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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
Q

Hyperosmotic renal medulla

A
  • 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
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26
Q

Factors creating hyperosmotic medulla

A
  • 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
Q

Process of concentrating urine

A

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
Q

Initial [ ] of urine entering distal

A
  • low…100

- no water reabsorption in ascending

29
Q

Urea and medullary osmolarity

A
  • 40-50% of total osmolarity

- excrete 50% of filtered load

30
Q

Urea and proximal tubule

A
  • 50% of filtered land reabsorbed

- [ ] goes up….more water reabsorbed

31
Q

Urea and thin loop

A
  • descending…[ ] up….water reabsorbed
  • descending/ascending…[ ] up…secretion of urea into tubule
    • via UT-A2
32
Q

Urea and thick ascending/distal/tubule/duct

A
  • urea not permeable

- [ ] up in duct as large amounts of water reabsorbed

33
Q

Urea and medulla collecting duct

A
  • 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
Q

How to feed medulla w/o washing away concentrated solute

A
  • low medulla blood flow….5% of renal flow

- vasa recta act as exchangers

35
Q

Vasa recta characteristics

A
  • 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
Q

Increase BF to vasa recta

A
  • will wash out solute
  • drop solute [ ] in renal medulla
    Caused by:
  • vasodilators
  • large BP increase (small is autoregulated)
37
Q

Change in osmolarity in proximal

A
  • 65% ions reabsorbed
  • flow goes from 125 to 44
  • normal osmolarity
38
Q

Change in osmolarity in descending

A
  • tubular osmolarity matches IF
  • higher…more so for [ ] urine
  • high water permeability / low ion
  • flow is 25
39
Q

Change in osmolarity in thin ascending

A
  • no water permeability
  • normal reabsorption of ions
  • drop in osmolarity
  • flow still 25…no change in water [ ]
40
Q

Change in osmolarity in thick ascending

A
  • no water permeability
  • large ion absorption….active
  • osmolarity drops more
  • flow still 25
41
Q

Change in osmolarity in early distal

A
  • diluting segment
  • no water out
  • large amount of ions out
  • flow still 25
42
Q

Change in osmolarity in late distal / cortical collecting tubule

A
  • osmolarity based on ADH
  • low ADH…no water reabsorption…flow still 25
  • high ADH…water in…flow drops to 8
43
Q

Change in osmolarity in medullary collecting tubule

A
  • depends on ADH
  • high ADH… high water reabsorb…urea [ ] up…flow 0.2
  • low ADH…urea slightly reabsorbed…flow down to 20 only
44
Q

How kidneys can make high [ ] urine

A
  • 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
Q

How kidneys can make lots of urine w/o Na excretion

A
  • change ADH…only affects H2O
46
Q

Obligatory urine volume dictated by…

A

Max ability to [ ] urine….normal is 1200

  • if kidney function drops….so does ability to [ ] urine
47
Q

Normal Na

A

142 mEq/L

48
Q

Normal Osmolarity

A
  • 300 mOsm/L

- 291-309 is range…+/- 2 to 3%

49
Q

Control over Na [ ] and osmolarity

A
  • very precise

- important for distribution of H2O between compartments

50
Q

Na and associated ions

A

94% of extracellular solute

  • glucose and urea….3-5%
  • Na not very permeable…large driving force
51
Q

Plasma osmolarity equation

A
  1. 1 x [plasma Na]

2. 1 x 142 = 298 mOsm/L

52
Q

2 systems that control ECF osmolarity and [Na]

A
  • osmoreceptors - ADH system

- thirst mechanism

53
Q

Osmoreceptor cells

A
  • in anterior hypothalamus
  • shrink if high ECF…send impulses to PP
  • PP release ADH
54
Q

Increase in osmolarity….

A
  • increase water permeability in distal tubules/ducts

- more water reabsorbed…Na excreted at normal

55
Q

Drop in BP/ volume

A
  • increase in ADH

- barroreceptors / reflex pathway

56
Q

ADH response to volume / osmotic changes

A
  • 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
Q

Hypoxia

A
  • increase ADH
58
Q

Morphine / Nicotine / cyclophosphamide

A

Increase ADH

59
Q

Alcohol / Clonidine / Haloperidol

A

Drop ADH

60
Q

Thirst mechanism

A
  • 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
Q

Increase in angiotensin II / dryness of mouth

A

Increase thirst

62
Q

Drop in angiotensin II / gastric distension

A

Drop in thirst

  • angio II acts on organum vasculosum
63
Q

How we maintain tight control over Na

A
  • 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
Q

Angiotensin II and aldosterone role

A
  • 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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