Regulation of blood glucose

Question 1

Where are the islets of Langerhans located?

Answer 1

Inside the pancreas.

Question 2

What are the cells inside the Islets?

Answer 2

Alpha cells (glucagon)
Beta cells (insulin and amylin)
D cells (somatostatin)
F cells (pancreatic and polypeptide)

Question 3

What two hormones work together to keep nutrient supply constant?

Answer 3

Insulin and Glucagon - pancreatic endocrine hormones.

Question 4

What is hypoglycemia and what are the consequences?

Answer 4

decrease in blood glucose. CNS cant use fatty acids for energy and so get disorientation, hunger, even coma and death.

Question 5

What is hypoglycemia? What are the consequences?

Answer 5

Increased blood glucose. Increased urine flow (water is pulled out of lumen of kidney and glucose can end up in the urine - takes water with it.

Question 6

What is the role of insulin?

Answer 6

Helps cells take nutrients in so that the glucose can be used or stored in liver mostly, fat and muscle. Inhibits endogenous nutrient stores from being used - signals the liver, muscle and fat to take in glucose from the blood.

Question 7

What happens when the body is fasting to maintain blood sugar levels?

Answer 7

Glucagon is increased with cortisol, growth hormone. Leads to increased release of endogenous nutrient store - go into bloodstream and make it available for other cells.

Question 8

Fasting means ______ increased and ______decreased.

Answer 8

Glucagon. Insulin.

Question 9

_______ stimulates breakdown of adipose tissue into fatty acids and glycerol. Which one of these can enter the citric acid cycle via acetyl co-A? Why?

Answer 9

Glucagon. Fatty acids. It can be used by some cells as the primary source of energy.

Question 10

How is glycerol used in the liver during fasting?

Answer 10

Uses pyruvate to create glucose 6 phosphate which leaves with glucose after phosphate is removed - more glucose to blood.

Question 11

When would adipose tissue be broken down?

Answer 11

In fasting to get glycerol and fatty acids.

Question 12

What are alternative sources of fuel to glycogen in the liver?

Answer 12

Glycerol released from lipolysis converted to glucose by gluconeogenesis in the liver. Ketone bodies formed from fat oxidation can be used an an alternative fuel by many tissues.

Question 13

What stimulates insulin secretion?

Answer 13

Blood glucose concentration increases - acts on beta cells - stimulates direct pathway to increase insulin secretion. Also with increased amino acids. Also when the stomach stretches (via parasympathetic nerve).

Question 14

What are the incretins? How is their action inactivated?

Answer 14

Glucagon-like peptide 1 and Gastric inhibitory peptide.

Dipeptidyl peptidase - 4 breaks both of these down when they are finished.

Question 15

What is the role of the incretins?

Answer 15

Increase satiety, inhibit glucagon release and stimulate insulin release.

Question 16

What can inhibit the islet beta cells from secreting insulin?

Answer 16

Sympathetic stimulation (adrenalin) and also somatostatin and some drugs.

Question 17

What is glucose stimulated insulin secretion?

Answer 17

A glut transporter allows glucose to move into the cell. Undergoes citric acid cycle so ATP can be formed. ATP increase K channels close. Depolarises membrane in small areas. Calcium channels open which stimulate vesicles of the insulin hormone to bind to the membrane - exocytosis of insulin to blood.

Question 18

What is the mechanism of insulins effect on glucose uptake?

Answer 18

1. Insulin binds to it’s receptor. Causes autophosphorylation of insulin phosphorylation substrates - like dominoes
2. Glut-4 vesicle moves into membrane
3. Glucose can come through to use for metabolism or stored as glycogen for later

Question 19

How does insulin effect fats?

Answer 19

Increases uptake of fat as triglycerides and decreases fat breakdown.

Question 20

How does insulin effect proteins?

Answer 20

Uptake of amino acids, more protein synthesis and less protein breakdown.

Question 21

What are “ special sites” in the liver and kidney?

Answer 21

In liver acts to stop breakdown of glycogen. In kidney insulin has no effect on glucose transport so kidney resorbs the glucose. Can only do a certain amount - this is how you get glucose in the blood - if there is too much.

Question 22

How does glucose act as an osmotic diuretic?

Answer 22

Glucose high in urine pulls water with it. Polyuria.

Question 23

Where is glucose transport independent of insulin?

Answer 23

Brain, intestine and muscle.

Question 24

Where is glucagon released from? When will this happen?

Answer 24

Alpha cells. Increased glucose, decreased fatty acids and increased amino acids.

Question 25

What is the role of glucagon?

Answer 25

Increases release of stored nutrients, glycogen breakdown and gluconeogenesis. Increases uptake of amino acids in liver and increases lipolysis and ketogenesis.