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Question 1

What are the three main cell types of the islets of langerhans?

Answer 1

The beta cells (~60% of all the cells of the islets), lie mainly in the middle of each islet and secrete insulin and amylin (function unclear).

2. The alpha cells (~25% of the total), secrete glucagon.
3. The delta cells (~10% of the total), secrete somatostatin.

Question 2

Where is insulin preprohormone cleaved?

Answer 2

preprohormone is then cleaved in the endoplasmic reticulum to form a proinsulin

Question 3

Where is insulin prohormone cleaved?

Answer 3

Most of the proinsulin is further cleaved in the Golgi apparatus

Question 4

What enzyme degrades insulin in the liver and to a lesser extent kidneys, muscles, and other tissues?

Answer 4

insulinase

Question 5

What is the mechanisim of insulin secretion from B-cells?

Remember MOL (Catalyst university)

Answer 5

The basic cellular mechanisms for insulin secretion by the pancreatic beta cells in response to increased blood glucose concentration which is the primary controller of insulin secretion.

● The beta cells have a large number of glucose transporters (GLUT 2) that permit a rate of glucose influx that is proportional to the blood concentration in the physiological range.

● Once inside the cells, glucose is phosphorylated to glucose-6-phosphate by glucokinase. (rate limiting step)

● The glucose-6-phosphate is subsequently oxidized to form adenosine triphosphate (ATP), which inhibits the ATP-sensitive K+ channels of the cell.
● Closure of the K+ channels depolarizes the cell membrane, thereby opening voltage-gated calcium channels, which are sensitive to changes in membrane voltage.
● This produces an influx of Ca++ that stimulates fusion of the docked insulin-containing vesicles with the cell membrane and secretion of insulin into the extracellular fluid by exocytosis

https://youtu.be/5SsS_PCrDTo?si=fu1brrJSQlAxEU_e

Question 6

What are two examples of sulfonylurea drugs and how do they work?

Answer 6

Examples: glipizide or Glucotrol

Mechanisim: inhibit K+ channels in the beta cell which depolarizes the membrane eventually causing insulin secretion

Question 7

What is the pattern of insulin release in a patient that was fasting and then had a sudden rapid increase in blood glucose? (increased to a level 2-3X normal)

Answer 7

It is released in two stages.

Stage 1: Plasma insulin concentration increases almost 10X within 3-5 minutes after the acute elevation of the blood glucose (results from dumping of preformed insulin).

Stage 2 happens within 15-20 minutes and is gradual bc new insulin being formed.