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Hormonal control of circulating nutrients Overview: The need for glucose and nutrient homeostasis Interchange of nutrients / fuel stores Insulin: secretion mechanism of action (resistance) effects: CHO, fat protein special sites Counter regulatory hormones Glucagon: control of secretion effects: CHO, fat, protein Cortisol Adrenalin Growth hormone Balance Insulin & glucagon from pancreatic islets insulin Supply of nutrients constant Nutrient availability in blood glucagon Time with insulin & glucagon this is converted to: Balance between insulin : glucagon (+ others) Converts irregular food supply into a near constant supply of nutrients Homeostasis Blood glucose concentrations 35 mmol/L Consequences of hypoglycemia ( blood glucose) CNS: (unable to use fatty acids for energy) disorientation, hunger, decreased consciousness convulsions coma death Early warning – features due to adrenalin release, sympathetic stimulation eg fast pulse, tremor, sweating Hyperglycemia ( blood glucose) urine flow, dehydration intracellular dehydration eg CNS Long term: glycation of proteins functional complications Nutrients in diet Bloodstream Endogenous nutrient stores Eating: Nutrients in diet Bloodstream Uptake & storage of nutrients Insulin released Endogenous nutrient stores Fasting: Nutrients in diet Bloodstream Available for cells Glucagon + others Endogenous nutrient stores Fasting ( insulin, glucagon +) Liver Glycogen Glucose-6-P Glucose Glucose Pyruvic acid Acetyl CoA Adipose tissue Fatty acids Ketone bodies Skeletal muscle Ketone bodies Amino acids Relative amounts of energy stored as glycogen (1800kcal vs fat (140,000kcal) and protein (41,000kcal). Glycogen glucose (but only liver able to release stored glucose blood) Inability to convert fatty acids into glucose – but the oxidation of fatty acids inhibits the oxidation of glucose so glucose is not wastefully oxidised glycerol released from lipolysis is converted into glucose by gluconeogenesis in the liver ketone bodies formed from fat oxidation can be used as an alternate to glucose by many tissues Protein amino acids glucose via gluconeogenesis Stimulators of insulin secretion Glucose concentration Amino acid concentration Food intake — GI hormones — parasympathetic stimulation Blood glucose concentration Gastrointestinal hormones Major control Islet cells Food intake Blood amino acid concentration Sympathetic stimulation (and epinepherine) Insulin secretion Parasympathetic stimulation Blood glucose Blood fatty acids Blood amino acids Protein synthesis Fuel storage Somatostatin Phenytoin Thiazide diuretics “Folded” proinsulin Golgi ---------- converting enzmes Secretion Granule Plasma insulin as a function of time following a rapid increase in blood glucose to 3-fold normal Insulin release Portal circulation Intestine liver Liver exposed to higher conc of insulin (and glucagon) than peripheral tissues Insulin Action Tyrosine kinase Response depends on adequate insulin, normal receptors, normal cellular responsiveness Insulin — anabolic Uptake Storage Breakdown of stored nutrients Insulin effects on Glucose Uptake esp. muscle, fat tissue: glucose transporter cell membrane facilated diffusion Glycogen synthesis Glycogenolysis Insulin effects on Fats Uptake: ( low density lipoprotein receptor) Fat as triglyceride Fat breakdown Insulin effects on Proteins Amino acid uptake Protein synthesis Protein breakdown Special sites: Insulin effects on Liver Glycogen Liver glucose Gluconeogenesis Bloodstream Also ketone production Cells Special sites cont: Kidney – insulin has no effect on glucose transport. Glucose Filtered blood glucose conc. reabsorbed Transport max. If excess glucose filtered. Not all reabsorbed Urine Glucose = osmotic diuretic water reabsorption Large volume sweet urine = Diabetes mellitus polyuria polydipsia Special sites: Brain – absolutely depends on glucose mostly glucose transport is insulin independent, except satiety centre Intestine – glucose absorption is insulin independent Muscle – glucose uptake with exercise is insulin independent Fasting: releases “counter regulatory hormones” Glucagon (pancreatic islets) Adrenalin Cortisol Also released by stress Growth hormone * All antagonize insulin actions * growth hormone does not protein breakdown Glucagon ( cells) release stimulated by: Glucose Fatty acids Amino acids (high protein, low CHO meal) Catabolic: release stored nutrients CHO: Glycogen breakdown Gluconeogenesis (liver) Amino acids: Protein breakdown liver Fats: Lipolysis Ketogenesis (liver) Absorption of meal ( glucose) Insulin Glucagon Insulin / Glucagon ratio Metabolism Fasting ( glucose) Insulin Glucagon Insulin / Glucagon ratio Formation of glycogen, fat and protein Hydrolysis of glycogen, fat and protein + Gluconeogenesis and ketogenesis Blood Glucose Amino acids Fatty acids Ketone bodies Blood Glucose Amino acids Fatty acids Ketone bodies Summary Diet vs endogenous stored substrates Uptake & storage vs release Insulin anabolic Glucagon (cortisol, adrenalin) catabolic Growth hormone catabolic & anabolic Balance between insulin & counter regulatory hormones
