Liver Anatomy: Lobes and Functions

• The liver, the largest internal organ, sits in the upper right abdomen, under the diaphragm, and above the stomach, right kidney, and intestines.
• Its crucial roles include bile production, protein synthesis, hemoglobin processing, and blood detoxification.
• Both anatomical and functional divisions are vital for surgical planning and understanding liver diseases.

Lobes of the Liver

• Traditionally, the liver has two major lobes: right and left.
• The falciform ligament separates these lobes and attaches the liver to the anterior abdominal wall.
• The right lobe is notably 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 and the fissure for the ligamentum venosum.
• The quadrate lobe sits on the inferior surface between the gallbladder and the fissure for the round ligament (ligamentum teres).
• These lobes are defined by external landmarks, not vascular or biliary supply.

Couinaud's Liver Anatomy (Functional Segmentation)

• Claude Couinaud developed a system dividing the liver into eight independent segments.
• Each segment has its own vascular inflow, biliary drainage, and lymphatic drainage.
• Segmentation is based on portal vein branch distribution.
• The main portal vein bifurcates into right and left, further dividing to supply each segment.
• Hepatic veins drain segments independently into the inferior vena cava.
• This segmentation is important for surgical resections, allowing removal of a segment without affecting others.
• Segment I is the caudate lobe, receiving blood from both right and left hepatic arteries and portal vein branches.
• Segments II and III are in the liver's left lateral section.
• Segment IV is in the left medial section, also known as the quadrate lobe.
• Segments V, VI, VII, and VIII are in the right lobe; V and VIII are anterior, VI and VII posterior.
• The Cantlie line, a principal plane from gallbladder fossa to inferior vena cava, divides the liver into right and left hemilivers.
• This plane is surgically relevant for hepatectomies.

Vascular Supply

• The liver has a dual blood supply.
• The hepatic artery provides oxygenated blood, about 25% of the total.
• The portal vein delivers nutrient-rich blood from the GI tract, spleen, and pancreas, making up 75%.
• The hepatic artery and portal vein enter at the porta hepatis.
• Blood from both mixes in liver sinusoids, lined by hepatocytes.
• Central veins of liver lobules converge to form hepatic veins, which drain into the inferior vena cava.

Biliary Drainage

• Bile, produced by hepatocytes, is collected in bile canaliculi.
• These canaliculi merge into small bile ducts, forming the right and left hepatic ducts.
• The right and left hepatic ducts join 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.

Microscopic Anatomy

• The liver is composed of functional units called liver lobules.
• Each lobule is roughly hexagonal, with a central vein at its center.
• Hepatocytes are arranged in plates radiating from the central vein.
• Sinusoids, specialized capillaries, run between hepatocyte plates.
• Kupffer cells, specialized macrophages, are in the sinusoids.
• Portal triads are at the corners of the lobules, containing a branch of the hepatic artery, portal vein, and bile duct.

Ligaments and Peritoneal Attachments

• Several ligaments attach and support the liver.
• The falciform ligament attaches the liver to the anterior abdominal wall and includes the ligamentum teres (remnant of the fetal umbilical vein).
• The coronary ligament attaches the superior surface to the diaphragm.
• Triangular ligaments are formed by coronary ligament reflections on the liver's lateral edges.
• The lesser omentum (hepatogastric and hepatoduodenal ligaments) connects the liver to the stomach and duodenum and contains the portal triad structures.

Clinical Significance

• Understanding liver anatomy is essential for diagnosing and treating liver diseases.
• Liver resections, like partial hepatectomies, often use Couinaud segmentation.
• Knowledge of vascular and biliary anatomy is crucial for these procedures.
• Liver biopsies diagnose disorders, with location guided by anatomical considerations.
• Imaging techniques like CT scans and MRIs use anatomical landmarks to identify and characterize liver lesions.
• Liver transplants require thorough anatomical understanding for successful implantation and vascular anastomosis.