Physio - Hu - Insulin and Glucagon AND Regulation of Apetite - 2/17

Question 1

Insulin is produced by what cell type?

Answer 1

Beta cells, in the islets of Langherhans of the pancreas.

Question 2

When is glucagon released?

Answer 2

Because it is a catabolic hormone (insulin is anabolic), it is released during times of food deprivation., exercise, stress, and in response to increased levels of alanine and arginine

Question 3

What hormones allow the utilization of stored nutrient reserves by mobilizing glycogen?

Answer 3

Glucagon, epi, norepi

Question 4

What hormone inhibits the release of insulin and glucagon, as well as gastrin, gastric acid secretion and gut hormones?

Answer 4

Somatostatin, produced by delta cells which are dispersed at the periphery of the islets.
**Somatostatin is the primary inhibitor of insulin.

Question 5

Alpha cells produce what hormone?

Answer 5

Glucagon, produced by alpha cells at the periphery of the islets.

Question 6

What is pancreatic polypeptide?

Answer 6

A gastro-intestinal hormone produced by F cells, located in the periphery of the islets. Pancreatic polypeptide inhibits gallbladder contraction and pancreatic exocrine secretion. It’s active during strenuous exercise, after a high protein meal or during periods of hypoglycemia

Question 7

Glucagon is inhibited by what:

Answer 7

somatostatin
insulin
hyperglycemia (>200)

Question 8

Why do counter-regulatory hormones, such as growth hormone, glucagon, cortisol and catecholamines, get released in times of stress/exercise/food deprivation?

Answer 8

To maintain glucose to the brain

Question 9

The primary target of glucagon is the ____. What does it do there?

Answer 9

Liver, where glucagon antagonizes insulin, stimulated glycogenolysis, and gluconeogenesis, increases lipolysis

Question 10

In adipose tissue, what is the role of glucagon?

Answer 10

Decreases glycolysis, promotes lipolysis and release of fatty acids

Question 11

How is insulin produced and processed?

Answer 11

Insulin is produced in beta cells, as pro-insulin with endopeptidase. Endopeptidase has activity similar to trypsin. Proinsulin and endopeptidase are secreted together. Proinsulin is cleaved and becomes C peptide and insulin, C-peptide has no biological activity, but can be used as a marker for endogenous insulin production.

Question 12

When do levels of blood glucose and insulin spike after a meal?

Answer 12

30-45 minutes

Question 13

Why is insulin response to glucose a spike, followed by more modest maintenance of levels?

Answer 13

First, stored insulin is released, then the body needs to make more insulin

Question 14

What are the 7 steps in insulin secretion by beta cells?

Answer 14

1. Glucose enters cell via GLUT2 transporter (facilitated diffusion)
2. Glucose metabolism occurs, leading to increase in ATP
3. ATP inhibits the ATP-sensitive K-channel.
4. Inhibition of K channel causes depolarization.
5. Depolarization activates voltage-gated Ca channel (influx of Ca)
6. Increased Ca through channel induced Ca-induced Ca release from ER.
7. Elevated Ca causes release of packets of insulin via exocytosis.
   * *Other modulators than glucose act via adenylate cycclase-cAMP-pKA/pKC pathways

Question 15

Explain the two phases of insulin response after feeding.

Answer 15

Cephalic phase - gastric acid secretion and small rise in plasma insulin mediated by Mr. Vagus.

Intestinal phase - glucose absorption and rise in plasma glucose is primary stimulus for insulin secretion.

Question 16

What are incretins?

Answer 16

CCK, GIP (gastric inhibitory peptide), GLP-1 (glucagon-like peptide)
These provide advance notice of feeding and stimulate insulin secretion (oral glucose more effect than IV glucose)

Question 17

What are the anabolic actions of insulin on an adipocyte?

Answer 17

1. Glucose uptake via GLUT-4
2. Glucose participate in increased glycolysis
3. Glycolysis produces alpha-glycerophosphate
4. alpha-glycerophosphate increases esterification of fats

Other effects:
Lipolysis is decreased
Stimulates synthesis of lipoprotein lipase which moves to the surface of endothelial cells where it releases fatty acids from chylomicrons and VLDL.

Question 18

How do diabetic perform in glucose tolerance tests?

Answer 18

The glucose hangs around for a lot longer in the blood be there is impaired/less uptake. Dx of diabetes if glucose >200 after 2 hours

Question 19

Sympathetic stimulation would have what effect on insulin secretion?

Answer 19

Decrease

Question 20

Many hormones stimulate insulin secretion. Name 5.

Answer 20

GIP
glucagon
CCK
Secretin
Gastrin
VIP
Epinephrine

Question 21

Serum free fatty acids, ie ketoacids, and serum ketone bodies, would have what effect on insulin secretion?

Answer 21

Increase

Question 22

During exercise, circulating epinephrine stimulates insulin secretion via a __1___ on the pancreatic beta cell. But, local autonomic adrenergic innervation releasing norepinephrine acts via ___2___ and predominates

Answer 22

1. Beta receptor

2. Alpha receptor

Question 23

What are the anabolic actions of insulin on the liver?

Answer 23

1. Insulin stimulates glucose uptake, and decreases glucose output.
2. Insulin stimulates the formation of glycogen.
3. Insulin inhibits glycogenolysis
4. Insulin promotes glycolysis and lipogenesis
5. Insulin decreases fat oxidation, gluconeogenesis and ketogenesis.
6. Insulin promotes protein synthesis and inhibits protein breakdown and the urea cycle.

Question 24

What are the anabolic actions of insulin on muscle?

Answer 24

1. Insulin stimulates glucose uptake via GLUT-4
2. Insulin promotes glycogenesis and inhibits glycogenolysis.
3. Insulin promotes glycolysis, supplying acetyl-CoA for fatty acid synthesis and lipogenesis
4. Insulin stimulates amino acid uptake and protein synthesis and decreases proteolysis.

Question 25

Give two methods of developing insulinemia.

Answer 25

1. IV insulin or shots

2. Insulinoma

Question 26

What is the effect of a glucagonoma?

Answer 26

Hyperglycemia, elevated levels of glucagon in the blood.

Question 27

What is neuropeptide Y?

Answer 27

Neurotransmitter that stimulates feeding, aka orixigenic factor (hypothalamus)

Question 28

Corticotropin releasing hormone (CRH), GLP-1, alpha-melanocyte stimulating hormone (alpha-MSH) and cocaine and amphetamine-regulating transcript (CART) are all examples of:

Answer 28

Anorexigenic factors, neurotransmitters that inhibit feeding (hypothalamus and NTS in hindbrain)

Question 29

T/F: Both leptin and insulin can cross the BBB.

Answer 29

True, they can cross the BBB and travel to the hypothalamus to influence energy homeostasis.

Question 30

Hoe does ghrelin work?

Answer 30

Ghrelin works to stimulate apetite by acting directly on the arcuate nucleus (ARC) of the hypothalamus to enhance NPY/AgRP pathways and inhibit POM/CART pathways.

Question 31

How do leptin and insulin work in the brain?

Answer 31

1. Leptin and insulin stimulate propiomelanocortin (POMC) neuronsto produce alpha-melanocyte stimulating hormone (alpha MSH) as a NT. Alpha-MSH binds on receptors in the brain and elsewhere to reduce food intake.
2. Leptin and insulin inhibit agouti-related peptide (AgRP) and NPY-containing neurons in the ARC. They also antagonize alpha-MSH.

Question 32

T/F: NPY and AgRP stimulate food intake.

Answer 32

True

Question 33

Satiation signals activate vagus nerve and pass the information to the NTS, which in turn __1__ POMC/CART neurons in the ARC. __2__ of POMC neurons inhibits LHA neurons but __3__ TRH/CRH neurons in the paraventrivcular nucleus.

Answer 33

1. stimulate
2. Activation
3. stimulate

Question 34

What signaling inhibits/decreases NPY/AgRP release?

Answer 34

Leptin, insulin