Liver Anatomy

1. General Features

2. Surfaces

• Diaphragmatic (anterior/superior) surface - smooth and convex, molds to the undersurface of the diaphragm
• Visceral (posterior/inferior) surface - irregular, bears impressions from adjacent organs (stomach, duodenum, right kidney, right adrenal, hepatic flexure of the colon)
• The bare area on the posterior surface is a region not covered by peritoneum, where the liver is in direct contact with the diaphragm

3. Ligaments and Peritoneal Attachments

4. Lobes - Morphological vs. Functional Division

Morphological (classical) lobes

• Right lobe - largest, makes up 60-70% of liver mass
• Left lobe - smaller, separated from the right by the falciform ligament (on the anterior surface) and the ligamentum venosum (on the posterior surface)
• Caudate lobe (lobe of Spigelius) - on the posterior surface, between the IVC on the right and the ligamentum venosum on the left, anterior to the porta hepatis
• Quadrate lobe - on the inferior surface, between the gallbladder fossa on the right and the ligamentum teres on the left

Functional (surgical) division - Cantlie's line

5. Segmental Anatomy - Couinaud's Classification

• Left lobe = segments II + III (left lateral) + IV (left medial)
• Right lobe = segments V + VI + VII + VIII
• Right hepatectomy removes segments V, VI, VII, VIII; leaving I, II, III, IV
• Each segment can be resected independently without disrupting blood supply or bile drainage to the remaining segments

6. Blood Supply

Portal Vein (~80% of hepatic blood flow)

• Formed behind the neck of the pancreas by the union of the superior mesenteric vein and the splenic vein
• Carries nutrient-rich, partially deoxygenated blood from the gastrointestinal tract and spleen
• Portal pressure is normally ~9 mmHg (rises in cirrhosis, causing portal hypertension)
• Divides into right and left portal vein branches at the porta hepatis

Hepatic Artery (~20% of hepatic blood flow)

• The common hepatic artery arises from the coeliac trunk, then gives off the gastroduodenal artery before continuing as the proper hepatic artery
• The proper hepatic artery divides into right and left hepatic arteries
• Significant anatomical variations are common:
  • A replaced right hepatic artery (from the superior mesenteric artery) occurs in ~20% of individuals
  • A replaced left hepatic artery (from the left gastric artery) is also common
  • Surgeons must identify and preserve these variants during cholecystectomy or hepatic resection

Hepatic Veins (venous outflow)

• Three main hepatic veins: right, middle, and left
• They drain directly into the inferior vena cava (IVC) just below the diaphragm
• The caudate lobe (segment I) drains independently via small venous tributaries directly into the IVC - this is clinically relevant in Budd-Chiari syndrome, where it can be spared from congestion

7. Porta Hepatis

• Common hepatic duct - anteriorly and to the right
• Proper hepatic artery - anteriorly and to the left
• Portal vein - posteriorly

8. Biliary Drainage

• Bile is produced in bile canaliculi between adjacent hepatocytes and flows toward the portal triad (opposite direction to blood flow)
• Canaliculi drain into bile ductules (canals of Hering), then into interlobular bile ducts at the portal triads
• These drain into the right and left hepatic ducts, which merge at the hepatic duct confluence to form the common hepatic duct
• The common hepatic duct joins the cystic duct (from the gallbladder) to form the common bile duct
• Biliary anatomy has considerable variation: in 30-40% of individuals, there is a non-standard hepatic duct confluence (trifurcation, aberrant ducts draining into the left hepatic duct, etc.) - these variants are a major source of bile duct injury during cholecystectomy

9. Lymphatic Drainage

• The liver produces approximately 50% of total body lymph
• Lymph drains to hepatic lymph nodes in the porta hepatis, then to coeliac lymph nodes, and ultimately to the cisterna chyli and thoracic duct
• Deep lymphatics follow the hepatic veins to superior diaphragmatic nodes

10. Innervation

• Parasympathetic: left vagus nerve (anterior hepatic branch) and right vagus (posterior hepatic branch)
• Sympathetic: greater thoracic splanchnic nerves via the coeliac ganglia
• Notably, the denervated liver after transplantation functions normally, indicating these nerves are not essential for metabolic function
• The right phrenic nerve provides sensory supply to the liver capsule, explaining why hepatic disease can cause referred pain to the right shoulder/scapula

11. Microanatomy - The Hepatic Lobule

• Portal triad - at the periphery of each lobule; contains a branch of the hepatic artery, portal vein, and bile duct
• Sinusoids - specialized capillaries between hepatocyte plates; blood flows from the portal triad inward toward the central vein; lined by fenestrated endothelium and Kupffer cells (resident macrophages)
• Space of Disse - the perisinusoidal space between the endothelium and hepatocyte basolateral membrane; allows free exchange of solutes and proteins; connects to lymphatics
• Bile canaliculi - tiny (~1 μm diameter) channels formed by the apical membranes of adjacent hepatocytes; bile flows in the opposite direction to blood (centrifugally, toward the portal triads)
• Hepatocytes account for ~80% of liver volume; they are polarized cells with a basolateral membrane facing the sinusoid (for uptake/secretion into blood) and an apical membrane forming the canaliculus (for bile secretion)
• Kupffer cells line the sinusoids and phagocytose bacteria, debris, and foreign matter from portal blood

Functional zones (acinar model):

• Zone 1 (periportal) - receives blood richest in oxygen and nutrients; most resistant to ischemia; most susceptible to toxins absorbed from the gut
• Zone 2 (midzonal)
• Zone 3 (centrilobular/perivenular) - receives blood lowest in oxygen; most susceptible to ischemic necrosis and alcohol-related damage

Summary Table