Block 3 Lecture 35

Question 1

what is the pancreas drained by

Answer 1

the pancreatic duct

Question 2

what do alpha cells produce

Answer 2

glucagon

Question 3

what do beta cells produce

Answer 3

insuline

Question 4

what do gamma cells produce

Answer 4

somatostatin

Question 5

what do F cells produce

Answer 5

pancreatic polypeptide (PP)

Question 6

what are the two factors delivery to the islet

Answer 6

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

Question 7

what does insulin do

Answer 7

decreases blood glucose

Question 8

what does glucagon do

Answer 8

increases blood glucose

Question 9

when is insulin released

Answer 9

when blood glucose is high

Question 10

when is glucagon released

Answer 10

when blood glucose is low

Question 11

what does insulin do to glucagon

Answer 11

inhibits it

Question 12

what does glucagon do to insulin

Answer 12

enhances it

Question 13

what does somatostatin do to insulin and glucagon

Answer 13

inhibits them

Question 14

what prevents from glucagon from acting on beta cells

Answer 14

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

Question 15

how do cells communicate directly

Answer 15

gap junctions

Question 16

what is the role of the sympathetic nervous system

Answer 16

adrenergic stimulation of beta cells will inhibit insulin secretion

Question 17

what is the role of the parasympathetic nervous system

Answer 17

cholinergic stimulation via ACh of beta cells will stimulate insulin secretion

Question 18

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

Answer 18

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

Question 19

what is the pathway of sympathetic stimulation in a beta cell

Answer 19

• 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

Question 20

when is sympathetic input to a B cell important

Answer 20

during exercise NOT after a meal

Question 21

what can sympathetic overactivity lead to

Answer 21

hypertension from increased inhibition of insulin secretion

Question 22

what same mechanism does somatostatin use

Answer 22

the sympathetic beta cell mechanism

Question 23

what is the pathway of parasympathetic input in a beta cell

Answer 23

• 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

Question 24

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

Answer 24

-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

Question 25

what is GLP-1

Answer 25

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

Question 26

what are the 3 major regulators of glucagon secretion

Answer 26

1. glucose levels 2. sympathetic nerve activity 3. amino acids

Question 27

what is the glucose transporter isoform in alpha cells

Answer 27

GLUT-1

Question 28

what happens when blood glucose is low

Answer 28

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

Question 29

what happens when blood glucose is high

Answer 29

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

Question 30

what happens in neural regulation of glucagon secretion

Answer 30

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

Question 31

how do amino acids regulate glucagon secretion

Answer 31

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