Pathology 104 Fall 2003

Dental Histology G. Meyer

THE LIVER AND PANCREAS

The exocrine pancreas consists of acini involved in the synthesis and secretion of several digestive enzymes. The combined aqueous and enzymatic product drains into the duodenum. In this lecture we will review the histologic organisation of a compound gland.

The endocrine function of the pancreas is formed by islets of Langerhans scattered throughout the pancreas. Each islet is formed of two components:

1. anastomising cords of endocrine cells – alpha (20%-glycogen), beta (68% insulin), delta (10%-gastrin and somatostatin), and F-cells (2%-pancreatic polypeptide) thus each cell type secretes a single hormone.

2. a vascular component (insuloacinar portal system).

Cell types in the islets can be identified by:

1. immunocytochemistry.

2. electron microscopy.

3. cell distribution in the islet.

The liver, a combined endocrine and exocrine gland, has extensive access to the blood circulation and releases bile into the duodenum to enable the absorption of fats by the small intestine.

A diagram will be presented to summaries the structure of the liver (detailed below):

Blood is supplied by the portal vein and the hepatic artery. Each vessel has an interlobar and interlobular branching system.

Blood from both sources mixes in the sinusoids of the liver lobules.

Sinusoidal blood converges to form the central venule of the liver lobule. These converge to form lobular veins etc. to return blood to the inferior vena cava.

The right and left hepatic bile ducts leave the liver and merge to form the hepatic duct which becomes the common bile duct after giving rise to the cystic duct, a thin tube connecting the bile duct to the gallbladder.

The hepatic lobule is the structural and functional unit of the liver.

In the diagram presented I will explain the components of the hepatic lobule including the plates of hepaotcytes, sinusoidal space, central venule, the portal triad, bile canaliculi, space of Disse, endothelial cells, Kupffer cells, stellate cells (cells of Ito).

Lastly, I will explain that there are 3 conceptual interpretations of the architecture of the liver lobule – the classic concept of the hepatic lobule (based on structural parameters), the portal lobule concept (based on the bile drainage pathway from adjacent lobules towards the same bile duct), and the liver acinus concept, based on the gradient distribution of oxygen along the venous sinusoids of adjacent lobules.