Regulation of Osmolality Flashcards
What hormone controls water regulation?
ADH aka anti-diuretic hormone
Where is ADH
-synthesised?
-stored?
Synthesised in the hypothalamus
Stored and released from posterior pituitary
What is the half-life of ADH?
10 minutes
->this means it can be rapidly adjusted depending on the body’s need for water
What primarily controls ADH secretion?
Plasma osmolarity
How does plasma osmolality determine the secretion of ADH?
When the osmotic pressure of plasma increased, the release of ADH-secreting hormones from the hypothalamus is increased, which in turns increased release of ADH from the posterior pituitary
->kind of like a negative feedback loop we learned about in endocrine. wordy but read through and understand cos rn I cba xx
What are changes in the neuronal discharge of ADH secreting hormones mediated by?
Osmoreceptors in the anterior hypothalamus
What are osmoreceptors?
Cells which can change their cellular volume in response to osmotic changes
What happens to osmoreceptors if osmolality increases?
Increased water out of cell so cells shrink
What happens to the release of ADH-secreting hormones and ADH when there is high osmolality?
Increased neuronal discharge meaning increased ADH secretion
What happens to osmoreceptors if osmolality decreases?
Water enters cell
Cells swell
What happens to the release of ADH-secreting hormones and ADH when there is low osmolality?
Decreased neuronal discharge meaning decreased ADH secretion
Therefore, what effect does the change in volume of osmoreceptors have?
Leads to changes in osmoreceptor discharge
What is the normal osmolality of plasma?
280-190mOsmoles/Kg water
If osmolality increases due to an increase in NaCl, what happens?
Decreased volume of osmoreceptor
Increased discharge and ADH release
If osmolality increases due to an increase in urea, what happens?
No change in volume, discharge or ADH release
->this is because urea is an ineffective osmole idk gal these slides confuse me
What is the amount of urine produced dependant on?
ADH
Amount of solute to be excreted
Okayyyyy so lets say there was 2400mOsmoles of solute to be excreted, how much urine would be produced?
2 litres
-> maximum urine concentration is 1200-1400mOsmol/L hence why two litres will be produced
Ingestion of hypertonic solutions, like seawater, can cause death. Why?
Increases solute load to be excreted meaning increased urine flow, leading to dehydration and potentially death
->okay just for interest but if you were stuck in the middle of the sea, drinking seawater would actually quicken death!
By addition of aquaporins into the luminal membrane, what effect does this have on permeability of the collecting ducts?
Increases the permeability towards water of the collecting ducts
If ADH is present, how does this effect the permeability of the collecting duct?
ADH increases the permeability for water
What amount/concentration of urine does the presence of ADH produce?
Smaller volume of highly concentrated urine
In the absence of ADH, what happens to the collecting duct’s permeability to water?
Collecting ducts become impermeable to water in absence of ADH
What happens to urine concentration/amount in the absence of ADH?
Larger volume of more dilute urine compensating for water excess as cannot be removed without ADH
So…. what happens to urine if there is excess water?
Want to get rid of water so more dilute, higher quantity of urine
