Appetite regulation Flashcards
What triggers thirst perception?
increase fluid osmolarity
reduced blood volume
BP reduced
small changes in plasma osmolarity more potent stimulus
Where are osmoreceptors located?
hypothalamus
OVLT - organum vasculosum
SFO - subfornical organ
both are circumventricular organs not completely protected by blood brain barrier (allow sensing of circulation)
What is the function of osmoreceptors?
sense changes in fluid osmolality
send signals to ADH producing cells in hypothalamus to alter ADH
also trigger thirst sensation in CNS
increase osmolality - drink, ADH release
Removal of final correction of thirst?
need to correct plasma osmolality
thirst is initially decreased by drinking before sufficient water absorbed by GI tract
What is the function of angiotensin II in terms of plasma osmolality?
triggers thirst
when plasma osmolality high
Ang2 reduced and SFO neurones stimulated to restore normal body fluid levels
What releases renin?
juxtaglomerular cells of renal afferent arteriole
How does the hypothalamus regulate body weight?
integrate neural input from periphery and other brain regions, leptin, ghrelin, PYY
result in differences in food intake/energy expenditure
Why complex system of hunger regulation?
redundancy in case part of system fails
What is the arcuate nucleus function?
circumventricular organ - can access peripheral hormones
regulates food intake
integrate peripheral and central feeling signals
two neuronal populations
stimulatory (NPY, Agrp)
Inhibitory (POMC)
How does it work?
circulating factors enter arcuate nucleus
cells bodies and receptors of neurones found in arcuate nucleus
axons extend to paraventricular nucleus or to different parts of brain to influence appetite/food intake /TRH- metabolism
NPY/Agrp increase feeding
POMC decrease feeding
both via PV nucelus
What is MC4R?
melanocortin 4 receptor
stimulation inhibits food intake
Agrp is an endogenous antagonist of MC4R –> feel hungry
POMC –> a-MSH
What is the effect of POMC and MC4-R mutations?
people typically morbidly obese
POMC –> lose control of ACTH
MC4R –> red hair, obese so no restraint on food intake
What else can influence appetite aside from arcuate nucleus?
higher centres
amygdala (emotion, memory)
lateral hypothalamus
brain stem
What is the adipostat mechanism?
circulating hormone produced by fat
hypothalamus sense [] of hormone and alter neuropeptides to adjust food intake
What is leptin?
made by adipocytes in white adipose tissue
circulates in plasma
acts on hypothalamus to regulate appetite and thermogenesis
- low when low body fat
- replacement decreases weight, increase thermogenesis and decrease food intake
What is leptin resistance?
fat people have high lpetin
obesity is due to high resistance as hormone is present but doesnt signal effectively
When can leptin be a useful treatment?
those with congenital leptin deficiency
mutation in ob gene
severely hyperphagic and obese
leptin effective in reducing body weight
Why do you feel less hungry after a meal?
changes in hormone levels that signal to the brain
- PYY (satiety)
36 AA chain
(PYY3-36 makes you full after a meal after cleave first 2 AAs)
- Ghrelin (hunger)
How does PYY modulate neurones in arcuate nucleus?
inhibit NPY release
stimulate POMC release
decrease appetite
raised for some time
How does ghrelin directly modulate neurones in arcuate nucleus?
FA attached on Ser3 which affects how it travels in circulation
stimulate NPY/Agrp neurons
inhibit POMC
increase appetite
What are consequences of obesity?
depression sleep apnoea bowel cancer osteoarthritis gout stroke/MI hypertension diabetes peripheral vascular disease
