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556 - Physiology & Pathophysiology II > Exam 9 - Urine Concentration & Osmolarity Control > Flashcards

Exam 9 - Urine Concentration & Osmolarity Control Flashcards

1
Q

Osmolarity determined by

A
  • total solute

- volume of ECF

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2
Q

Body water determined by

A
  • fluid intake

- renal excretion of H2O…GFR and reabsorption

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3
Q

If ECF [solute] increases…

A
  • Kidneys hold onto more H2O
  • ECF solutes are diluted
  • Opposite is also true
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4
Q

Water / solute changes to maintain homeostasis

A
  • solute excretion same each day
  • solue [ ] in ECF stays same
  • changes in water excretion adjusted to keep ECF constant
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5
Q

Posterior pituitary and ECF osmolarity

A
  • ECF osmolarity increases…. PP releases more ADH

- more ADH….more water reabsorption in distal and collecting

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6
Q

Urine volume and [ ]

A
  • more water uptake…less urine volume…
  • NORMAL amount of solute now in less water…
  • produce small amount of very concentrated urine
  • opposite also true
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7
Q

Max urine [ ]

A
  • 500 mls/day

- 1200-1400 mOsm/L

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8
Q

Min urine [ ]

A
  • 20 L/day
  • 50 mOsm/L
  • Low [ADH]
  • drop water reabsorption from 124 to 111 mls/min
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9
Q

Normal GFR

A

125 mls/min

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10
Q

Normal urine output

A

1 ml/min

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11
Q

Drink 1 L of water

A
  • decrease in ADH release
  • changes in 45 min
  • slight increase in solute excretion…due to drop in bulk flow/leak back
  • slight decrease in plasma osmolarity…due to ingestion of H2O
  • large decrease in urine osmolarity…600-100
  • large increase in urine output…1-6
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12
Q

Filtrate Osmolarity = ?

A

Plasma osmolarity

300 mOsm/L

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13
Q

Main mechanism to get dilute urine

A
  • decrease water reabsorption…no change in solute reabsorption
  • increase in ADH
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14
Q

How to increase solute reabsorption

A
  • increase angiotensin/aldosterone
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15
Q

Dilute urine… proximal tubule

A
  • solute and water reabsorbed at same rate
  • no change in osmolarity
  • 300
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16
Q

Dilute urine…descending loop

A
  • water absorbed following osmotic gradient
  • urine [ ] increases 2-4x
  • 300 to 600
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17
Q

Dilute urine…ascending loop

A
  • Na/K/Cl reabsorption
  • No water reabsorption
  • tubular osmolarity drops to 100 by early distal
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18
Q

Dilute urine…distal and collecting

A
  • variable amount of water reabsorbed…depending on ADH
  • Normal solute reabsorption
  • can drop to min of 50 mOsm/L
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19
Q

Obligatory urine volume

A
  • minimum urine needed to excrete waste products
  • normal 70kg person needs to excrete 600 mOsm/day
  • 1200 mOsm/L…max renal osmolarity…max we can get rid of
    • less in renal disease
  • So…..0.5L/day is minimum urine we can excrete
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20
Q

If drinking 1L of 3.5% sea water

A
  • get rid of normal 600 mOsm PLUS 1200 from sea water
  • need to remove 1800mOsm…max is 1200 mOsm/L
  • 1.5 liters need to be removed a day
  • So….losing 500 mls day…get dehydrated
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21
Q

What is needed for high [ ] urine

A
  • high ADH
  • high osmolarity in renal interstitial fluid
    • drives reabsorption too
    • set up by countercurrent mechanism
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22
Q

Vasa recta and [ ] urine

A
  • removes water as it is reabsorbed so that we keep osmolarity gradient which drives water out of tubule into body
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23
Q

Countercurrent mechanism and anatomy

A
  • Long loops of henle in juxtameduallry nephrons (25%)
  • vasa recta help pull away water…parallel to loops
  • collecting ducts…parallel to loops also
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24
Q

Urine osmolarity and IF osmolarity

A
  • urine [ ] cant exceed IF…gradient is what drives movement
  • normal at bottom of loop is 600
  • to get to 1200 (max)…need to move more solute into medulla
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25
Hyperosmotic renal medulla
- made by accumulating solute - maintained by inflow/outflow of water and solutes - out of loop and collecting tubules/ducts - into vasa recta...carry water and solute away to maintain gradient
26
Factors creating hyperosmotic medulla
- Na/K/2Cl transporter out of thick ascending - can get 200 gradient - active transport of ions from duct to medulla - facilitated diffusion of urea from ducts to IF - more solute absorbed in medullary IF than water
27
Process of concentrating urine
1 - pump solute out of ascending...100 mOsm out - urine now more dilute 2 - water diffuses out of descending...100 also - urine now more [ ] on this side...matches IF 3 - [ ] urine disperses throughout loop...over all osmolarity increases 4 - pump solute out of aces ending again...get overall 200 gradient 5 - water diffuses out of descending again... matches IF again 6 - repeats until urine [ ] is 1200 at bottom of medulla
28
Initial [ ] of urine entering distal
- low...100 | - no water reabsorption in ascending
29
Urea and medullary osmolarity
- 40-50% of total osmolarity | - excrete 50% of filtered load
30
Urea and proximal tubule
- 50% of filtered land reabsorbed | - [ ] goes up....more water reabsorbed
31
Urea and thin loop
- descending...[ ] up....water reabsorbed - descending/ascending...[ ] up...secretion of urea into tubule - via UT-A2
32
Urea and thick ascending/distal/tubule/duct
- urea not permeable | - [ ] up in duct as large amounts of water reabsorbed
33
Urea and medulla collecting duct
- urea permeability increases...more urea into IF - via UT-A1 and UT-A3 (A3 activated by ADH) - water still reabsorbed...[ ] of urea still high - some urea back into thin loop via UT-A2 - called urea loop
34
How to feed medulla w/o washing away concentrated solute
- low medulla blood flow....5% of renal flow | - vasa recta act as exchangers
35
Vasa recta characteristics
- permeable to solute...except protein - start at cortical-medullary boundary - as they descend...water out into IF / solute in from IF - as ascend... water into blood from IF / solute out into IF - carry away only enough to maintain gradient...nothing more
36
Increase BF to vasa recta
- will wash out solute - drop solute [ ] in renal medulla Caused by: - vasodilators - large BP increase (small is autoregulated)
37
Change in osmolarity in proximal
- 65% ions reabsorbed - flow goes from 125 to 44 - normal osmolarity
38
Change in osmolarity in descending
- tubular osmolarity matches IF - higher...more so for [ ] urine - high water permeability / low ion - flow is 25
39
Change in osmolarity in thin ascending
- no water permeability - normal reabsorption of ions - drop in osmolarity - flow still 25...no change in water [ ]
40
Change in osmolarity in thick ascending
- no water permeability - large ion absorption....active - osmolarity drops more - flow still 25
41
Change in osmolarity in early distal
- diluting segment - no water out - large amount of ions out - flow still 25
42
Change in osmolarity in late distal / cortical collecting tubule
- osmolarity based on ADH - low ADH...no water reabsorption...flow still 25 - high ADH...water in...flow drops to 8
43
Change in osmolarity in medullary collecting tubule
- depends on ADH - high ADH... high water reabsorb...urea [ ] up...flow 0.2 - low ADH...urea slightly reabsorbed...flow down to 20 only
44
How kidneys can make high [ ] urine
- use urea - contains little/no Na or Cl...even though NaCl make 50-60% - dehydration / low Na intake...increase angiotensin II and aldosterone - kidneys can control urea and NaCl separately
45
How kidneys can make lots of urine w/o Na excretion
- change ADH...only affects H2O
46
Obligatory urine volume dictated by...
Max ability to [ ] urine....normal is 1200 - if kidney function drops....so does ability to [ ] urine
47
Normal Na
142 mEq/L
48
Normal Osmolarity
- 300 mOsm/L | - 291-309 is range...+/- 2 to 3%
49
Control over Na [ ] and osmolarity
- very precise | - important for distribution of H2O between compartments
50
Na and associated ions
94% of extracellular solute - glucose and urea....3-5% - Na not very permeable...large driving force
51
Plasma osmolarity equation
2. 1 x [plasma Na] | 2. 1 x 142 = 298 mOsm/L
52
2 systems that control ECF osmolarity and [Na]
- osmoreceptors - ADH system | - thirst mechanism
53
Osmoreceptor cells
- in anterior hypothalamus - shrink if high ECF...send impulses to PP - PP release ADH
54
Increase in osmolarity....
- increase water permeability in distal tubules/ducts | - more water reabsorbed...Na excreted at normal
55
Drop in BP/ volume
- increase in ADH | - barroreceptors / reflex pathway
56
ADH response to volume / osmotic changes
- small change in osmolarity (1%) trigger ADH release - but low ceiling - CBV must drop 10% to see ADH change - but 15-20% drop in CBV has HUGE change in ADH - not much ceiling
57
Hypoxia
- increase ADH
58
Morphine / Nicotine / cyclophosphamide
Increase ADH
59
Alcohol / Clonidine / Haloperidol
Drop ADH
60
Thirst mechanism
- control fluid intake...fluid loss in sweating, breathing, GI - thirst center in brain...organum vasculosum - stimulates ADH release if thirsty - shuts off before we reach target value...prevent over-hydration - don't want to get into roller coaster situation - stimulated with Na [ ] just 2 mEq above normal
61
Increase in angiotensin II / dryness of mouth
Increase thirst
62
Drop in angiotensin II / gastric distension
Drop in thirst - angio II acts on organum vasculosum
63
How we maintain tight control over Na
- with thirst control AND osmoreceptor-ADH systems - prevent large changes in Na even if Na intake is 6x normal - only when both fail do we see change in Na [ ]
64
Angiotensin II and aldosterone role
- Na reabsorption - NOT Na [ ]....water moves with Na so [ ] stays same.... - just overall AMOUNT changes with angio/ald - high levels of ald will only move [ ] 3-5 mEq - increase in both will increase Na and water uptake - LOSS of ald system can drop Na [ ]

556 - Physiology & Pathophysiology II (8 decks)

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