3b. Pancreas (Glucagon)

Question 1

What is glucagon

Answer 1

peptide hormone produced by alpha cells of the pancreatic islet cells - it is a glucose-mobilising hormone that acts mainly on the liver

Question 2

what is the primary purpose of glucagon and how does it do this

Answer 2

to increase blood glucose levels by

1. increasing gluconeogenesis (from amino acids and glycerol)
2. increasing glycogenolysis
3. increasing ketogenesis (from fatty acids)

Question 3

what four hormones make up the glucose counter-regulatory control system

Answer 3

1. GLUCAGON
2. epinephrine
3. cortisol
4. growth hormone

Question 4

what kind of receptors does glucagon bind to

Answer 4

G-protein coupled receptors linked to the adenylate cyclase/cAMP system - activates phosphorylate specific liver enzymes that ultimately lead to increased blood glucose

Question 5

describe the rate of glucagon release

Answer 5

relatively constant although secretion increases dramatically when [GB] <5.6mM

(normal range 4.2-6.3mM)

Question 6

What is a potent stimulant for both glucagon and insulin release and why

Answer 6

amino acids - an adaptation to adjust for the composition of a meal very high in protein (typical for omnivores/carnivores)

Question 7

what would happen if amino acids weren’t a potent stimulus for glucagon secretion

Answer 7

HYPOGLYCAEMIA - amino acids stimulate insulin release which in the absence of glucagon stimulates glucose uptake leading to low [BG]

this is why it is important for amino acids to also stimulate glucagon - its glucose mobilising effects maintain [BG]

Question 8

5 stimuli that promote glucagon release

Answer 8

1. LOW [BG]
2. HIGH [AMINO ACIDS]
3. sympathetic innervation and epinephrine, beta2 effects
4. coritsol
5. stress eg exercise, infection

Question 9

4 stimuli that inhibit glucagon release

Answer 9

1. glucose
2. free fatty acids (FFAs) and ketones
3. insulin (fails in diabetes so glucagon levels rise despite high [BG]
4. somatostatin

Question 10

what does parasympathetic (vagus) innervation of islet cells cause

Answer 10

1. increased insulin

2. to a lesser extent increased glucagon - in association with the anticipatory phase of digestion

Question 11

what does sympathetic innervation of islet cells cause

Answer 11

promotes glucose mobilisation by

1. increasing glucagon
2. increasing epinephrine
3. inhibits insulin

*all appropriate for flight or fight response

Question 12

what is somatostatin (SS)

Answer 12

peptide hormone secreted by D-cells of the pancreas (and hypothalamus aka GHIH)

Question 13

what is the main pancreatic action of SS

Answer 13

to inhibit activity in the GI tract - appears to slow down absorption of nutrients to prevent exaggerated peaks in plasma concentrations

Question 14

what secretion does GHIH inhibit

Answer 14

Growth hormone from the anterior pituitary

Question 15

when is SS be used clinically

Answer 15

to help patients with life-threatening diarrhoea associated with gut or pancreatic tumours

Question 16

why do patients with SS-secreting tumours develop the symptoms of diabetes

Answer 16

SS strongly suppresses the release of both insulin and glucagon in a paracrine fashion

Question 17

How is the entry of glucose into skeletal muscle increased during exercise?

Answer 17

active muscles allow GLUT 4 transporters to migrate to the membrane without insulin being present - therefore exercise cases glucose uptake INDEPENDENT of insulin.

Exercise also produce a prolonged increase to the sensitivity of the muscle to insulin

Question 18

where does the body get energy from during starvation (i.e. when nutrients are scare)

Answer 18

energy stores - adipose tissue is broken down and fatty acids are released

Question 19

how are FFAs used by the body

Answer 19

are readily used by most tissues to produce energy - excess is converted by the liver to ketone bodies which provide an additional source for the muscle and BRAIN

Question 20

When does the brain use ketone bodies instead of just glucose for energy

Answer 20

during periods of starvation the brain adapts to be able o use ketone bodies for energy

Question 21

how does the synthesis of ketone bodies “spare protein”

Answer 21

if FFAs were not converted into ketone bodies, protein would be excessively broken down to provide gluconeogenic substrates

Question 22

why is it important that protein is spared

Answer 22

loss of protein is very weakening to the body and leaves you vulnerable to infection - that is why it is the last store to be depleted in starvation