Gastroenterology Syllabus

In alcoholic liver disease, what is the characteristic AST:ALT ratio?

An AST:ALT ratio $> 2:1$ is characteristic of alcoholic liver disease. In most other causes of hepatocellular injury (e.g., viral hepatitis, NAFLD), ALT is typically higher than AST.

What laboratory tests best reflect the liver's synthetic function?

Serum albumin and prothrombin time/INR. Both albumin and clotting factors are synthesized by the liver, so low albumin and prolonged PT/INR indicate impaired synthetic function.

What is the significance of an elevated serum lipase in acute abdominal pain?

Serum lipase $\geq 3$ times the upper limit of normal supports a diagnosis of acute pancreatitis. Lipase is more specific and stays elevated longer than amylase.

What non-invasive tests are used to detect Helicobacter pylori infection?

Urea breath test, stool antigen test, and serology (antibodies). Endoscopic tests include rapid urease (CLO) test and histology. Breath and stool tests can confirm eradication after treatment.

What is achalasia and its characteristic manometry finding?

Achalasia is failure of the lower esophageal sphincter (LES) to relax with loss of esophageal peristalsis due to degeneration of myenteric plexus neurons. Manometry shows incomplete LES relaxation and aperistalsis; barium shows a 'bird's beak' narrowing.

What is Barrett's esophagus and why is it clinically important?

Barrett's esophagus is metaplastic replacement of the normal squamous epithelium of the distal esophagus with columnar (intestinal) epithelium due to chronic GERD. It is a premalignant condition associated with esophageal adenocarcinoma.

What is the mechanism and typical presentation of GERD?

Gastroesophageal reflux disease results from inappropriate relaxation or incompetence of the LES, allowing acidic gastric contents to reflux into the esophagus. It presents with heartburn (pyrosis), regurgitation, and sometimes cough or dysphagia.

What are the two main causes of peptic ulcer disease?

Helicobacter pylori infection and chronic NSAID use. Both disrupt the protective mucosal barrier. Less commonly, gastrin-secreting tumors (Zollinger-Ellison syndrome) cause ulcers.

How do duodenal and gastric ulcers differ in their relationship to meals?

Duodenal ulcer pain is typically relieved by eating and worsens 2-5 hours after meals (and at night). Gastric ulcer pain is often worsened by eating, sometimes causing weight loss and food aversion.

What is Zollinger-Ellison syndrome?

A gastrin-secreting tumor (gastrinoma), usually in the pancreas or duodenum, causing excessive gastric acid secretion, multiple/refractory peptic ulcers, and diarrhea. It may be associated with MEN type 1 syndrome.

Compare Crohn's disease and ulcerative colitis in terms of distribution and depth.

Crohn's: affects any part of the GI tract (mouth to anus), with skip lesions and transmural inflammation. Ulcerative colitis: confined to the colon, continuous inflammation starting at the rectum, involving only the mucosa and submucosa.

What is celiac disease and its underlying mechanism?

Celiac disease is an immune-mediated enteropathy triggered by gluten (gliadin) in genetically susceptible individuals (HLA-DQ2/DQ8). It causes villous atrophy in the small intestine, malabsorption, and is diagnosed with anti-tissue transglutaminase (tTG) antibodies plus biopsy.

What distinguishes irritable bowel syndrome (IBS) from inflammatory bowel disease (IBD)?

IBS is a functional disorder with no structural or inflammatory abnormality, diagnosed clinically (Rome criteria) by abdominal pain related to defecation with altered bowel habits. IBD (Crohn's, UC) involves true inflammation with mucosal damage detectable on endoscopy/biopsy.

What is diverticulitis and how does it differ from diverticulosis?

Diverticulosis is the presence of outpouchings (diverticula) in the colon wall, often asymptomatic. Diverticulitis is inflammation/infection of these diverticula, causing left lower quadrant pain, fever, and altered bowel habits.

What are the stages of alcoholic and non-alcoholic fatty liver disease progression?

Steatosis (fatty infiltration) → steatohepatitis (fat plus inflammation, e.g., NASH) → fibrosis → cirrhosis, potentially leading to hepatocellular carcinoma. Early stages are reversible; cirrhosis is generally not.

What are the major complications of liver cirrhosis due to portal hypertension?

Esophageal and gastric varices (bleeding risk), ascites, splenomegaly, caput medusae, and hepatic encephalopathy. Portal hypertension is defined as a hepatic venous pressure gradient $> 5$ mmHg (clinically significant $\geq 10$ mmHg).

What are the hallmark serological markers for hepatitis B: HBsAg, anti-HBs, and HBcAb?

HBsAg indicates active infection. Anti-HBs (surface antibody) indicates immunity (recovery or vaccination). Anti-HBc (core antibody) indicates prior or ongoing natural infection - IgM anti-HBc suggests acute infection.

What is hepatic encephalopathy and its main precipitant?

Hepatic encephalopathy is neuropsychiatric dysfunction (confusion, asterixis, coma) from accumulation of neurotoxins, chiefly ammonia, that the failing liver cannot clear. Precipitants include GI bleeding, infection, constipation, and electrolyte imbalance. Treated with lactulose and rifaximin.

What are the two most common causes of acute pancreatitis?

Gallstones and chronic alcohol use account for the majority of cases. Other causes include hypertriglyceridemia, hypercalcemia, ERCP, certain drugs, and trauma (mnemonic: I GET SMASHED).

What are the components of the Ranson criteria concept for pancreatitis severity?

Ranson criteria predict acute pancreatitis mortality using parameters at admission (age, WBC, glucose, LDH, AST) and at 48 hours (hematocrit drop, BUN rise, calcium, $\ce{PaO2}$, base deficit, fluid sequestration). More criteria met indicates higher mortality.

What is the classic triad of chronic pancreatitis?

Pancreatic calcifications, steatorrhea (from fat malabsorption due to exocrine insufficiency), and diabetes mellitus (from endocrine/islet destruction). Chronic epigastric pain is also characteristic.

What is Charcot's triad and what does it indicate?

Charcot's triad is right upper quadrant pain, fever, and jaundice, indicating acute cholangitis (biliary infection). Adding hypotension and altered mental status forms Reynolds' pentad, indicating severe suppurative cholangitis.

What is the difference between cholelithiasis, choledocholithiasis, and cholecystitis?

Cholelithiasis: gallstones in the gallbladder. Choledocholithiasis: stones in the common bile duct. Cholecystitis: inflammation of the gallbladder, usually from a stone obstructing the cystic duct.

What is Murphy's sign and what does it suggest?

Murphy's sign is arrest of inspiration due to pain when the examiner palpates the right upper quadrant during deep inhalation. A positive sign suggests acute cholecystitis (inflamed gallbladder contacting the examining hand).

How do proton pump inhibitors (PPIs) work, and give examples.

PPIs irreversibly inhibit the $\ce{H+/K+}$ ATPase (proton pump) in gastric parietal cells, blocking the final step of acid secretion. Examples: omeprazole, pantoprazole, esomeprazole. They are more potent acid suppressors than $\ce{H2}$ blockers.

What is the standard triple therapy for Helicobacter pylori eradication?

A proton pump inhibitor plus two antibiotics, classically clarithromycin and amoxicillin (or metronidazole), given for 10-14 days. Bismuth-based quadruple therapy is used in areas of high clarithromycin resistance.

How do H2 receptor antagonists reduce gastric acid, and name an example.

$\ce{H2}$ blockers competitively inhibit histamine at $\ce{H2}$ receptors on parietal cells, reducing acid secretion. Examples include famotidine and ranitidine. They are less potent than PPIs and useful for milder or nocturnal symptoms.

What is the mechanism of ondansetron as an antiemetic?

Ondansetron is a $5\text{-HT}_{3}$ (serotonin) receptor antagonist. It blocks serotonin receptors in the gut and the chemoreceptor trigger zone, effectively preventing nausea and vomiting, especially from chemotherapy.

What surgical procedure is standard for symptomatic gallstones, and how is it typically performed?

Cholecystectomy (removal of the gallbladder), most commonly performed laparoscopically. It is the definitive treatment for symptomatic cholelithiasis and cholecystitis.

What is intussusception, and what is its classic presentation in infants?

Intussusception is telescoping of one segment of bowel into an adjacent segment (commonly ileocolic), causing obstruction. Classic infant presentation: intermittent colicky pain, 'currant jelly' (bloody, mucoid) stools, and a sausage-shaped abdominal mass. It can often be reduced with an air or contrast enema.