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CRAAB 7 > Katz: Water regulation > Flashcards

Katz: Water regulation Flashcards

1
Q

What does urine mostly consist of and what is the normal total urine osmolality?

A

Water

osmolality can range from 50-1300 mOsms depending on how much water is being excreted

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2
Q

What happens to urine volume and urine osmolality when there is a positive water balance? Why is this impt?

A

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.

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3
Q

What happens to urine osmolality when the body is in water balance?

A

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.

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4
Q

What happens to urine volume and urine osmolality when there is a negative water balance? Why is this impt?

A

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.

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5
Q

What happens to cortical nephron collecting duct fluid?

A

It moves into juxtamedullary collecting ducts then passes through the medullary interstitium.

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6
Q

What percent of water is reabsorbed in the PCT, the DL and the TAL?

A

PCT- 65%
DL- 10%
CCD/MCD- 5-24.5%

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7
Q

How much water is excreted with and without ADH?

A

Without ADH- 36 L

With ADH- less than 1 L water/day

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8
Q

What is the theoretical maximal urine output with out ADH? Why can’t this rate be maintained? Why does it fall quickly?

A

36 L/day max urine output

If you pee 36 L/d you run out of plasma volume

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9
Q

Why does the extracellular osmolality with and wtihout ADH differ?

A

w/out ADH= 300mM NaCL= 600

w/ ADH= 300 mM NaCl + 600 mM urea = 1200

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10
Q

What forms the intracellular osmolality? How does this differ from intracellular osmolality with ADH?

A

W/out ADH:
300 mOsms usuall solutes + 300 mOSMS osmomlytes = 600

W/ ADH:
300 mOsms + 600 mM urea + 300 mOsms osmolytes = 1200 mOsms

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11
Q

Why/how are intracellular osmolytes formed?

A

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.

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12
Q

Why is osmolality high in the medulla?

A

It’s a function of ADH!

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13
Q

What does countercurrent multiplication do?

A

it LOADS the medullary extracellular space with NaCl through NaCl pumps and osmosis.

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14
Q

How is urea formed?

A 
AA> Keto acids and NH3
NH3>
Hepatic urea production>
plasma urea>
filtered
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15
Q

What percent of urea is reabsorbed proximally?

A

50% of filtered urea

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16
Q

What does urea recycling do?

A

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
17
Q

What percent of filtred urea urea is excreted?

A

50% rest is reabsorbed

18
Q

What percent of urine solute is urea?

A

50%

19
Q

What percent of the medullary osmolality is ure?

A

50%

20
Q

What happens when ADH is present in the CCD?

A

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.

21
Q

What does ADH do to urine? Why is this important?

A

LOW volume
HIGH osmolality urine

SAVES WATER!

22
Q

What happens when water leaves the CD b/c of ADH?

A

It is returned to peritubular capillaries called the vasa recta

23
Q

Do the vasa recta have net reabsorptive starling forces? Why is this impt?

A

YES! Therefore they reabsorbe water that moves out of hte descending limb and the medullary cortical collecting ducts.

24
Q

Do the vasa recta disturb the medullary osmolality gradients? how can this be?

A

NO

They are also arrange din a counter current arrangement.

25
Q

What happens in the presence and absence of ADH to AQPs?

A

ADH> cAMP signaling> membrane insertion of channels via exocytosis

ADH absent> endocytosis of AQP

26
Q

What happens in the CCD without ADH when there is a POSITIVE water balance?

A

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

27
Q

What is the urine like when there is NO ADH present in the CCD?

A

HIGH volume
LOW osmolality

(excrete water)

28
Q

What triggers ADH secretion?

A
  1. High osmolality> osmoreceptors> Hypothalamus> posterior pituitary> ADH secreted
  2. Decreased PV> Decreased MAP (AA and Carotid baroreceptors) and decreased venous and atrial volumes (atrial and low pressure baroreceptors)> Hypothalamus> posterior pituitary> secrete ADH
29
Q

What are the 5 actions of ADH?

A
  1. Last 1/3 of distal tubule and CD increased water permeability d/t insertion of AQP
  2. UT upregulated in ascending limb and CD> urea recycling
  3. Vasonconstriction
  4. Incraesed TAL Na/K/2CL pumping
  5. Possible thirst mediation
30
Q

What happens if the ADH mechanism fails?

A

Central diabetes insipidus

No plasma vasopressin>
increased urine flow and thirst

31
Q

What happens if ADH is overactive?

A

Syndrome of Inappropriate ADH secretion

Plasma ADH high>
reabsorb water like crazy>
chronically hypervolemic

CRAAB 7 (4 decks)

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