Endocrine Pancreas/Insulin

Question 1

What is the function of the exocrine pancreas?

Answer 1

The function of the exocrine pancreas is to produce and release digestive enzyme.

Question 2

What does the endocrine part of the pancreas do? and what are these known as?

Answer 2

They contain cells that synthesise and secrete hormones and these cells are known as the islets of langerhans.

Question 3

Islets are composed of 4 main cell types. What are they and what effect do the cells produce?

Answer 3

alpha cells, beta cells, delta cells and PP cells.
Alpha cells secrete glucagon.
Beta cells secrete insulin and amylin
Delta cells secrete somostatin inhibiting actions of alpha and beta.
PP cells secrete polypeptide.

Question 4

What tissue is the pancreas composed of?

Answer 4

The pancreas is composed of both endocrine and exocrine tissue.

Question 5

What is the most important factor in stimulating insulin secretion?

Answer 5

Blood glucose levels are the most important factor in stimulating secretion but it can also be stimulated by incretins. (Amino Acids, GI hormones, Fatty acids)

Question 6

What other effect do incretins have?

Answer 6

They also inhibit glucagon secretion from alpha cells and decrease gastric emptying.

Question 7

How do parasympathetic nerves stimulate insulin secretion?

Answer 7

They act on muscarinc receptors to stimulate secretion.

Question 8

What effect does the sympathetic nervous system have on insulin secretion?

Answer 8

They act on alpha2 receptors to inhibit secretion.

Question 9

From what cells is insulin secreted?

Answer 9

Insulin is secretes from pancreatic beta cells.

Question 10

What occurs after an increase in blood glucose?

Answer 10

After an increase in blood glucose occurs glucose enter pancreatic beta cells via GLUT2.

Question 11

What occurs when glucose interacts with glucokinase?

Answer 11

When glucose interacts with glucokinase it becomes phosphorylated producing G6P.

Question 12

What happens with G6P after it is produced?

Answer 12

GP6 is metabolised causing an increase in ATP and decrease in ADP.

Question 13

With the fluctuating levels of ATP and ADP what happens to the cell?

And what does this influence the activation of?

Answer 13

With the increased ATP level the cell becomes slightly positive due to potassium ion accumulation leading to depolarisation causing the activation of voltage-gated calcium ion channels.

Question 14

With the activation of Calcium ion channels what moves into the pancreatic cells and what does this influence?

Answer 14

With the activation of calcium ion channels calcium ions move into the cell this stimulates the secretion of insulin from granules.

Question 15

How would anti-diabetic medication impact the insulin secretion cycle?

Answer 15

Sulphonylurea medication binds to ATP/K+ inhibiting channel conductance causing depolarisation, causing calcium ions influx and secretion of insulin.

Question 16

How does the secretion of insulin affect glucose?

Answer 16

When insulin is secreted it promotes the uptake and storage of glucose into insulin responsive tissue reducing blood glucose level.

Question 17

What other effects does insulin have on glucose besides promoting its uptake and storage?

Answer 17

Insulin also promotes the production of glycogen and inhibits the output of glucose.

Question 18

What is the overall consequence of insulin secretion?

Answer 18

The overall consequence is the rapid movement of nutrients to meet energy and metabolic body demands.

Question 19

When does hyperglycaemia occur?

Answer 19

Hyperglycaemia occurs when insulin levels or insulin responsiveness tissues are inadequate.

Question 20

What immediate effects are caused by the activation of insulin receptors?

Answer 20

The immediate effects are metabolic effect by increasing glucose uptake and them promotion of glycogen production and inhibition of its breakdown.

Question 21

What long term effects are produced from insulin activated receptors?

Answer 21

Long term effect promote gene expression and the synthesis of key enzymes involved in glucose regulation, and cell growth and division.

Question 22

What receptor does insulin bind to on its target cells and what is promoted as a result?

Answer 22

Insulin binds to alpha subunits which promotes the auto phosphorylation of tyrosine residues.

Question 23

What action does the phosphorylated Tyr express?

Answer 23

The phosphorylated tyrosine acts as a docking site for many signalling proteins.

Question 24

What happens with the activated Tyr residues?

Answer 24

The activated Tyr residues cluster into vesicles and downregulation of the receptor.

Question 25

What does PIP3 recruit and what does this recruitment mediate?

Answer 25

PIP3 recruits protein kinase B which then mediates 2 important signalling responses.

Question 26

What is the first signalling response mediated by recruitment of protein kinase B?

Answer 26

The first signalling response promotes the movement of GLUT-4 storage vesicles increasing its expression at cell surfaces, which increases glucose uptake.

Question 27

What is the second signalling response mediated by recruitment of protein kinase B?

Answer 27

The second signalling response involves PKB phosphorylation deactivating GSK-3, activating glycogen synthesis.