Insulin

Site of Production

2-chain peptide hormone
- synthesised as one proinsulin molecule
- sulphur bridges appear between A and B chains
- C peptide then cleaved from middle of proinsulin

Phases
- cephalic
- gastric
- intestinal
Glucose level
- glut-2 transports glucose into cell
- cell depolarises
- insulin released
also stimulated by basic amino acids
Stimulus-secretion coupling

Acts at membrane-bound receptors with tyrosine kinase activity
- activates the MAP-kinase pathway
- regulates the translocation of glucose transporters to the plasma membrane
Promotes anabolism
- induces storage of excess nutrients and decreased mobilisation of endogenous stores
Lowers raised plasma glucose
At low concentrations
- regulates hepatic glucose and fat production
At high concentrations:
- promotes cellular uptake of glucose, amino acids and fatty acids
- inhibits ketone formation in the liver
- stimulates glycogen synthesis in skeletal muscle and liver
- inhibits lipolysis in adipocytes

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