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Physiology > Renal 6 - Urine Concentration and Dilution > Flashcards

Renal 6 - Urine Concentration and Dilution Flashcards

1
Q

normal function requires ECF osmolarity of:

A

300 mOsm

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2
Q

what are the mechanisms that maintain water balance

A
  • elimination of excess water by excreting a dilute urine
  • conservation of water by excreting a concentrated urine
  • renal feedback mechansims that control extracellular fluid sodium concentration and osmolarity
  • thirst and salt appetite mechanisms that determine the intakes of water and salt
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3
Q

what controls how concentrated/dilute urine is

A

ADH

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4
Q

what is the maximal and minimal urine concentrations

A

-max: 1200 mOsm
-min: 50 mOsm

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5
Q

urine formed without ADH is ____

A

dilute

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6
Q

describe how urine is dilute without ADH

A
  • filtrate is isosmotic in PT
  • filtrate becomes hyperosmotic in tDL bc water reabsorption
  • filtrate becomes hypoosmotic in TAL and early DT bc solute reabsorption
  • filtrate stays hypoosmotic in absence of ADH through DT and CD
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7
Q

what does ADH do

A

increases water permeability of DT and CD
-causes large volume of water diffusion into interstitium
- enters capillaries via vasa recta and removed
-creates concentrated urine

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8
Q

what is obligatory urine volume

A

the maximal concentrating ability of the kidney dictates how much urine volume must be excreted each day to rid the body of metabolic waste products and ions that are ingested

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9
Q

what is osmotic load (Definition and number)

A

-solutes ingested and wastes produced by metabolism
- 600 mosmol/day

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10
Q

how do you calculate OUV

A

OUV = osmotic load/ max urine concentration

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11
Q

what are the requirements for excreting a concentrated urine

A
  • high levels of ADH
  • hyperosmotic medullary ISF
  • high interstitial fluid osmolarity
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12
Q

what does hyperosmotic medullary ISF set a gradient for

A

water reabsorption

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13
Q

what does hyperosmotic medullary ISF require

A

counter current multiplier system

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14
Q

what is a hyperosmotic medullary ISF a function of

A

juxtamedullary nephrons
-long loop of henle
-vasar recta
-slow flow rate

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15
Q

what is high interstitial fluid osmolarity a result of

A
  • active transport of Na+ and other ions by ascending limb of LOH
    -active transport of ions from CD into interstitium
  • facilitated diffusion of urea by inner medullary CD
    -movement of only small amounts of water into medullary interstitium
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16
Q

summarize filtrate handling along the nephron

A

-continuous delivery of NaCl from PCT into loop of henle
- concentration of filtrate by water reabsorption by descending limb of henle
- continuous reabsorption of solute into interstitium by TAL
- Na+ K+ pumps in CD pump Na+ into interstitium to increase osmolarity and form interstitial osmolar gradient

17
Q

what happens in the distal tubule and collecting duct in the absence of ADH

A
  • reabsorb solute
  • little to no water reabsorption
18
Q

what happens in the distal tubule and collecting duct in the presence of ADH

A
  • DT and CD become highly permeable to water and reabsorb much water into cortical interstitium
  • medullary CD cells reabsorb water but overall amounts much lower
    -reabsorbed water carried away by vasa recta
19
Q

what is urea and what makes it

A
  • waste product of protein metabolism
  • produced continuously by liver
20
Q

how much urea is excreted

A

normally excrete 20-50% of filtered load

21
Q

is urea toxic

A

no but constitutes an osmotic load that must be excreted

22
Q

what percentage of interstitial osmolarity does urea contribute

A

40-50% (500-600 mOsm/L)

23
Q

what is urea passively reabsorbed by

A

medullary collecting duct cells

24
Q

where is urea secreted and what is required for urea secretion

A
  • secreted into descending limb and thin ascending limb of loop of henle
    -requires ADH
25
Q

what does ADH do in urea secretion

A

concentrated urea in filtrate through water reabsorption in cortical and medullary collecting ducts

26
Q

what does the loop of henle do with urea

A

activates carries UT-A1 and UT-A3 for the facilitated diffusion of urea by medullary collecting duct cells

27
Q

what does the countercurrent multiplier mechanism depend on

A

anatomical relationships of loop of henle, vasa recta and collecting ducts

28
Q

what percentage of nephrons are juxtamedullary in the countercurrent multiplier mechanism

A

25%

29
Q

how does filtrate in the ascending and descending loops of henle travel in relation to blood flow in vasa recta

A

opposite directions

30
Q

what does the countercurrrent multiplier system do

A

clears reabsorbed water so it does not dilute the medullary interstitial fluid

31
Q

what happens in the countercurrent multiplier system is blood vessels are not close to each other

A

heat is lost to the environment

32
Q

what does the countercurrent heat exchanger allow for

A

warm blood entering the limb to transfer heat directly to blood flowing back into the body

33
Q

what does the vasa recta do for the medullary interstitium

A

preserves hyperosmolarity

34
Q

describe countercurrent exchange in the vasa recta

A
  • filtrate enters the descending limb and becomes more concentrated as it loses water
  • blood in the vasa recta removes water leaving the loop of henle
  • the ascending limb pumps out Na+ K+ and Cl- and filtrate becomes hyposmotic
35
Q

what is % waater reabsorbed in the PT and filtrate osmolarity

A
  • 70%
  • isosmotic
36
Q

what is water % reabsorbed in the descending LOH and filtrate osmolarity

A

20%
- hyperosmotic

37
Q

what is % water reabsorbed in the ascending limb of LOH and filtrate osmolarity

A
  • 0%
  • hyposmotic
38
Q

what is % water reabsorbed in the late DT and CCD and filtrate osmolarity

A
  • % variable based on ADH
  • variable osmolarity based on ADH
39
Q

what is % water reabsorbed in the MCD and filtrate osmolarity

A
  • both variable based on ADH

Physiology (41 decks)

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