Insulin Secretion and Action

Question 1

On which chromosome is insulin coded for? Where is it synthesised?

Answer 1

Chromosome II // Rough ER of pancreatic beta cells

Question 2

What type of hormone is insulin? It is actually synthesised as what?

Answer 2

Peptide hormone // Synthesised as a larger preprohormone- preproinsulin

Question 3

What is an important byproduct of the cleavage of preproinsulin to insulin? What is its function?

Answer 3

C-protein // No physiological function but is a good marker of insulin production

Question 4

Glucose enters the pancreatic beta cell via what transporter? In association with which enzyme?

Answer 4

GLUT2 // Glucokinase

Question 5

What is the function of glucokinase?

Answer 5

Glucose –> Glucose-6-phosphate

Question 6

Metabolism of glucose in the beta cell generates ATP. What does this cause within the cell?

Answer 6

Closure of K+ channels in the cell membrane

Question 7

What does closure of the K+ channels in the cell membrane of the beta cell cause?

Answer 7

Depolarisation, which results in opening of Ca++ channels and entrance of Ca++ into the cell

Question 8

The entrance of Ca++ into the pancreatic beta cell has what action?

Answer 8

Exocytosis of insulin from the granules

Question 9

After secretion, where does the insulin enter? Where is it carried to?

Answer 9

Portal circulation // Liver

Question 10

C peptide is mainly broken down by which organ?

Answer 10

Kidneys

Question 11

Blood glucose is closely regulated and rarely strays outwit what range?

Answer 11

3.5-8mmol/L

Question 12

What is the principle organ of glucose homeostasis?

Answer 12

Liver

Question 13

What are the roles of the liver in glucose homeostasis?

Answer 13

Absorbs and stores glucose as glycogen // Releases glucose into the circulation between meals to match glucose utilisation // Forms glucose via gluconeogenesis if really needed

Question 14

What is broken down to form glucose in gluconeogenesis?

Answer 14

Fat, muscle and protein

Question 15

What organ is the major consumer of glucose? Its function depends on what?

Answer 15

The brain // Relies on uninterrupted supply of glucose

Question 16

Glucose uptake by the brain has what relationship with insulin?

Answer 16

It is not insulin dependent

Question 17

Tissues such as muscle and fat have insulin responsive glucose transporters and absorb glucose in response to what?

Answer 17

Post-prandial peaks in glucose and insulin

Question 18

What happens to glucose taken up by muscles?

Answer 18

Stored as glycogen or metabolised to either lactate or CO2 and H2O

Question 19

Fat uses glucose as a substrate for what?

Answer 19

Triglyceride synthesis

Question 20

What products are released from lipolysis?

Answer 20

Fatty acids and glycerol

Question 21

What is the action of insulin in the fasting state?

Answer 21

Regulation of glucose release by the liver

Question 22

What is the action of insulin in the post-prandial state?

Answer 22

Promotes glucose uptake by fat and muscle

Question 23

What hormones counteract insulin?

Answer 23

Glucagon, adrenaline, cortisol, GH

Question 24

Are cell membranes permeable to glucose?

Answer 24

Not inherently

Question 25

What are used to carry glucose through the cell membrane and into cells?

Answer 25

GLUT transporter proteins

Question 26

Which transporter enables basal, non-insulin stimulated glucose uptake into many cells?

Answer 26

GLUT1

Question 27

What is the function of GLUT2?

Answer 27

Transports glucose into the pancreatic beta cell

Question 28

Which transporter enables non-insulin dependent mediated glucose uptake into brain neurones and the placenta?

Answer 28

GLUT3

Question 29

What is the function of GLUT4?

Answer 29

Transports glucose into muscle and adipose tissue cells following stimulation of the insulin receptor

Question 30

What subunits does the insulin receptor involve? Which includes the insulin binding site?

Answer 30

2 alpha and 2 beta // Alpha

Question 31

When insulin binds to the alpha subunit of its receptor, what happens?

Answer 31

There is a conformational change in the beta subunit, activation of tyrosine kinase and an intracellular cascade

Question 32

The intracellular cascade which occurs after insulin has bound to its receptor results in what?

Answer 32

Transport of the GLUT4 transporter to the cell surface and hence increased transport of glucose into the cell