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30 Cards in this Set

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What hormone is secreted by the alpha cells of the islets of Langerhans?
glucagon
In what part of the islet are the alpha cells located?
outer rim
What hormone is secreted by the beta cells of the islets of Langerhans?
insulin
In what part of the islet are the beta cells located?
center
What hormone is secreted by the delta cells of the islets of Langerhans?
somatostatin (and gastin)
In what part of the islet are the delta cells located?
intermixed
What are 3 ways in which the cells communicate with each other?
1) gap jns (a-a, b-b, and a-b)
2) portal blood supply (venous blood from one cell type bathes other cell types)
3) via nervous innervation
What is the structure of proinsulin?
A chain and B chain connected by C peptide
What is the significance of the C peptide?
it's conc is used to monitor beta cell fn in diabetic pts receiving exogenous insulin (b/c it's secreted along w/insulin)
Describe the cellular mechanism of insulin secretion.
1. Gluc binds GLUT 2 on beta cell, moves into cell
2. Gluc is oxidized to ATP
3. ATP binds and closes K channel, cell depolarizes
4. Ca channels open, Ca rushes in
5. Stimulates insulin release
Which is a more powerful stimulant for insulin secretion: oral glucose or intravenous glucose? Why?
oral; it stimulates s/c of gastric inhibitory peptide (GIP), which has independent stimulatory effect on insulin
What class of drugs mimics the action of ATP in beta cells (closing K channels to depolarize the cell)?
sulfonylurea drugs (e.g. tolbutamide, glyburide)
For what condition are sulfonylurea drugs most commonly administered?
type II (non-insulin dependent) diabetes mellitus
What is the structure of the insulin receptor?
2 extracellular alpha subunits which connect 2 membrane spanning beta subunits with tyrosine kinase activity (autophosphorylation)
Under what conditions does insulin up-regulate and down-regulate its own receptor? How?
up-regulates during starvation, down-regulates during obesity (type II diabetes); it internalizes receptor after binding, and can inc or dec degradation/recycling
What are the mechanisms by which insulin decreases blood glucose concentration?
1. directs insertion of glucose transporters in cell membranes
2. promotes formation of glycogen in musc & liver, and inhibits glycogenolysis
3. inhibits gluconeogenesis
By what biochemical mechanism does insulin inhibit gluconeogenesis?
stimulates fructose 2,6-biphosphatase, which increases phosphofructokinase activity
What are the mechanisms by which insulin decreases blood fatty acid and ketoacid concentration?
stimulates fat deposition and inhibits lipolysis, which decreases amount of available acetyl CoA, which inhibits ketoacid formation
What are the mechanisms by which insulin decreases blood amino acid concentration?
stimulates AA uptake, increases protein synthesis, inhibits protein degradation
What are the menchanisms by which insulin decreases blood K concentration?
increases K uptake into cells by increasing activity of Na-K ATPase
What is the overall effect on insulin on blood levels of glucose, amino acids, fatty acids, ketoacids, and potassium?
decreased gluc, aa, fatty acids, ketoacids, and K
What are some factors that stimulate insulin secretion?
inc blood glucose, aa's, and fatty acid, glucagon, GIP, ACh, growth hormone, and cortisol (neg feedback?)
What are some factors that inhibit insulin secretion?
dec blood glucose, somatostatin, epinephrine, NE
What symptoms would a patient with type I (insulin-dependent) diabetes mellitus present with?
hyperglycemia, hyperkalemia, hypotension (gluc acts as osmotic diuretic), ketone breath, metabolic acidosis (from ketoacids), hyperventilation (respiratory compensation)
What factors stimulate glucagon secretion?
dec blood glucose, INCREASED AAs (esp arginine), CCK, NE, epin, ACh
What factors decrease glucagon secretion?
inc blood glucose, insulin, somatostatin, fatty acids, ketoacidds
What are the major actions of glucagon?
stimulates glycogenolysis and gluconeogenesis, inhibits glycogen formation, increases lipolysis and ketoacid formation
What is the 2nd messanger mechanism of action for glucagon?
cAMP
What is the effect of somatostatin?
inhibit secretion of both insulin and glucagon (modulatory effect)
What stimulates secretion of somatostatin?
ALL forms of nutrients, various GI hormones, glucagon, beta-adrenergic agonists (is inhibited by insulin)