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Glucagon receptors PowerPoint PPT Presentation


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Glucagon. Epinephrine. Insulin. Glycogen synthesis. Glucagon receptors. Parasympathetic nervous system activation. Glycogenolysis. Sympathetic nervous system activation. glycogen. glucose 1- phosphate. glycogen. Etiology: Classification. Inadequate production

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Glucagon receptors

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Glucagon

Epinephrine

Insulin

Glycogen

synthesis

Glucagon

receptors

Parasympathetic

nervous system

activation

Glycogenolysis

Sympathetic

nervous system

activation

glycogen

glucose 1- phosphate

glycogen


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Etiology: Classification

  • Inadequate production

  • Increased utilization


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Hormonal Response to Hypoglycemia

  • Suppression of insulin secretion

  • Glucagon release

  • Epinephrine and cortisol levels increase

  • Growth hormone levels increase

  • Results in suppression of glycogenolysis, activates gluconeogenesis, promotes lipolysis, and stimulates ketogenesis


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Etiology: inadequate production of glucose

  • Prematurity, IUGR, Perinatal stress

  • Glycogen storage disease

    • GSD type 1: glucose-6-phosphatase deficiency, catalyzes final common step in glycogenolysis and gluconeogenesis

    • GSD type 3: debrancher deficiency, inability to degrade stored glycogen. Autosomal recessive and manifestations include hepatomegaly, hypoglycemia, skeletal myopathy, cardiomyopathy


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Congenital Hyperinsulinism

  • Sporadic and familial, incidence from 1/50,000-1/2500

  • In the presence of hypoglycemia:

    • inadequately suppressed insulin level and evidence of excessive insulin action for the degree of hypoglycemia:

      • inappropriately low plasma ketones and free fatty acids, inappropriately large glycemic response to glucagon.


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Congenital Hyperinsulinism

  • To date, mutations in 4 different genes have been identified

    • Mutations in either of the two subunits of the ß-cell ATP-sensitive potassium channel (KATP)

    • Mutations in glucokinase (glucose sensor of the ß-cell)

    • Mutations in glutamate dehydrogenase

    • At least 50% of cases have no identified genetic cause


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Congenital Hyperinsulinism


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Congenital Hyperinsulinism

  • Recessive hyperinsulinism

    • Previous referred to as nesidioblastosis

    • Islet hyperplasia throughout pancreas

    • Severe hypoglycemia

    • LGA newborns

    • Genetic defect: SUR1 or kir6.2 components of the KATP channel. Thus, therapeutic interventions that act via the SUR such as diazoxide are ineffective

  • Most infants require near-total pancreatectomy


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Congenital Hyperinsulinism

  • Focal Hyperinsulinism

    • Area of islet hyperplasia is localized to a small 3-5 mm diameter region described as focal adenomatous hyperplasia

    • Clinical presentation similar to diffuse disease (severe early hypoglycemia)

    • Results as a localized clonal loss of the maternal 11p15 region and expression of a paternally inherited SUR1 or Kir6.2 mutation. The 11p15 region contains several maternally imprinted tumor suppressor genes.

    • Can respond to partial pancreatectomy


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Treatment of hyperglycemia

  • Decrease glucose infusion rate!

  • Only administer insulin if osmotic diuresis is present or glucose levels remain significantly elevated despite a reduction in glucose infusion rate.


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