Digestive System Lecture 4: Liver and Pancreas

The Liver

• The liver is the largest organ in the body, weighing approximately 1.5 kg, with the exception of the skin.
• Functions of the liver:
  • Major role in lipid, carbohydrate, and protein metabolism
  • Inactivates and detoxifies drugs and substances through oxidation, conjugation, etc.
  • Participates in iron metabolism
  • Produces bile
  • Synthesizes plasma proteins and blood coagulation factors

Liver Histology

• The liver is covered by a thin connective tissue capsule called the Glisson capsule
• The capsule sends trabeculae that divide the liver into lobules called hepatic lobules
• Each hepatic lobule is hexagonal in shape, with a central vein and portal spaces at each angle
• The portal space contains the portal triad:
  • Branch of portal vein
  • Arteriole branch of hepatic artery
  • Interlobular bile duct lined by simple cuboidal epithelium
  • Lymphatic vessels (not very important)

Hepatic Lobules and Acini

• Hepatic lobule: a triangular area with a portal space in the center and a central vein at each angle
• Hepatic acinus: represents the part of 2 adjacent areas of 2 different hepatic lobules
• Hepatic acinus is supplied by terminal branches of the hepatic portal vein, terminal branches of the hepatic artery, and drained by terminal branches of the bile duct
• Three zones can be distinguished in the hepatic acinus: Zone 1, Zone 2, and Zone 3

Hepatocytes

• Hepatocytes are arranged in plates and are anastomosed freely with the central vein
• The space between the plates of hepatocytes is occupied by sinusoids
• The surface of each hepatocyte contacts the wall of sinusoids through the space of Disse
• Hepatocytes have large, rounded, centrally located nuclei (most cells have one nucleus, and 15% have 2 nuclei)

Bile Canaliculi and Ducts

• Bile canaliculi: the first portion of the bile duct system, formed by the plasma membrane of two hepatocytes
• Bile flow is in the opposite direction of blood flow, from the center of the classic lobule to its periphery
• Bile enters the bile ductule (Hering's canal) and then becomes the interlobular bile ducts, which fuse to form the right and left hepatic ducts
• The common hepatic duct receives the cystic duct from the gallbladder and forms the common bile duct, which drains into the duodenum

Liver Sinusoids

• Liver sinusoids have an irregular outline and a discontinuous layer of fenestrated endothelial cells
• In addition to lining epithelial cells, there are phagocytic cells known as Kupffer cells
• The space between the lining hepatic sinusoid and hepatocytes is known as the space of Disse

Liver Blood Supply

• The liver receives blood from two sources:
  • Portal vein, carrying oxygen-poor, nutrient-rich blood from the abdominal visceral organs
  • Hepatic artery, supplying oxygen-rich blood