Unit 2 – Digestion ModuleHistology 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 componentsecretes an alkaline fluid rich in digestive enzymes into the duodenum

endocrine componentprimary 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

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