questions 4

Insulin and Glucagon

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Topic updated on 10/27/16 12:39pm

Snapshot
  • A 15-year-old high school student presents with sudden weight loss, increased urination and increased thirst.  He is an otherwise healthy individual who plays soccer on his schools team.  On physical exam you see a lean young man with dry mucous membranes.  Fingerstick glucose reveals a blood glucose of 469 mg/dL.
Insulin Overview  
  • Synthesis/Release 
    • synthesized as proinsulin in β cells of pancreas
      • proinsulin = insulin + C-peptide
      • C-peptide secreted with insulin 
      • detection in serum is a mechanism to determine origin of hyperinsulinemia
        • present with endogenous insulin, but absent with exogenous administration
    • hyperglycemia, GH, and cortisol ↑ insulin while hypoglycemia and somatostatin ↓ insulin secretion
    • β agonists ↑ release of insulin while α agonists ↓ insulin secretion
  • Function 
    • ↓ glucagon release by α cells of pancreas
    • ↑ Na+ retention (kidneys)
    • ↑ glycogen synthesis and storage
    • ↑ triglyceride synthesis and storage
      • recall babies of diabetic mothers are macrosomic
    • ↑ protein synthesis (muscles)
      • recall babies of diabetic mothers are macrosomic
    • ↑ cellular uptake of K+
      • recall used with glucose to treat hyperkalemia
    • ↑ glucose transport into skeletal muscle and adipose      
      • see Glucose transport topic
  • Pathology
    • a patient with an insulinoma will secrete abnormally high levels of insulin as well as C-peptide and will not produce anti-insulin antibodies
    • these patients will have severe hypoglycemia
Glucagon Overview
  • Production
    • secreted by the pancreas (alpha cells)
    • major stimulus for secretion is hypoglycemia
    • major inhibition of secretion in hyperglycemia
      • also inhibited by insulin and somatostatin
  • Function 
    • increase blood glucose
      • glycogenolysis
      • gluconeogenesis
      • inhibition of insulin release
    • increase blood levels of other energy forms
      • lipolysis
      • ketone body production
  • Pathology
    • a glucogonoma is a tumor that secretes excess glucagon leading to hyperglycemia as well as the characteristic rash of necrolytic migratory erythema 


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Qbank (2 Questions)

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(M1.EC.50) A researcher is tracing the fate of C-peptide, a product of preproinsulin cleavage. Which of the following is a true statement regarding the fate of C-peptide? Topic Review Topic

1. C-peptide is immediately degraded by the proteasome
2. C-peptide is packaged with insulin in secretory vesicles
3. C-peptide exits the cells via a protein channel
4. C-peptide is further cleaved into insulin
5. C-peptide activates an intracellular signaling cascade

PREFERRED RESPONSE ▶
TAG
(M1.EC.75) Pancreatic islets were isolated from a healthy, non-diabetic donor to perform an experiment to look at insulin secretion inhibition. Compounds would be added to separate wells containing the islets bathed in a high glucose solution for one hour. After one hour, the supernatant would be collected, and the insulin content would be measured with an enzyme-linked immunosorbent assay (ELISA). Which of the following compounds would result in the least insulin secretion when added to the islets? Topic Review Topic

1. Dobutamine
2. Isoproterenol
3. Tolbutamide
4. Clonidine
5. Glyburide

PREFERRED RESPONSE ▶
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Recent Videos

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This video gives an overview of insulin.
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This video gives an overview of glucagon.
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