Lecture 5: Urinary Concentration and Dilution Flashcards

1
Q

how do diuretics reduce water reabsorption?

A

by preventing sodium absorption (on apical membrane)

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2
Q

how do calcium anhydrase (CA) inhibitor diuretics prevent Na reabsorption in the PT

A

by blocking Na/H exchanger

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3
Q

Loop diuretics target what to inhibit Na uptake in the LoH

A

NKCC2 in the thick ascending limb of the loop of henle

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4
Q

How do thiazide diuretics inhibit Na uptake in the distal tubule

A

by inhibiting Na-Cl transporter (NCC) in the distal tubule

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5
Q

how do potassium-sparing diuretics work in the CD to reduce Na uptake and K secretion

A

by blocking ENaC

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6
Q

a plasma concentration of glucose that exceeds the tubular maximum causes ?

A

osmotic diuresis

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7
Q

what is osmotic diuresis

A

occurs when reabsorption of water is prevented by osmotically active substances in the urinary filtrate

causes a loss of water and electrolytes in urine

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8
Q

what is the average number of osmolality for dogs/cats?

A

about 300 mOsm/kg

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9
Q

what factors can cause fluid deficiency?

A
  • volume depletion (hypovolemia) caused by hemorrhage for example
  • dehydration
  • circulatory shock, neurological dysfunction
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10
Q

what factors can cause fluid excess?

A
  • volume excess (Na and H20 retention)
  • hypotonic hydration
  • pulmonary or cerebral edema
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11
Q

What 2 mechanisms maintain medullary hypertonicity which draws water out of the descending limb

A
  1. urea accumulation in the inner medulla & NaCl accumulation in outer medulla
  2. variable water and salt permeability in LoH
    • The descending limb of LoH reabsorbs water
    • The ascending limb is impermeable to water but NaCl is reabsorbed
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12
Q

what is the amount of urea that enters into the proximal tubule

A

= to GFR x plasma concentration
b/c urea is freely filtered

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13
Q

between what parts of the tubular system does urea recycling occur

A

b/w the inner medullary CD and the descending limb of LoH

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14
Q

how is filtered urea reabsorbed into the inner medullary CD?

A

via urea transporters (UT-A1, UT-A3)

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15
Q

in the outer medulla, it is mostly _____ that creates the ‘medullary osmotic gradient’

A

NaCl

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16
Q

the ascending limb LoH is impermeable to _______ but permeable to _______

A

impermeable to water, permeable to Na

17
Q

what causes Na to be drawn into the medullary interstitium

A

Na concentration gradient
secondary active transport

18
Q

what transporter is used for NaCl reabsorption in the ascending limb LoH

19
Q

what causes the tubule osmolarity in the ascending limb of LoH to decrease

A

b/c NaCl is leaving the tubule fluid via NKCC

20
Q

what prevents dilution of the medullary interstitial space

A

rapid reabsorption of water by the vasa recta

21
Q

what segment of the tubule system determines whether urine will be dilute or concentrated

A

the collecting duct

22
Q

what determines how permeable the collecting duct is to water

A

ADH (anti diuretic hormone)

23
Q

The level of ADH in the CD determines the ______ of excreted urine

A

osmolality

24
Q

what is the effect of hypertension (water overload) on ADH and urine concentration

A

ADH absent, urine becomes diluted

25
what is the effect of dehydration, hypotension and volume depletion on ADH and urine concentration?
ADH levels rise, urine becomes more concentrated
26
what determines the maximum concentration of urine
tonicity in inner medulla amount of urea stored in the interstitial space