9 Osmoregulation Flashcards
Where is osmolality detected?
anteriocentral third ventricle
AV3V
The BBB is incomplete here
What is ADH released with?
neurophysin
What is the half life of ADH, what is the significance of this?
only about 10 mins
it can be controlled easily, although not very useful to give ADH as a replacement
an analogue (desmopressin) is given instead
Where are V2 receptors found?
basolateral membrane of the cortical collecting ducts
What are V1 receptors for and what cell signalling pathway do they use?
vasoconstriciton of veins
PLC pathway
What does oxytocin do?
triggers thirst
associated with the let-down reflex during breast feeding
breast feeding commonly triggers thirst
What is our normal plasma osmolality?
Why is this significant?
around 285 mOsm/kg
at around 280 mOsm/kg our ADH release is utterly nothing
Why is rate of ADH production almost proportional to ADH level in plasma?
because its’ half life is so short
What is our maximum urine osmolality, what is the significance of this?
1400 mOsm/kg
if we take in loads of salt we have to lose a lot of water to clear it out, we therefore get dehydrated
What is the maximum osmolality of neonates, what is the significance of this?
500 mOsm/kg
gotta watch that our baby feed isn’t too concentrated as they will just piss themselves to death
Why does Na have a far greater impact on plasma osmolality than fats and carbs?
fats and carbs are taken into cells, and therefore do not contribute significantly to osmolality
Why do proteins have little effect on osmolality?
they contain nitrogen which is excreted as urea, urea has a high renal clearance
What is clearance?
the volume of body fluid removed of a substance per unit time
What is measuring clearance useful for?
judging the method of elimination or metabolism of a drug
quantitative predictions of changes over time
Why doesn’t KCl ingestion adversely affect osmolality?
what is the significance of this?
all cells are relatively permeable to K, so this creates a large reservoir of K
therefore K+ is cleared by the kidney much more rapidly than Na+
