HBG 18 ( Fed & Starved State)

• Main storage macromolecules:

  • Carbohydrates
  • Proteins
  • Lipids
• Organs responsible for the synthesis of these molecules:

  • Liver
  • Muscle
  • Adipose tissue
• Main energy source for organs after a meal:

  • Liver: glucose
  • Brain: glucose
  • Muscle: glucose, fatty acids, ketone bodies
  • Red blood cells: glucose
• Metabolic pathways active in tissues:

  • Fed state: glycolysis, glycogenesis, fatty acid synthesis, lipogenesis, protein synthesis
  • Fasting state: gluconeogenesis, glycogenolysis, beta-oxidation/ketogenesis, lipolysis, protein breakdown
• Molecules passing through the liver are processed and passed on to organs through:

  • Glucose uptake by muscle and adipose tissue
  • Fat synthesis in liver and adipocytes
  • Gluconeogenesis in the liver
• Metabolic pathways active in liver that are also active in muscle or adipose tissue:

  • Glycolysis
  • Glycogenesis
  • Lipogenesis
  • Gluconeogenesis
  • Glycogenolysis
• In the fed state:

  • Insulin is secreted in response to increased blood glucose
  • Liver and muscle synthesize glycogen
  • Liver accelerates glycolysis and increases fatty acid synthesis
• In the fasting state:

  • Nutrient flow from intestine decreases
  • Glucagon promotes glycogenolysis and gluconeogenesis in the liver
  • Low insulin levels promote lipolysis and release of amino acids from muscle
• In the fasting state, all energy requirements are met by:

  • Oxidation of the body's energy stores
• Glucagon effects in the fasting state:

  • Stimulates glucose production in the liver
  • Promotes fatty acid catabolism in muscles
  • Inhibits glycogen synthesis in the liver
• Brain metabolism during fasting:

  • Unaffected until fasting has progressed for 3-4 days
  • Uses glucose as the only source of fuel except during prolonged starvation
• Muscle metabolism during fasting:

  • Uses glucose, fatty acids, and ketone bodies as major fuels
  • Resting muscle uses fatty acids instead of glucose
• Brain and muscle lack glucose 6-phosphatase and cannot export glucose
• Additional metabolic changes induced by starvation:

  • Free fatty acids released for energy in muscles and liver
  • Ketone bodies produced in the liver
  • Brain shifts metabolism to ketone bodies
  • Lactate and alanine used for gluconeogenesis by the liver
• Metabolic adaptations in prolonged starvation:

  • Provide glucose to the brain and other tissues
  • Preserve protein by shifting from glucose to fatty acids and ketone bodies
• Death by starvation occurs with loss of:

  • Roughly 40% of body weight
  • 30-50% body protein
  • 70-95% body fat
• Re-fed state:

  • Fat processed as in the normal fed state
  • Liver does not initially absorb glucose, leaves it for peripheral tissues
  • Liver in gluconeogenic mode to replenish glycogen stores
• Regulation of processes to ensure opposite processes do not occur simultaneously:

  • Carbohydrate, lipid, and protein metabolism are coordinated and regulated to meet bodily energy requirements under various conditions