Glucagon glycogenolysis

Glucagon is secreted as a response to hypoglycemia and activates both glycogenolysis and gluconeogenesis in the liver, causing release of glucose into the blood. 

Gs Glucagon, 3-adrenergics T Adenylyl cyclase T Cardiac Ca +, CL, and Na+ channels Gluconeogenesis, lipolysis, glycogenolysis... 

Epinephrine stimulates glycogenolysis in skeletal muscle, whereas glucagon does not because of absence of its receptors. 

Glycogen phosphorylase isoenzymes have been isolated from liver, brain and skeletal muscle. All forms are subject to covalent control with conversion of the inactive forms (GP-b) to the active forms (GP-a) by phosphorylation on specific serine residues. This phosphorylation step, mediated by the enzyme phosphorylase kinase, is initiated by glucagon stimulation of the hepatocyte. Indeed, the same cAMP cascade which inhibits glycogen synthesis simultaneously stimulates glycogenolysis, giving us an excellent example of reciprocal control. 

Insulin inhibits glycogenolysis and gluconeogenesis. Glucagon opposes the effects of insulin and therefore helps to maintain the blood glucose level so that it has the same end result as that of fatty acid oxidation (See Figure 12.14). 

The decreased insulin/glucagon ratio leads to inhibition of glycogen synthesis and increased glycogenolysis to supply some of the body s glucose needs on an immediate basis. 

The steps of the signaling pathway also distribute the signal to several response pathways in the cell (eg, glucagon action to increase glucose production by the liver is mediated by increases in both gluconeogenesis and glycogenolysis). 

Glucagon Polypeptide (29 residues) Glycogenolysis, release of lipid... 

The release of insulin is closely coupled with the glucose level. Hypoglycemia results in a low level of insulin and a high level of glucagon and, hence, favors the processes of glycogenolysis and gluconeogenesis. 

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