LOs 1 & 2 — Hepatic Blood Supply, Architecture & Clinical Definitions

Dual Blood Supply

Vessel	Flow Rate & % of Total	O₂ Saturation	Content / Source
Portal Vein	~1,000 mL/min; 70–75% of total hepatic blood flow	Low (venous blood — partially deoxygenated by gut/spleen)	Nutrient-rich blood from GI tract + spleen
Hepatic Artery	~350 mL/min; 25–30% of total hepatic blood flow	High (arterial — fully oxygenated from celiac axis)	Oxygen-rich blood from celiac trunk (branch of abdominal aorta)

Despite portal vein's low O₂, each vessel contributes ___% of hepatic O₂ delivery because ___

~50%; the high volume of portal blood compensates for lower O₂ saturation → each delivers roughly equal O₂

Liver receives ___% of resting cardiac output

~30% of resting cardiac output

Hepatic Acinus Zones — Rappaport Model

Zone	Location	O₂ Status	Primary Functions	Vulnerable to
Zone 1 (Periportal)	Adjacent to portal triad (first to receive blood)	Highest O₂ and nutrients	Gluconeogenesis, β-oxidation, urea synthesis	Viral hepatitis, phosphorus toxicity
Zone 2 (Midzonal)	Intermediate zone between portal triad and central vein	Intermediate O₂	Mixed zone 1 and zone 3 functions	Yellow fever
Zone 3 (Centrilobular)	Adjacent to central vein (furthest from portal triad)	Lowest O₂ and nutrients	Glycolysis, lipogenesis, drug metabolism (CYP450 — esp. CYP2E1)	Ischemia, acetaminophen (APAP), alcohol, halothane

Hepatic Cell Types

Kupffer cells = ___; located ___; largest population of ___ in the body

Resident macrophages; lining hepatic sinusoids; largest population of tissue macrophages in the body — phagocytose bacteria, old RBCs, and portal blood debris

Hepatic stellate cells (Ito cells): quiescent = store ___; when activated → ___ → collagen → ___

Store vitamin A; when activated by injury → myofibroblasts → collagen production → fibrosis → cirrhosis

Sinusoidal endothelial cells are ___; allow ___

Fenestrated (have pores/gaps); allow free exchange between sinusoidal blood and Space of Disse → hepatocyte access to nutrients and plasma proteins

Hepatocytes (~80%): perform ___ functions

Metabolic (glucose, lipid, protein), secretory (bile, bilirubin conjugation), and detoxification (CYP450, urea cycle) functions

Clinical Definitions (LO 2)

Hepatomegaly defined as liver > ___ cm; top 3 causes: ___

>~12–15 cm (percussion in MCL); causes: viral hepatitis/infection, NAFLD, congestive heart failure ("nutmeg liver"), malignancy (HCC/mets)

Jaundice = yellowing of ___ due to bilirubin >___mg/dL; first visible in ___ because ___

Skin, sclerae, mucous membranes; >2–3 mg/dL; first visible in sclerae because elastin binds bilirubin avidly

Cirrhosis = irreversible replacement of parenchyma with ___ + ___; most common cause in US = ___

Fibrous scar tissue + regenerative nodules; most common cause: chronic alcohol use; also chronic viral hepatitis B/C, NASH

3 mechanisms of ascites in cirrhosis: (1) ___, (2) ___, (3) ___

(1) Portal HTN → ↑hydrostatic pressure → fluid transudation; (2) Hypoalbuminemia → ↓oncotic pressure; (3) Splanchnic vasodilation (NO) → RAAS activation → Na⁺/H₂O retention

Ascites vs. Peripheral Edema

⚠ Portal hypertension is the key distinguishing driver of ascites. Hypoalbuminemia alone causes leg edema but NOT ascites.

Feature	Ascites	Peripheral Edema
Location	Peritoneal cavity (abdominal fluid accumulation)	Subcutaneous tissue (ankles, legs — dependent areas)
Required component	Portal hypertension (key driver) + possible ↓oncotic pressure	↑Capillary hydrostatic pressure OR ↓oncotic pressure — no portal HTN required
SAAG	≥1.1 g/dL = portal HTN etiology; <1.1 g/dL = exudative (malignancy, TB, nephrotic)	Not applicable to peripheral edema

Portal Hypertension Classification

Type	Example Causes	LFTs / Liver Function
Pre-hepatic	Portal vein thrombosis (PVT); splenic vein thrombosis	Normal LFTs and liver function — liver itself is normal
Intra-hepatic (sinusoidal)	Cirrhosis (most common); hepatic venous obstruction causing sinusoidal congestion	↑AST, ALT, bilirubin; ↓albumin, ↑PT (synthetic dysfunction)
Post-hepatic	Budd-Chiari syndrome (hepatic vein thrombosis); constrictive pericarditis; right heart failure	Hepatic congestion; centrilobular necrosis; ↑bilirubin (conjugated)

LOs 3 & 4 — Carbohydrate, Lipid, Cholesterol & Protein Metabolism

Carbohydrate Metabolism

Process	Metabolic State	Hormonal Control	Outcome
Glycogenesis	Fed (postprandial)	Insulin ↑	Glucose → glycogen stored in liver (~100 g max)
Glycogenolysis	Short-term fasting	Glucagon ↑ + Epinephrine ↑	Glycogen → glucose released into blood
Gluconeogenesis	Prolonged fasting or stress	Glucagon ↑ + Cortisol ↑	AA (Ala, Gln), lactate, glycerol → glucose (Zone 1)
Glycolysis	Fed state (high glucose)	Insulin ↑	Glucose → pyruvate → acetyl-CoA → energy + lipid synthesis

Acute liver failure → profound ___ because ___

Profound hypoglycemia; loss of glycogen stores + impaired gluconeogenesis — hallmark of acute (not chronic) liver failure; poor prognostic sign

Liver uses ___ (not GLUT4) for glucose uptake because it is ___ (insulin-independent/dependent)

GLUT2; constitutive (insulin-independent) — uptake proportional to portal glucose concentration

Lipid Metabolism & Lipoproteins

VLDL is made by ___ and carries ___; degraded to ___ → ___

Liver (hepatocytes); endogenous TG + cholesterol + apoB100; degraded to IDL → LDL by LPL + hepatic lipase

HDL produced by ___ + ___; performs ___ cholesterol transport

Liver + intestine; reverse cholesterol transport (periphery → liver)

NAFLD/NASH mechanism: insulin resistance → ↑___ delivery to liver + ↓___ + ↓___ export → ___ accumulation

↑FFA delivery from adipose; ↓β-oxidation; ↓VLDL export; triglyceride accumulation in hepatocytes

Lipoprotein	Origin	Primary Cargo	Key Clinical Point
Chylomicrons	Intestinal epithelium	Dietary (exogenous) TG; apoB48	Degraded by LPL; remnants → liver; LPL deficiency → severe hypertriglyceridemia
VLDL	Liver	Endogenous TG; apoB100	↑ in hypertriglyceridemia, metabolic syndrome, alcohol; VLDL → IDL → LDL
LDL	Derived from VLDL (via IDL)	Cholesterol (to peripheral tissues); apoB100	"Bad cholesterol" — atherogenic; lowered by statins (↑LDLR); FH = LDLR mutation
HDL	Liver + intestine (nascent HDL with apoAI)	Cholesterol from periphery	"Good cholesterol"; reverse cholesterol transport; ↑ with exercise

Cholesterol Metabolism & Statins (LO 4)

5 main uses of cholesterol: ___, ___, ___, ___, ___

(1) Cell membranes; (2) Bile acids (CYP7A1); (3) Steroid hormones; (4) Vitamin D; (5) Myelin sheath

Rate-limiting step: HMG-CoA → ___ catalyzed by ___

Mevalonate; HMG-CoA reductase

High dietary cholesterol → ___ (suppresses/stimulates) HMG-CoA reductase via ___

Suppresses HMG-CoA reductase via feedback inhibition (high intracellular cholesterol inhibits SREBP-2 cleavage → ↓HMG-CoA reductase transcription)

Statins mechanism: competitive inhibit ___ → ↓hepatic cholesterol → ↑___ → ↑LDL clearance → ↓serum LDL

HMG-CoA reductase; LDL receptors (LDLR) upregulated (SREBP-2 activated when intrahepatic cholesterol falls)

Statin side effects: ___, ___

Myopathy (↑CK — check for muscle pain); rhabdomyolysis (rare); transaminase elevation (hepatotoxicity)

Familial hypercholesterolemia = mutation in ___ → ↑LDL despite normal ___

LDL receptor (LDLR) — cannot clear LDL from plasma; normal HMG-CoA reductase (endogenous synthesis is normal)

Protein Metabolism & Liver Failure Consequences

Liver makes all plasma proteins EXCEPT ___ (made by ___)

Immunoglobulins (antibodies); produced by plasma cells (B cells)

Albumin t½ = ___ days → ↓albumin indicates ___ (acute/chronic) liver dysfunction

~20 days; CHRONIC liver dysfunction (long t½ means weeks of poor synthesis before albumin falls)

Clotting factor NOT made by liver: Factor ___ (made by ___)

Factor VIII; made by endothelial cells and megakaryocytes

Factor with shortest t½ = Factor ___; rises first in ___; why it's an early marker of liver failure

Factor VII (t½ ~4–6 hours); PT/INR rises first; shortest half-life → falls fastest when liver synthetic function is impaired

Urea cycle: NH₃ → ___ (in hepatocytes only); failure → ___ → hepatic encephalopathy; treatment = ___ + ___

Urea (NH₃ → citrulline → argininosuccinate → arginine → urea + ornithine); hyperammonemia → hepatic encephalopathy; lactulose + rifaximin

First-pass effect: oral drug absorbed → ___ → ___ → substantial metabolism before reaching systemic circulation

Portal vein → liver → extensive hepatic metabolism; explains why oral bioavailability << IV (e.g., oral morphine dose >> IV morphine dose)

Signs of Liver Failure (HY)

⚠️ Step 1 Favorite: Know ALL 6 consequences of hepatocyte failure

Lost Function	Consequence / Clinical Sign
↓ Albumin	↓Oncotic pressure → ascites + peripheral edema; ↑free drug levels (altered pharmacokinetics)
↓ Clotting factors (II, VII, IX, X)	↑PT/INR; bleeding tendency; Factor VII (shortest t½) rises first
↓ Urea cycle	Hyperammonemia → hepatic encephalopathy (asterixis, confusion, fetor hepaticus, coma)
↓ Gluconeogenesis/glycogenolysis	Hypoglycemia — especially in acute liver failure; hallmark + poor prognostic sign
↓ Estrogen metabolism	↑Estrogen → spider angiomata, palmar erythema, gynecomastia, testicular atrophy
↓ Bile production	Steatorrhea; fat-soluble vitamin deficiency (A, D, E, K); ↓vitamin K → worsened coagulopathy

LO 5 — Bilirubin Metabolism & 4 Types of Jaundice

Bilirubin Pathway — Step by Step

Step	Location	Process	Product
1–3	Spleen / RES macrophages	Aged RBCs → Hgb → heme → biliverdin → ___	Unconjugated bilirubin (indirect; fat-soluble, albumin-bound, neurotoxic)
4	Bloodstream	Unconjugated bilirubin bound to ___ → transported to liver	Albumin–bilirubin complex
5	Hepatocyte	Uptake via ___; conjugated with ___ by ___	Conjugated bilirubin (direct; water-soluble, non-toxic) — uptake via OATP transporters; conjugated with glucuronic acid by UGT1A1
6	Bile canaliculi → bile duct → duodenum	Secreted via ___ into bile → duodenum	Bile (yellow-green) — secreted via MRP2 transporter
7–8	Large intestine → colon → kidneys	Bacteria → urobilinogen → ___ (stool) + ___ (urine)	Stercobilin (brown stool color) + urobilin (yellow urine; ~20% of urobilinogen reabsorbed → kidneys)

Unconjugated bilirubin: fat or water soluble? Can it be filtered by kidneys? Can it cross BBB?

Fat-soluble (albumin-bound); CANNOT be filtered by kidneys → NO bilirubinuria; CAN cross BBB → kernicterus in neonates

Conjugated bilirubin: solubility? Appearance in urine → ___ urine; cannot cross ___

Water-soluble; CAN be filtered by kidneys → bilirubinuria → dark urine; cannot cross blood-brain barrier (no kernicterus)

4 Types of Jaundice — Lab Differentiation

Type	Mechanism	Direct Bili	Indirect Bili	Urine Bili	Urobilinogen	Stool
Hemolytic (Pre-hepatic)	↑RBC destruction overwhelms conjugation capacity	Normal	↑↑	Negative	↑↑	Dark (↑stercobilin)
Hepatocellular (Intrahepatic)	↓Conjugation + regurgitation of conjugated bili into blood	↑	↑	Positive	Variable	Normal to pale
Obstructive (Post-hepatic)	Bile duct obstruction → conjugated bili backs up into blood	↑↑	Normal/mild ↑	Positive (dark urine)	↓ or absent	Pale/clay-colored
Neonatal (Physiologic)	Immature UGT1A1 + high fetal Hgb turnover	Normal	↑↑	Negative	Variable	Normal

⚠ Obstructive jaundice classic triad: dark urine + clay-colored stools + pruritus. Courvoisier sign = painless jaundice + palpable non-tender gallbladder → pancreatic head malignancy until proven otherwise.

Congenital Hyperbilirubinemias

Condition	Defect	Bili Type	Key Clinical Feature
Gilbert Syndrome	↓UGT1A1 promoter activity (TATA repeat) — mild 30–50% reduction	↑Indirect (unconjugated)	Benign; episodic jaundice triggered by fasting, illness, exercise; very common (5–10% of population)
Crigler-Najjar Type I	Complete absence of UGT1A1	↑↑Indirect (severely elevated)	Kernicterus in infancy; requires liver transplant; phototherapy (16–18 hrs/day) as bridge
Crigler-Najjar Type II	Severely reduced UGT1A1 (<10% of normal)	↑Indirect (less severe than Type I)	Responds to phenobarbital (induces UGT1A1 expression)
Dubin-Johnson	Defective MRP2 transporter (↓conjugated bilirubin secretion into bile)	↑Direct (conjugated)	Black liver on autopsy (melanin-like pigment); benign prognosis
Rotor Syndrome	Defective OATP1B1/1B3 (↓hepatocyte uptake of conjugated bilirubin)	↑Direct (conjugated)	Similar to Dubin-Johnson but NORMAL liver color on biopsy (no pigment)

LOs 6–10 — Bile, EHC, Secretion, Regulation & Clinical Predictions

Bile Composition (LO 6)

Component	% of Solutes	Function / Note
Bile salts	~67%	Emulsify fats; form micelles; derived from conjugated primary bile acids
Phospholipids (lecithin)	~22%	Solubilize cholesterol in micelles; protect bile duct epithelium
Cholesterol	~4%	Primary excretion route from the body
Conjugated bilirubin	~0.3%	Bile color; excreted → urobilinogen → stercobilin

Primary bile acids (made in liver from cholesterol): ___ + ___; rate-limiting enzyme: ___

Cholic acid + Chenodeoxycholic acid; rate-limiting enzyme: cholesterol 7α-hydroxylase (CYP7A1)

Gallstone formation: when ___ exceeds ___ + ___ → cholesterol crystallizes → ___ gallstones (___% of stones)

Cholesterol concentration exceeds bile salts + phospholipids → crystallizes → cholesterol gallstones (80% of gallstones in the West)

Conjugation & Secondary Bile Acids (LO 7)

Bile acids conjugated with ___ or ___ → bile salts; significance: ↓pKa → ___ at intestinal pH → cannot be ___ reabsorbed

Taurine or glycine; ionized at intestinal pH → cannot be passively reabsorbed → stays in lumen for fat emulsification + micelle formation

Secondary bile acids formed by gut bacteria via 7α-dehydroxylation: cholic acid → ___; chenodeoxycholic acid → ___

Cholic acid → Deoxycholic acid; Chenodeoxycholic acid → Lithocholic acid (poorly absorbed; mostly excreted; hepatotoxic in excess)

Enterohepatic Circulation Sequence (LO 7)

Step 1: Hepatocytes synthesize primary bile acids → conjugate with ___ → bile salts → secreted to ___

Taurine or glycine; secreted into bile canaliculi → common bile duct → duodenum (via sphincter of Oddi)

Step 2: Bile salts enter duodenum via ___ → emulsify ___ throughout small intestine

Sphincter of Oddi (relaxed by CCK); emulsify dietary fats for micelle formation and absorption

Step 3: ___% of bile salts actively reabsorbed in ___ via ASBT transporter

~95% reabsorbed in terminal ileum via ASBT (apical sodium-dependent bile acid transporter)

Step 4: Absorbed bile salts → ___ vein → liver reconjugates → cycle repeats ___× per day

Portal vein (hepatic extraction ~90–95%); cycle repeats 6–10× per day

Total bile acid pool ≈ ___ g; liver synthesizes only ___ g/day to replace fecal losses

~3–5 g total pool; synthesizes only ~0.5 g/day (18–50 g secreted/day due to cycling efficiency)

Bile acid sequestrants (cholestyramine) mechanism: bind ___ in gut → ↑CYP7A1 → ↑cholesterol → bile acid synthesis → ↓serum ___

Bind bile acids in gut (interrupt EHC) → liver converts more cholesterol to bile acids (↑CYP7A1) → ↑LDLR expression → ↓serum LDL

Bile Secretion & Gallbladder Concentration (LO 8)

Stage 1 (hepatocytes): bile salts secreted via ___ pump; organic anions via ___

BSEP (bile salt export pump); MRP2 (secretes conjugated bilirubin and glutathione conjugates)

Stage 2 (cholangiocytes): secrete ___ and water stimulated by ___ via cAMP/CFTR

HCO₃⁻ (bicarbonate) and water; stimulated by secretin → cAMP → CFTR → Cl⁻/HCO₃⁻ exchange

Gallbladder concentrates bile ___-fold by absorbing ___, ___, ___, and water

5–20-fold (average ~10×); absorbs Na⁺, Cl⁻, HCO₃⁻, and water

Between meals: sphincter of Oddi ___ → bile diverted to ___ (capacity ~___ mL)

Contracts (tonic contraction); gallbladder; ~40–70 mL capacity

Regulation of Bile Secretion (LO 9)

⚠ CCK contracts the gallbladder AND relaxes the sphincter of Oddi. Secretin stimulates ductal HCO₃⁻ but does NOT contract the gallbladder.

Regulator	Cell / Source	Stimulus	Effect on Bile/Gallbladder
CCK	I cells (duodenum + proximal jejunum)	Fat + protein entering duodenum	↑Gallbladder contraction + sphincter of Oddi RELAXATION → bile flows to duodenum; also stimulates pancreatic enzymes
Secretin	S cells (duodenum)	Acid (H⁺) entering duodenum	↑Ductal HCO₃⁻ secretion → alkalinizes duodenum; does NOT contract gallbladder
Bile salts (choleresis)	Portal blood (returning bile salts from EHC)	Bile salts arriving at hepatocytes in portal blood	↑Hepatic bile secretion (bile salt-dependent fraction via FXR-mediated transcription)
Vagal stimulation	Vagus nerve (CN X)	Cephalic phase (sight/smell of food)	↑Bile secretion; mild gallbladder contraction via ACh
Somatostatin	D cells (stomach and intestine)	Postprandial counterregulation; high acid	↓Gallbladder contraction; ↓bile secretion; inhibits CCK release

Clinical Predictions (LO 10)

Cholecystectomy: bile now delivered ___ (continuously/in bolus); total bile production ___; symptoms with large fatty meals: ___

Continuously (constant drip — no concentrated storage); total bile production UNCHANGED; bloating, loose stools, fatty food intolerance with large fat loads

Ileal resection: ASBT destroyed → bile salts ___ in feces → pool ___ → insufficient ___ → steatorrhea + ___ diarrhea + fat-soluble vitamin ___

Lost in feces; bile acid pool depletes; insufficient micelle formation → steatorrhea; bile acid (cholerheic) diarrhea; fat-soluble vitamin deficiency (A, D, E, K)

Ileal resection also impairs ___ absorption (absorbed in terminal ileum with ___) → ___ anemia

Vitamin B₁₂; intrinsic factor–B₁₂ complex (IF-B₁₂ receptor cubilin in terminal ileum); megaloblastic anemia

Cholecystectomy vs. ileal resection: which causes steatorrhea? ___. Why the other does not: ___

Ileal resection causes steatorrhea (bile acid pool depleted). Cholecystectomy does NOT — bile acid pool is INTACT; only delivery pattern changes (continuous drip vs. bolus); fat malabsorption mild, mainly with large fatty meals

Practice Questions — GI14 USMLE-Style

Q1. A patient with acetaminophen overdose develops acute liver failure. Liver biopsy shows centrilobular necrosis. Which zone of the hepatic acinus is injured, and why is it preferentially affected?

A. Zone 1 — first to receive toxic metabolites via portal blood
B. Zone 2 — intermediate oxygen tension increases susceptibility
C. Zone 3 — highest CYP2E1 concentration + lowest O₂ tension
D. Zone 3 — direct toxin absorption from the central vein
E. Zone 1 — highest oxygen exposure activates APAP to NAPQI

✅ C — Zone 3 (centrilobular) is preferentially damaged by acetaminophen because it has the highest concentration of CYP2E1 (the enzyme that converts APAP to toxic NAPQI) and the lowest O₂ tension (last to receive blood from the portal triad). At therapeutic doses, NAPQI is detoxified by glutathione; overdose depletes glutathione → centrilobular necrosis. Zone 1 is preferentially damaged by viral hepatitis (first to encounter virus-containing portal blood).

Q2. A patient with cirrhosis develops confusion, asterixis, and a flapping hand tremor. Labs show NH₃ of 180 μg/dL. Which two medications would you prescribe and why?

A. Lactulose + rifaximin
B. Neomycin + vancomycin
C. Lactulose + metronidazole
D. Cholestyramine + lactulose
E. Rifaximin + proton pump inhibitor

✅ A — Hepatic encephalopathy results from impaired urea cycle → NH₃ accumulation → CNS toxicity. Lactulose: acidifies colon → converts NH₃ → NH₄⁺ (trapped, non-absorbable) + cathartic effect. Rifaximin: non-absorbable antibiotic → reduces ammonia-producing gut bacteria. Together they reduce serum ammonia. Rifaximin is preferred over neomycin (better evidence, less nephrotoxicity/ototoxicity).

Q3. A 45-year-old woman with cirrhosis has ascites (SAAG = 1.4 g/dL) and bilateral leg edema. A classmate says "the edema is from low albumin — remove albumin-rich fluid and she'll get better." What is wrong with this reasoning?

A. SAAG <1.1 indicates malignancy, not portal hypertension
B. Ascites requires portal hypertension in addition to ↓oncotic pressure; removing fluid doesn't address portal HTN
C. Bilateral leg edema in cirrhosis is always from DVT, not albumin
D. Albumin levels are always normal in cirrhosis because the liver compensates
E. Ascites in cirrhosis is due to infection, not portal hypertension

✅ B — SAAG ≥1.1 g/dL confirms portal hypertension etiology (SAAG = 1.4 here). Ascites requires portal hypertension as the primary driver — hypoalbuminemia alone (e.g., nephrotic syndrome) causes leg edema but NOT ascites. The triad for cirrhotic ascites: portal HTN + hypoalbuminemia + RAAS activation. Treating only albumin without addressing portal HTN is insufficient.

Q4. A physician prescribes atorvastatin to a patient with an LDL of 190 mg/dL. The patient asks why the drug helps. Which sequence correctly describes statin's mechanism?

A. Statin blocks LDLR → less LDL cleared → LDL falls because less is produced
B. Statin blocks HMG-CoA reductase → ↓hepatic cholesterol → upregulate LDLR → ↑LDL clearance from plasma
C. Statin blocks MRP2 → ↓cholesterol secretion into bile → LDL falls
D. Statin activates SREBP-1c → ↑cholesterol synthesis but ↑LDL receptor too → net LDL falls
E. Statin blocks lipoprotein lipase → TG cleared faster → LDL falls indirectly

✅ B — Statins competitively inhibit HMG-CoA reductase → ↓endogenous hepatic cholesterol → hepatocytes sense low intracellular cholesterol → SREBP-2 activated → ↑LDLR on hepatocyte surface → ↑LDL uptake from plasma → ↓serum LDL by 30–50%. Side effects: myopathy (↑CK), rhabdomyolysis (rare), transaminase elevation. FH = LDLR mutation → statins less effective alone.

Q5. A 28-year-old man has recurrent mild jaundice after fasting and a recent illness. Bilirubin = 3.0 mg/dL (all indirect). Direct bilirubin, LFTs, CBC, and hemolysis panel are all normal. What is the diagnosis and mechanism?

A. Dubin-Johnson syndrome — defective MRP2 secretion of conjugated bilirubin
B. Gilbert syndrome — mildly reduced UGT1A1 promoter activity triggered by fasting/stress
C. Crigler-Najjar Type II — severely reduced UGT1A1 activity
D. Hemolytic anemia — RBC destruction overwhelming conjugation
E. Rotor syndrome — defective OATP1B1/B3 uptake of bilirubin

✅ B — Gilbert syndrome: most common congenital unconjugated hyperbilirubinemia (5–10% of population). UGT1A1 promoter TATA box repeat → mildly reduced activity (30–50%) → ↑indirect bilirubin during fasting, illness, exercise, or stress. Completely benign — no treatment needed. Key distinguisher from hemolysis: no anemia, no ↑reticulocytes, no ↑LDH, normal haptoglobin.

Q6. A patient presents with dark urine, pale clay-colored stools, and intense pruritus for 3 weeks. Labs: total bilirubin 12 mg/dL (direct 10, indirect 2), ALP ↑↑↑, GGT ↑↑, ALT/AST mildly elevated. What type of jaundice is this, and what additional sign should you look for?

A. Hemolytic jaundice — look for splenomegaly and reticulocytosis
B. Obstructive jaundice — look for Courvoisier sign (palpable non-tender gallbladder)
C. Hepatocellular jaundice — look for spider angiomata and asterixis
D. Neonatal jaundice — look for unconjugated hyperbilirubinemia only
E. Gilbert syndrome — look for fasting as a precipitant

✅ B — Classic obstructive (post-hepatic) jaundice: ↑↑direct bili, dark urine (bilirubinuria), pale/clay stools (no stercobilin), pruritus (bile salt skin deposition), markedly ↑ALP (cholestasis marker). Courvoisier sign (painless jaundice + palpable non-tender gallbladder) = pancreatic head malignancy until proven otherwise (gallstones cause GB wall fibrosis → GB cannot distend — Courvoisier's law).

Q7. A patient undergoes extensive terminal ileal resection for Crohn's disease. Which of the following is NOT an expected consequence?

A. Steatorrhea
B. Fat-soluble vitamin deficiency (A, D, E, K)
C. Bile acid (cholerheic) diarrhea
D. Vitamin B₁₂ deficiency → megaloblastic anemia
E. Improved fat digestion due to ↑hepatic bile acid synthesis compensating for lost reabsorption

✅ E — The liver CANNOT adequately compensate through increased synthesis. Hepatic de novo capacity is limited (~0.5 g/day). Terminal ileal resection eliminates ASBT (95% reabsorption) → rapid pool depletion → insufficient intraluminal bile acid concentration → steatorrhea + fat-soluble vitamin deficiency + bile acid diarrhea + B₁₂ deficiency. Key distinction: cholecystectomy (reservoir only, pool intact) does NOT cause steatorrhea.

Q8. A medical student is tested on bile secretion regulation. She writes: "Both CCK and secretin contract the gallbladder." What is incorrect in her statement, and what does secretin actually do?

A. She's correct — both hormones contract the gallbladder
B. CCK relaxes the gallbladder; secretin contracts it
C. Only CCK contracts the gallbladder; secretin stimulates ductal HCO₃⁻ secretion but does NOT contract the gallbladder
D. Secretin contracts the gallbladder only in the fasted state
E. Neither CCK nor secretin contracts the gallbladder — vagal stimulation is the sole driver

✅ C — Classic trap: secretin does NOT contract the gallbladder. CCK (I cells; fat + protein stimulus) → contracts gallbladder + relaxes sphincter of Oddi → bile delivered to duodenum. Secretin (S cells; H⁺ stimulus) → cholangiocytes and pancreatic ductal cells secrete HCO₃⁻-rich fluid → alkalinizes duodenum. Secretin = "the bicarb hormone," not the bile-contracting hormone.

Overview of the Liver — Active Recall