Digestive System Lecture 4: Liver and Pancreas

Study Notes

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

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 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 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: 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 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

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