Water-Muster Flashcards
What are the 2 main stimuli for ADH secretion?
Osmolality (increasing)
Volume depletion
What is extremely sensitive in sensing an increase in osmolality?
Brain osmoreceptors
Where is ADH released?
Posterior Pituitary
What percentage of water is reabsorbed in the proximal tubule, Loop of Henle, and Collecting duct respectively?
65 % proximal tubule
10 % Loop of Henle (thin descending limb)
5-24.5 % in the Collecting Duct
What is the osmolarity produced by NaCl movement in the thick ascending tubule?
600 mOsoms/L.
With ADH, we have the addition of ____________ to reach a total osmolarity of ______________.
Urea
1200 mOsms/L (so Urea adds another 600 mOsoms/L by creating a stronger gradient for water to move across)
How do cells prevent water themselves from shrinking when there is water loss to the interstitium?
They create osmolytes to equalize the osmolality!
In what part of the Loop of Henle is the concentration of urea constantly increasing? why?
Thin descending tubule: because water is being reabsorbed!
Where are UT2 transporters?
Ascending limb
Where are UT1 transporters?
Collecting duct
What percentage of urea is excreted?
50 %
Describe the process by which ADH induces aquaporin insertion into the cell membrane.
ADH binds V2 receptor on basolateral side of cell.
cAMP is produced.
Protein Kinase A is activated.
Protein Kinase A phophorylates CREB to CREB-P
CREB-P is a transcription factor that promotes mRNA transcription and protein translation of Aquaporins.
Aquaporins are inserted into vesicles that fuse with cell membrane in response to ADH.
AQP 2 is inserted into membrane!
Net result: MORE WATER REABSORBED!
Why can the aquaporin insertion process be upregulated quickly?
The channels are already made! ADH just causes them to be put into the membrane.
MOA of Tolvaptan?
Blocks V2 receptor to force a water diuresis
[approved for heart failure]
What happens in a genetic mutation of V2?
Prevents adequate response to ADH thereby causing a water loss. This is a form of Nephrogenic Diabetes Insipidus!
