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Renal Final > 3. Mechanisms to Adjust Urine Concentration > Flashcards

3. Mechanisms to Adjust Urine Concentration Flashcards

1
Q

How is sodium reabsorbed in the TAL? How much is reabsorbed?

A

Ka,K,2Cl cotransport
35-40%
*there is also a Cl/Na cotransport but not affected by diuretics. Leaky K channels also important here

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2
Q

How is sodium reabsorbed in the early distal convoluted tubule? How much is reabsorbed?

A

Na,Cl cotransport

5-8%

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3
Q

How is sodium reabsorbed in the LDCT and CD? How much is reabsorbed?

A

Luminal Na membrane channel

2-3%

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4
Q

What is the luminal potential in the Proximal tubule?

A

+/- 2 mV

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5
Q

What is the luminal potential in the TAL? why?

A

+6 to +10 mV because of K leak channels and tight junctions dont allow Cl through and electroneutrallity is more difficult to maintain

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6
Q

What is the luminal potential in the Distal tubule? why?

A

-70 mV

Cl is left behind

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7
Q

The descending limb of henle is freely permeable to ______ and impermeable to ______

A

Water

Na,Cl

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8
Q

What is the thick ascending limb permeable and not permeable to?

A

Permeable to Na/K/2Cl through active cotransport

ALWAYS impermeable to water

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9
Q

What part of the nephron is considered the diluting segment?

A

Thick segment, it dilutes the urine and concentrates the renal medullary interstitium

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10
Q

What drives paracellular reabsorption of K, Ca, and Mg in the TAL?

A

K leaky channels
Makes the tubular urine + and thus driving the cations to be reabsorbed by paracellular diffusion
Major site for reabsorption of the cations
*there is also a Cl/Na cotransport but not affected by diuretics. Leaky K channels also important here

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11
Q

What is the major site of physiological control of salt and water balance?

A

Late DCT and collecting duct

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12
Q

What does aldosterone stimulate?

A

Na reabsorption, K secretion, H secretion in the late DCT and CD

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13
Q

ANP inhibits Na reabsorption where?

A

medullary collecting duct

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14
Q

ADH stimulates water reabsorption where?

A

Late DCT and CD

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15
Q

How does aldosterone increase Na reabsorption in principal cells?

A

Goes to the nucleus and causes proteins to be transcribed and inserted into the principal cell membrane. Incorporation of Na channels in luminal membrane and Na,K ATPase ion pumps in basolateral membrane. Sodium comes in and K is exchanged to maintain electroneutrallity

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16
Q

How does ADH increase water permeability ?

A

In late distal tubule and collecting duct, it attaches to V2 receptors and inserts aquaporin channels on the tubular lumen side

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17
Q

What part of the kidney has the highest solute concentration? why?

A

Inner medulla

Because of low blood flow

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18
Q

The countercurrent multiplier mechanism requires integrated function of what 3 components?

A

Descending, ascending limbs of henle loop
Vasa recta capillaries
Collecting ducts

19
Q

Why is the countercurrent multiplier mechanism important?

A

It allows us to concentrate solute in medullary interstitium to pull water out of tubular. Enables kidneys to excrete highly concentrated urine, and conserve water during periods of dehydration

20
Q

How is sodium reabsorbed in the proximal tubule? How much is reabsorbed?

A

Cotransport with glucose, amino acids, phosphates
Antiporter with H
50-55%

21
Q

How does the medullary interstitium become hyperosmolar?

A

Na gradient that the Na,K, Cl cotransporter establishes in TAL

22
Q

The countercurrent multiplier mechanism is augmented by action of what?

A

ADH in CD

23
Q

What increases the BUN/Creatine ratio?

A

Urea, if we are dehydrated and need to concentrate the urine more, more urea will be reabsorbed in Proximal tubules and under direction of ADH, promote urea from inner medullary collecting duct

24
Q

Does the vasa recta pull a lot of solutes out of the medullary interstitium?

A

No, the slow flow allows for most of the solutes to remain in the interstitium to help concentrate the urine. They do not disturb the high concentration

25
Q

The countercurrent multiplier system contributes to half of the high concentration in the medullary insterstitium. what contributes the other half?

A

Urea recycling

26
Q

What are the tubular fluid osmolalities at the distal end of each segment of a juxtamedullary nephron during antidiuresis?

A 
High presence of ADH so
PCT - 300 (no change)
DL - 1200 (no change)
TAL - 100 (no change)
DCT - 150
CCD - 300
MCD - 1400
27
Q

What are the tubular fluid osmolalities at the distal end of each segment of a juxtamedullary nephron during diuresis?

A 
PCT - 300 (no change)
DL - 1200 (no change)
TAL - 100 (no change)
DCT - 90
CCD - 80
MCD - 50
28
Q

What part of the nephron is effected by thiazide diuretics?

A

Na/Cl cotransport in DCT

29
Q

In a well hydrated person, CD is ________ to water

A

impermeable

30
Q

Chloride reabsorption is always linked to what?

A

Na reabsorption either directly or indirectly

31
Q

How much waste does the body generate a day?

A

600 mOsm/day

32
Q

How much urine must be excreted a day?

A

0.5 L/day

33
Q

Osmolar clearance =

A

(Cosm) = Uosm * (V/Posm)

34
Q

What is free water clearance?

A

excretion of water in excess of amount needed to excrete isosmotic urine
i.e. excretion of solute-free water by kidneys

35
Q

CH20 =

A

V-Cosm

36
Q

If Uosm > Posm then CH20 is what?

A

Positive and pure water is cleared from the body

37
Q

If Uosm > Posm then CH2O is what?

A

negative; pure water is retained

38
Q

What is fractional excretion?

A

the fraction of the filtered load of a substance that is excreted in urine

39
Q

Fex = ?

A

(UxV)/(PxGFR)

Amt excreted/amt filtered

40
Q

If creatinine clearance = GFR what is Fex = to?

A

(UxPcr)/(PxUcr)

41
Q

If FE Na is below 1% then…

A

Prerenal and AGN (acute glomerular nephritis) - Na avidly reabsorbed. (edema)

42
Q

FeNa is greater than 2% then….

A

ATN and intrarenal disease. cant reabsorbed Na

43
Q

What do diuretics do?

A

Decrease ADH
Prevent water reabsorption in CCD and OMCD
Prevents concentration of urine

Renal Final (8 decks)

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