3b. Pancreas (Glucagon) Flashcards Preview

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Flashcards in 3b. Pancreas (Glucagon) Deck (22)
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1
Q

What is glucagon

A

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

2
Q

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

A

to increase blood glucose levels by

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

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

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

what kind of receptors does glucagon bind to

A

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

5
Q

describe the rate of glucagon release

A

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

(normal range 4.2-6.3mM)

6
Q

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

A

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

7
Q

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

A

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]

8
Q

5 stimuli that promote glucagon release

A
  1. LOW [BG]
  2. HIGH [AMINO ACIDS]
  3. sympathetic innervation and epinephrine, beta2 effects
  4. coritsol
  5. stress eg exercise, infection
9
Q

4 stimuli that inhibit glucagon release

A
  1. glucose
  2. free fatty acids (FFAs) and ketones
  3. insulin (fails in diabetes so glucagon levels rise despite high [BG]
  4. somatostatin
10
Q

what does parasympathetic (vagus) innervation of islet cells cause

A
  1. increased insulin

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

11
Q

what does sympathetic innervation of islet cells cause

A

promotes glucose mobilisation by

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

*all appropriate for flight or fight response

12
Q

what is somatostatin (SS)

A

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

13
Q

what is the main pancreatic action of SS

A

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

14
Q

what secretion does GHIH inhibit

A

Growth hormone from the anterior pituitary

15
Q

when is SS be used clinically

A

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

16
Q

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

A

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

17
Q

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

A

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

18
Q

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

A

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

19
Q

how are FFAs used by the body

A

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

20
Q

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

A

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

21
Q

how does the synthesis of ketone bodies “spare protein”

A

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

22
Q

why is it important that protein is spared

A

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