Post on 14-Jun-2015
description
InsulinSecreted only by pancreas
First synthesized polypeptide hormone
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I to 2 million islets of Langerhans
Islet formation in the fetusStarts by 10 weeks
Islets of Langerhans
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Three major types of cellsAlpha
Beta
Delta cells
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Islets
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Constitute 70 %
Secrete insulin and amylin
Beta cells
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Anabolic
Insulin
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20% of the total islets
Secrete glucagon
Alpha cells
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Liver
Main site of action of insulin and glucagon
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50% degraded by the liver
50% enters the systemic circulation
Binds to insulin receptors
Insulin secreted into the portal vein
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2 amino acid chains linked by disulphide bridges
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Insulin is a polypeptide
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Stored together
Co-secreted from the beta cells
Insulin and C peptide
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Connecting peptide
Connects A and B segments of insulin
Facilitates folding to form proinsulin
C peptide has no other action
C peptide
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C peptideReleased in equal amounts as that of insulin.
Index of B cell function.
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Index of B cell function
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Useful marker of insulin secretion
Less susceptible than insulin to hepatic degradation
C peptide
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Main regulator of insulin secretion by the pancreatic beta cells
Glucose
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Controls glucose-regulated insulin secretion
Rate-limiting step
Glucokinase
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Stimulate insulin synthesis and insulin secretion
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Diabetes Mellitus
Glucose > 70 mg/dL
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