A. Lecture 26 - regulation of water balance Flashcards
what is the value of plasma osmolality?
280-290 mosmol/Kg H2O (± 3)
what is diuresis?
increased production of urine.
what does ADH increase H2O permeability of?
Cortical collecting duct (2/3 reabsorption)
Medullary collecting duct (1/3 reabsorption)
how much hypotonic fluid reaches collecting ducts daily?
23 litres
in the absence of ADH how much dilute urine can be produced?
approx 20 litres.
in the presence of ADH how much concentrated urine can be produced?
300 ml
what is ADH?
Vasopressin
where is ADH produced?
Synthesised in the supraoptic (SON) and paraventricular nuclei (PVN)
where are the SON and the PVN found?
in the hypothalamus.
what is the half life of ADH?
15 minutes
where is ADH degraded?
liver and kidney
what happens to ADH after synthesis?
moves to neurohypophysis
how does ADH travel to neurohypophysis?
in axons of hypothalamophypophyseal tract
what happens to ADH during the movement?
progressively cleaved.
how is ADH stored in nerve terminals?
with neurophysin.
what causes ADH release?
primary stimulus is plasma osmolality.
how is plasma osmolality sensed?
osmoreceptors.
where are osmoreceptors found?
located near SON
what is the activation threshold for osmoreceptors?
280 mosmol/kg H2O
what happens when osmoreceptors are activated?
small amount of tonic ADH release