Glucagon

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GLUCAGON
-has a major role in maintaining normal concentrations of glucose in blood, and is often described as having the opposite effect of insulin that is, glucagon has the effect of increasing blood glucose levels while insulin lowers blood glucose levels. The pancreas releases glucagon when blood sugar glucose levels fall too low -linear peptide of 29 amino acids.

-Glucagon causes the liver to convert stored glycogen into glucose, which is released into the bloodstream. -Glucagon and insulin are part of a feedback system that keeps blood glucose levels at a stable level. Secretin- family of peptide hormones.

Regulation

Secretion of glucagon is stimulated by:

• Hypoglycemia
• Epinephrine Arginine
• Alanine 
• Acetylcholine
• Cholecystokinin
Secretion of glucagon is inhibited by:

• Somatostatin
• Insulin 
• Increased free fatty acids and keto acids into the blood • Increased urea production

Structure
Glucagon is a 29-amino acid polypeptide.

Its primary structure in humans is:NH2-His-Ser-Gln-Gly-Thr-Phe-Thr-Ser-Asp-Tyr-Ser-Lys-Tyr-Leu-Asp-Ser-Arg-Arg-Ala-Gln-Asp-Phe-Val-Gln-Trp-Leu-Met-Asn-Thr-COOH.

[pic]

The polypeptide has a molecular weight of 3485 daltons. Glucagon is a peptide (nonsteroid) hormone.

Glucagon is generated from the cleavage of proglucagon secreted by pancreatic islet α cells. In intestinal L cells, proglucagon is cleaved to the alternate products glicentin, GLP-1 (an incretin), IP-2, and GLP-2 (promotes intestinal growth).

GIP, a related member of the glucagon peptide superfamily, also regulates nutrient disposal via stimulation of insulin secretion. The actions of these peptides are mediated by distinct members of the glucagon receptor superfamily of G protein-coupled receptors. These receptors exhibit unique patterns of tissue-specific expression, exhibit considerable amino acid sequence identity, and share similar structural and functional properties with...
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