Glucagon & Somatostatin Flashcards
Origin of Glucagon
A cells of pancreatic islets & Upper GIT
Chemistry of glucagon
Polypeptide hormone
Site of preproglucagon
A cells & L Cells
(GIT & brain)
Mechanism of action of glucagon
- Binds to Gs receptors on liver cells
- Activates adenyl Cyclase –> cAMP
- cAMP activates protein Kinase A Phospholipase C
- Stimulate Glycogenolysis (breakdown of glycogen)
Action of Glucagon on Carbohydrate metabolism
- Breakdown of liver glycogen (not muscle)
- stimulates Gluconeogensis
Action of Glucagon on Protein metabolism
increases enzymes required for:
* amino acid uptake by liver
* Gluconeogenesis
Action of Glucagon on Fat metabolism
activates hormone sensitive lipase –> Lipolysis
Action of Glucagon on metabolic rate
as a result of deamination of aa & gluconeogenesis, Cardiogenic –> increased metabolic rate
Action of Glucagon on the Heart
if Exogenous & in large dose —> positive inotropic
Glucagon induces the secretion of which hormones ?
- Insulin
- Growth hormone
- Somatostatin
Explain how hypergylcemia inhibits glucagon secretion
- B cells release GABA
- GABA activates GABAA receptor on A cells, causing Cl- influx –> Hyperpolarisation
- Inhibits A cell from secreting glucagon
In order for glucagon to exert its gluconeogenic effect during fasting or starvation , it requires:
glucocorticoids
effect of exercise on glucagon secretion
Increases glucagon secretion by:
* Increasing glucose utilisation –> lower plasma glucose
* Autonomic nervous stimulation of Pancreatic islets
Factors stimulating glucagon secretion
- Hypoglycemia
- Exercise
- Beta adrenergic innervation
- Vagal stimulation
- CCK
- Gastrin
Factors inhibiting glucagon secretion
- Hyperglycemia
- Alpha adrenergic innervation
- Secretin
- Somatostatin
- Insulin
