The Endocrine Pancreas

Question 1

What is the function of the pancreas?

Answer 1

• Endocrine = 1% tissue, hormone prod, Islets of Langerhans

- Exocrine = 99% tissue, prod digestive enzymes

Question 2

What cell type prod insulin?

Answer 2

Beta-cells

Question 3

What cell type prod glucagon?

Answer 3

Alpha-cells by rough-ER due to low glucose

Question 4

Describe the actions of insulin

Answer 4

• Keeps plasma glucose levels in a very narrow range
• Removes plasma glucose, into tissue
• Hormone of feeding
• Anabolic compound
• Liver = increases glycogen synthesis, inhib AA breakdown
• Muscle = increase AA uptake

Question 5

What are the actions of glucagon?

Answer 5

• Acts on liver, to mobilise glycogen (glycogenlysis) to raise plasma glucose
• Stim gluconeogenisis, glycogenolytic
• Stim lipolysis, ketogenic
• Hormone of fasting
• Catabolic compound

Question 6

Why do we need to reg glucose?

Answer 6

Regulates osmolarity of plasma

Brain requires glucose, sensitive to fall

Question 7

What is insulin?

Answer 7

• Water soluble, short half-life, no carrier
• Anti-gluconeogentic, anti-lipolitic and anti-ketotonic
• Action favours storage
• Structure = alpha helix peptide, 2 disulfide bridges that ensure stability

Question 8

Outline the synthesis of insulin

Answer 8

• Preproinsulin made in ER, signal cleaved
• Proinsulin produced, goes to golgi, cleaved
• Insulin, C-peptide produced

Question 9

What is the function of C-peptide?

Answer 9

Prevents vascular damage

Question 10

Describe how the ultrastructure of the beta-cell relates to the synthesis and storage of insulin

Answer 10

• Channel = ATP sensitive K+ channel, when ATP not-bound = open it allows K to efflux out the cell = more -ve MP, hyperpolarise cell
• Inhib by ATP
• Glucose high = enters GLUT2 = glycolysis inside cell = ATP, when ATP high channel closes = MP less -ve = threshold reached = Ca2+ channels open = influx = insulin vesicles bind membrane = released

Question 11

What happens to the ATP sensitive K channels in insulin def?

Answer 11

Glucose high = enters GLUT2 = glycolysis = ATP = binds ATP sensitive K channels BUT the channel is NOT sensitive and remains open = K efflux = remains less -ve

Question 12

Briefly outline he stages of how insulin-uptake effects metabolism?

Answer 12

1) insulin binds insulin-receptor
2) GLUT4 takes up glucose
3) insulin stim: glycolysis, glycogenesis, FA synthesis

Question 13

What is the only un-opposing effect of insulin and glucagon?

Answer 13

High AA stim insulin AND glucagon