State the dual blood supply of the liver: which vessel provides 25%/75% of blood, which provides 75%/50%, and what is the total hepatic blood flow?
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Answer
Hepatic artery: 25% of blood volume, 75% of O₂ supply (oxygenated) Portal vein: 75% of blood volume, 50% of O₂ supply (partially deoxygenated, nutrient-rich) Total hepatic blood flow: ~1500 mL/min
Unique: liver receives blood from BOTH arterial AND venous sources
LO 1 — Hepatic Acinus
Name the three zones of the hepatic acinus from periportal (Zone 1) to centrilobular (Zone 3). Which zone is most vulnerable to ischemia and which to toxins?
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Answer
Zone 1 (periportal): receives blood first (highest O₂) → first-hit toxins (viral hepatitis, yellow fever) Zone 2 (middle): intermediate oxygenation Zone 3 (centrilobular/pericentral): receives blood last (lowest O₂) → ischemia-sensitive + CYP-rich (drug metabolism toxicity)
Mnemonic: "Z3 is three ways screwed" — lowest O₂, highest drug toxicity, site of centrilobular necrosis
LO 1 — Kupffer Cells
What are Kupffer cells? Where are they located, and what is their primary function?
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Answer
Kupffer cells: resident macrophages of the liver; specialized hepatic sinusoidal endothelial cells Location: line the hepatic sinusoids (blood-liver interface) Function: phagocytose bacteria, old RBCs, and cellular debris → immune defense; part of reticuloendothelial system
LO 2 — Clinical Definitions
Define hepatomegaly, jaundice, and cirrhosis.
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Answer
Hepatomegaly: enlarged liver (>12 cm at midclavicular line or palpable below costal margin) Jaundice: yellow discoloration of skin/sclera from hyperbilirubinemia (>2–3 mg/dL) Cirrhosis: end-stage liver disease characterized by extensive fibrosis + nodular regeneration → loss of normal architecture & function
LO 2 — Ascites vs. Edema
What is ascites? How does it differ pathophysiologically from peripheral edema in liver disease?
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Answer
Ascites: accumulation of fluid in peritoneal cavity (TRANSUDATE — low protein) Mechanism in liver disease: ↓hepatic albumin synthesis → ↓plasma oncotic pressure + portal hypertension (↑hydrostatic pressure) Peripheral edema (RV failure): ↓oncotic pressure + venous congestion → accumulation in dependent areas
Key difference: ascites is "pulled" by decreased oncotic pressure, not just gravity
LO 3 — Liver Functions
Name the five main metabolic/synthetic functions of the liver.
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Answer
1. Metabolic: carbohydrate (glycogenesis, glycogenolysis, gluconeogenesis), lipid (β-oxidation, ketogenesis, lipoprotein synthesis VLDL), protein (transamination, urea cycle) 2. Detoxification: Phase I (CYP450), Phase II (conjugation) 3. Synthetic: albumin, clotting factors (II, V, VII, IX, X), other plasma proteins 4. Storage: glycogen, fat-soluble vitamins (A, D, E, K), B12, iron 5. Immune: Kupffer cells, complement synthesis
LO 3 — Carbohydrate Metabolism
Describe hepatic carbohydrate metabolism: glycogenesis, glycogenolysis, and gluconeogenesis. When does each occur?
Bile is produced by hepatocytes → secreted into canaliculi → concentrated in gallbladder 5–20×
LO 7 — Bile Acids & Enterohepatic Circulation
Name the primary bile acids and describe the enterohepatic circulation (EHC): synthesis, conjugation, reabsorption, recycling rate.
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Answer
Primary bile acids: cholic acid & chenodeoxycholic acid (made from cholesterol via 7α-hydroxylase) Conjugation: hepatocytes conjugate to glycine/taurine → more soluble, lower pKa, ionized at gut pH EHC: secreted in bile → ileum absorption via ASBT transporter → portal vein return to liver → re-secreted Recycling: 6–10 cycles/day; ~95% reabsorbed in terminal ileum
Efficient system — only ~0.5 g/day of new bile acid synthesis needed
LO 8 — Bile Secretion & Storage
Describe bile secretion from hepatocytes and storage/concentration in the gallbladder. What happens to bile salts?
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Answer
Hepatocytes: secrete canalicular bile (hepatic bile) into bile canaliculi → Ductules → bile ducts → CBD → Gallbladder (between meals): stores & concentrates via active Na⁺/H₂O reabsorption (5–20× concentration) → CCK stimulation: gallbladder contracts + Sphincter of Oddi relaxes → bile enters duodenum
Key: bile salts NOT reabsorbed in gallbladder — they drive water reabsorption osmotically
LO 9 — Bile Regulation
Describe the hormonal and neural regulation of bile secretion. Compare CCK vs. secretin effects.
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Answer
CCK (cholecystokinin): fat/protein in duodenum → I cells → gallbladder CONTRACTION + Oddi RELAXATION + pancreatic enzyme secretion Secretin: acid in duodenum → S cells → ↑ ductal (watery, HCO₃⁻-rich) bile secretion Vagal stimulation: enhances bile secretion Bile acid feedback: bile acids inhibit 7α-hydroxylase → ↓ new bile acid synthesis (negative feedback)
Net: dietary fat/protein → ↑bile flow; acid → ↑HCO₃⁻ in bile
LO 10 — Cholecystectomy
What are the consequences of cholecystectomy? How does loss of gallbladder storage affect fat absorption?
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Answer
Loss of bile storage → continuous low-volume bile flow instead of bolus after meals Mild fat malabsorption: especially with large fatty meals (reduced bile micellar concentration) Bile acid diarrhea (post-cholecystectomy diarrhea): excess bile acids reach colon → ↑secretion + motility No jaundice, no clotting defect (EHC still intact)
Most patients tolerate well; fatty food intolerance improves over time
LO 10 — Ileal Resection
What are the GI and nutritional consequences of ileal resection or disease (Crohn's, etc.)?
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Answer
Loss of bile acid reabsorption (ASBT site) → • Bile acid diarrhea: ↑fecal loss → ↓EHC cycling → hepatic demand ↑ synthesis → ↓bile acid pool • Fat malabsorption: insufficient bile salts → steatorrhea • Gallstones: ↓bile acid pool → ↑cholesterol saturation • Vitamin B12 deficiency: if terminal ileum involved (intrinsic factor-B12 complex absorbed there) • Fat-soluble vitamin deficiency: A, D, E, K from malabsorption
Management: bile acid sequestrants (cholestyramine) or low-fat diet
LO 3 — Protein Metabolism
What is the urea cycle? Name it as the major hepatic protein metabolism pathway and explain its clinical significance.
Which liver-synthesized clotting factors are Vitamin K-dependent? Why is PT/INR elevated in liver disease?
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Answer
Vitamin K-dependent factors (liver-synthesized): II (prothrombin), VII, IX, X (mnemonic: 2,7,9,10) Also synthesized in liver (NOT Vit K-dependent): V, fibrinogen, XIII In liver failure: • ↓ALL clotting factor synthesis → prolonged PT/INR • Factor V particularly sensitive to liver damage • Factor V/VIII ratio useful marker: normal ~1:1, in liver disease VIII relatively spared → ratio <1 • PT/INR NOT corrected by vitamin K (unlike biliary obstruction where K-malabsorption is primary)
LO 1 — Liver Detoxification
Describe Phase I and Phase II detoxification pathways in the liver. Which drugs are metabolized primarily in Zone 3?
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Answer
Phase I (Oxidation): CYP450 monooxygenase system (esp. CYP3A4) → oxidative metabolism of drugs (often creates reactive metabolites) Phase II (Conjugation): UDP-glucuronosyltransferase, sulfotransferase, glutathione S-transferase → attach water-soluble groups → more excretable Zone 3 (centrilobular) enriched in CYP450 → • Acetaminophen toxicity (NAPQI metabolite) → centrilobular necrosis • Isoniazid, barbiturates, carbon tetrachloride (CCl₄) also cause Zone 3 damage • Risk ↑ with enzyme induction (phenobarbital, rifampicin)
FIB 01 — LO 1
The hepatic artery provides ___________ % of blood volume and ___________ % of the liver's O₂ supply. The portal vein provides ___________ % of blood volume.
Hint: Artery has LESS volume but HIGHER O₂; portal vein opposite.
FIB 02 — LO 1
Zone 3 (centrilobular) hepatocytes are most vulnerable to ___________ (toxin type) and ischemia because they have ___________ O₂ and ___________ CYP enzyme content.
Hint: Zone 3 = Last to get blood, first to die in hypoxia, richest in drug-metabolizing enzymes.
FIB 03 — LO 2
Cirrhosis is defined by extensive ___________ and ___________ __________. It represents end-stage liver disease with loss of ___________.
FIB 04 — LO 3
Hepatic carbohydrate metabolism occurs via three processes: ___________ (glucose → glycogen, fed state), ___________ (glycogen breakdown, fasting), and ___________ (amino acids/lactate → glucose).
Ketone bodies are produced from excess ___________ via ___________. They serve as an important fuel source during ___________.
FIB 06 — LO 4
Cholesterol synthesis is negatively regulated by dietary cholesterol via the transcription factor ___________. ___________ drugs competitively inhibit HMG-CoA reductase and reduce LDL-C by ~30–50%.
Hint: HMG-CoA reductase is the rate-limiting enzyme in cholesterol synthesis.
FIB 07 — LO 5
The enzyme ___________ converts heme to biliverdin. Bilirubin is then transported in the blood bound to ___________. In hepatocytes, ___________ conjugates bilirubin to glucuronic acid.
FIB 08 — LO 5
In ___________ jaundice, bilirubin (mainly unconjugated) is elevated and urine urobilinogen is ___________, but urine bilirubin is ___________.
Hint: "Prehepatic" = problem BEFORE the liver; unconjugated bili cannot pass through kidneys.
FIB 09 — LO 6
Bile salts comprise approximately ___________ % of bile by weight. The primary bile acids are ___________ acid and ___________ acid. Both are synthesized from ___________.
Hint: Primary bile acids are made in the liver from cholesterol via 7α-hydroxylase.
FIB 10 — LO 9
___________ (hormone) released by duodenal I cells in response to fat/protein stimulates gallbladder ___________ and Sphincter of Oddi ___________. The hormone ___________ stimulates watery, HCO₃⁻-rich ductal bile secretion in response to acid.
Instructions: Drag and drop the items into the correct order, then click "Check Order." Use "Show Answer" if you get stuck.
Drill 1 — Bilirubin Metabolism: Pathway from Heme → Urobilinogen
Arrange these steps in the correct sequence of bilirubin metabolism.
⠿Secretion into bile
⠿Biliverdin (via heme oxygenase)
⠿Gut bacteria metabolism → Urobilinogen
⠿Heme (from RBC breakdown)
⠿Conjugation by UGT1A1 → Conjugated bilirubin
⠿Unconjugated bilirubin + albumin transport to liver
Heme from RBC breakdown in spleen/RES
Biliverdin (via heme oxygenase enzyme)
Unconjugated bilirubin + albumin → liver transport
UGT1A1 conjugation → conjugated bilirubin
Secretion into bile
Gut bacteria → urobilinogen (some reabsorbed)
Drill 2 — Bile Acid Enterohepatic Circulation (EHC): Complete Cycle
Arrange the steps of the EHC in the correct order.
⠿Reabsorption in terminal ileum via ASBT transporter
⠿Passage through duodenum & small intestine
⠿Re-secretion into bile (cycle repeats 6–10×/day)
⠿Primary bile acids synthesized from cholesterol
⠿Portal vein return to liver
⠿Conjugation to glycine/taurine → bile salts secreted
Cholesterol → primary bile acids (via 7α-hydroxylase)
Conjugation to glycine/taurine → soluble bile salts
Passage through SI — emulsify fats
Terminal ileum absorption via ASBT (>95% reabsorbed)
Loss of ASBT function → bile acid diarrhea + fat malabsorption
No storage → continuous low-volume bile flow → mild fat malabsorption + post-CCK diarrhea
Score: 0/3 correct
Test Trap Mode: Each statement is either TRUE or FALSE as written. Many are designed to catch common exam errors. Click T or F — then read the explanation carefully.
Trap 01 — LO 1
"The hepatic artery provides the majority of blood volume to the liver, while the portal vein provides most of the O₂."
FALSE. This is REVERSED! Portal vein = 75% blood volume (but O₂-poor from GI tract). Hepatic artery = 25% blood volume, 75% of O₂ (oxygenated). Students often mix this up because the artery is arterial (expect more volume), but the portal vein actually delivers MORE volume due to its dual inputs (superior & inferior mesenteric veins, splenic vein).
Trap 02 — LO 1
"Zone 3 (centrilobular) hepatocytes are protected from drug toxicity because they receive blood from the hepatic artery (well-oxygenated) first."
FALSE. Zone 3 is VULNERABLE to both ischemia AND drug toxicity because: (1) lowest O₂ (receives blood LAST) → ischemia-sensitive, and (2) HIGHEST CYP450 enzyme content → maximum drug metabolism → max toxic metabolites. This is why acetaminophen toxicity causes centrilobular necrosis.
Trap 03 — LO 2
"Ascites in cirrhosis is caused primarily by impaired hepatocyte clearance of aldosterone, leading to sodium retention and edema."
FALSE. While secondary hyperaldosteronism DOES occur in cirrhosis, the PRIMARY driver of ascites is: (1) ↓plasma oncotic pressure (↓albumin synthesis), and (2) portal hypertension (↑hydrostatic pressure). It's a transudate, not retention from aldosterone alone. Aldosterone excess contributes but is secondary.
Trap 04 — LO 5
"In Gilbert syndrome, jaundice occurs because the liver cannot produce bilirubin-binding proteins."
FALSE. Gilbert syndrome is caused by ↓UGT1A1 enzyme activity (mild, ~20% normal), NOT a problem with binding proteins or production. Bilirubin is produced normally but conjugated slowly → accumulates as unconjugated hyperbilirubinemia (mild, 1–3 mg/dL). Stress, fasting, or illness worsens it. Albumin binding is completely normal.
Trap 05 — LO 5
"Conjugated (direct) hyperbilirubinemia always means cholestasis because bilirubin is being forced backward into the blood."
FALSE. Conjugated hyperbilirubinemia occurs in TWO contexts: (1) Cholestasis — bile duct obstruction (posthepatic), AND (2) Hepatocellular injury (intrahepatic) where hepatocytes are damaged but still leak conjugated bili back into blood. Both cause ↑conjugated bilirubin, but for different reasons. Check AST/ALT and ALP to differentiate.
Trap 06 — LO 7
"Bile acids are reabsorbed in the colon, so >95% are recycled back to the liver daily."
FALSE — PARTIALLY. While >95% ARE recycled, this happens in the TERMINAL ILEUM, not the colon. The ileum has ASBT transporters for active absorption of bile acids. The colon plays no role in bile acid reabsorption. This is why terminal ileum disease/resection causes bile acid diarrhea and steatorrhea — the acids reach the colon where they increase fluid secretion.
Trap 07 — LO 8
"The gallbladder concentrates bile by actively reabsorbing bile salts and cholesterol."
FALSE. The gallbladder concentrates bile by actively reabsorbing Na⁺ and H₂O via the mucosal epithelium (isosmotic reabsorption). Bile salts and cholesterol are NOT reabsorbed in the gallbladder — they remain behind, becoming increasingly concentrated (5–20×). Bile salts are reserved for the ileum (terminal, ASBT-mediated reabsorption).
Trap 08 — LO 9
"Secretin is released in response to dietary fat, and it stimulates the pancreas to release digestive enzymes."
FALSE. Secretin is released by S cells in response to ACID (not fat), and it stimulates watery, HCO₃⁻-rich ductal bile secretion (from hepatocytes/ducts) — NOT pancreatic enzymes. CCK (released by fat/protein) stimulates gallbladder contraction AND pancreatic enzyme secretion. Don't mix them up!
Hepatic Blood Supply & Acinus Zones
Feature
Hepatic Artery
Portal Vein
% Blood Volume
25%
75%
% O₂ Supply
75%
50%
Blood Type
Oxygenated arterial
Nutrient-rich, partially deoxygenated
Total Flow
~1500 mL/min (unique dual blood supply)
Acinus Zones (Z1 → Z3): Z1 (periportal) = high O₂, first-hit toxins (viral hep); Z2 (mid) = intermediate; Z3 (centrilobular) = low O₂, CYP-rich, ischemic necrosis, drug toxicity (acetaminophen)
Four Types of Jaundice — Lab Differentiation
Type
Main Cause
↑Unconj?
↑Conj?
Urine Bili
Urine Urobilinogen
AST/ALT
ALP/GGT
Prehepatic (hemolytic)
↑RBC breakdown
↑↑
Normal
NO
↑↑
Normal
Normal
Intrahepatic (hepatocellular)
Liver cell damage
↑
↑
YES
↑
↑↑
Mild ↑
Posthepatic (obstructive)
Bile duct block
Normal/mild
↑↑
DARK
↓/Normal
Normal
↑↑
Congenital: Gilbert
↓UGT1A1 (20%)
Mild ↑
Normal
NO
Normal
Normal
Normal
Crigler-Najjar Type I: Absent UGT1A1 → severe unconj hyperbilirubinemia, kernicterus risk. Dubin-Johnson: Conj bili ↑, BLACK liver. Rotor: Conj bili ↑, normal liver color.
Bilirubin Metabolism Pathway
Step
Location
Enzyme/Carrier
Product
1. Heme breakdown
Spleen/RES
Heme oxygenase
Biliverdin
2. Reduction
Spleen
Bilirubin reductase
Unconjugated bilirubin
3. Transport
Blood
Albumin (tight binding)
Albumin-bili complex
4. Conjugation
Liver hepatocytes
UGT1A1
Conjugated bilirubin (more soluble)
5. Secretion
Hepatocyte canaliculi
BSEP pump
Bile
6. Metabolism
Colon
Bacterial enzymes
Urobilinogen → stercobilin (stool) or reabsorbed
Bile Composition & Secretion
Component
% by Weight
Function
Reabsorbed?
Bile acids/salts
~50%
Emulsify fats; facilitate absorption
Yes, in terminal ileum (ASBT, >95%)
Phospholipids (lecithin)
~40%
Micellar formation with bile acids
Partially
Cholesterol
~4%
Component of micelles
No
Bilirubin
~0.3%
End product of heme metabolism
No (excreted)
Electrolytes + water
Remainder
Osmotic balance; pH ~7–8
Gallbladder concentrates via NaCl/H₂O reabsorption
EHC Cycling: Primary bile acids (cholic & chenodeoxycholic) synthesized from cholesterol via 7α-hydroxylase. Conjugated to glycine/taurine → bile salts (soluble). Reabsorbed in terminal ileum (ASBT) → portal vein → hepatic re-uptake. Cycles 6–10×/day; only ~0.5 g/day new synthesis.