Katz: Water regulation Flashcards
What does urine mostly consist of and what is the normal total urine osmolality?
Water
osmolality can range from 50-1300 mOsms depending on how much water is being excreted
What happens to urine volume and urine osmolality when there is a positive water balance? Why is this impt?
Positive water balance (water intake > water excretion>
DECREASE in extra/intracellular osmolality>
INCREASED urine volume>
DECREASED urine osmolality
Excretion of more water relative to solute will increase extra/intracellular osmolarity and return total body water back to normal.
What happens to urine osmolality when the body is in water balance?
Water balance (intake = excretion)
Associated with extra/intracellular osmolality of 285-295 mOsms.
Loss of water in urine (sweat, fecal matter, expired air) equals water intake.
Urine osmolarity is VARIABLE and depends on the relative water to solute intakes.
What happens to urine volume and urine osmolality when there is a negative water balance? Why is this impt?
Negative water balance (intake< excretion)>
increase in extra/intracellular osmolality>
decrease urine volume>
increase urine osmolality
Excretion of less water relative to solute will DECREASE extracellular and intracellular osmolality and return total body water back to normal.
What happens to cortical nephron collecting duct fluid?
It moves into juxtamedullary collecting ducts then passes through the medullary interstitium.
What percent of water is reabsorbed in the PCT, the DL and the TAL?
PCT- 65%
DL- 10%
CCD/MCD- 5-24.5%
How much water is excreted with and without ADH?
Without ADH- 36 L
With ADH- less than 1 L water/day
What is the theoretical maximal urine output with out ADH? Why can’t this rate be maintained? Why does it fall quickly?
36 L/day max urine output
If you pee 36 L/d you run out of plasma volume
Why does the extracellular osmolality with and wtihout ADH differ?
w/out ADH= 300mM NaCL= 600
w/ ADH= 300 mM NaCl + 600 mM urea = 1200
What forms the intracellular osmolality? How does this differ from intracellular osmolality with ADH?
W/out ADH:
300 mOsms usuall solutes + 300 mOSMS osmomlytes = 600
W/ ADH:
300 mOsms + 600 mM urea + 300 mOsms osmolytes = 1200 mOsms
Why/how are intracellular osmolytes formed?
Medullary cells can synthesize intracellular osmolytes to equalize extracellular osmolality increases d/t ADH
Done by a TF named TonEBP with promotes the intracellular accumulation of organic osmolytes.
Why is osmolality high in the medulla?
It’s a function of ADH!
What does countercurrent multiplication do?
it LOADS the medullary extracellular space with NaCl through NaCl pumps and osmosis.
How is urea formed?
AA> Keto acids and NH3 NH3> Hepatic urea production> plasma urea> filtered
What percent of urea is reabsorbed proximally?
50% of filtered urea
What does urea recycling do?
Loads the medulla w/ urea in response to ADH
ADH> upregulation of urea transporters> urea transported out of collecting duct> transported back into TAL> Causes urea to become a major solute in the hyper osmotic medulla and papilla
What percent of filtred urea urea is excreted?
50% rest is reabsorbed
What percent of urine solute is urea?
50%
What percent of the medullary osmolality is ure?
50%
What happens when ADH is present in the CCD?
ADH= AVP = vasopressin
Greatly incrased insertion of luminal AQP2 and basolateral AQP 3/4 into last 1/3 of distal tubule and collecting duct as well as upregulation of urea transporters.
What does ADH do to urine? Why is this important?
LOW volume
HIGH osmolality urine
SAVES WATER!
What happens when water leaves the CD b/c of ADH?
It is returned to peritubular capillaries called the vasa recta
Do the vasa recta have net reabsorptive starling forces? Why is this impt?
YES! Therefore they reabsorbe water that moves out of hte descending limb and the medullary cortical collecting ducts.
Do the vasa recta disturb the medullary osmolality gradients? how can this be?
NO
They are also arrange din a counter current arrangement.
What happens in the presence and absence of ADH to AQPs?
ADH> cAMP signaling> membrane insertion of channels via exocytosis
ADH absent> endocytosis of AQP
What happens in the CCD without ADH when there is a POSITIVE water balance?
NO ADH>
decreased/no insertion of luminal AQP2 into last 1/3 of distal and collecting tubule>
no urea transporters>
no collecting duct water permeability>
water is TRAPPED in nephron lumen and excreted
What is the urine like when there is NO ADH present in the CCD?
HIGH volume
LOW osmolality
(excrete water)
What triggers ADH secretion?
- High osmolality> osmoreceptors> Hypothalamus> posterior pituitary> ADH secreted
- Decreased PV> Decreased MAP (AA and Carotid baroreceptors) and decreased venous and atrial volumes (atrial and low pressure baroreceptors)> Hypothalamus> posterior pituitary> secrete ADH
What are the 5 actions of ADH?
- Last 1/3 of distal tubule and CD increased water permeability d/t insertion of AQP
- UT upregulated in ascending limb and CD> urea recycling
- Vasonconstriction
- Incraesed TAL Na/K/2CL pumping
- Possible thirst mediation
What happens if the ADH mechanism fails?
Central diabetes insipidus
No plasma vasopressin>
increased urine flow and thirst
What happens if ADH is overactive?
Syndrome of Inappropriate ADH secretion
Plasma ADH high>
reabsorb water like crazy>
chronically hypervolemic
