The Endocrine Pancreas 2 (Insulin and Glucagon)

Question 1

What factors can increase insulin secretion?

Answer 1

Increased blood glucose concentration
Presence of food within the gut 
Presence of certain hormones 
Vagal nerve activity
Glucagon

Question 2

What is insulin’s function?

Answer 2

To lower blood glucose

Question 3

Where is insulin secreted from?

Answer 3

The pancreas

Question 4

What is a Katp channel?

Answer 4

Specific potassium ion channel found on B-cells which is sensitive to the concentration of ATP within the cell

Question 5

Through what channel does insulin enter on a B-cell?

Answer 5

GLUT transporter

Question 6

What does an increase in glucose uptake of a B-cell cause?

Answer 6

Increases metabolism and thus increases the concentration of ATP via glycolysis and the critic acid cycle.

Question 7

An increase in B-cell [ATP] within cells causes what?

Answer 7

The closure of the Katp channel

Question 8

Closure of the Katp channel on B-cells leads to what?

Answer 8

Increase in intracellular potassium concentration leading to the depolarisation of the cell and thus voltage gated calcium channels open, triggering the release of insulin form the vesicles via exocytosis.

Question 9

What second messenger does insulin then initiate on cell membranes?

Answer 9

Tyrosine kinase

Question 10

What does insulin do to proteins?

Answer 10

Phosphorylates them

Question 11

Where can you find GLUT-4 transporters?

Answer 11

In the cytoplasm of unstimulated muscle and adipose tissues

Question 12

What is the function of GLUT-4 when stimulated?

Answer 12

Migrates to the cell membrane via exocytosis, to allow the uptake of glucose in muscle and fat cells.

Question 13

Is the activation of GLUT-4 insulin dependant?

Answer 13

Yes, need insulin to bind to initiate the signal transduction cascade

Question 14

Do most tissues require insulin to take up glucose?

Answer 14

No only fat and muscle, however this does make up around 60% of body weight

Question 15

What is GLUT-1’s function? (and GLUT-3’s)

Answer 15

Required for basal glucose uptake by many cells such as brain, kidneys and RBC’s

Question 16

Which transporter is required by beta-cells of the pancreas and liver to take up glucose?

Answer 16

GLUT-2

Question 17

Are GLUT-2 transporters insulin dependant or independant? What is the consequence of this?

Answer 17

Insulin indépendant, therefore glucose enters down the concentration gradient

Question 18

When insulin binds to its receptor on a liver cell what is the outcome of the signal cascade?

Answer 18

Hexokinase is activated which lowers the intracellular glucose concentration by converting it to GGP. This maintain the glucose concentration gradient

Question 19

Describe the 5 anabolic or inhibiting catabolic process of of insulin

Answer 19

1. Increases glycogen synthesis
2. Increases amino acid uptake
3. Increases protein synthesis
4. Increases lipogenesis and inhibits lipolysis
5. Inhibits the enzymes of gluconeogenesis

Question 20

Give 2 non-anabolic effects of insulin

Answer 20

Permissive effect on growth hormone

Promotes potassium ion entry into cells by stimulating Na+/K+ ATPase

Question 21

How does insulin bring about changes in cell metabolism?

Answer 21

Binds to receptor
Phosphorylates insulin-receptor substrates
Initiates second messier pathways, altering protein synthesis and existing proteins such as GLUT 4 to alter tenspot activity
Also up or down regulates enzymes which leads to a change in the metabolism of the cell

Question 22

What is the half life of insulin?

Answer 22

5 minutes

Question 23

Where is insulin degraded?

Answer 23

Liver and kidneys

Question 24

What 2 enzymes are responsible for insulin degradation?

Answer 24

Insulin protease - breakdowns the remnants of insulin after it has been used in metabolic processes
Insulinase - breakdown free insulin in the plasma

Question 25

What stimuli inhibit the secretion of insulin?

Answer 25

Low blood glucose
Somatostatin
Sympathetic alpha effects
Stress eg hypoxia

Question 26

Vagal nerve stimulation of insulin has what consequence for type 1 diabetics?

Answer 26

You will not see as great an increase in IV glucose from injected glucose compared to the same dose taken orally.

Question 27

What is glucagon and what produces it?

Answer 27

Linear peptide hormone produced by alpha-cells of the pancreatic islets

Question 28

What is the primary action of glucagon?

Answer 28

To raise blood glucose

Question 29

What is glucagon’s half life?

Answer 29

5-10 minutes

Question 30

What type of receptor are glucagon receptors?

Answer 30

G-protein coupled linked to adenylate cyclase cAMP system

Question 31

What happens when glucagon receptors are activated?

Answer 31

Phosphorylate liver enzymes causing:
1. Increased glyconeolysis
2. Increased gluconeogenesis
Formation of ketones from fatty acids - lipolysis

Question 32

What are stimuli for the release of glucagon?

Answer 32

Low blood glucose
Amino acid presence in a high protein meal to stabilise [BG] and prevent hypoglycaemia 
Sympathetic innervation and epinephrine
Cortisol 
Stress - exercise and infection

Question 33

What stimuli inhibit release of glucagon?

Answer 33

Free fatty acids
Insulin
Somatostatin

Question 34

What is somatostatin and what is its activity?

Answer 34

Peptide hormone secreted by B-cells of the pancreas

Inhibit the activity of the GI tract

Question 35

What effect does somatostatin have on insulin and glucose?

Answer 35

Surprises their release

Question 36

What is somatostatin otherwise known as?

Answer 36

GHIH

Question 37

What is the effect of exercise on [BG]?

Answer 37

Glucose entry is increased even in the absence of insulin , increases the number of GLUT4 transporters to maintain blood glucose