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PSIO303 > Block 3 Lecture 35 > Flashcards

Block 3 Lecture 35 Flashcards

1
Q

what is the pancreas drained by

A

the pancreatic duct

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2
Q

what do alpha cells produce

A

glucagon

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3
Q

what do beta cells produce

A

insuline

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4
Q

what do gamma cells produce

A

somatostatin

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5
Q

what do F cells produce

A

pancreatic polypeptide (PP)

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6
Q

what are the two factors delivery to the islet

A
  1. systemic circulation (blood glucose, insulin, glucagon, FFAs)
  2. paracrine delivery of pancreatic hormones
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7
Q

what does insulin do

A

decreases blood glucose

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8
Q

what does glucagon do

A

increases blood glucose

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9
Q

when is insulin released

A

when blood glucose is high

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10
Q

when is glucagon released

A

when blood glucose is low

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11
Q

what does insulin do to glucagon

A

inhibits it

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12
Q

what does glucagon do to insulin

A

enhances it

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13
Q

what does somatostatin do to insulin and glucagon

A

inhibits them

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14
Q

what prevents from glucagon from acting on beta cells

A

the blood flow from the islets of langerhans is from the center region rich in beta cells past alpha cells to the periphery of the islet

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15
Q

how do cells communicate directly

A

gap junctions

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16
Q

what is the role of the sympathetic nervous system

A

adrenergic stimulation of beta cells will inhibit insulin secretion

17
Q

what is the role of the parasympathetic nervous system

A

cholinergic stimulation via ACh of beta cells will stimulate insulin secretion

18
Q

what is the mechanism of secretion of insulin in response to a glucose stimulus

A
  1. glucose enters the beta cell via facilitated diffusion via GLUT1
  2. glucose transported in will be metabolized in the cytoplasm and mitochondria to produce
  3. the increase in ATP concentration will inhibit an ATP sensitive K+ channel, decreasing K+ movement out of the cell, making the membrane potential less negative, causing depolarization
  4. the depolarizing of the membrane of beta cell activates a Ca2+ channel allowing Ca2+ movement into the cell. the increased intracellular Ca2+ will enhance Ca2+ release from ER
  5. the increase of Ca2+ in the cytoplasm results in movement of vesicles containing insulin to the plasma membrane and release contents into extracellular space
19
Q

what is the pathway of sympathetic stimulation in a beta cell

A
  • norepinephrine is delivered from adrenergic neurons
  • NE stimulates Alpha2 receptors
  • alpha2 adrenergic receptors are GPCRs that interact with Gi which reduced adenylate cyclase, the catalysis of cAMP production and decreases PKA activity which diminishes the exocytosis of insulin containing vesicles and decreases insulin secretion
20
Q

when is sympathetic input to a B cell important

A

during exercise NOT after a meal

21
Q

what can sympathetic overactivity lead to

A

hypertension from increased inhibition of insulin secretion

22
Q

what same mechanism does somatostatin use

A

the sympathetic beta cell mechanism

23
Q

what is the pathway of parasympathetic input in a beta cell

A
  • delivers ACh to the beta cell and binds to the muscarinic cholinergic receptor which are GPCRs that interact with Gq
  • Gq stimulates Phospholipase C to cleave PIP2 into DAG and IP3
  • DAG stays in the plasma membrane and activates IP3
  • IP3 will be released from the cytosol and stimulates Ca2+ release from the ER
  • both of these effects enhances insulin release from the beta cell
24
Q

what is the mechanism for the stimulatory impact of glucagon on insulin

A

-binding of glucagon to its receptor causes that GPCR to interact with Gs which stimulate adenylate cyclase, an increase in cAMP, and increase in PKA and promotes insulin secretion

25
Q

what is GLP-1

A

a product of a proglucagon molecule in the intestine that up regulates glucose stimulated insulin secretion from beta cells

26
Q

what are the 3 major regulators of glucagon secretion

A
  1. glucose levels
  2. sympathetic nerve activity
  3. amino acids
27
Q

what is the glucose transporter isoform in alpha cells

A

GLUT-1

28
Q

what happens when blood glucose is low

A

the reduction in glucose transport into the alpha cell causes Na+ channels to open inducing membrane depolarization which causes Ca2+ channels to open and glucagon is secreted

29
Q

what happens when blood glucose is high

A

glucose entry via GLUT1 is increased, inhibiting Na+ entry into the cell and preventing membrane depolarization, which keeps the Ca2+ channels close and inhibits glucagon secretion

30
Q

what happens in neural regulation of glucagon secretion

A

norepinephrine released by postganglionic sympathetic neurons will bind to alpha1 adrenergic receptors leading to an increase in intracellular Ca2+ and increases the secretin of glucagon

31
Q

how do amino acids regulate glucagon secretion

A

they can act as secretagogues, stimulating the release of glucagon from alpha cells

PSIO303 (31 decks)

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