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How does insulin affect carbohydrate metabolism?
What tissues are affected the most?
Liver, muscle, adipose tissue.
1. Glycogenesis in liver & muscle: Activates PP1 which destroys cAMP and activates glycogen synthase.
2. Increase in glucose uptake in muscle & tissue via GLUT 4: Insulin activates GLUT 4 transporters --> glycerol 3P for fat synthesis.
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How does insulin affect lipid metabolism? (2)
Adipose tissue responds within minutes to insulin, significantly decreasing release of FAs.
- 1. Decreases TAG degradation - inhibits HSLby breaking down cAMP, decreasing PKA, thus decreasing activation of HSL. WHILE, p'lating HSL.
- 2. Increased TAG synthesis - increases transport & metabolism of glucose into adipocytes, providing substrate glycerol 3-P for TAG synthesis. Insulin also increases LPL activity, allowing VLDL/chylomicrons to provide FAs for esterification.
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How does insulin affect protein synthesis?
In most tissues, insulin stimulates entry of amino acids into cells and protein synthesis.
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What stimulates glucagon secretion? 3
- 1. Low blood glucose
- 2. Amino acids - from a meal stimulate both glucagon and insulin. Glucagon effectively prevents hypoglycemia that would occur as a result of insulin increase.
- 3. Epinephrine = by adrenal medulla and/or NE. Thus, during periods of stress, trauma, or severe exercise, elevated ep can override. Despite glucose levels in blood, glucagon levels will be raised and insulin will be lowered.
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What inhibits glucagon secretion?
Elevated blood glucose and by insulin.
Both increased after carb-rich meal & ingestion of glucose.
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What are the metabolic effects of glucagon on carb, lipid, and protein metabolism?
- 1. Carb: Increases glycogenolysis, gluconeogenesis.
- 2. Lipids: increases lipolysis (cAMP), B-oxidation (cAMP), and ketogenesis.
- 3. Proteins: Increases uptake of AAs by liver --> increased substrates for GNG --> decreases plasma levels of AAs.
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