Osmoregulation Flashcards
What are the 3 big picture goals of osmoregulation?
Maintain an osmolality of fluid appropriate for cells to bathe in
Maintain a fluid volume appropriate for filling vascular tree
Allow heart to generate arterial pressure necessary for perfusion
What receptors regulate water excretion?
Osmoreceptors
Baroreceptors
Where are osmoreceptors found?
Supraoptic and paraventricular areas pf anterior hypothalamus
What do osmoreceptors regulate?
Release of ADH
Where is ADH synthesized?
Hypthalamus as a large precursor molecule
Where is the precursor molecule transported to?
Posterior pituitary where it’s cleaved to a nonpeptide
What is ADH stored as in nerve terminals?
Insoluble complexes in secretory granules
What happens upon release?
Dissociate rapidly due to dilution and pH increase
What does ADH act on?
Principal cells of collecting duct
What other factors stimulates ADH secretion?
Nicotine
nausea
angiotensin II
What other factors inhibits ADH secretion?
Atrial natriuretic peptides
Ethanol
What are intrarenal baroreceptors?
Pressure sensitive juxtaglomerular cells of afferent arteriole
What do intrarenal baroreceptors secrete?
Renin
How do baroreceptors control ADH secretion?
Decrease their rate of firing which increases ADH release
What does haemorrhage cause?
Increases ADH release via baroreceptors so water is retained
What are 3 malfunctions of the ADH system?
Central diabetes insipidus
Nephrogenic diabetes insipidus
Syndrome of inappropriate ADH secretion
What area of the brain controls thirst?
Lateral pre optic area
Define free water clearance.
Volume of pure water that must be removed from, or added to, the flow of urine to make it iso-osmotic with plasma
CH2O = V - Cosm
What does osmolar clearance equal to?
Cosm = Uosm X V/Posm
What does positive free water clearance mean?
Hypotonic
What does negative free water clearance mean?
Hypertonic
