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