Insulin

• 51 amino acid peptide hormone produced by beta cells of the islets of Langerhans in the pancreas

• C-chain is removed from proinsulin to form insulin
• Insulin molecule comprises A and B chains joined by three disulphide bonds
• Second messenger system for insulin utilises tyrosine kinase

• Like many other hormones including adrenaline, PTH, TSH, glucagon, FHSH/LH and ADH use cAMP

• Half-life is 10-30 minutes
• Stimulated by:
• Increased blood glucose
• Increased amino acids
• Glucagon
• Increased fatty acids
• Functions
• Increases glucose uptake into tissues:

• Increases the number and activity of glucose-transporting proteins in cell membrane (GLUT)

• GLUT1: all tissues including erythrocytes
• GLUT-2: high concentrations in the pancreas
• GLUT-3: most cells including the brain
• GLUT-5: fructose absorption
• Promotes glycogen production
• Inhibit lipolysis
• Inhibits gluconeogenesis
• Inhibits glucagon production
• Increases Na/K ATPase activity
• Promotes potassium reuptake into cells
• Deficiency leads to
• Diuresis (glycosuria)
• Plasma hyperosmolality
• Acidosis (ketone production)
• Increased glucagon concentration

Summary Table: second messenger systems