Insulin secretion and signalling

Question 1

What do pancreatic:
-Acinar cells
-beta cells
-alpha cells
-delta cells
-PP-cells
secrete?

Answer 1

Acinar cells are the exocrine tissue of pancreas
-digestive proteins

Pancreatic islets (islets of langerhans) = endocrine

• Beta cells: insulin
• Alpha cells: glucagon
• Delta cells: somatostatin
• PP-cells: pancreatic polypeptide

Question 2

Describe the secretion of insulin in B-cells

Answer 2

1: glucose is uptaken by B cells via GLUT2 transporter
2: this increases ATP conc. inside cells via glucokinase/glycolysis/TCA cycle which closes potassium channels and potassium can’t be shunted out
=cell depolarises
3: ca2+ influx = insulin exocytosis

release of glucose is biphasic (1st phase to stop glucose levels going too high, 2nd phase is to maintain glucose levels)

Question 3

Which drug acts on the ATP gated potassium channels?

Answer 3

sulphonylureas

• channel has two units and both are needed for ion channel to be functional
• one unit = Kir6.1
• one unit = sulphonylurea receptor (SUR1)

Question 4

What receptor does insulin act on?

Answer 4

Insulin receptor - consists of alpha and beta subunit
-insulin binds to alpha subunit
-causes beta subunit to autophosphorylate
=stimulates cell

Question 5

What affect does insulin have on cells?

Answer 5

-Amino acid uptake to muscles
-DNA synthesis
-Protein synthesis
-Growth response
-Glucose uptake in muscle and adipose tissue
-lipogenesis in adipose tissue and liver
-glycogen synthesis in liver and muscle
-gene expression
-lipolysis and glucneogenesis in liver
=CELL GROWTH

Question 6

What happens if glucose isnt available to cells because of lack of insulin in type 1 diabetes?

Answer 6

-energy is derived from break down of fatty acids = ketone bodies accumalate

Question 7

What is the difference between:

• Type 1 diabetes
• Type 2 diabetes
• MODY

Answer 7

Type 1 diabetes:
loss of insulin secreting B cells

Type 2 diabetes:
defect in insulin secretion with insulin resistance

MODY:
defective glucose sensing in pancreas and/or loss of insulin secretion