Appetite Flashcards
the body regulates/controls thirst through which main triggers?
body fluid osmolality
blood volume is reduced
blood pressure is reduced
why is plasma osmolality the most potent stimulus in thirst
change of 2-3% induces strong desire to drink
- 10-15% decrease in blood vol/pressure required to produce same response
what is the role of adh in thirst and osmolality
acts on collecting duct in kidneys - aquaporin 2 channels
and regulates olume and osmolality of urine
what is water diuresis
when plasma ADH is low and water is excreted
what is anti diuresis
when plasma ADH is high, small volume of urine is excreted
where is adh stored
posterior pituitary gland
what are osmoreceptors
sensory receptors
responsible for osmoregulation
found in the hypothalamus
which regions of hypothalamus are osmoreceptors found?
organum vasculosum of lamina terminalis
subfornical organ
how do osmoreceptors regulate adh release
cells shrink when plasma is more concentrated
proportion of cation channels increases - membrane depolarises
sends signals to adh producing cells
fluid retention invokes drinking
when is thirst completely satisfied
once plasma osmolality is decreased/ blood vol/arterial pressure is corrected
what happens in kidneys when blood pressure drops
juxtaglomerular apparatus secretes renin which activates angiotensin system by cleaving angiotensinogen to angiotensin1 which is converted to angiotensin2 by ACE
What are the effects of angiotensin 2
induces thirst
most important effect is on aldosterone
what is the role of aldosterone
influences reabsorption of sodium and potassium excretion influencing water retention
what is role of angiotensin 2
vasoconstriction - increases sympathetic activity
adh secretion
what 2 gut hormones are involved in peripheral signalling in appetite regulation
ghrelin
pyy
- travels through vagus nerve which connects to brainstem which communicates with hypothalamus - cns e.g amygdala
what is the long term hormones involved in appetite regulation
leptin
what is orexigenic
appetite stimulant
what is anorectic
appetite suppressive
what does the lateral hypothalamus produce
orexigenic petides
what is the ventromedial hypothalamus associated with
satiety
- lesions can lead to severe obesity
when does food intake decrease
when arcuate nucleus pro opio melanocortin neurones activate
what are some other hypothalamic factors which implicate appetite regulations
endocannabinoids
amp - activated protein kinase
protein tyrosine phosphotase
what is the arcuate nucleus
brain area involved in regulation of food intake
incomplete bbb - allows access to peripheral hormones
- integrates peripheral and central feeding signals
what are the 2 neuronal populations in the arcuate nucleus
stimulatory - NPY/agrp neuron
inhibitory - pomc neurone
where are npy/agrp neurones found
only in arcuate nucleus in hypothalamus
what is the role of npy/agrp neurones
potentially stimulate food intake by increasing neuropeptide y signalling and reducing melanocortin signalling
what is agrp
endogenous melanocortin receptor antagonist
what effect does leptin have on npy/agrp
inhibitory effects
what effect does leptin have on pomc/cart
stimulatory effects
what conditions can cause increased food intake via leptin mechanism
fasting
uncontrolled diabetes
genetic leptin deficiency
other than feeding what are 2 factors the arcuate nucleus is responsible for
fertility and cardiovascular regulation
what is the central melanocortin system
collection of central nervous circuits e.g npy/agrp and pomc
what is melanocortin
product of pomc gene
what are some human cns mutations affecting appetite
no npy/agrp mutations associated with appetite
- pomc deficiency and mc4r mutations cause morbid obesity
- mutations not responsible for obesity - but useful to explain signalling
what is the adipostat mechanism
circulating hormone produced by fat
- hypothalamus senses concentration of hormone and then alters neuropeptides to increase/decrease food intake
what is leptin
hormone made by adipocytes in white adipose tissue and enterocytes
circulates in plasma
acts on hypothalamus regulating appetite and thermogenesis
what is congenital leptin deficiency
rare condition
causes severe obesity very early in life
what is leptin resistance
leptin circulates in plasma in conc proportional to fat mass
obesity due to leptin resitance
leptin is ineffective as weight control drug
why do we feel less hungry after a meal
hormone signals from gut aka gi hormones
what are gi hormones secreted by
enteroendocrine cells in stomach, pancreas and sb
what gi hormones is appetite regulated by
ghrelin - stimulates appetire, increases gastric emptying
peptide yy - inhibits food intake
what is ghrelin
*help prepare food intake by increasing gastric mobility and acid secretion
directly modulates neurones in arcuate nucleus
stimulates npy/agrp neurones
inhibits pomc neurones
- increases appetite
- regulation of reward, taste sensation, memory and circadian rhythm
what is peptide tyrosine tyrosine
short peptide released in terminal ileum and colon in response to feeding
reduces appetite
food arriving at ti and colon results in pyy release
inhibits npy release
stimulates pomc neurones
what cormobidities is obesity associated with
depression sleep apnoea bowel cancer stroke mi osteoarthiritis peripheral vascular disease gout hypertension diabetes
