract, along with hyperpigmented macules on mouth, lips, hands, genitalia. ↑ risk of GI and breast cancers. Juvenile polyposis syndrome: Children (typically < 5 years old) with numerous hamartomatous polyps. Lynch syndrome/Hereditary Non-Polyposis Colorectal Cancer (HNPCC): AD mutation of mismatch repair genes (eg, MLH1, MSH2) with subsequent microsatellite instability. Associated with endometrial, ovarian, and skin cancers.

Polyposis Syndromes: Important Points

Familial adenomatous polyposis (FAP): APC tumor suppressor gene mutation leading to numerous pancolonic polyps after puberty, necessitating prophylactic colectomy.
Gardner syndrome: FAP + Osteomas
Turcot syndrome: FAP + CNS tumors
Peutz-Jeghers syndrome: Numerous hamartomas throughout GI tract, along with hyperpigmented macules on mouth, lips, hands, genitalia. ↑ risk of GI and breast cancers.
Juvenile polyposis syndrome: Children (typically < 5 years old) with numerous hamartomatous polyps.
Lynch syndrome/Hereditary Non-Polyposis Colorectal Cancer (HNPCC): AD mutation of mismatch repair genes (eg, MLH1, MSH2) with subsequent microsatellite instability. Associated with endometrial, ovarian, and skin cancers.

High-Risk Polyps:

Adenomatous polyps (Villous > Tubular) → Malignant potential.
Serrated polyps → CpG island methylation, BRAF mutations → Precursor to CRC.

Colorectal Cancer (CRC)

Most Common Location: Rectosigmoid > Ascending > Descending colon.
Key Associations:
○ Iron deficiency anemia in elderly (>50 y.o.) → Always screen for CRC.
○ S. bovis (gallolyticus) bacteremia/endocarditis → Prompt colonoscopy.
○ Imaging: Apple core lesion on barium enema X-ray.
○ Tumor Marker: CEA → Used for monitoring, NOT screening.
○ NSAIDs Role: Overexpression of COX-2 linked to CRC → NSAIDs may be chemoprotective.
Right-Sided vs Left-Sided CRC

Feature	Right-Sided CRC (Ascending)	Left-Sided CRC (Descending)
Growth Pattern	Exophytic mass	Infiltrating mass
Symptoms	Occult bleeding → Iron deficiency anemia, weight loss	Colicky pain, hematochezia, obstruction
Lumen Size	Larger lumen → Late obstruction	Smaller lumen → Early obstruction

Colorectal Cancer Pathogenesis – Chromosomal Instability Pathway

Normal Colon: Healthy epithelium, APC gene intact.
Colon at Risk (APC Mutation): ↓ Intercellular adhesion, ↑ Proliferation.
Adenoma Formation (KRAS Mutation): KRAS activation → Uncontrolled growth.
Carcinoma Formation (TP53 Loss): Loss of tumor suppressors → Malignant transformation.

Who to Screen for CRC?
○ Average Risk (No family history) → Start at age 45 and repeat every 10 years
○ First-degree relative with CRC → Start at 40 or 10 years before their diagnosis
○ High-Risk Conditions (e.g., Lynch syndrome, FAP, IBD, history of CRC/polyps) → Earlier & more frequent screening
○ Colonoscopy is gold standard

Hepatobiliary and pancreatic pathologies

System	Pathophysiology	Clinical Features	Key Lab Findings
Liver	Fibrosis → Disrupted architecture → Portal HTN	Hepatomegaly (early), Small liver (late)	↑ AST/ALT (early), Normal/↓ AST/ALT (late)
Portal System	↑ Resistance to blood flow → Portal HTN	Esophageal varices, Caput medusae, Splenomegaly, Ascites	↓ Platelets (splenic sequestration, ↓thrombopoietin)
Synthetic Function	↓ Albumin & Clotting Factors	Edema, Easy bruising/bleeding	↑ PT/INR {*SAAG= Serum Albumin- Ascitic fluid albumin; SAAG ≥1.1 g/dL suggestive of portal hypertension i.e. high pressure ascites}*
Metabolic	↓ Ammonia clearance	Hepatic encephalopathy (asterixis, confusion)	↑ Ammonia {Treatment of HE is with Lactulose and rifaximin}
Metabolic	↓ Estrogen metabolism	Gynecomastia, Spider angiomas, Palmar erythema
Renal	↓ Effective circulating volume (hepatorenal syndrome)	Oliguria, ↑ Creatinine, ↓ Urine Na+	↑ BUN/Cr>20, ↓ Urine Na+
GI	↑ Risk of bacterial translocation (SBP) (MC organism-E. coli)	Fever, Abdominal pain, ileus in cirrhotic patient with ascites	PMNs >250 in ascitic fluid on paracentesis Note: DOC ceftriaxone

Hepatic Encephalopathy (HE)

Pathophysiology: ↓ Ammonia clearance → CNS toxicity
Triggers: GI bleeding, infections, electrolyte imbalances, TIPS
Clinical Features: Confusion, asterixis (flapping tremor), coma
Treatment:
First-line → Lactulose (acidifies colon → converts NH₃ → NH₄⁺)
Second-line → Rifaximin (reduces ammonia-producing gut bacteria)

Liver Function Tests & Patterns of Injury

AST > ALT (2:1) → Alcoholic hepatitis
↑ ALP & ↑ GGT → Cholestatic pattern (e.g., biliary obstruction, PBC, PSC)•
○ GGT differentiates from bone disease causing ALP elevations
Aminotransferases > 1000 U/L → Suggests severe hepatocellular injury•
○ DDx: Drug-induced liver injury, ischemic hepatitis, autoimmune hepatitis, acute viral hepatitis

Liver Tumor	Features
Hepatic Hemangioma	Most common benign liver tumor, risk of hemorrhage (NEVER biopsy).
Hepatic Adenoma	Associated with OCP use, may rupture in pregnancy.
Hepatocellular Carcinoma (HCC)	↑ AFP, hematogenous spread.
Angiosarcoma	Arsenic, Vinyl chloride exposure.

Metabolic & Autoimmune Liver Disorders

Reye Syndrome

Fatal childhood encephalopathy
Cause: Aspirin use in viral illness → ↓ β-oxidation in mitochondria
Findings:
○ Microvesicular fatty liver change, hypoglycemia, vomiting, hepatomegaly, coma
○ Avoid aspirin in children (exception: Kawasaki disease)

Acetaminophen Toxicity

Pathophysiology: Excess acetaminophen → ↑ NAPQI (toxic metabolite) → depletes glutathione → hepatocellular necrosis (centrilobular/liver failure).
Presentation: Initial mild symptoms (nausea, vomiting) → ↑ AST/ALT (>1000 U/L) → jaundice, coagulopathy, encephalopathy.
Diagnosis: Elevated liver enzymes, ↑ PT/INR, metabolic acidosis in severe cases.
Treatment:
○ N-acetylcysteine (NAC) → replenishes glutathione, best if given within 8 hours.
○ Activated charcoal (if early ingestion).
○ Monitor acetaminophen levels (Rumack-Matthew nomogram for risk assessment).
○ Risk Factors: Chronic alcohol use (induces CYP2E1 → ↑ NAPQI production), fasting/malnutrition (↓ glutathione stores).

Autoimmune Hepatitis

- Histology: Portal & periportal lymphoplasmacytic infiltrate
- Serology:
  ○ ⊕ ANA (antinuclear antibody)
  ○ ⊕ ASMA (anti-smooth muscle antibody)
  ○ ⊕ anti-LKM1 (anti-liver/kidney microsomal-1)

Alcoholic Liver Disease

Hepatic Steatosis → Macrovesicular fatty change (reversible with abstinence)
Alcoholic Hepatitis
○ Swollen hepatocytes, neutrophilic infiltrate, Mallory bodies (eosinophilic inclusions of damaged keratin)
○ AST > ALT (2:1), ↑ GGT
Alcoholic Cirrhosis → Irreversible fibrosis → Portal HTN, liver failure

Non-Alcoholic Fatty Liver Disease (NAFLD)

Metabolic syndrome (insulin resistance, obesity)
Progression: Fatty infiltration of hepatocytes → Cellular ballooning and necrosis→ Cirrhosis/HCC

Vascular Liver Disorders

Budd-Chiari Syndrome

Hepatic venous outflow obstruction → Congestive liver disease- Hepatomegaly, ascites, varices, abdominal pain
Causes: Hypercoagulability (e.g., pregnancy, HCC, polycythemia vera) or compression
Findings:
○ Nutmeg liver (mottled appearance)
○ Centrilobular congestion & necrosis

Genetic Liver Diseases

α₁-Antitrypsin Deficiency

Young patient with cirrhosis + panacinar emphysema (without smoking history)
Pathophysiology:
○ Misfolded AAT (serine protease inhibitor) aggregates in hepatocytes → Cirrhosis (PAS⊕ globules in liver)
○ ↓ AAT → Uninhibited elastase → Alveolar damage → Panacinar emphysema

Wilson Disease (Hepatolenticular Degeneration)

ATP7B gene mutation → ↓ Copper excretion → Accumulation in organs
Findings:
○ Liver → Hepatitis, cirrhosis, liver failure
○ Basal ganglia → Dystonia, Parkinson-like symptoms
○ Cornea → Kayser-Fleischer rings (Descemet membrane)
○ Kidney → Fanconi syndrome
Diagnosis: ↓ Ceruloplasmin, ↑ Urinary copper
Treatment: Penicillamine, Trientine, Zinc

Hemochromatosis

HFE gene mutation → ↑ Iron absorption → Iron overload
Findings:
○ “Bronze Diabetes” → Cirrhosis + DM + Skin pigmentation
○ ↑ Ferritin, ↑ Iron, ↓ TIBC, ↑ Transferrin saturation
○ Prussian blue stain ⊕ for iron deposits in liver
Treatment: Phlebotomy, Iron chelators

Gallbladder & Biliary Tract Pathologies

Primary Sclerosing Cholangitis (PSC)

♂, Associated with Ulcerative Colitis (UC)
Findings:
○ “Onion skin” bile duct fibrosis
○ Beading on ERCP, MRCP due to alternating strictures and dilation of intra- and extrahepatic bile ducts
○ p-ANCA ⊕
Complication: ↑ Cholangiocarcinoma risk

Primary Biliary Cholangitis (PBC)

♀, Autoimmune destruction of bile ducts
Findings:
○ Lymphocytic infiltrate + granulomas
○ Anti-mitochondrial antibody ⊕
Treatment: Ursodeoxycholic Acid (UDCA)

Acute Cholecystitis

Cause: Impacted gallstone in cystic duct → inflammation; acalculous cholecystitis in acutely ill patients
Findings:
○ Murphy’s sign → Inspiratory arrest with RUQ palpation
○ Pain radiating to right shoulder (phrenic nerve irritation)

Cholelithiasis

Predisposing factors for gallstone: Fat, Female, Fertile, Forty
Cholesterol stones: ↑ Cholesterol, ↓bile salts, gallbladder stasis→ supersaturation of bile with cholesterol
Pigment stones: Black-Hemolysis; Brown- Infection

Gallstone Ileus

Fistula between gallbladder & GI tract → Stone enters lumen → SBO
Rigler’s Triad:
1. Pneumobilia
2.Small bowel obstruction
3.Gallstone in ileocaecal junction

Porcelain Gallbladder is a precancerous condition with calcified GB on imaging due to chronic cholecystitis. (Requires prophylactic cholecystectomy)

Pancreatic Disorders

Pancreatic Adenocarcinoma

CA 19-9 tumor marker
Risk factors: Chronic pancreatitis, smoking
Findings:
○ Epigastric pain radiating to back, weight loss
○ Courvoisier sign → Painless jaundice + palpable GB
○ Trousseau syndrome → Migratory thrombophlebitis

Acute Pancreatitis

Causes: Gallstones, alcohol, hypertriglyceridemia, sulfa/NRTI drugs
Diagnosis (Requires 2 of 3):
1.Epigastric pain radiating to back
2.↑ Amylase/Lipase (>3× ULN)
3.Imaging (peripancreatic fluid, necrosis)
Complications: Pseudocyst (lined by granulation tissue), Hypocalcemia (saponification)

Chronic Pancreatitis

Findings:
○ Pancreatic calcifications, atrophy
○ Amylase/Lipase not always elevated (unlike acute pancreatitis)

GI Pharmacology

Acid Reducing Agents

H2 Blockers: Cimetidine, Famotidine, Nizatidine

Reversible H₂ receptor blockade → ↓ H⁺ secretion
Adverse Effects (Cimetidine especially)
CYP450 inhibitor → drug interactions
Antiandrogenic effects (gynecomastia, impotence, ↓ libido)

Proton Pump Inhibitors (PPIs): Omeprazole, Pantoprazole, Esomeprazole, Lansoprazole

Irreversible inhibition of H⁺/K⁺ ATPase in parietal cells
Clinical Use
Peptic ulcer, gastritis, GERD
Zollinger-Ellison syndrome
H. pylori therapy (part of triple/quadruple therapy)
Stress ulcer prophylaxis
Adverse Effects:
↑ C. difficile infection risk
↓ Mg²⁺ and Ca²⁺ absorption → fracture risk
Vitamin B12 malabsorption
Acute interstitial nephritis

Antacids

Antacid	Side Effects
Aluminum hydroxide	Constipation, Hypophosphatemia, Osteodystrophy, Proximal muscle weakness, Seizures (CHOPS)
Calcium carbonate	Hypercalcemia (milk-alkali syndrome), rebound acid ↑
Magnesium hydroxide	Diarrhea, hyporeflexia, hypotension, cardiac arrest

Clinical Correlation-

Ulcer Protective Agents

Bismuth, Sucralfate
○ Mechanism: Bind ulcer base → protective barrier
○ Clinical Use:
Ulcer healing
Traveler’s diarrhea (bismuth)
Quadruple therapy for H. pylori
(Note: Sucralfate requires acidic pH → avoid PPIs/H₂ blockers)
Misoprostol (PGE₁ analog)
○ Mechanism: ↑ mucus secretion, ↓ acid production
○ Clinical Use: NSAID-induced ulcer prevention
○ Adverse Effects: Diarrhea, contraindicated in pregnancy (abortifacient)

Motility & Antiemetic Agents

Metoclopramide (D₂ antagonist)
○ Mechanism: ↑ gastric motility, LES tone; does not affect colonic transit
○ Clinical Use:
–Diabetic & post-op gastroparesis
-Antiemetic
-Persistent GERD
○ Adverse Effects:
Extrapyramidal symptoms (Parkinson-like effects, tardive dyskinesia)
Contraindications: Parkinson’s disease, small bowel obstruction
Loperamide (μ-opioid receptor agonist, poor CNS penetration → non-addictive)
○ Mechanism: Slows gut motility
○ Clinical Use: Diarrhea
○ Adverse Effects: Constipation
Ondansetron (5-HT₃ antagonist, antiemetic)
○ Clinical Use: Post-op & chemotherapy-induced nausea/vomiting
○ Adverse Effects: QT prolongation, serotonin syndrome, headache
Aprepitant (Substance P antagonist, NK₁ receptor blocker)
○ Clinical Use: Chemotherapy-induced nausea/vomiting

Laxatives

Bulk-forming (Psyllium, Methylcellulose)
○ Mechanism: Soluble fiber draws water → ↑ peristalsis
○ Adverse Effects: Bloating
Osmotic (Magnesium hydroxide, Lactulose, PEG, Magnesium citrate)
○ Mechanism: Osmotic water retention → bowel movement
○ Lactulose Use: Hepatic encephalopathy (NH₄⁺ production)
○ Adverse Effects: Diarrhea, dehydration, metabolic alkalosis
Stimulants (Senna, Bisacodyl)
○ Mechanism: Enteric nerve stimulation → colonic contraction
○ Adverse Effects: melanosis coli- pigmentation in intestines (Benign)
Emollient (Docusate)
○ Mechanism: Incorporates water & fat into stool

Other GI Agents

Sulfasalazine
Colonic activation to active metabolite, 5-aminosalicylic acid (5-ASA) → anti-inflammatory effect
○ Clinical Use: Ulcerative colitis, Crohn’s disease (colitis component)
Octreotide (Long-acting somatostatin analog)
○ Clinical Use:
Acute variceal bleeding
Carcinoid syndrome, VIPoma, acromegaly
○ Adverse Effects: Steatorrhea, cholelithiasis (↓ CCK)
Orlistat (Lipase inhibitor → ↓ dietary fat absorption)
○ Clinical Use: Weight loss
○ Adverse Effects: Steatorrhea, ↓ fat-soluble vitamin absorption

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USMLE Step 1 High‐Yield Gastrointestinal Topics

Gastroenterology

High Yield USMLE Step 1 Notes

Table of Contents

Congenital & Pediatric GIT

Upper GIT System

High Yield Manometry findings:

Lower GIT System

Watershed regions of colon

Liver, Biliary, and Pancreatic Systems

GI Pharmacology

🏁 Final Thoughts

Disclaimer

Narrative Format

High-Yield Gastrointestinal Topics

Table of Contents

Embryology

Liver Anatomy

Portosystemic anastomoses in portal hypertension

Intestinal Atresia

Hypertrophic pyloric stenosis

Midgut malrotation and Volvulus

Intussusception

Necrotising enterocolitis

Hemorrhoids

GI Hormones

GI secretions

Carbohydrate absorption

Bilirubin Metabolism and Jaundice

High Yield Pathology

Esophageal disorders

Gastrointestinal pathologies

Colorectal Cancer (CRC)

Hepatobiliary and pancreatic pathologies

GI Pharmacology

Acid Reducing Agents

Antacids

Ulcer Protective Agents

Motility & Antiemetic Agents

Laxatives

Other GI Agents

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