Liver Anatomy: Lobes, Ligaments, and Function

• The liver, the largest internal organ, is in the upper right quadrant of the abdomen, directly below the diaphragm
• Critical functions include metabolism, storage, detoxification, and bile production

Lobes of the Liver

• Traditional anatomy describes the right and left lobes
• The falciform ligament separates these lobes and connects the liver to the anterior abdominal wall
• The right lobe is larger than the left lobe
• The caudate and quadrate lobes are also present
• The caudate lobe is on the posterior surface near the inferior vena cava
• The quadrate lobe is on the inferior surface between the gallbladder and the fissure for the ligamentum teres
• Surface features define these lobes, not functional divisions

Ligaments and Surface Anatomy

• Ligaments secure the liver to surrounding structures
• The falciform ligament runs from the anterior abdominal wall, dividing the right and left lobes
• The ligamentum teres, a remnant of the fetal umbilical vein, is in the falciform ligament's free edge
• The coronary ligament attaches the liver's superior aspect to the diaphragm
• The triangular ligaments result from the coronary ligament's reflection on the liver's lateral sides
• The bare area is where the liver directly attaches to the diaphragm without peritoneal covering

Functional (Segmental) Anatomy

• Clinically, the liver is divided into eight independent segments based on function
• Each segment possesses its own vascular inflow/outflow and biliary drainage
• Segmentation relies on the distribution of the portal vein, hepatic artery, and biliary ducts
• Hepatic veins delineate the intersegmental planes
• Functional segmentation is vital for surgical planning, enabling segment resection without affecting remaining tissue
• The segments are numbered I-VIII using Roman numerals

Couinaud Classification

• The Couinaud classification is the accepted system for liver functional anatomy
• This divides the liver into eight segments, each having independent vascular and biliary supplies
• Segment I is the caudate lobe, receiving blood from both right and left hepatic arteries
• Segments II and III reside in the liver's left lateral section
• Segment IV is in the left medial section
• Segments V, VI, VII, and VIII are in the liver's right lobe
• A plane from the inferior vena cava to the gallbladder divides the liver into right and left
• The principal portal scissura, or Cantlie's line, functionally divides the liver
• The right hepatic vein divides the right lobe into anterior (segments V & VIII) and posterior (segments VI & VII) sections
• The left hepatic vein divides the left lobe into medial (segment IV) and lateral (segments II & III) sections
• The middle hepatic vein is in the principal plane (Cantlie’s line)
• Segments are functionally independent, allowing resection of one without impacting others

Vascular Supply

• The liver has a dual blood supply from the hepatic artery and portal vein
• The hepatic artery supplies oxygenated blood from the aorta, roughly 25% of total supply
• The portal vein delivers nutrient-rich blood from the digestive tract, spleen, and pancreas, about 75% of supply
• Both the hepatic artery and portal vein enter at the porta hepatis
• These vessels branch into smaller vessels supplying hepatic sinusoids internally
• Blood from sinusoids drains into central veins, which join to form hepatic veins
• Hepatic veins drain into the inferior vena cava

Biliary Drainage

• Hepatocytes produce bile, secreting it into bile canaliculi
• These canaliculi combine into bile ducts, gradually forming left and right hepatic ducts
• The left and right hepatic ducts merge to form the common hepatic duct
• The cystic duct from the gallbladder joins the common hepatic duct, creating the common bile duct
• The common bile duct empties into the duodenum at the ampulla of Vater, joined by the pancreatic duct

Microscopic Anatomy

• Lobules are the functional units of the liver
• Each lobule is roughly hexagonal, with plates of hepatocytes radiating from a central vein
• Sinusoids (capillaries) are between the hepatocyte plates
• Kupffer cells (specialized macrophages) line the sinusoids, removing bacteria and debris from blood
• Portal triads at the lobule corners contain a hepatic artery branch, portal vein branch, and bile duct

Clinical Significance

• Liver anatomy knowledge is critical for diagnosing/treating liver diseases
• Liver resections, based on functional segmentation, remove tumors or damaged tissue, preserving liver function
• Liver biopsies assess inflammation, fibrosis, and other changes
• Vascular anatomy knowledge aids imaging interpretation and procedures like transjugular intrahepatic portosystemic shunts (TIPS)
• Liver transplantation is life-saving for end-stage liver disease, requiring thorough understanding of liver anatomy and vascular supply