Appetite Flashcards
What are the three main stimuli in regulation of thirst?
body fluid osmolality
a reduced blood volume
a reduced blood pressure
What is the most potent stimulus?
changes in plasma osmolality
How does the body regulate osmolality?
Via anti diuretic hormone
What is the mechanism of action of ADH?
Mediates it effect via V2 RECEPTORS
increases the transcription and insertion of aquaporin -2 into the apical membrane of the collecting duct
this allows water to move down the osmotic gradient
What is water diuresis?
when plasma ADH is low a large volume of urine is excreted
What is anti diuresis?
when plasma ADH is high a small volume of urine is excreted
Where is ADH stored in the body?
the posterior pituitary gland
What are osmoreceptors?
sensory receptors found in the hypothalamus mediating osmoregulation
Which regions of the hypothalamus are osmoreceptors found in?>
the organum vasculosum of the lamina terminalis and the subfornical organ
How do osmoreceptors mediate the release of ADH?
- increase is plasma concentration results in hypertonic stimulation leading to cell shrinkage
the proportion of cation channels increase -> resulting in membrane depolarisation
the depolarisation is converted into signal which stimulate the posterior pituitary to release ADH
fluid retention invokes drinking
- decrease in plasma concentration results in hypotonic stimulation leads to cell swelling
proportion of cation channel decreases resulting in hyperpolarisation of the membrane
reduced signalling to the posterior pituitary inhibiting the production of the ADH
reduced fluid retention inhibits the need to drink
How is the sensation of thirst stopped?
relief of thirst once plasma osmolality decreases, or blood volume and arterial pressure is corrected
Outline the renin angiotensin system
- blood pressure drops
- the juxtaglomerular cells of renal afferent arteriole secrete renin
- renin cleaves angiotensinogen formed in the liver into angiotensin-1
- angiotensin 1 is converted by ACE in the lungs into angiotensin 2
What are the physiological effects of angiotensin 2?
vasoconstriction, increase sympathetic activity, ADH secretion, aldosterone secretion
How does angiotensin 2 lead to aldosterone release?
- angiotensin 2 binds to receptors on the intraglomerular mesangial cells
- results in contraction of blood vessels around the cells
- stimulating the release of aldosterone from the zona glomerulosa of adrenal cortex
What are the physiological effects of aldosterone?
h2o retention via NaCL absorptions and k+ excretion
What are common drugs that affect the renin angiotensin system?
ACE inhibitors and direct renin inhibitors
What do ACE inhibitors and direct renin inhibitors treat?
hypertension
Where does appetite regulation occur?
in the hypothalamus
Which gut hormones that travel through the vagus nerve regulate appetite?
ghrelin, PYY and other gut hormones
What is the arcuate nucleus?
aggregation of neurone in the medial basal part of the hypothalamus involved in the regulation of food intake
How is the arcuate nucleus involved in appetite regulation?
produces orexigenic (appetite stimulating) and anorectic (appetite supressing) neurones
What is the paraventricular neurone related to appetite?
orexigenic and anorectic neurones project terminally to the paraventricular nucleus
neurones to posterior pituitary -> which stimulate secretion of oxytocin and ADH which affects appetite
Which part of the hypothalamus is associated with satiety?
ventromedial hypothalamus - lesions can lead to severe obesity
Which part of the hypothalamus is associated with hunger?
lateral hypothalamus which produces orexigenic peptides
