The endocrine pancreas 2

Question 1

Control of [blood glucose] depends on the balance between _______ & ________

Answer 1

Insulin and glucagon

Insulin - acts to lower [BG] when in fed state

Glucagon - acts to increase [BG] when in fasted state

Question 2

What is glucagon?

Answer 2

Peptide hormone released by alpha cells in the pancreas

(exocytosed in the usual way)

It acts to raise blood sugar - it is a glucose mobilizing hormone

It mainly acts on the liver

Question 3

What is glucagons half-life and where is it degraded?

Answer 3

Plasma half-life 5-10mins

Degraded mainly by liver

Question 4

What are the main actions of glucagon?

Answer 4

Primarily opposes the action of insulin, forming part of the glucose counter-regulatory control system

When acting in the liver - glucagon stimulates:

1) increased glycogenolysis
2) increased gluconeogenesis - using amino acids and glycerol from lipolysis
3) Formation of ketones from fatty acids (lipolysis)

*net effect of this = raised [blood glucose]*

Question 5

Describe the basic pathway through which decreased blood glucose stimulates glucagon and the effects of this

Answer 5

1. Decreased [BG] stimulates A cells and inhibits B cells
2. Glucagon yeeted out
3. At liver, glucagon stimulates gluconeogenesis, glycogenolysis and (if prolonged hypoglycaemia) ketone production
4. Net effect of this is to increase blood glucose

(meanwhile - decreased insulin causes Lactate, pyruvate, amino acids & fatty acids release from muscle & adipose. some of these supply the glucose producing in the liver)

Question 6

What is the effect of amino acids on glucagon production?

Answer 6

Amino acids stimulate glucagon release

So both insulin and glucagon release are stimulated by amino acids

Question 7

Why do amino acids stimulate glucagon release?

Answer 7

If we didn’t, then we couldn’t eat high protein meals (meat) without getting hypoglycaemic

Meat provides little carbohydrate content so glucagon is required to stop [BG] levels getting dangerously low

Question 8

Why is it that some tissues can not access glucose in the fasted state

Answer 8

In the post-absorptive state, lower insulin levels mean a large mass of tissue, i.e. muscle and fat, cannot readily access glucose

This is so there is glucose sparing for obligatory glucose users

Question 9

What are the stimuli that promote the release of glucagon?

Answer 9

Low [blood glucose] < 5mM

High [amino acids] - to prevent hypo after high amino acid meal

Sympathetic innervation and epinephrine, b2 effect

Cortisol

Stress - such as infection or exercise

Question 10

What are the stimuli that inhibit the release of glucagon?

Answer 10

Glucose

Free fatty acids (FFA) and ketones

Insulin (fails in diabetes so glucagon levels rise despite high [BG])

Somatostatin