Appetite regulation Flashcards
What is the main centre for appetite regulation called and where is it?
Arcuate nucleus which is located in the hypothalamus
What are orexigenic signals? Give examples.
- appetite stimulants
- melanocrotin receptor antagonists
Examples:
- agouti related peptide
- NPY neurone
What are anorexigenic signals? Give examples.
- melanocortin receptor agonists
- appetite inhibiting
Examples:
- proopiomelanocortin (POMC)
- cocaine and amphetamine regulated transcript (CART)
How is satiety stimulated by chemoreceptors in the GIT?
- nutrients activate receptors on enteroendocrine cells
- these cells release signalling molecules
- this stimulates vagal afferents which mediate the response to the brain
- stimulate anorexigenic signals and inhibits orexigenic signals
How is satiety stimulated by mechanoreceptors?
- distension of the GIT stretches the mechanoreceptors
- sends signals along the vagus nerve and stimulates anorexigenic signals and inhibits orexigenic signals
Give examples of hormones/peptides that are anorexigenics?
- leptin
- CCK
- PYY3-36
- insulin
- GLP-1
- oxyntomodulin
- POMC
- CART
- melanocyte-simulating hormones
- serotonin
Give examples of hormones/peptides that are orexigenics?
- ghrelin
- orexin
- neuropeptide Y
- AgRP
- melanin-concentrating hormone
- galanin
Leptin:
- what is its pattern of secretion?
- what is its effect on hunger and satiety centres?
- when can leptin be used as a treatment?
- what is its pattern of secretion? Diurnal (active during day/inactive at night)
- what is its effect on hunger and satiety centres?
1. inhibits NPY/AgRP
2. activates POMC/CART - when can leptin be used as a treatment? give leptin injections in congenital leptin deficiency in children
Cholecystokinin:
- where is it synthesised?
- what is its effect on hunger and satiety?
- where is it synthesised? duodenum (released in response to fat and protein)
- what is its effect on hungry and satiety? slows gastric emptying, releases bile and pancreatic enzymes
- -> helps promote feelings of satiety via activation of vagus n
Pancreatic peptide Y 3-36:
- where is it released?
- what stimulates its release?
- what is its effect on hunger and satiety centres?
- where is it released? L cells (type fo ECC)
- what stimulates its release? high fat/protein
- what is its effect on hunger and satiety centres? inhibits NPY and activates POMC
Insulin?
- what is its effect on hunger and satiety centres?
- inhibit NPY/AgRP
- activate alpha MSH/CART
How does GLP-1 regulate appetite?
- released in response to food intake
- reduced blood glucose and therefore reduces food intake
How does oxyntomodulin regulate appetite?
reduces ghrelin levels in plasma which may increase energy expenditure and increase weight loss
(suppresses appetite)
How does Ghrelin affect appetite?
- stimulates NPY and AgRP
- acts directly on the hypothalamus via the vagus
Where is ghrelin synthesised?
- fundus of the stomach
- duodenum
- ileum
What does chronic administration of ghrelin result in?
hyperphagia
What role does the ventromedial nucleus of the hypothalamus play in appetite?
Promotes satiety
What receptor is activated by NPY? What is the effect of this?
Y1 receptors
Effect:
- increased food intake (by activating 2nd order neurones)
- inhibits POMC/CART
What receptor is antagonised by AgRP?
Melanocortin receptor
What can be the result of POMC deficiency?
Hyperphagia and obesity
What is the effect of activation of POMC/CART?
Reduced food intake via release of melanocortins
What is the effect of melanocortin release?
alpha-melanocyte-stimulating hormone
- activates 2nd order neurones (MCR4 receptors)
- inhibits NPY/AgRP (MCR3 receptors)
How does malonyl CoA regulate appetite?
- inhibits lipolysis (carnitine shuttle) at high levels
- lipolysis is stimulated at low levels
- malonyl CoA increases in the cytoplasm (for FA synthesis) –> sensed by hypothalamus
- suppresses AgRP and NPY
- decreases appetite
- malonyl CoA reduces in cytoplasm (no FA synthesis)
- sensed by hypothalamus
- activates AgRP and NPY
What effect does serotonin have on appetite?
- augmentation of brain 5-HT inhibits food intake + depletion of 5-HT promotes weight gain
- serotonin increases signalling in POMC (via 5HT2cR)
- decreases signalling in AgRP (via 5HT1bR)
How can cannabinoids be used as drug treatments in relation to hunger/satiety?
- cannabinoids increase food intake
- THC and CBD are exogenous; anandamide and 2-arachadonylglycerol are endogenous
- high expression of CB1 receptors in the hypothalamus
