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Physiology- Renal > Renal 7: Renal Mechanisms for Concentration/Dilution of Urine > Flashcards

Renal 7: Renal Mechanisms for Concentration/Dilution of Urine Flashcards

1
Q

Where is the major site in which solute and water are separated?

A

Henle’s Loop

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2
Q

What value is the plasma osmolality held at?

A

300 mOsm/Kg H2O

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3
Q

What is antidiuresis?

A

state of dehydration that is typical for land dwellers.

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4
Q 
What is the state of the following during antidiuresis?
ADH
water reabsorption
urea reabsorption
urine
A

Increased
Increased
Increased
Decreased (low volume high concentration urine)

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5
Q

What is diuresis

A

state of over-hydration. atypical and caused by administration of hypotonic solutions.

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6
Q 
What is the state of the following during water diuresis?
ADH
water reabsorption
urea reabsorption
urine
A

Decreased
Decreased
Decreased
Increased (high volume, low concentration urine)

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7
Q

What is the osmolality of the following with respect to the plasma?
renal cortex
outer medulla
inner medulla

A

Renal Cortex: Isotonic
Outermedulla: mild hyperosmolality
Inner Medulla: strong hyperosmolality

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8
Q

What are the 3 major species and their % contribution to the gradient that contribute to the inner medullary hyperosmolality?

A

Na+(25%) Cl-(25%) urea (50%)

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9
Q

Rank the following from most to least hyperosmotic with respect to plasma:
outer medulla
inner medulla
renal cortex

A

inner medulla > outer medulla > cortex

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10
Q

What are the 3 mechanisms that generate and regulate medullary hyperosmolality?

A

Countercurrent Multiplier: generates initial osmotic gradient
Urea Cycle: Strengthens osmotic gradient
Countercurrent Exchanger: maintains osmotic gradient

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11
Q

What happens to the osmolality of the medullary interstitium during water diuresis?

A

reduced due to increased vasa recta blood flow and entry of some urea into collecting duct
No ADH so collecting duct is impermeable to water

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12
Q

What happens to the osmolality of the medullary interstitium during antidiuresis

A

Max ADH levels -> collecting duct highly permeable to water

Medullary interstitial gradient maxed

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13
Q

What is the countercurrent multiplier?

A

countercurrent flow in the 2 limbs of Henle’s loop that results in differential fluid and solute movements, generating vertical osmotic gradients

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14
Q

The thin descending loop of Henle has high/low water permeability, high/low salt permeability, and water/salt moves out of tubule.

A

high water permeability
low salt permeability
water moves out of tubule

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15
Q

The thin ascending loop of Henle has high/low water permeability, high/low salt permeability, and water/salt moves out of tubule

A

low water permeability
high salt permeability
salt moves out of tubule

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16
Q

What is the difference in salt movement between the thin and thick ascending limbs?

A

Thin: passive movement
Thick: active salt pumping

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17
Q

Where is the most active salt pumping site in the kidney?

A

Thick ascending loop of Henle

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18
Q

What part of the loop of Henle has high water perm. but low salt. perm.

A

Thin descending loop

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19
Q

What part of the loop of Henle has low water perm. but high salt. perm

A

Thin ascending loop

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20
Q

The thick ascending loop of Henle is diluting/concentrating segment. It becomes hyper/hypo-osmotic

A

Diluting segment
Hypoosmotic

Impermeable to water

21
Q

What occurs in the distal tubule?

A

increased water permeabilty and salt transport -> reabsorption

22
Q

What happens in the lower collecting duct but not the upper collecting duct?

A

Urea reabsorption

23
Q

In the collecting duct, salt reabsorption is active/passive, and water reabsorption is active/passive.

A

active salt reabsorption

passive water reabsorption under ADH control

24
Q

What occurs in the collecting duct?

A

active salt reabsorption and passive water reabsorption

25
Q

What hormone regulates urea and water permeability in the lower collecting duct?

A

ADH

26
Q

What is the path of urea from the upper collecting duct all the way around?

A 
upper collecting duct (impermeable to urea)
lower collecting duct (urea perm regulated by ADH
inner medulla
ascending vasa recta
outer medulla
descending thin loop of Henle
tubular system (recycled through)
lower collecting duct
END OF 1 CYCLE
27
Q

What are the 3 purposes of high medullary urea concentration?

A
  1. does not set up an osmotic gradient for the reabsorption of H2O
  2. protects vasa recta RBCs against crenation in a hyperosmotic environment
  3. sets up a gradient for urea to be excreted in low-volume urine
28
Q

How does urea clearance vary with urinary flow rate?

A

directly, but passively and nonlinearly

More urea is lost to urine with increases in urinary flow rate

29
Q

At what flow rate does urea clearance plateau? What does this mean for GFR?

A

flow rate greater than 10 mL/min. Then urea clearance estimates GFR

30
Q

Describe the countercurrent exchanger

A

Water, salt, and urea move passively across vasa recta capillary walls in renal medulla.

31
Q

What happens in the descending vasa recta

A

water moves out of capillary

salt and urea move into capillary

32
Q

What happens in the ascending vasa recta

A

water moves into capillary

salt and urea move out of the capillary

33
Q

At the end, the vasa recta exits the medulla with slightly more/less solutes than water.

A

slightly more solutes than water

34
Q

What is water shunt with respect to countercurrent exchanger?

A

Excess water kept out of deep medulla

35
Q

What is solute trapping with respect to countercurrent exchanger?

A

Excess solutes kept in lower medulla

36
Q

What kinds of factors wash out the medullary gradient?

A

anything that increases the vasa recta blood flow -> washes out the medullary gradient and causes increased urine flow

^ vasa recta flow => v medullary osmolality ]> ^ urine flow (V)

37
Q

How long does it take for the medullary osmotic gradient to be reestablished after it has been diluted?

A

few days (3 days)

38
Q

What are the requirements for renal medullary hyperosmolarity?

A

long loops of henle
blood and urine flow
active salt pumping (TAL, DT, CD)
differential permeabilities of salt and water in thin ascending and descending loops

39
Q

How do you calculate osmolar clearance?

A

C osm (ml/min) = Uosm * V/Posm = V* (Uosm/Posm)

40
Q

What is the condition of urine when Uosm/Posm is more than 1?

A

concentrated urine -ADH antidiuresis

41
Q

What is the condition of urine when Uosm/Posm is less than 1

A

dilute urine (water diuresis)

42
Q

What is free water clearance (Ch2o)?

A

amount of pure water kidney adds to urine -> dilutes urine below osmolality of blood
(-) if kidney subtracts pure water from urine -> concentrate urine above blood osmolality

43
Q

How do we calculate water clearance?

A

Ch2o = V-Cosm

44
Q

What is negative free water clearance (-Ch2o)?

A

Uosm >Posm : dark amber urine

Water stolen from urine by kidney

45
Q

What is positive free water clearance (Ch2o)

A

Uosm <Posm: pale dilute urine

Water is added to urine by kidney

46
Q

What is tubular conservation of water?

A

TCh2o = -Ch2o

47
Q

What is/are the endogenous factors controlling tubular water movement?

A

ADH

48
Q

What are the exogenous factors that contribute to controlling tubular water movement?

A

Diuretics: furosemide (most potent, potassium wasting)
spironolactone: less potent, potassium sparing

Physiology- Renal (8 decks)

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