appetite & disorders Flashcards
what is the strongest stimulus for thirst
plasma osmolarity
over blood volume/arterial pressure
action of vasopressin
regulates volume and osmolarity of urine
via aquaporin 2 channels on collecting duct
more adh = small amount of urine (less water)
where are the osmoreceptors?
organum vasculosum of lamina terminalis
subfornical organ
within hypothalamus
stimulus of thirst?
cells shrink via osmosis if plasma is more concentrated (no BBB)
proportion of cation channels increases - membrane depolarises
sends signals to ADH producing cells for ADH release
fluid retention and invokes drinking
how is the sensation of thirst satiated?
decreased by drinking (before sufficient water has yet been absorbed to correct osmolarity)
receptors in mouth, pharynx and oesophagus
but SHORT LIVED release - only completely satiated when plasma osmolarity decreased/blood volume/arterial pressure
how is a reduction in blood pressure regulated by the body, starting in the kidney
fall in bp detected by juxtaglomerular cells in renal afferent arteriole
renin produced
angiotensinogen converted to angiotensin I in liver
angiotensin I- II in lungs by ACE
results in vasoconstriction, thirst, stimulation of aldosterone secretion in zona glomerulosa, H2O retention and Na retention, ADH secretion
where in the brain is responsible for appetite
hypothalamus:
arcuate nucleus
lateral hypothalamus (feeding centre)
ventromedial hypothalamus (satiety centre)
what is the arcuate nucleus
brain area involved with regulation of food intake (via lateral and ventromedial hypothalamus)
with 2 neuron groups: neuropeptide Y/agouti-related peptide and POMC
how is appetite regulated by the hypothalamus
stimuli - insulin and leptin (levels of circulating factors)ghrelin, vagus nerve stimulation of AN
arcuate nucleus - orexigenic and anorectic neurons send signals to inhibit/stimulate:
paraventricular nucleus - ADH
lateral hypothalamus - orexigenic peptides (feeding centre)
ventromedial hypothalamus - anorexigenic peptides /melanocortins (satiety centre)
where is the arcuate nucleus
medial-basal part of hypothalamus, adjacent to 3rd ventricle
what is the paraventricular nucleus
collection of neurons around 3rd ventricle in hypothalamus
controls energy expenditure and appetite
produces ADH and oxytocin
terminal field of arcuate nucleus neurons (appetite neurons)
what mechanisms of weight homeostasis kick in if weight reduces
reduced sympathetic activity
reduced energy expenditure
reduced thyroid activity
increased hunger/food intake
what weight homeostasis mechanisms kick in when weight is increased?
increased sympathetic activity
increased energy expenditure
reduced hunger/food intake
how does peripheral input for appetite reach the brain (not through blood)
vagus nerve
what are the orexigenic neurons
neuropeptide Y and AGRP neurons
what are the anorexic neurons
POMC neurons
how do melanocortins produce their effect
alpha-MSH (melanocyte stimulating hormone) released by POMC neurons in arcuate nucleus
binds to MC4R in paraventricular nucleus
this decreases appetite and suppresses food intake
how does the arcuate nucleus know to increase appetite?
receptors for insulin and leptin
decrease of either will stimulate NPY/AGRP neurons to increase appetite
what is leptin
anorexigenic hormone made by adipocytes
proportional to body fat
inhibits NPY and AGRP, stimulates POMC neurons
what is ghrelin
orexigenic gut hormone from enteroendocrine cells
increase before every meal
how does ghrelin work for appetite
stimulates NPY/AGRP neurons
inhibits POMC neurons
increases gastric motility and secretions
displays a diurnal rhythm
what is peptide YY
anorexigenic gut hormone produced by terminal ileum and colon
suppresses appetite
inhibits NPY, stimulates POMC
how does peptide YY work for appetite
inhibits NPY neurons
stimulates POMC neurons
suppresses appetite
what gene mutations are associated with obesity?
POMC neuron mutations
what hormone is related to obesity
lepin resistance
what is secondary polydipsia
due to a medical issue disruptinf any step in osmoregulation or alter ADH
causes of secondary polydipsia
diabetes I and M kidney failure conns syndrome addisons disease sickle cell diuretics and laxatives antidepressants dehydration
name some causes of dehydration
sweating acute illness fevers vomiting diarrhoea underhydration
causes of primary polydipsia
its mentaw iwwness innit
brain injuries
organic brain damage
what issues may be caused by polydipsia
hyponatraemia causing: kidney/bone damage headaches nausea/cramps slowed reflexes/slurred speech low energy confusion/seizures
what is adipsia
absence of thirst
categories of anorexia nervosa
mild - BMI >17
moderate 16-16.99
severe - 15-15.99
extreme <15
signs of anorexia nervosa
low BMI continuous weight loss amenorrhoea halitosis mood swings dry hair/skin/ thinning
causes of anorexia nervosa
genetic
environmental
psychological
sociological
what is an eating disorder
mental illness characterised by altered eating habits
what is the mechanism behind anorexia
serotonin
what is the treatment of obesity?
best results - diet and exercise
bariatric surgery if severe
when is bariatric surgery offered to an obese individual
BMI 40+ OR 35+ Comorbidities
most common bariatric surgery
roux-en Y gastric bypass
2nd most - sleeve gastrectomy
what are the hormonal changes after bariatric surgery
ghrelin reduced
Glucagon-like peptide 1&2, PYY elevated
role of lateral hypothalamus in appetite
produce only orexigenic (appetite) peptides
role of ventromedial hypothalamus in appetite
produce anorexigenic peptides only
types of appetite stimuli
ghrelin - orexigenic PYY - anorexigenic vagus nerve - mechanoreceptors in stomach (increased firing = anorexigenic) leptin - adipose tissue anorexigenic insulin - anorexigenic
mechanisms of leptin dysfunction
not enough produced
receptor signalling defective
decreased sensitivity to leptin
levels of leptin depend on
levels of body fat - doesnt fluctuate much during day
high fat = high leptin
what is congenital leptin deficiency
constant hunger as a result of no leptin circulating body
leptin effective when replaced in body - body weight reduced
