Describe the structure, secretion, function and regulation of glucagon?
Glucagon
Structure, Sythesis & Transport
- A peptide hormone made of 29 amino acids
- Formed as a prohormone named pro-glucagon and cleaved to glucagon
Function
- Key to glucose homeostasis - 'hyperglycaemic catabolic hormone':
- Actions virtually all in the Liver:
- Promotes glycogenolysis - low levels
- Promotes gluconeogenesis - medium levels
- Promotes lipolysis, fatty acid oxidation, and ketogenesis - high levels
- Acts synergistically with catecholamines, glucocorticoids, and growth hormone
Mechanism of Action
- Binds to a specific G protein coupled receptor on the plasma membrane stimulating adenylyl cyclase
- Results in the phosphorylation and activation of numerous regulatory enzymes and other protein substrates
Regulation
Stimulated by:
- Low plasma glucose
- Sympathetic stimulation
Inhibited by:
- Raised plasma glucose
- Somatostatin
- Raised plasma fatty acid & ketone bodies