Insulin secretion seen in
A i.e. Glucose B i.e. Vagal Stimulation C i.e. Acetyl choline Insulin Embryology Insulin containing granules can be identified in the human fetal pancreas by 9 to 10 weeks and detectable in fetal plasma by 12 weeksQ. Glucagon secretion begins by 8tt week. Thyroxin secretion begins by 10th to 12th week. Substance with Insulin like Activity Insulin Proinsulin Nonsuppressible insulin-like activity (NSILA) - Low-molecular-weight fraction IGF-I IGF-II - High molecular-weight fraction (mostly IGF bound to protein) Insulin causes hypoglycemia. Hormones causing hyperglycemia (opposite action) - CatecholaminesQ (epinephrine, norepinephrine) - GlucagonQ - Growth hormoneQ, ACTH - Glucocoicoids - Thyroid hormonesQ Principal Actions Rapid (seconds) - Increased transpo of glucose, amino acids, and K+ into insulin-sensitive cellsQ Intermediate (minutes) - Stimulation of protein synthesis - Inhibition of protein degradation - Activation of glycolytic enzymes and glycogen synthaseQ - Inhibition of phosphorylase and gluconeogenic enzymesQ Delayed (hours) - Increased in mRNAs for lipogenic and other enzymes Insulin Stimulates lipogenesis by - Increasing acetyl - Co A carboxylase activityQ, (most impoant enzyme in regulation of lipogenesis). This allosteric enzyme is activated by citrate, which increases in concentration in well fed state and is an indicator of a plentiful supply of acetyl CoA. - Increasing transpo of glucose into cellsQ like adipose tissue. - Increasing availability of pyruvate for fatty acid synthesis and glycerol 3 phosphate for easterificationQ of newly formed fatty acids. - Activates pyruvate dehydrogenase in adipose tissue but not in liverQ. - Decreases intracellular C- AMP levelQ - thus inhibitibiting lipolysis in adipose tissue and thereby reducing concentration of plasma free fatty acid and thus long chain acetyl CoAQ, an inhibitor of lipogenesis. Effects on Various Tissue Adipose tissue - Increased glucose entry - Increased fatty acid synthesis and lipogenesisQ - Increased glycerol phosphate synthesis - Increased triglyceride deposition - Activation of lipoprotein lipaseQ increased clearance of VLDL & chylomicron. - Inhibition of hormone-sensitive lipaseQ inhibits lipolysis - Increased K' uptake Muscle - Increased glucose entry - Increased glycogen synthesis - Increased amino acid uptakeQ - Increased protein synthesis in ribosomesQ - Decreased protein catabolism - Decreased release of gluconeogenic amino acids - Increased ketone uptake - Increased K+ uptakeQ Liver - Decreased ketogenesisQ - Increased protein synthesisQ - Increased lipid synthesis - Decreased glucose output due to decreased gluconeogenesis; increased glycogen synthesis; and increased - GlycolysisQ - Inhibits glycogenolysis & glucose uptake. General - Increased cell growth
Glucose
Vagal stimulation
Acetylcholine
All