Unit 2 – Digestion Module Histology of the pancreas and biliary tract Safaa El Bialy (MD,PhD) Ottawa University

Objectives  Outline the normal basic histology of the pancreas, gall bladder and biliary ducts  Describe the histology of the exocrine pancreas and the function of the exocrine glands

duodenum liver stomach main pancreatic duct (duct of Wirsung) pancreas gall bladder

Pancreas  The pancreas extends transversely from the duodenum to the spleen and lies behind the stomach.  Located in the upper abdomen, pancreas is a deep organ explaining the difficulties in early diagnosis of its pathologic conditions.  It consists of 4 parts : the head and neck that fit within the duodenum, the body and tail ( intraperitoneal ) that extends to the edge of the spleen.

Pancreas  exocrine and endocrine organ  surrounded by connective tissue (CT)  CT enters the parenchyma of the pancreas and forms septa that divide the pancreas into lobules

Pancreas endocrine pancreas - island of Langerhans exocrine pancreas CT

Pancreas  Parenchyma is formed by 2 types of glands: exocrine component secretes an alkaline fluid rich in digestive enzymes into the duodenum endocrine component primary products of secretion are hormones involved in carbohydrate metabolism

Exocrine pancreas  makes up most of the organ  composed of acini – clusters of acinar cells surrounding a lumen  acinar cells contain zymogen granules at their apical aspect  these granules contain inactive forms of digestive enzymes  acini secrete enzymes into the lumen; a series of ducts convey the secretions to the duodenum  the proximal end of these ducts, projecting into the acinar lumen, is lined with centroacinar cells; these cells secrete bicarbonate

Exocrine pancreas centroacinar cells acinar cells

Secretory granules apical acidophilic (proteinic) contain precursors of digestive enzymes (zymogens)

Pancreatic digestive enzymes  carbohydrate digestion - amylase  digestion of proteins (proteases) - trypsin, chymotrypsin, etc.  lipid digestion - lipase, phospholipase, etc.

Control of pancreatic secretion  secretion of digestive enzymes stimulated primarily by:  cholecystokinin (secreted by endocrine cells of the mucosa of the duodenum and proximal jejunum)  acetylcholine (secreted by parasympathetic fibres of the vagus nerve and by nerves of the enteric nervous system)  secretion of bicarbonate and water stimulated primarily by:  secretin (secreted by endocrine cells of the mucosa of the duodenum and proximal jejunum )

Exocrine pancreas  This section shows several acini (A). Acinar cells contain acidophilic granules. The base of these acinar cells is basophilic due to the abundance of ribosomes. Some acini show in their center pale centroacinar cells ( blue arrows).  In the center of the field we observe a longitudinal section of a small intercalated duct. The canal is lined with flattened epithelial cells ( arrowheads)

Exocrine pancreas interlobular duct intralobular duct

Interlobular duct

 “Acute pancreatitis is the most terrible of all the calamities that occur in connection with the viscera, The suddenness of its onset, the illimitable agony which accompanies it, and the mortality attendant upon it, all render it the most formidable of catastrophes” Lord Moynihan

duodenum right and left hepatic ducts stomach main pancreatic duct (duct of Wirsung) gall bladder and cystic duct ampulla of Vater common hepatic duct common bile duct

Canal of Santorini

Extrahepatic bile ducts  the intrahepatic bile ducts unite to form the right and left hepatic ducts, which anastomose to form the common hepatic duct, which becomes the common bile duct (draining into the duodenum)  the extrahepatic bile ducts are lined by a simple columnar epithelium supported by dense (fibrous) connective tissue

Extrahepatic bile ducts

Gall bladder  Functions:  storage site for bile  concentration of bile  wall is formed by a mucosa, a muscularis and an adventitia/serosa (no submucosa or muscularis mucosa)  the mucosa has numerous folds and is lined by simple columnar epithelium  the muscularis is a layer of smooth muscle containing receptor cells for cholecystokinin (CCK) – main stimulus for contraction of the gall bladder

Bile  secreted by the liver  composed of: water, electrolytes, bile acids (salts), bilirubin, cholesterol, lecithin, etc.  bile acids are synthesized by smooth ER of hepatocytes and undergo enterohepatic recirculation  bile acids emulsify food lipids, facilitate their digestion by pancreatic enzymes, and assist in lipid absorption by the small intestine

Gall bladder mucosa muscularis serosa

lamina propria Gall bladder mucosa simple columnar epithelium –appearance of cells opening into the lumen that are covered by microvilli –no goblet cells epithelium

Gall Bladder  The flow of the bile and of the pancreatic secretion in the duodenum is controlled by a complexity of smooth muscles  Sphincter of Oddi 1. Sphincter Choledochus at the distal extremity of the bile duct 2. Pancreatic sphincter at the extremity of the pancreatic canal 3. Sphincter of the ampulla around Ampulla of Vater

Sphincter of Oddi

Gall bladder stones  There are two types of stones:  cholesterol stones, represent about 80% of the stones, and  pigment stones, which are composed of bilirubin and constitute the remaining 20%  Gallbladder stones are more common in women and in the elderly and in certain groups such as Americans of Indian origin and overweight people  4 F’s rule: female, fair, fatty, forty