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Physio II (Exam 3) > Topic 9: Urine Concentration > Flashcards

Topic 9: Urine Concentration Flashcards

1
Q

Solute concentration & osmolarity determined by:

A

Total amount of solute / Volume of extracellular fluid

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2
Q

Changing extracellular water has what effect on solute concentration and osmolarity?

A

significant

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3
Q

Body water determined by:

what two things?

A 
Fluid intake (controlled by thirst)
Renal excretion of water (controlled by changing GFR and tubular reabsorption
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4
Q

If ECF solute concentration increases, kidneys hold onto water so ECF volume ____ diluting ___ solutes

A

increases

ECF

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5
Q

If ECF solute concentration decreases, kidneys excrete ___ water so ECF volume ____ concentrating ECF ____

A

more
decreases
solutes

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6
Q

Assuming normal solute intake and metabolic

production, what two things will remain relatively constant?

A

Solute excretion will remain relatively constant each day
Total amount of solute in ECF relatively constant

(Quantity of water excreted each day adjusted to keep solute concentration of ECF constant)

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7
Q

What is the concept of holding onto water when there is increased ECF osmolarity?

A

Holding onto water will spread the total amount of solute over larger volume of water thus decreasing solute concentration of ECF

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8
Q

Posterior pituitary responds to changes in ECF osmolarity by changing what?

A

ADH release

Increased ECF osmolarity results in an increased release of ADH

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9
Q

Quantity of water excreted controlled by what?

A

[ADH]
Increased [ADH] results in an increase in water
reabsorption by the distal tubule & collecting duct

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10
Q

Changes in water reabsorption control urine volume and _____

A

urine solute concentration

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11
Q

Increased water reabsorption means less water enters collecting duct decreasing overall ____
Normal amount of excreted solutes now dissolved in ____production of small amounts of ____________
MAX CONCENTRATION Solute to urine

A

volume of urine-
less volume
very concentrated urine

At max concentration: 500 mls/day with osmolarity of 1200 to 1400 mOsm/Liter

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12
Q

Increase in [ADH] produces an increase in water permeability where?

A

distal tubule and collecting duct

  • increased water reabsorbed
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13
Q

Increase in water reabsorption decreases water volume in urine so total excreted solute is what?

A

spread out over less water volume increasing urine osmolarity (less urine with higher osmolarity)

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14
Q

Max amount of dilute urine can excrete

A

20 liters/day with minimal concentration of 50 mOsm/Liter

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15
Q

Water Diuresis: Drink 1 liter of water
Changes begin to occur within?
Slight increase in ___ excretion
Slight decrease in _____ osmolarity

A

within 45 minutes
solute
plasma

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16
Q

Water Diuresis: Drink 1 liter of water
Large decrease in urine____
Large increase in urine _____

A

osmolarity [600 mOsm/L to 100 mOsm/L]

output [1 ml/min to 6 mls/min]

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17
Q

To produce dilute urine, what has to happens faster than what?

A

solute has to be reabsorbed at a faster rate than water

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18
Q

Producing Dilute Urine
Proximal Tubule
Solute & water reabsorbed ____

A

at same rate

No change osmolarity

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19
Q

Producing Dilute Urine
Descending Loop
Water reabsorbed how?
what happens to osmolarity?

A

following gradient into hypertonic interstitial fluid

Osmolarity increases 2 to 4 times osmolarity of plasma

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20
Q

Producing Dilute Urine
Ascending Loop
what is reabsorbed?
what happens to tubular osmolarity?

A

Sodium, potassium, chloride reabsorbed
No water reabsorbed regardless of [ADH]
Tubular osmolarity decreases to 100mOsm/L
1/3 osmolarity of plasma

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21
Q

Distal Tubule & Collecting Tubules
water reabsorped based on what?
tubular osmolarity?
Max dilution?

A

Variable amount of water reabsorption based on [ADH]
No ADH=No water reabsorption
Solute reabsorption continues further decreasing tubular osmolarity
Max dilution of 50 mOsm/Liter

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22
Q

Excretion of Concentrated Urine
High Concentration of what hormone?
reabsorption of water and solutes amount?

A

High Antidiuretic Hormone concentration
Reabsorb normal amounts of solute
Increased water reabsorption in late distal tubule and collecting ducts

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23
Q

Normal 70 kg person needs to excrete

___ mOsm/day of waste?

A

600 mOsm/day

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24
Q

If the only water you have is sea water and you drink 1 Liter of sea water each day you need to remove 1200 mOsm of salt PLUS 600 mOsm of waste each day
what does this mean?

A

Means you are losing 500 mls of volume each day which means you quickly become dehydrated

25
Q

What two things are needed to create concentrated urine?

A

High concentration of ADH
(Increased permeability of distal tubules & collecting ducts)
High osmolarity of renal medullary interstitial fluid
(Water reabsorption is driven by osmotic forces
Interstitial osmolarity setup by the countercurrent mechanism)

26
Q

Interstitial osmolarity setup by what mechanism?

A

countercurrent mechanism

27
Q

Interstitial fluid surrounding collecting ducts normally _____ which provides the gradient for ____ reabsorption

A

hyperosmotic

water

28
Q

Countercurrent Mechanism

Made possible by anatomical arrangement of what 3 parts of the nephron?

A

Loops of Henle
Especially the loops of the juxtamedullary nephrons that go deep into the renal medulla, 25% of total nephrons
Corresponding vasa recta capillaries
Parallel the loops
Collecting ducts
Carry urine down through the renal medulla

29
Q

Countercurrent Mechanism: Urine osmolarity cannot exceed osmolarity what?

To produce concentrated urine of 1200mOsm/Liter the osmolarity at the bottom of the renal medulla must be at least?

A

of interstitial fluid in renal medulla

least 1200 mOsm/L

30
Q

Creating A Hyperosmotic Renal Medulla: Active ion transport & co-transport __what ions?___ out of thick portion of ascending loop into medullary interstitium.
Able to create a____ mOsm concentration gradient

Thin descending limb ____ permeable to water–As water is reabsorbed, osmolarity of tubular fluid ___ until it matched osmolarity of ____

A

(Na+, K+,Cl-)

200 mOsm

highly

decreases

interstitial fluid

31
Q

Creating A Hyperosmotic Renal Medulla: must accumulate solute where?

A

Must accumulate solute in the medulla

Once solute accumulated, hyperosmolarity maintained by a balanced inflow/outflow of water and solutes

32
Q

Collecting duct water permeability

depends on what hormone?

A

ADH concentration

33
Q

Medullary collecting duct _____ permeable to water

A

highly permeable to water but only small % of water is left
Since amount of water relatively small, water permeability is high, and vasa recta able to carry water away, osmolarity inside collecting duct quickly equilibrates with interstitial osmolarity

34
Q

Why is Osmolarity of tubular fluid entering distal tubule is LOW?

A

NO water permeability in thick ascending segment

Minimal water permeability in late distal tubule

35
Q

Urea accounts for what % of total osmolarity of inner renal medulla

A

40 to 50%

36
Q

Normally excrete what % of filtered urea load?

A

50
Excretion rate depends on:
Plasma concentration &GFR

37
Q

Thick Ascending Loop, Distal Tubule,
Cortical and Outer Medullary Collecting
Duct Urea Permeability?

A

Urea not permeable in all but collecting duct

In collecting duct urea concentration
rises quickly as large volume of water is
reabsorbed

38
Q

Inner Medullary Collecting Duct
Urea permeability increases so urea will diffuse out of duct into interstitial space
Facilitated by what urea transporters ?

A

UT-A1
and UT-A3
UT-A3 activated by ADH

39
Q

Inner Medullary Collecting Duct

Some of the urea is secreted back into where? why?

A

the thin segments of the loop of Henle
Recirculation of urea (from collecting duct back into the loop of Henle) works to increase concentration of urea in the urine and inner medullary interstitium

40
Q

In Vasa Recta - How to meet metabolic needs without washing out concentrated solute???

A

Medullary blood flow very low (5% of total renal flow)

Vasa recta function as countercurrent exchangers

41
Q

Vasa Rects - starts where and goes to where?

A

Start at cortical-medullary boundary
Descend all way through medulla parallel to
medullary loops of Henle

42
Q

Vasa Recta permeability to what? where is fluid moving?

A

Highly permeable to solute (except protein)

As vasa recta descend through medulla exposed to ever increasing solute concentration of interstitium
Water follows concentration gradient from blood to interstitium
Solute follows concentration gradient from interstitium to blood
As vasa recta ascend through medulla, now
exposed to decreasing interstitial solute
concentration
Water now follows gradient into blood
Solute follows gradient out of blood

43
Q

Vasa Recta carries what?

A

Carry away the amount of solute and water as is absorbed FROM the medullary tubules

44
Q

Increasing the blood flow through the vasa recta will do what to solute concentration?

A

“washout” solute thus reducing the overall

solute concentration in the renal medulla

45
Q

What affects BF thru Vasa Recta? (3)

A

–Some vasodilators
—Large increases in arterial blood pressure
Flow through renal medulla affected more than flow through other areas of kidney
—Decreased medullary osmolarity means less reabsorption of water more urine output

46
Q

Proximal tubule
% of filtered electrolytes are reabsorbed along with proportional amount of water?
Filtrate flow?

A

65%
goes from 125 mls/minute to 44 mls/minute

NO ADH EFFECTS!

47
Q

Descending Loop - tubular flow rate?

Does ADH affect?

A

25 mls/minute tubular flow
Low levels of ADH

Urea absorption from collecting duct reduced so interstitial osmolarity also reduced

48
Q 
Thin Ascending Loop
Tubular Flow rate?
Permability to Water/solutes?
Osmolarity?
ADH affect?
A 
No change in tubular flow (25 mls/minute)
No water permeability
Some reabsorption of sodium, chloride
Some diffusion of urea into tubule
Net result–decrease in osmolarity
Yes
49
Q 
Thick Ascending Loop
Tubular Flow rate?
Permability to Water/solutes?
Osmolarity?
ADH affect?
A

No change in tubular flow (25 mls/minute)
No water permeability
Active reabsorption of sodium, chloride, potassium (Large amount reabsorbed)
Tubular osmolarity continues to decrease 100 to 200 mOsm/L
YES

50
Q 
Early distal Tubule
Tubular Flow rate?
Permability to Water/solutes?
Osmolarity?
ADH affect?
A

Diluting segment
No change in tubular flow (25 mls/minute)
No water permeability
Active reabsorption of sodium, chloride, potassium, (Large amount reabsorbed)
Tubular osmolarity continues to decrease 50 mOsm/L

51
Q

Late Distal Tubule / Cortical

Collecting Tubules - LOW ADH effect?

A

LOW: Minimal water reabsorption and further decrease in osmolarity (ions still being reabsorbed)
Tubular flow still around 25 mls/minute

52
Q

Late Distal Tubule / Cortical

Collecting Tubule - HIGH ADH effect?

A

HIGH:High water reabsorption so osmolarity increases

Tubular flow drops to 8 mls/minute

53
Q

Medullary Collecting Duct -HIGH ADH effect?

A

HIGH [ADH]: High water permeability / reabsorption–Solute concentration increases (especially of urea)
Tubular flow drops to 0.2 mls/minute

54
Q

Medullary Collecting Duct - LOW ADH Effect?

A

LOW [ADH]: Low water permeability–Solute concentration drops as urea is reabsorbed
Slight decrease in tubular flow to 20mls/minute

55
Q

Increased flow through vasa recta does what to Meduallary Collecting Duct reabsorption?

A

Increased flow through vasa recta decreases overall solute concentration of interstitial fluid which decreases water reabsorption

Not able to concentrate urine to as high a level or reabsorb as much water

56
Q

under normal conditions sodium and chloride

make up what % of interstitial solute at max concentration

A

50 to 60%

57
Q

Dehydration / low sodium intake–stimulate release of what?

A

angiotensin II and aldosterone

58
Q

Kidneys can produce large quantities of dilute urine without changing sodium excretion
TRUE or FALSE?

A

TRUE

Changing [ADH] which changes water reabsorption in later segments of nephron without changing sodium reabsorption

Physio II (Exam 3) (6 decks)

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