Insulin physiology
biochemistry
5800 Da molecule
acts by activating tyrosine kinase
- gene expressed in beta cells of pancreatic islets → preproinsulin
- 🏠 Golgi apparatus - proteolytic cleavage forms mature insulin + C-peptide
- THUS C-peptide serves as proxy measure of endogenous insulin production
homeostasis
secretion increased by:
- parasympathetic stimulation
- ACh
- ↑ blood glucose/fatty acids/amino acids in blood
- glucagon
- growth hormone
- cortisol
- obesity
- sulphonylureas
secretion inhibited by:
- somatostatin
- leptin
- hypoglycaemia
- alpha adrenergic activity/catecholamines
Effects
- Inhibits gluconeogenesis (biosynthesis of glucose from certain non-carbohydrate carbon substrates)
- Inhibits glycogenolysis (breakdown of glycogen to glucose 1-phosphate)
- Stimulates glycolysis (conversion of glucose into pyruvate)
- Stimulates glycogenesis (formation of glycogen utilising glucose)
- Inhibits lipolysis in adipose tissue (lowering plasma fatty acid levels)
- Stimulates lipogenesis (conversion of fatty acids and glycerol into triglycerides(fat). Note fatty acid synthesis starts with acetyl CoA)
- Stimulates the uptake of triglycerides from the blood into adipose tissue and muscle.
- Promotes protein synthesis
- Promotes uptake of K ions into cells