Unit 2 – Endocrine Module Histology of the endocrine pancreas Safaa El Bialy (MD, PhD)

Unit 2 – Endocrine Module

Histology of the endocrine pancreas

Safaa El Bialy (MD, PhD)

Objectives

• Describe the histology of the hormone producing cells and their molecular signaling pathways.

duodenum

liver

stomach

main pancreatic duct (duct of

Wirsung)

pancreas

gall bladder

Pancreas

endocrine pancreas -islet of Langerhans

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 that affect carbohydrate (and lipid and protein) metabolism

Endocrine pancreas

• < 5% of the pancreas• innervated by autonomic

nerve fibres• endocrine cells are grouped

into islets of Langerhans– islets contain numerous

capillaries– islets are more numerous in the

tail of the pancreas– endocrine cells are small, pale,

round and arranged in cords

Endocrine Pancreas

• Endocrine cells• Smaller than exocrine

cells• Polygonal or round

with pale cytoplasm

Endocrine pancreas

• main endocrine cells of the islets of Langerhans:– alpha

• produce glucagon• second most common cell • acidophilic

– beta• produce insulin• most common cell (> 60%)• Large sperical , pale and central

– delta• produce somatostatin -- F cells (PP cells)• produce pancreatic polypeptide

( inhibits action of exocrine cells )

Pancreas endocrine

Immunohistochemistry

Alpha cells ßcells

Endocrine pancreas – immunohistochemistry

Anti-insulin antibodies

Anti-glucagon antibodies

Anti-somatostatin antibodies

Insulin and glucagon

Hyperglycemia Hypoglycemia

Cells Cells Cells Cells

Glucagon GlucagonInsulin Insulin

- + -+

Maintain glycémia

Medical application

• Diabetes:• 1. Type 1 diabetes• Starts in infancy or adolescence• Autoimmune• Insulin deficiency• 2. Type 2 diabetes• Resistance of cells targeted by insulin

Autonomic Innervation of the Pancreas

• The islets of Langerhans receive autonomic innervation via 2 neurones (preganglionic in the SNC and postganglionic in the autonomic ganglia

• The parasympathetic stimulation of insulin secretion is part of the cephalic phase. It refers to sensory stimuli and neural inputs that are activated when food is first eaten. There is an activation of the parasympathetic preganglions

• Those will activate the postganglionic neurones and stimulate the secretion of insulin even before the elevation of the blood glucose levels in the blood. An example of feedforward regulation.

• The sympathetic stimulation inhibits insulin secretion and stimulates glucagon secretion

Local retroaction of the pancreatic cells• Glucagon stimulates or modulates the local secretion of insulin

• Insulin inhibits glucagon secretion

• Negative/positive feedback between insulin and glucagon so between A and B cells.

• Somatostatin (cells D) inhibits secretion of cells A et B and glucagon the secretion of D cells.

• A paracrine effect which regulates homeostasis