Regulation of Osmolarity Flashcards
where is AHD synthesised?
supraoptic and paraventricular nuclei in the hypothalamus
what is the primary control of ADH secretion?
plasma osmolarity
true or false:
an increase in the effective oncotic pressure of the plasma causes an increased rate of discharge of ADH
true
what endocrine organ releases ADH?
the posterior pituitary
what mediates changes in the neural discharge of ADH secreting hormones?
osmoreceptors in the anterior hypothalamus
what is the effective of an increase in osmolarity on the osmoreceptors?
they activates as the cell shrinks due to H20 moving out of the cell
True or false:
an increase in osmolarity causes a decrease in neural discharge and ADH secretion
false:
this causes ad increase in ADH secretion and neural discharge and the stretch sensitive ion channels (in the osmoreceptors) are activated
how does a decrease in osmolarity cause a decrease in ADH secretion?
> H20 enters the cell (osmoreceptors) causing it to swell
> osmoreceptors do not fire and so there is an increase in ADH secretion
what is normal plasma osmolarity?
280-290 mOsm/kg H20
what is tonicity?
The effective osmotic pressure gradient
penetrating solutes that move with the water and do not create an osmotic drag
Name that missing word:
An increase in osmolarity that does not cause and increase in ??? is ineffective in causing an increase in ADH
tonicity
how does aquaporin 2 increase the permeability of the collecting duct to H20?
it incorporates channels into the luminal membrane
how does ADH increase water reabsorption in the collecting duct?
by binding to cell surface receptors it creates the release of aquaporin 2 which increases the permeability of the cell to water
why does the contents of the collecting duct become highly concentrated at the tip if the medulla?
> ADH is present so it equilibrates with the medullary interstitium through H20 osmotic effect
the medullary interstitium has become hypertonic due to the loop of henle counter current multiplier
is ADH is absent is the medullary interstitial gradient still ineffective at inducing H20 movement out of the collecting duct?
yes as the collecting duct would be impermeable to H20
what is the effect of ADH on the permeability of the collecting ducts to urea?
it increases the permeability
Tue or Flase:
urea reinforces the interstitial gradient in the region of the thin ascending loops of henle
True
why must urea be reabsorbed?
it would exert an osmotic effect and hold H20 in the tubule reducing potential for rehydration
would and increase or an decrease in ECF volume cause an increase in ADH?
a decrease
there is an inverse relationship with the rate of ADH secretion and what?
the rate of discharge of the stretch receptor afferent in low and high pressure areas of circulation
where are the low pressure receptors?
> left and right atria
> great veins
where are the high pressure receptors?
> carotid baroreceptors
> aortic arch baroreceptors
what is the normal effect of atrial receptors on ADH secreting neurons?
inhibition of discharge
what is the effect of a decrease in ECF volume on atrial receptor discharge?
there is a decrease in discharge
in haemorrhage which receptors will contribute to changes in ADH secretion?
carotid and aortic receptors
what stimuli would cause in increase in ADH?
> morphine > nicotine > exercise > emotion > pain > stress > traumatic surgery
what is the effect of alcohol on ADH secretion?
it decreases it
what us the effect on ADH secretion of:
> high osmolarity
> decreased atrial stretch
> decreased BP
an increase in ADH secretion
what will a deficiency in ADH cause?
diabetes insipidus
what could cause central diabetes insipidus?
damage to the hypothalamic areas synthesising ADH:
> Tumour
> meningitis
> surgery
what could cause peripheral diabetes insipidus?
collecting duct insensitivity to ADH
what is diabetes insipidus usually secondary to?
> hypercalcaemia
> hypokalaemia
