Insulin: counter regulatory hormones Flashcards
What stimulates the secretion of glucagon?
- low glucose concentration
- increased blood volume
- exercise
What inhibits the secretion of glucagon?
insulin and somatostatin
How does insulin inhibit glucagon signalling?
insulin activates phosphodiesterase –> cAMP –> 5’AMP –> glucagon dependent signalling switched off
What type of receptor is the glucagon receptor?
GPCR
Explain the effect of glucagon on glycogenolysis.
- low glucose –> no insulin secretion –> no glucose transport
- Glycogen + triglycerides are not synthesised
- Processes that release glucose/fatty acids are not inhibited
- glucagon increases glycogenolysis
- glycogen breakdown is stimulated via PKA and phosphorylase kinase a
Explain the effect of glucagon on gluconeogenesis.
- low glucose –> no insulin secretion
- gluconeogenesis is not inhibited
- lipolysis is not inhibited
- glucagon increases gluconeogenesis and inhibits glycolysis
- increased amino acid uptake
- inhibition of PFK-1 (mediated by cAMP/PKA)
- inhibition of pyruvate kinase (mediated by cAMP/PKA)
Explain the effect of glucagon on lipolysis.
triglycerides –> free fatty acids and glycerol
- hormone sensitive lipase is inhibited by insulin/activated by glucagon
- malonyl-CoA inhibits transport of FFAs into mitochondria via CPT-I –> inhibits beta-oxidation
* glucagon stimulates CPT-I
State the effect of insulin/glucagon on ketogenesis.
Insulin = inhibits Glucagon = activates
What are catecholamines and when are they released?
- Monoamines synthesised from phenylalanine and tyrosine
- released in response to stress/hypoglycaemia
What stimulates/inhibits epinephrine? What are the effects of epinephrine being released?
Inhibits: insulin
Stimulates: glycogenolysis (liver + muscle) and glucagon
- increases lipolysis in adipose tissue
- end result: increased blood sugars and fatty acid levels
What is secreted by cortex cells of the adrenal gland and what stimulates this?
- secretes glucocorticoids and other steroids
- stimulated by ACTH (pituitary)
What stimulates/inhibits cortisol? What are the effects of cortisol being released?
Inhibits: glucose uptake and utilisation
Stimulates: muscle proteolysis and adipose tissue lipolysis
- enhances gluconeogenesis
- end result: rapid mobilisation of amino acids and fatty acids from cellular stores
What can occur if cortisol is elevated for too long?
proteolysis and muscle wasting
What is the effect of growth hormone on adipose tissue?
- increased lipolysis
- reduced glucose uptake
- reduced lipogenesis
- reduced re-esterification of FFAs
What is the effect of growth hormone on skeletal muscle?
- reduced glucose uptake
- increased LPL activity
= increased beta-oxidation
What is the effect of growth hormone on liver?
- stimulates IGF-1 production
- increases VLDL secretion
- increased HPL activity
- reduced PPAR alpha expression
= increased production + uptake of IDL, LDL, HDL
What are the thyroid hormones T4 and T3 called?
T4 = thyroxine T3 = triiodothyronine
What are the roles of the thyroid hormones?
- increase number and activity of mitochondria = increase rate of ATP synthesis
- increase insulin secretion
- increase fat metabolism
- increase BMR
- enhances glycolysis and gluconeogenesis
- increased glucose uptake
Give examples of incretins.
glucagon-like peptide 1
gastric inhibitory peptide
What is the effect of GLP-1 on glucagon secretion and hepatic glucose production?
glucagon secretion: inhibited
hepatic glucose production: inhibited
*augments glucose-induced insulin secretion
What is hypoglycaemia?
plasma glucose level: <70 mg/dL (<3.9 mmol/L)
What causes hypoglycaemia?
- reactive hypoglycaemia (excessive insulin secretion in response to high carb meal –> hyperdiabetic condition)
- excessive exercise (increase glucose utilisation)
- insulinoma (tumour of pancreatic beta cell)
- alcohol excess (inhibition of gluconeogenesis)
- high insulin doses
What are the S+S of hypoglycaemia?
- Autonomic:
- trembling
- palpitation
- sweating
- anxiety
- hunger
- tingling - Neuroglycopaenic:
- difficulty concentrating/speaking
- confusion
- weakness
- drowsiness/tiredness
- vision changes
- dizziness - other neuro symptoms:
- disorientation
- convulsion/fitting/seizures
- loss of consciousness
- coma
What are the effects of hypoglycaemia?
- GH and cortisol secreted –> reduced glucose utilisation cells convert to FAT utilisation
- storage of glucose for the brain
- -> prolonged and repeated hypoglycaemia = permanent brain damage
