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CPR Final > Concentration and Dilution of Urine > Flashcards

Concentration and Dilution of Urine Flashcards

1
Q

Production of Concentrated Urine

A
  • Hyperosmotic urine: urine osmolarity>blood osmolarity
  • Produced when circulating ADH levels are high
    • Water deprivation
    • Hemorrhage
    • SIADH
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2
Q

Corticopapillary osmotic gradient in High ADH

A
  • Gradient of osmolarity from cortex to papilla
    • 300 mOsm/L to 1200 mOsm/L
    • Composed mainly of NaCl and urea
  • Established by countercurrent multiplication and urea recycling
  • Maintained by countercurrent exchange in vasa recta
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3
Q

Countercurrent multiplication in the loop of henle

A
  • Depends on NaCl reabsorption in TAL
  • and countercurrent flow in descending and ascending limbs
  • Augmented by ADH that stimulates NaCl reabsorption in TAL
    • Increases size of coricopapillary osmotic gradient
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4
Q

Urea Recycling

A
  • From inner medullary collecting ducts into medullary interstitial fluid
  • Also augmented by ADH
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5
Q

Vasa Recta

A
  • Capillaries that supply the loop of henle
  • Maintain corticopapillary gradient
  • Serve as osmotic exchangers
  • Blood equilibrates osmotically w/ interstitial fluid of medulla and papilla
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6
Q

Proximal Tubule in presence of high ADH

A
  • Osmolarity of glomerular filtrate identical to plasma (300mOsm/L)
  • 2/3 filtered H2O reabsorbed isosmotically
    • w/ Na+, Cl-, HCO3-, Glc, AA, etc
  • TF/Posm=1.0 thru out proximal tubule b/c H2O reabsorbed isosmotically w/ solute
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7
Q

Thick ascending limb in presence of high ADH

A
  • Diluting segment
  • Reabsorbs NaCl by Na/K/2Cl- cotransporter
  • Impermeable to H2O and TF becomes more dilute
  • Fluid leaving TAL has osmolarity of 100 mOsm/L
  • TF/Posm<1.0 due to dilution
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8
Q

Early distal tubule in high ADH

A
  • Cortical diluting segment
  • Reabsorbs NaCl
  • Impermeable to H2O
  • Tubular fluid further diluted
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9
Q

Late Distal Tubule in Presence of High ADH

A

-Increases H2O permeability of principal cells
-HO reabsorbed from tubule until osmolarity of TF equal to surrounding interstitial fluid
300 mOsm/L
-TF/Posm=1.0 b/c equilibration

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10
Q

Collecting Duct in presence of high ADH

A
  • ADH increases H2O permeability of principal cells
  • As TF flows thru collecting duct, it passes thru the corticopapillary gradient (increasingly higher osmolarities)
  • H2O reabsorbed from collecting ducts until osmolarity of TF equals that of surrounding interstitial fluid
  • Osmolarity of final urine -that of bend in loop (1200mOsm/L)
  • TF/Posm>1.0 b/c osmotic equilibration occurs w/ gradient
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11
Q

Production of Dilute Urine

A
  • Hyposmotic urine
  • Urine osmolarity<blood osmolarity
  • Produced when ADH levels are low
    • Water intake
    • central diabetes insipidus
  • Produced when ADH is ineffective
    • Nephrogenic diabetes insipidus
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12
Q

Corticopapillary osmotic gradient with No ADH

A
  • Smaller than when ADH present

- B/c ADH stimulates countercurrent multiplication and urea cycling

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13
Q

Proximal Tubule if No ADH

A
  • As w/ ADH present, 2/3 filtered H2O reabsorbed isosmotically
  • TF/Posm=1.0
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14
Q

TAL of Loop of Henle w/ No ADH

A
  • As w/ ADH present, NaCl reabsorbed w/o H2O
  • Tubular fluid further diluted
  • Not quite as dilute as in the presence of ADH
  • TF/Posm<1.0
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15
Q

Early Distal Tubule w/ No ADH

A
  • As w/ ADH present, NaCl reabsorbed w/o H2O
  • Tubular fluid further diluted
  • TF/Posm<1.0
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16
Q

Late distal tubule and collecting ducts w/ no ADH

A
  • In the absence of ADH, impermeable to H2O
  • Even though TF flows thru corticopapillary osmotic gradient, equilibration doesn’t occur
  • Osmolarity of final urine will be dilute, as low as 50 mOsm/L
  • TF/Posm<1.0
17
Q

Free Water Clearance

A

-Used to estimate ability to concentrate or dilute urine
-Free water (solute free water) produced in diluting segments
-Absence of ADH: free water excretion (C-H2O is positive)
-Presence of ADH: free water not excreted (C-H2O is negative)
C-H2O=V-Cosm
C-H2O is free water clearance
V is urine flow rate
Cosm is osmolar clearance

18
Q

Urine that is isosmotic to plasma

A
  • Isosthenuric
  • C-H2O is zero
  • Produced during tx w/ loop diuretic
    • Inhibits NaCl reabsorption in TAL
    • Inhibits TAL dilution and gradient formation
  • Urine cannot be diluted during high water intake
  • Cannot be concentrated during water deprivation
19
Q

Urine that is hyposmotic to plasma

A
  • Low ADH
  • C-H2O is positive
  • Produced w/ high water intake (ADH release suppressed)
    • Central diabetes insipidus (insufficient ADH)
    • Nephrogenic diabetes insipidus (collecting ducts unresponsive to ADH)
20
Q

Urine that is hyperosmotic to plasma

A
  • High ADH
  • C-H2O is negative
  • Produced in water deprivation (ADH release)
    • Also SIADH

CPR Final (29 decks)

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