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Renal Exam 2 > Mechanisms to adjust urine concentration > Flashcards

Mechanisms to adjust urine concentration Flashcards

1
Q

Renal control of salt and water balance

-Normal function of these mechanisms allows?

A
  • Water retention during dehydration
  • Excretion of dilute urine when well hydrated
  • Sodium excretion when blood pressure rises (Na retention when BP falls)
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2
Q

Failure of renal control of salt and water balance can cause?

A
  • Edema
  • Hyper/hypokalemia
  • Undesirable changes in BP
  • Acid/base disorders
  • Neurological problems-shrinking/swelling of brain
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3
Q

Sodium reabsorption mechanisms

-Proximal tubule?

A
  • Cotransport with glucose, aas, and phosphate

- Countertransport with H

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4
Q

Sodium reabsorption mechanisms

-Thick ascending limb?

A

Na, K, 2Cl cotransport

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5
Q

Sodium reabsorption mechanisms

-Early DCT?

A

-Na, Cl cotransport

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6
Q

Sodium reabsorption mechanisms

-Late DCT, CD?

A

Luminal Na membrane channels

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7
Q

Water and chloride follow sodium

-Water reabsorption?

A
  • Always passive, can be transcellular or paracellular

- Follows osmotic gradients established by reabsorption of sodium

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8
Q

Water and chloride follow sodium

-chloride reabsorption?

A
  • Always linked, either directly or indirectly, to Na reabsorption (Cl can balance the pos and neg charges)
  • Different mechanisms in different segments
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9
Q

Loop of Henle-Descending limb

  • Freely permeable to?
  • Impermeable to?
A
  • Freely permeable to water

- Impermeable to Na, Cl

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10
Q

Loop of Henle-Ascending limb

  • Always impermeable to?
  • Thin segment?
  • Thick segment?
  • Referred to as the?
A
  • Always impermeable to water
  • Thin segment-NaCl reabsorption mechanism is controversial
  • Thick segment-active Na, K, 2Cl cotransport
  • Referred to as the “diluting segment”
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11
Q

Positive potential in tubular urine

-Function?

A

Drives the reabsorption of solutes-if it becomes less positive, the solute reabsorption will decrease

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12
Q

Late DCT and CD

-Major site of?

A

-Major site of physiological control of salt and water balance

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13
Q

Late DCT and CD

-Aldosterone-function?

A

Stimulates Na reabsorption and secretion of K and H

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14
Q

Late DCT and CD

-ANP-function?

A

Inhibits Na reabsorption (medullary CD)

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15
Q

Late DCT and CD

-ADH-function?

A

Stimulates water reabsorption

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16
Q

Water permeability of CD is physiologically controlled

-Well-hydrated individuals?

A
  • CD is impermeable to water

- Water remains in tubular lumen, dilute urine excreted

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17
Q

Water permeability of CD is physiologically controlled

-Dehydrated individuals?

A
  • CD is highly permeable to water

- Water is reabsorbed, low volume of concentrated urine is excreted

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18
Q

ADH MOA?

A

ADH increases water permeability (reabsorption) of late DT/CD via V2 receptors and insertion of aquaporin channels

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19
Q

Solute concentrations in peritubular interstitium

-Inner medullary interstitial fluid?

A

Very high solute concentration

20
Q

Countercurrent multiplier mechanism

-Function?

A
  • Concentrates solute in medullary interstitium
  • High solute concentrations enables kidneys to excrete highly concentrated urine, conserve water during periods of dehydration
21
Q

Countercurrent Multiplier Mechanism

-Requires the integrated function of 3 components?

A
  • Descending, ascending limbs of loop of Henle
  • Vasa recta capillaries
  • Collecting ducts
22
Q

Components of Countercurrent Multiplier

A
  • Na gradient that the Na, K, Cl cotransporter can establish in TAL
  • Interstitium becomes hyperosmolar and pulls water out of the descending limb
  • Urine in descending limb is concentrated
  • Process repeats
23
Q

Components of Countercurrent Multiplier

-Augmented by?

A

Augmented by action of ADH in CD

24
Q

Get half of the gradient from Na-K-Cl cotransporter

-The other half comes from?

A

Get the other half of the gradient from from reabsorption of urea

  • Recycling concentrates urea in the inner medulla
  • Reabsorption of urea is promoted by ADH from medullary CD
25
Q

Role of urea in the coutercurrent mechanism

-In the presence of ADH (cortical collecting tubule)?

A
  • In the presence of ADH, water but NOT urea is reabsorbed in the cortical collecting tubule
  • Results in an increase in the tubular fluid urea concentration
26
Q

Role of urea in the coutercurrent mechanism

-In the presence of ADH (medullary collecting tubule)?

A
  • In the presence of ADH, more water but NOT urea is reabsorbed in the medullary collecting tubule, further raising the concentration
  • The inner medullary collecting tubule is relatively permeable to urea
  • As a result, urea passively diffuses into the interstitium, increasing the interstitial osmolality
27
Q

Countercurrent multiplier

  • Vasa recta function?
  • What feature allows them to do this?
A
  • Maintain solute gradient
  • Low blood flow allows them to equilibrate with surrounding interstitium-allows waste to be taken out but keep what the body needs
  • Water and NaCl are exchanged between descending and ascending limbs
  • Solute gradient is maintained while small amounts of NaCl and water are returned to systemic circulation
28
Q

Countercurrent mechanism review figure

A

slide 26

29
Q

Antidiuresis-high ADH

  • Effect on the collecting duct?
  • Characteristics of urine excreted?
A
  • ADH makes the collecting duct epithelium highly water permeable
  • Water is reabsorbed in this segment and a LOW VOLUME, HIGHLY CONCENTRATED URINE is excreted
30
Q

Diuresis-Low ADH

  • Effect on the collecting duct?
  • Characteristics of urine excreted?
A
  • Collecting duct epithelium is impermeable to water

- HIGH VOLUME OF DILUTE URINE is excreted

31
Q

Diuresis-Low ADH

-Solute concentrations in the medullary interstitium?

A

LOW

32
Q

Osmolar clearance

A

Cosm = (Uosm x V)/Posm

33
Q

Osmolar clearance

-What happens to Cosm, when kidneys excrete excess solute?

A

Cosm increases (decreases when solute is retained)

34
Q
  • Free water clearance*

- Definition?

A

Excretion of water in excess of amount needed to excrete isosmotic urine, i.e. excretion of solute-free urine by the kidneys

35
Q
  • Free water clearance*

- Equation?

A

Cwater = V - Cosm

36
Q

Free water clearance

-What is Cwater if Uosm is less than Posm?

A

Cwater is positive-pure water is cleared from the body (opposite if Uosm is greater than Posm)

37
Q

Does ADH affect Cwater? If so, how?

A

Yes, it would decrease free water clearance

-water reabsorption is increased

38
Q

Fractional excretion

-Definition?

A

The fraction (percentage) of the filtered load of a substance that is excreted in urine

39
Q

Fractional excretion

-Equation?

A

(Ux x Pcr)/(Px x Ucr)

40
Q

Normal fractional excretion?

A

1%

41
Q

Fractional excretion

  • If fractional excretion is below 1% what does it suggest about what the problem might be?
  • What does it say about sodium?
A
  • It suggests the problem is prerenal and acute glomerulonephritis
  • Na avidly reabsorbed
42
Q

Fractional excretion

-If fractional excretion is above 2% what does it suggest about what the problem might be?

A

-Acute tubular necrosis, renal

43
Q

Case presentation

A

at the end

44
Q

Renal control of salt and water balance

-Crucial for regulation of?

A
  • Blood pressure
  • Extracellular fluid concentration
  • Concentrations of Na and K in body fluids
45
Q

Why is the ascending limb referred to as the diluting segment?

A

Because it is impermeable to water so the water stays in the tubule while Na and Cl are pumped out

46
Q

Which part of the countercurrent multiplier mechanism is inhibited by loop diuretics?

A

The Na-K-Cl cotransporter

47
Q

What if a drug was given that increases blood flow to peritubular capillaries?

A

Concentrating ability of the kidneys is decreased (medullary interstitial osmolarity gradient is abolished)

Renal Exam 2 (6 decks)

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