RP6: Urine Concentration and Dilution Flashcards
Normal function requires ECF Osmolarity of _____ mOsm
300 mOsm
Maximal urine concentration _____ mOsm
1200 mOsm
Minimal urine concentration ___ mOsm
50 mOsm
Urine Formed Without ADH is…
Dilute
Filtrate is ________ in proximal tubule
isosmotic
Filtrate becomes ________ as passes
through thin descending loup
hyperosmotic
What happens in the thin descending loup?
– Water reabsorption
– No solute reabsorption
Becomes _______ as it passes through thick ascending and early distal tubule
hyposmotic
What happens in the thick ascending and early distal tubule?
– Solute reabsorption
– No water reabsorption
What hormone increases H2O permeability of distal tubule and collecting duct?
ADH
What is obligatory urine volume (OUV)?
The maximal concentrating ability of the kidney dictates how much urine volume must be excreted each day to rid the body of metabolic waste products and ions that are ingested.
Adults must excrete ____ mosmol daily of urine
600 mosmol
What is the equation for obligatory urine volume (OUV)?
OUV (vol/day) = Osmotic Load (mOsmol/day)/Max. [Urine] (mOsm)
What is the obligatory urine volume when maximum urine
concentration = 300 mOsm?
600 mosmol/day / 300 mOsm
= 2 L/day
What are the requirements for excreting a concentrated urine?
- high levels of ADH
- hyperosmotic medullary interstitial fluid
- counter courrent multiplier mechanism
Continuous delivery of ______ from proximal convoluted tubule into loop of Henle
NaCl
Concentration of filtrate by H2O ________ by Descending Limb of Henle
reabsorption
In the absence of ADH the distal tubule and collecting duct do what?
- reabsorb solute
- little to no water reabsorption
In the presence of ADH the distal tubule and collecting duct do what?
- become highly permeable to water and reabsorb much water into the cortical interstitium
What sections of the nephron are permeable to urea?
- proximal tubule
- thin ascending and descending limbs of the loop of henle
- medullary collecting duct
What sections are impermeable to urea?
thick ascending limb of loop of henle
early and late distal tubule
cortial collecting duct
What is the countercurrent multiplier mechanism?
➢ Filtrate in descending & ascending
limbs of loop of Henle flows in
opposite directions of blood flow
in Vasa Recta
➢ Clears Reabsorbed water so does
not dilute medullary interstitial
fluid
➢prevents osmolarity changes in the vase recta (blood)
What is the filtrate osmolarity in the proximal tubule?
isomotic
What is the filtrate osmolarity in the descending loop of henle?
hyperosmotic
What is the filtrate osmolarity in the ascending limb of the loop of henle?
hyposmotic
What is the filtrate osmolarity in the distal tubule and collecting ducts?
variable (depends on ADH)
What percent of water is reabsorbed in the proximal tubule?
70%
What percent of the water is reabsorbed in the descending loop of henle?
20%
What percent of the water is reabsorbed in the ascending loop of henle?
0%
