Metabolism

Terms:

1. Glycogenolysis
2. Lipolysis
3. Gluconeogenesis (aa, glycerol)
4. Lipogenesis

Metabolic States

1. Post-absorptive state- > 4 hrs meal
   1. Catabolic state
      Goal : maintain blood glucose via
      1. glycogenolysis (liver, skeletal muscle)
      2. lipolysis (liver, adipose)
      3. Protein catabolism (skeletal muscle)
   2. Hormonal & Neural Control
      1. Glucagon (+ other hyperglycemic hormones)
      2. sympathetic (epinephrine)lipolysis,glycogenolysis
2. Absorptive State (just after/during a meal)
   1. Insulin directs all events
      1. glucose uptake (carrier-mediated transport)
      2. increases AA uptake--> protein synthesis
      3. inhibits glucogenogenesis (liver)
      4. enhances triglyceride synthesis (favors an anabolic state)
      5. parasympathetic, GI hormones stimulate pancreas

Role of the Liver in Metabolism

1. Protein metabolism- essential
   1. AA deaminated (NH2 removed)
   2. Urea formed (removes ammonia)
   3. makes plasma proteins, clotting
2. CHO metabolism
   1. gluconeogenesis factors
   2. Fructose--> glucose
   3. glucose --> fats (storage)
   4. glycogenolysis
3. Fat metabolism
   1. Beta oxidation (fats-->acetyl CoA)
   2. Lipoproteins (fat transport in blood)
   3. Makes cholesterol from acetyl CoA
4. Liver- main source of VLDL
   1. cholesterol, Triglyceride insoluble so need carrier
   2. VLDL - mostly lipid
      1. released to blood, lipase breaks down
      2. converted to LDL (major cholesterol carrier)(85%, 15% made in intestine)
      3. liver can take up chylomicron, LDL
   3. HDL -transports cholesterol to liver to make bile salts

Regulation of Food intake:

1. hypothalamus (satiety/ hunger centers)
   1. various theories regarding hunger stimulation
      1. Glucostatic theory - neurons sensitive to glucose levels
      2. Lipostatic Theory - adipose tissue release substance (FA, Glycerol?) to depress hunger
      3. Thermostatic Theory
         1. hi temp depress feeding while low body temp stimulates feeding
      4. Hormonal influences:
         insulin may suppress hunger
2. CCK depress hunger (may also be released & bound in brain)
3. psychological factors:
   1. stress
   2. sight of food
   3. eating disorders