Nutrient homeostasis

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  • Nutrient homeostasis
    • Nutrient source
      • Glycogenesis
        • formation of glycogen from glucose
      • Lipogenesis
        • formation of triglycerides from fatty acids and glycerol
      • Glycogenolysis
        • breakdown of glycogen to glucose
      • Lipolysis
        • triglycerides broken down into fatty acids and glycerol
      • Gluconeogenesis
        • formation of glucose from non -carbohydrate sources
    • Catabolic reactions
      • Complex molecules are broken down to simpler ones and energy is released.
    • Glucose sensing
      • Beta cells in pancreas
        • Glucose is phosphorylated and is oxidised to produce ATP
        • ATP drives closure of potassium/ATP-channels
        • This causes the opening of voltage-dependent calcium channels
        • Ca moves into the cell which drives insulin secretion (exocytosis of insulin)
      • in liver
        • glucose-sensitive vagal afferent nerve is excited by increase in glucose - sends signal to hypothalamus which increases food intake
      • in brain
        • glucose sensitive neurones via altering firing rates in response to ambient glucose levels
    • Anabolic reactions
      • build up metabolites and require energy
    • Metabolic efficiency
      • amount of 'work' achieved for a given amount of energy expended
    • Turnover of nutrient stores
    • Daily fluctuations in nutient homeostasis
      • Mainly nutrient anabolism ( > catabolism)
      • Glucose intake: replacement of glycogen stores and fuel processes. Glucose and FFA stored as triglyceride in adipose tissue
    • Insulin role
      • key regulator of fuel selection and balance of anabolism to catabolism
      • Stimulate
        • glycogenesis, lipogenesis and reduced lipid catabolism
      • Inhibit
        • lipolysis, gluconeogenesis and protein catabolism
      • Action
        • Inhibits lipolysis in liver and adipose tissue
        • Facilitates transport of glucose into cells
        • Inhibits glycogenolysis in liver and muscle
        • Increases the uptake of amino acids by cells and increases the rate of protein synthesis
    • Glucagon actions
      • Stimulates gluconeogenesis in liver
      • Increases lipolysis
      • Binds to receptor on liver cells, stimulating glycogenolysis

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