Endocrine Pancreas

Question 1

The endocrine pancreas

Answer 1

INSULIN 
- beta cells 
- regulation of metabolism 
GLUCAGON 
- alpha cells 
- regulation of metabolism 
SOMATOSTATIN 
- delta cells 
- islet cell secretion regulation 
PANCREATIC POLYPEPTIDE 
- F cells 
- GI function 
GHRELIN 
- appetite stimulant

Question 2

Insulin

2 unbranched pp commented by 2 disulphide bridges

Answer 2

Feeding hormone
Targets liver, adipose and skeletal muscle
Affects the metabolism of carbohydrates, lipids and proteins
Is anabolic - STORAGE
High energy signal
Anti-ketotic
Single chain precursor is called preproinsulin
C peptide is cleaved in Golgi and released via vesicles by exocytosis into the blood stream with the insulin when needed
- promotes glycogen synthesis, uptake of AA promoting protein synthesis, increases the storage of TAG in adipose, inhibits breakdown of AA in liver, and inhibits the breakdown of fatty acids
Abnormally High - hypoglycaemia
Abnormally low - hyperglycaemia (diabetes mellitus)

Question 3

Glucagon

Answer 3

Fasting hormone
Targets adipose tissue and liver
Affects the metabolism of carbohydrates and lipids
Is catabolic - BREAKDOWN
Is ketotic
Margination - movement of storage vesicles to cell surface so they are ready to be released during hypoglycaemia
Flexible structure - no disulphide bridges
- stimulates the synthesis of glucose from AA
- stimulates lipolysis to increase plasma FA
- increases the rate of glycogen breakdown (glycogenlysis)
Abnormally high - makes diabetes worse
Abnormally low - may contribute to hypoglycaemia

Question 4

Insulin and glucagon

Answer 4

• water soluble - carried dissolved in the plasma
• short half lives (5mins)
• interacts with cell surface receptors on target cells
• receptor with hormone can be internalised - inactivation
  Increase AA in in blood stimulates both as there needs to be a balance

Question 5

Insulin receptors

Answer 5

• insulin binds to receptor of cell surface
• receptor is a dimer - two identical subunits spanning the cell membrane - each subunit is one alpha and one beta chain connected by a single disulphide bond
• alpha chain is on the exterior of the cell membrane
• beta chain spans the cell membrane in a single segment
  Activation
• alpha chains move together and fold around insulin - causing beta chains to move together - beta chains an active tyrosine kinase
• initiates a phosphorylation cascade results in an increase of GLUT4 expression - glucose carrier - cells can take up more glucose

Question 6

The Pancreas

Answer 6

• large gland
• develops embryologically as an outgrowth of the foregut
  EXOCRINE ACTION
• produces digestive enzymes - secretes directly into the duodenum
• 99% exocrine tissue
  ENDOCRINE ACTION
• hormone production from the islets on Langerhans
• 1% endocrine tissue