PANCREASPANCREAS

ObjectivesObjectives

The student should be able to describe:The student should be able to describe:

1.1.The The endocrine partendocrine part of the pancreas of the pancreas within the within the exocrine partexocrine part..

2.2.The The histological featureshistological features of the cells of of the cells of islet of Langerhans.islet of Langerhans.

3.3.The The functionfunction of different cells of islets of of different cells of islets of Langerhans.Langerhans.

PANCREASPANCREAS

Stroma:Stroma: capsule, capsule, septa & reticular fibers.septa & reticular fibers.

Parenchyma:Parenchyma: Pancreas is a Pancreas is a mixedmixed gland:gland:– Exocrine part Exocrine part (acini & (acini &

ducts): produces ducts): produces digestive pancreatic digestive pancreatic enzymesenzymes..

– Endocrine part Endocrine part (islets (islets of Langerhans): of Langerhans): produces produces hormoneshormones..

Exocrine PancreasExocrine Pancreas

Pancreatic Acini:Pancreatic Acini: They are serous aciniThey are serous acini: :

secreting a thin fluid rich secreting a thin fluid rich in digestive pancreatic in digestive pancreatic enzymes.enzymes.

Centroacinar cellsCentroacinar cells::Their nuclei appear in Their nuclei appear in the center of the acini. the center of the acini. They represent the They represent the beginning of the ducts. beginning of the ducts.

No myoepithelial cellsNo myoepithelial cells around the acini.around the acini.

Exocrine PancreasExocrine Pancreas

Pancreatic Acinar Cells:Pancreatic Acinar Cells: PyramidalPyramidal in shape. in shape. NucleiNuclei are basal. are basal. CytoplasmCytoplasm::

– Basal part basophilic Basal part basophilic (due to abundant rER).(due to abundant rER).

– Apical part acidophilic Apical part acidophilic (due to secretory (due to secretory granules).granules).

Exocrine PancreasExocrine Pancreas

Duct System:Duct System: CentroacinarCentroacinar cells. cells. IntercalatedIntercalated ducts (low ducts (low

cuboidal).cuboidal). IntralobularIntralobular ducts (NOT ducts (NOT

prominent).prominent). InterlobularInterlobular ducts. ducts. MainMain pancreatic duct. pancreatic duct.

Endocrine PancreasEndocrine Pancreas

Islets of Langerhans:Islets of Langerhans: Pale-staining spherical Pale-staining spherical

collections of endocrine cells, collections of endocrine cells, scattered among the acini.scattered among the acini.

Richly vascularized by Richly vascularized by fenestrated capillaries.fenestrated capillaries.

Each islet is surrounded and Each islet is surrounded and supported by reticular fibers.supported by reticular fibers.

1 million islets in human 1 million islets in human pancreas.pancreas.

Most numerous in the tail of Most numerous in the tail of pancreas.pancreas.

Endocrine PancreasEndocrine Pancreas

Cells of the Islets:Cells of the Islets: 5 types of cells in each islet:5 types of cells in each islet:

1.1. ββ (B) cells: (B) cells: secrete insulin.secrete insulin.

2.2. αα (A) cells: (A) cells: secrete glucagon.secrete glucagon.

3.3. δδ (D) cells: (D) cells: secrete secrete somatostatin.somatostatin.

4.4. G cells: G cells: secrete gastrin.secrete gastrin.

5.5. PP cells: PP cells: secrete pancreatic secrete pancreatic polypeptide.polypeptide.

Cannot be differentiated from Cannot be differentiated from one another by routine stains.one another by routine stains.

Endocrine PancreasEndocrine Pancreas

Cells of the Islets:Cells of the Islets: ββ (B) cells: (B) cells:

– Constitute 70% of islet cells.Constitute 70% of islet cells.– Concentrated in islet center.Concentrated in islet center.– Function: secrete Function: secrete insulininsulin which which

↓ blood sugar.↓ blood sugar.

αα (A) cells: (A) cells:– Constitute 15-20%.Constitute 15-20%.– Concentrated in islet periphery.Concentrated in islet periphery.– Granules are much more Granules are much more

numerous, more tightly numerous, more tightly packed, smaller, and denser packed, smaller, and denser than those of β cells.than those of β cells.

– Function: secrete Function: secrete glucagonglucagon which ↑ blood sugar.which ↑ blood sugar.

Endocrine PancreasEndocrine Pancreas

Cells of the Islets:Cells of the Islets: δ (δ (D) cells:D) cells:

– Constitute 5-10% of islet Constitute 5-10% of islet cells.cells.

– Scattered throughout the Scattered throughout the islet.islet.

– Granules are less dense Granules are less dense than those of β and than those of β and α α cells.cells.

– Function: secrete Function: secrete somatostatinsomatostatin which ↓ release which ↓ release of hormones from endocrine of hormones from endocrine pancreas and enzymes from pancreas and enzymes from exocrine pancreas.exocrine pancreas.

Endocrine PancreasEndocrine Pancreas

Cells of the Islets:Cells of the Islets: G cells:G cells:

– Constitute 1% of islet cells.Constitute 1% of islet cells.– Scattered throughout the islet.Scattered throughout the islet.– Function: secrete Function: secrete gastringastrin which ↑ production of HCl which ↑ production of HCl

by parietal cells of the stomach.by parietal cells of the stomach.

PP cells:PP cells:– Constitute 1% of islet cells.Constitute 1% of islet cells.– Scattered throughout the islet.Scattered throughout the islet.– Function: secrete Function: secrete pancreatic polypeptidepancreatic polypeptide which ↓ which ↓

exocrine secretions of pancreas.exocrine secretions of pancreas.

Best wishes

Best wishes