Appetite Flashcards
what is the most potent stimulus of thirst?
plasma osmolality increase
what are less potent stimuli of thirst?
blood volume reduction
blood pressure reduction
what hormone is important for the regulation of osmolality?
ADH (vasopressin)
main physiological action of ADH
acts on kidneys to transport aquaporin 2 channels to the collecting duct membrane > reabsorption of water
low plasma ADH produces what urine?
large, dilute volumes
high plasma ADH produces what urine?
small, concentrated volumes
where in the hypothalamus are osmoreceptors found?
subfornical organs
organum vasculosum of the lamina terminalis
osmoreceptor response to more concentrated plasma
cells shrink > ^proportion of cation channels > membrane depolarises > sends signals to ^ADH > fluid retention, invokes drinking
AND VICE VERSA
when is thirst decreased after drinking?
decreased even before sufficient water has been absorbed by the GI tract to correct plasma osmolality
receptors involved in thirst are found where?
mouth
pharynx
oesophagus
is relief of thirst sensation via receptors in the mouth, pharynx, oesophagus short lived or long acting?
short lived
when is thirst completely satisfied?
once plasma osmolality is decreased or blood volume or arterial pressure corrected
effect of RAAS on blood pressure/volume
angiotensin II > ADH secretion, vasoconstriction, ^ sympathetic activity, thirst, (aldosterone release > H20 retention via electrolytes)
aldosterone is released from where?
zona glomerulosa of adrenal cortex
effect of aldosterone on electrolytes
Na+ absorption
K+ excretion
effects of a reduction in fat mass
increases food intake and reduces energy expenditure
effects of adipose tissue expansion
reduces food intake and increases energy expenditure
what mechanism defends against reduction of body fat?
central circuit
what molecules/hormones are involved in appetite regulation?
ghrelin
PYY
gut hormones
leptin
briefly outline the structures of the hypothalamus
arcuate nucleus
paraventricular nucleus
lateral hypothalamus
ventromedial hypothalamus
what is the arcuate nucleus involved in?
regulation of food intake
how does the arcuate nucleus have access to peripheral hormones?
incomplete blood brain barrier
the arcuate nucleus has what two neuronal populations?
Stimulatory (NPY/Agrp neuron)
Inhibitory (POMC neuron)
neurons in the arcuate nucleus give feedback to?
paraventricular nucleus
the melanocortin system
POMC > alpha-MSH > MC4R
Agrp >Agrp > MC4R
what human CNS mutation affect appetite?
POMC deficiency
MC4-R mutation
what signals from other brain regions affect appetite?
higher centres
amygdala
other parts of hypothalamus e.g. lateral hypothalamus
vagus > brain stem > hypothalamus
adipostat mechanism
circulating hormone produced by fat > sensed by hypothalamus > alter neuropeptides to increase or decrease food intake
where is leptin made?
adipocytes in white adipose tissue
main physiological actions of leptin
acts on hypothalamus regulating appetite (intake)
thermogenesis (expenditure)
what is condition involving leptin?
congenital leptin deficiency
mechanism of action of leptin
leptin > receptor (LRb) in the brain > regulate energy balance and neuroendocrine function. LRb signaling via STAT3 and a number of other pathways is required for the totality of leptin action.
levels of leptin when body fat is low
low
levels of leptin when body fat is high
high
leptin in obesity
leptin resistance > hormone is present but doesn’t signal effectively
is leptin a viable weight control drug?
no, ineffective
GI hormones are secreted from?
enteroendocrine cell in the stomach, pancreas and small bowel
list GI hormones that regulate appetite
Ghrelin
Peptide YY
effect of ghrelin
stimulates appetite
increases gastric emptying
effect of peptide YY
inhibits food intake
when are blood levels of ghrelin highest?
before meals
how does ghrelin help prepare for food intake?
increases gastric motility
increases acid secretion
effect of ghrelin on neurons in arcuate nucleus
stimulates NPY/Agrp neurons
inhibits POMC neurons
apart from appetite regulation, ghrelin has a role in?
regulation of reward
taste sensation
memory
circadian rhythm
PYY is released from?
terminal ileum
colon
PYY is released in response to?
in response to feeding
effects on PYY
reduces appetite
PYY inhibits what?
inhibits NPY release
PYY has what effect on neurons in the arcuate nucleus?
stimulates POMC neurons
obesity is associated with what comorbidities?
depression, stroke, sleep apnoea, MI, hypertension, diabetes, bowel cancer, osteoarthritis, peripheral vascular disease, gout
describe the global trend of obesity and related comorbidities
increasing worldwide
