Anatomy of the Liver

Location & Size

The liver occupies most of the right upper quadrant and part of the epigastrium, tucked under the right hemidiaphragm and protected by the lower rib cage.[1,3,6]

In adults, the liver is typically described as:

• Located beneath the diaphragm, on top of the stomach, right kidney, and proximal small intestine.[1]
• The largest internal organ, with an average weight of about 1.3–1.8 kg (~3–4 lb) depending on sex and body size.[1–2]
• Shaped like a wedge or cone, with a smooth diaphragmatic surface and a visceral surface that molds to adjacent organs (stomach, duodenum, right kidney, and colon).[1,3]

This strategic position allows portal venous blood from the entire gastrointestinal tract to pass through the liver before reaching the systemic circulation (the hepatic portal system).[10]

Lobes & Segmental Anatomy

Externally, the liver is divided into right and left lobes, plus caudate and quadrate lobes; functionally, it is divided into eight Couinaud segments, each with its own vascular inflow, outflow, and biliary drainage.[3–4]

• Right and left lobes: Separated anteriorly by the falciform ligament and inferiorly by the fissure containing the round ligament (ligamentum teres).[3,13]
• Caudate and quadrate lobes: Smaller accessory lobes on the visceral surface, bordering the inferior vena cava and gallbladder fossa.[3,13]
• Couinaud segments (I–VIII): The liver is divided into eight functional segments; each segment contains a branch of the portal vein, hepatic artery, and bile duct at its center, with hepatic veins at the periphery.[4,17]

Segmental anatomy is critical for hepatic surgery, interventional radiology, and living-donor or split-liver transplantation, allowing surgeons to resect or transplant specific segments while preserving adequate functional remnant.[4,13,17]

Dual Blood Supply & Venous Drainage

The liver has a unique dual blood supply: oxygen-rich blood from the hepatic artery and nutrient-rich blood from the portal vein mix in the hepatic sinusoids before draining into the hepatic veins.[1,10,13]

• Hepatic artery proper: Branch of the celiac trunk that provides about 20–30% of hepatic blood flow but a large share of the organ’s oxygen supply.[1,13]
• Portal vein: Formed by the superior mesenteric and splenic veins; delivers ~70–80% of hepatic blood flow, carrying absorbed nutrients, toxins, and hormones from the gut.[1,10,13]
• Within hepatic sinusoids, arterial and portal blood mix; hepatocytes line these fenestrated vessels, allowing rapid exchange of solutes, drugs, and metabolites.[1,3]
• Blood then drains into central veins → hepatic veins → inferior vena cava, returning to the heart.[1,3]

Disturbances in this flow—such as fibrosis and cirrhosis—can increase resistance within the sinusoids, producing portal hypertension with varices, ascites, and splenomegaly.[5–6,14]

Major Hepatic Cell Types

Microscopic architecture is organized into lobules with specialized cell populations that share metabolic, immune, and structural roles.[1–3]

• Hepatocytes: Represent ~80% of liver volume; perform carbohydrate, lipid, and protein metabolism; synthesize albumin and clotting factors; and carry out phase I/II drug metabolism.[1–3]
• Kupffer cells: Macrophages residing in sinusoids that phagocytose bacteria, endotoxin, and cellular debris arriving from the gut.[1–2]
• Stellate (Ito) cells: Located in the space of Disse; store vitamin A and transform into collagen-producing myofibroblasts during chronic injury, driving hepatic fibrosis.[3,19]
• Sinusoidal endothelial cells: Fenestrated cells that regulate exchange between blood and hepatocytes and respond to shear stress and inflammatory signals.[1,3]
• Cholangiocytes: Epithelial cells lining intrahepatic and extrahepatic bile ducts; modify bile volume and composition and are central to cholestatic liver diseases.[1,18]

Bile Production & Biliary Tree

The liver continuously produces bile—a fluid rich in bile salts, phospholipids, cholesterol, and bilirubin—that is critical for fat digestion and excretion of waste products.[1,5,18]

Key steps in bile flow include:

• Hepatocytes secrete bile into tiny bile canaliculi formed between adjacent cells.[18]
• Canaliculi drain into bile ductules and then into progressively larger intrahepatic bile ducts.[18]
• Right and left hepatic ducts join to form the common hepatic duct, which merges with the cystic duct from the gallbladder to create the common bile duct.[18]
• The common bile duct empties into the second part of the duodenum, usually at the major duodenal papilla, delivering bile to mix with partially digested chyme.[18]

The gallbladder stores and concentrates bile between meals. Gallstones—solid particles of cholesterol or bilirubin—can obstruct the cystic duct or common bile duct, causing biliary colic, jaundice, or pancreatitis.[5,11,19]

Key Anatomical Features & Ligaments

Several peritoneal reflections and surface landmarks help orient imaging and guide surgical approaches.[1,3,13]

• Falciform ligament: Peritoneal fold that anchors the liver to the anterior abdominal wall and separates right and left lobes anteriorly; its free edge contains the round ligament (ligamentum teres), a remnant of the fetal umbilical vein.[3,13]
• Coronary and triangular ligaments: Attach the superior surface of the liver to the diaphragm, forming the “bare area.”[3]
• Ligamentum venosum: Remnant of the fetal ductus venosus on the posterior surface, helping delineate the caudate lobe.[3,13]
• Porta hepatis: Transverse fissure on the visceral surface where the portal vein, hepatic artery, and bile ducts enter or leave the liver (the “portal triad”).[3,13,17]

Mastery of these landmarks is essential for interpreting cross-sectional imaging (CT, MRI, ultrasound) and for planning resections, ablative procedures, and transplant anastomoses.[4,13,16]

Core Functions of the Liver

The liver is central to homeostasis, integrating metabolism, detoxification, digestion, and immune defense.[1–2,5–6]

• Metabolism: Glycogen storage and gluconeogenesis for glucose balance; synthesis and oxidation of fatty acids; urea cycle to handle nitrogen from amino acid breakdown.[1–2]
• Protein synthesis: Production of albumin, clotting factors, binding proteins, and many transport proteins.[1–2]
• Detoxification: Biotransformation of drugs, alcohol, and xenobiotics via phase I and phase II enzymes; conversion of ammonia to urea.[1–2]
• Bile formation: Excretion of bilirubin, cholesterol, and bile salts, which are essential for fat digestion and absorption of vitamins A, D, E, and K.[1,5,18]
• Storage: Reservoir for glycogen, iron (in ferritin), copper, and vitamins (A, D, B₁₂).[1–2]
• Immune function: Kupffer cells and resident immune cells clear bacteria and endotoxin from portal blood and modulate systemic inflammation.[1–2,5]

Clinical Significance

Understanding liver anatomy underpins modern hepatology, oncology, and transplantation.[5–6,9]

Common liver diseases include viral hepatitis, alcohol-associated liver disease, metabolic dysfunction–associated steatotic liver disease (MASLD, formerly NAFLD), cholestatic diseases, and hepatocellular carcinoma.[5–6,14,20] Many of these conditions progress through fibrosis to cirrhosis, where architectural distortion increases portal pressure and impairs hepatocellular reserve.

Imaging modalities such as ultrasound, CT, MRI, and elastography rely heavily on segmental and vascular anatomy to stage disease, guide biopsies, and plan locoregional therapies.[4,13,16,17] In transplantation, precise mapping of hepatic inflow and outflow is essential for graft selection, anastomosis, and long-term graft function.[9,20]

For patients, appreciating basic liver anatomy can make discussions about “segments,” “portal hypertension,” “biliary obstruction,” or “living donation” much more understandable during clinic visits and pre-operative counseling.[5–6,9,20]