6. Endocrine Cells of the Pancreas

Question 1

How do α-cells and β-cells communicate in the islets of Langerhans?

Answer 1

Gap junctions and paracrine actions.

Question 2

What changes in the incretin effect in type II diabetic patients?

Answer 2

The incretin effect loses the ability to increase insulin secretion.

Question 3

What is the effect of glucosuria on blood electrolyte levels?

Answer 3

The osmotic diuresis of type I diabetes blunts the reabsorption of electrolytes and therefore decreases their serum levels.

Question 4

What causes insulin independent mobilization of GLUT4?

Answer 4

Muscle contraction stimulates AMPK, which causes GLUT4 translocation to the plasma membrane.

Question 5

What are the stimulatory factors of insulin? (9 things)

Answer 5

↑ Glucose / amino acid concentration.
↑ Fatty acid / ketoacid concentration.
Glucagon (facilitates).
Cortisol.
GIP.
K+.
Acetylcholine (parasympathetic).
Sulfonylurea drugs.
Obesity (leptin).

Question 6

Which phase of insulin secretion is lost first in diabetic individuals?

Answer 6

The initial spike – “first phase insulin secretion.”

Question 7

What is secreted by the F cells of the islets of Langerhans?

Answer 7

Pancreatic polypeptide. (Satiety signal.)

Question 8

How does glucose stimulate insulin secretion?

Answer 8

Glucose enters via GLUT2 -> is converted to glucose 6-phosphate -> is oxidized into ATP -> ↑ ATP closes ATP -dependent K+ channels -> membrane depolarizes -> voltage gated calcium channels open -> calcium scratch that Ca2+ causes the release via exocytosis of insulin.

Question 9

Through which cell population in the islets of Langerhans does blood travel first?

Answer 9

The β-cells of the islets of Langerhans.

Question 10

Both insulin increase or decrease blood ketoacid levels?

Answer 10

Decreases blood ketoacid levels.

Question 11

Why might blood glucose be normal when some of the patient’s β-cells have been destroyed by autoantibodies?

Answer 11

Because the remaining β-cells will become overactive to compensate.

Question 12

What are the two incretin hormones discussed in class?

Answer 12

GLP-1

GIP

Question 13

What is the effect of insulin on the hexose monophosphate shunt?

Answer 13

Favors metabolism towards the hexose monophosphate shunt.

Question 14

What is a diagnostic relevance of C-peptide in the blood?

Answer 14

C-peptide is released along with insulin in equimolar amounts.

It is a way to determine beta cell function independent of blood insulin levels – which may be masked by the patient taking therapeutic insulin.

Question 15

Do we see diabetic ketoacidosis more frequently in insulin-dependent or non-insulin-dependent diabetes?

Answer 15

Insulin-dependent (type I) diabetics are more likely to develop diabetic ketoacidosis.

Question 16

What are the inhibitory factors of insulin?

Answer 16

Decreased blood glucose.
Fasting.
Exercise.
Somatostatin.
α-adrenergic agonists.
Norepinephrine.
Diazoxide.

Question 17

What is the effect of intracellular and extracellular potassium in type I diabetes?

What causes this symptom?

Answer 17

Intracellular levels of potassium will be low, and extracellular levels of potassium will be high.

Insulin stimulates the Na/K ATPase, so its absence diminishes the ability of the Na/K ATPase to push potassium into the cells.

Question 18

What causes polyuria in type I diabetes?

Answer 18

Once blood glucose rises above about 180, it begins to appear in the urine. This results in an osmotic diuresis by pulling water into the renal tubules.

Question 19

What is the effect of the phosphorylation of PI3K/AKT/mTOR and MAPK’s as discussed in this lecture?

Answer 19

They are responsible for cell growth, differentiation, and insertion of GLUT4 transporters on the cell membrane. GLUT4 is responsible for insulin mediated glucose uptake.

Question 20

What important step in glycolysis regulation is inhibited by glucagon?

Answer 20

Creation of Fructose 2,6-bisphosphate. (PFK2)

(Fructose 2,6-bisphosphate activates phosphofructokinase, and promotes glycolysis.

Question 21

What is secreted by the β-cells?

Answer 21

Insulin.

C-peptide.

Question 22

What four things, discussed in class, inhibit glucagon?

Answer 22

Insulin.

Somatostatin.

Fatty acids.

Ketoacids.

Question 23

Why do type I diabetics appear emaciated – specifically with atrophy of muscle tissue?

Answer 23

Insulin is necessary for the anabolic reactions which build muscle.

Question 24

What is the function of sulfonylurea drugs?

Answer 24

Sulfonylurea drugs close the ATP -dependent K+ channel in the same way that ATP would from glucose. This helps the beta cells of the pancreas produce more insulin.

Question 25

What is the overall effect of incretin hormones?

Answer 25

Stimulate insulin secretion.

Inhibit glucagon secretion.

Delay gastric emptying.

Question 26

What would we expect to see in blood insulin levels in a type II prediabetic vs. a normal individual?

Answer 26

Because of the developing insulin resistance, a type II prediabetic will produce much more insulin than a normal person to respond to the same amount of glucose.

Question 27

How do δ-cells communicate with α and β-cells?

Answer 27

Through “dendrite -like” processes.

Question 28

What is the effect of insulin on glycolysis and carbohydrate oxidation in the liver?

Answer 28

Increases carbohydrate oxidation and glycolysis.