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+ CAPS 301: Respiratory, Renal, GI, Endocrinology, Reproduction > Urine Concentration and Dilution > Flashcards

Urine Concentration and Dilution Flashcards

1
Q

What is the renal medullary osmotic gradient?

A

gradient in renal medulla of increasing osmolality from base (corticomedullary junction) to apex (papilla tip)

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2
Q

What does countercurrent multiplication do?

What structures are involved?

A

establishes/generates medullary osmotic gradient

mechanism involves renal tubule and surrounding interstitium

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3
Q

What does countercurrent exchange do?

What structures are involved?

A

maintains medullary osmotic gradient

mechanism involves vasa recta (in vasculature of medulla) and surrounding interstitium

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4
Q

What does the osmotic gradient do?

A

allows for production of hyperosmotic urine

makes urine osmolality > plasma osmolality

tubule can become super concentrated without affecting plasma concentration

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5
Q

Why is the osmotic gradient important?

A

allows for large excretion of solutes with minimal loss of H2O

if we aren’t able to concentrate our urine to eliminate all the waste products we need to get rid of, we would lose tons of water, and would have to drink water all day long

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6
Q

What is concurrent flow?

A
  • same direction
  • best possible exchange with parallel flow is 50%
  • gradient driving diffusive transport lessen progressively and is ultimately lost
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7
Q

What is counterconcurrent flow?

A
  • opposite direction
  • nearly complete (100%) transfer occurs anti-parallel flow
  • donor flow (high temperature or electrochemical gradient) is always entering a region where acceptor flow (low temperature or electrochemical gradient) is lower
  • thus, gradient that drives flux never collapses
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8
Q

What is countercurrent multiplication driven by?

A

active Na+ reabsorption in TAL

main contributor to establishing gradient

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9
Q

What structures does urine concentration and dilution involve?

A

coordinated function of all segments from loop of Henle (DTL) to collecting duct (IMCD)

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10
Q

What do transport and permeability properties along nephron allow?

A
  • generation of medullary osmotic gradient

- regulation of urine osmolality

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11
Q

Countercurrent Multiplication

What is the TAL important for?

A

active Na+ reabsorption (transport)

main motor that drives generation of osmotic gradient in medulla

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12
Q

Countercurrent Multiplication

What is the ATL important for?

A

important for urea handling – changes in handling impact establishment of gradient in deeper region, closer to apex

(absent in short loop nephrons)

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13
Q

Segments of Tubule with Active Na+ Transport

A 
PT (++)
DTL (0)
ATL (0)
TAL (++)
DCT (+)
CCD (+)
IMCD (+)
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14
Q

Segments of Tubule Permeable to H2O?

A 
PT (++)
DTL (++)
ATL (0)
TAL (0)
DCT (+AVP)
CCD (+AVP)
IMCD (+AVP)
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15
Q

Segments of Tubule Permeable to NaCl?

A 
PT (+)
DTL (0)
ATL (+)
TAL (0)
DCT (0)
CCD (0)
IMCD (0)
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16
Q

Segments of Tubule Permeable to Urea?

A 
PT (+)
DTL (+)
ATL (+)
TAL (0)
DCT (0)
CCD (0)
IMCD (+AVP)
17
Q

Can H2O and Na+ move when descending loop of Henle?

A

(DTL)

H2O can move but Na+ cannot

18
Q

Can H2O and Na+ move when ascending loop of Henle?

A

(ATL)

Na+ can move but H2O cannot

19
Q

What does active Na+ reabsorption in TAL separate?

A

separates H2O from solutes

20
Q

Permeabilities of which segments of the tubule are modifiable by hormones (AVP)?

A

distal tubule and onwards

  • involved in determining how much H2O permeability there is in the tubule region
  • determines urea permeability in collecting duct
21
Q

What is the loop of Henle of a short loop nephron composed of?

A

thin descending limb – H2O permeable, Na+ impermeable

thick ascending limb – H2O impermeable, Na+ permeable

(ATL absent)

22
Q

Countercurrent Multiplication – Mechanism

A

see notes

23
Q

What does urea handling do?

What structures are involved?

A

contributes to generation of medullary osmotic gradient in long-loop nephrons

  • ATL contributes to increase in osmotic gradient, especially in inner medullary region
  • start to dilute tubular fluid as we move out of that region
24
Q

Ultimately, what are changes we see in osmolality of interstitium due to?

A

primarily due to Na+ movement occurring as a response to what we see with urea transport

passive Na+ transport contributes to inner medullary gradient that’s occurring in response to urea transport that’s occurring in ATL

NO NA+ ACTIVE TRANSPORT – TAL ONLY

25
Q

Where is the most concentrated portion of the interstitium?

A

peak (apex)

26
Q

Which segments of the tubule are impermeable to urea?

A

TAL
DCT
CCD
OMCD

27
Q

Urea Handling – Mechanism

A

see notes

28
Q

What are the two structures involved in countercurrent exchange?

A

descending vasa recta

ascending vasa recta

29
Q

Countercurrent Exchange

Descending Vasa Recta – What is the gradient?

A

plasma_osmolality < interstitium_osmolality

gradient for:

  • solutes to move from interstitium to plasma
  • H2O to move from plasma to interstitium
  • (both contribute to concentrating plasma)

loss of H2O and gain of solute contributes to increase in osmolality

30
Q

Countercurrent Exchange

Ascending Vasa Recta – What is the gradient?

A

plasma_osmolality > interstitium_osmolality

gradient for:

  • solutes to move from plasma to interstitium
  • H2O to move from interstitium to plasma
  • (both contribute to diluting plasma)

gain of H2O and loss of solute contributes to decrease in osmolality

31
Q

Countercurrent Exchange

Why is the U-shaped design of the vasa recta important?

A

critical for preventing washout of medullary osmotic gradient

hypothetical straight tube exchanger:

  • loss of H2O from vessel as we move into more concentrated regions
  • movement of solute into vessel as we move into more concentrated regions
  • problem: plasma leaving would be hyperosmotic – will make you very thirsty
  • problem: will dilute concentration we’ve worked hard to establish in this region

+ CAPS 301: Respiratory, Renal, GI, Endocrinology, Reproduction (32 decks)

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