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_Physiology Exam 5 > 4/15: VI - Urine Concentration and Dilution > Flashcards

4/15: VI - Urine Concentration and Dilution Flashcards

1
Q

What is the normal function of ECF osmolarity?

A

300 mOsm

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2
Q

What happens to H2O and Na+ via diet?

A

Too much
not enough

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3
Q

How is H2O and Na lost?

A

Insensible
Sweat
Feces
Urine - to a large extent, kidneys balance the books by adjusting water reabsorption and excretion

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4
Q

Urine formed without ADH is ________

A

Dilute

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5
Q

What is the osmolarity of filtrate in the proximal tubule?

A

Isosmotic

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6
Q

What is the osmolarity of urine as it passes through the tDL?

A

Hyperosmotic
- water reabsorption
- no solute reabsorption

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7
Q

What is the osmolarity of urine as it passes through the TAL and early distal tubule?

A
  • solute reabsorption
  • no water reabsorption
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8
Q

What is the osmolarity of fluid as it passes through the distal tubule and collecting duct?

A

Vary
- stays hyposomotic in absence of ADH (dilute urine)
- dilute urine (as low as 50 mOsm)

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9
Q

What does ADH do to H2O permeability in distal tubule and collecting duct?

A

ADH increases permeability

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10
Q

Where does a large volume of H2O diffuse?

A

Into intestitium
- enters capillaries of vasa recta and removed
- creates concentrated urine (as high as 1200 mOsm/L)

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11
Q

What does the maximal concentrating ability of the kidney dictate?

A

How much urine volume must be excreted each day to rid the body of metabolic waste products and ions that are ingested

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12
Q

How much mosmol must an adult excrete daily?

A

600 mosmol
o OUV = (solute load that must be excreted) / (maximum concentrating ability)
o Normal OUV = (600 mOsm/L)/(1200 mOsm/L) = 0.5 L/day

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13
Q

What are requirements for excreting a concentrated urine?

A
  1. High levels of ADH
  2. Hyperosmotic medullary interstitial fluid
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14
Q

What does the medullary hyperosmotic insterstiial fluid surround?

A

Collecting duct

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15
Q

What gradient does the hyperosomotic medullary insterstitial fluid set gradient for?

A

Water reabsorption

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16
Q

What does hyperosmotic for water reabsorption require?

A

Counter current multiplier mechanism

17
Q

What nephrons function in hyperosmotic medullary interstitial fluid?

A

Juxtamedullary nephrons
- long loop of henle
- vasa recta
- slow flow rate

18
Q

What is high interstitial fluid osmolarity a result of?

A

o Active transport of Na+ and other ions by ascending limb of Loop of Henle
o Active transport of ions from collecting duct into interstitium
o Facilitated diffusion od urea by inner medullary collecting ducts
o Movement of only small amounts of water into medullary interstitium

19
Q

What does the concentrating uring require?

A

A hyperosmotic interstitial fluid

20
Q

What is the mechanism for creating hyperosmotic medullary interstitial fluid?

A
  1. Isosmotic fluid
  2. Thick ascending limb reabsorbs solute. Concentration of osmolarity in interstitial fluid goes up
  3. Thin descending limb reabsorbs water. Water moves out making concentration of filtrate increase
    - Water leaving LOH is not diluting interstitial fluid because it is being picked up by vasa recta
  4. Gradients begin to set up with more filtrating being added
    o If steps are repeated 4-6x you will end up with a filtrate that is isosmotic near the cortex/medullary border and concentration becomes higher and high as you move into the medulla
    - Tip of thick ascending limb is the most concentrated
21
Q

What happens in the distal tubule and collecting duct in absence of ADH?

A
  • reabsorb solute
  • little to no water reabsorption
22
Q

What happens in the distal tubule and collecting duct in presence of ADH?

A
  • distal tubule and collecting duct become highly permeable to water and reabsorb much water into cortical insterstitium
  • medullary collecting duct cells reabsorb water but overall amounts much lower (keeps medullary interstitium from being diluted)
  • reabsorbed water carried away by vasa recta
23
Q

What is urea?

A

Waste product of protein metabolism; produced continuously by liver

24
Q

How is urea reabsorbed?

A

Passively by medullary collecting duct cells

25
Q

Where is urea secreted into?

A

Descending limb and thin ascending limb of loop of henles -> requires: ADH
- concentrates urea in filtrate (water reabsorption in cortical and medullary collecting ducts)
- activates carriers (UT-A1; UT-A3) for the facilitated diffusion of urea by medullary collecting duct cells

26
Q

What region does concentrating urine require?

A

Hyperosmotic interstitial region

27
Q

What does the countercurrent multiplier mechanism depend on?

A

Anatomical relationship of loop of henle, vasa recta, and collecting ducts

28
Q

What are 25% of nephrons?

A

juxtamedullary nephrons (25% of all nephrons with long loops of Henle that extend into renal medulla parallel to vasa recta and collecting ducts)

29
Q

What is the flow of filtrate in descending and ascending limbs of loops of henle?

A

Filtrate in descending and ascending limbs of loop of Henle (and collecting duct) flows in the opposite directions of blood flow in the vasa recta

30
Q

What does the countercurrent multiplier mechanism clear?

A

reabsorbed water so does not dilute medullary interstitial fluid

31
Q

What is the basic mechanism of the countercurrent multiplier mechanism?

A

two tubes running in opposite directions and one picks up what the other one is losing

32
Q

What is the countercurrent exchange mechanism?

A

IN VASA RECTA preserves hyperosmolarity in the medulla intersitium

33
Q

What is the omsolarity of the loop of henle?

A

isosmotic -> hyperosmotic -> hypoosmotic

34
Q

Describe the thick ascending limb cell

A

as it reabsorbs solute into the interstitial fluid which equilibrates with the blood causing an increase blood concentration

35
Q

Describe the thin ascending limb cell

A

as water is reabsorbed from the loop of Henle into the interstitial fluid it then equilibrates with the blood causing decrease in blood solute concentration (diluted so when it leaves the nephron it goes back to being isosmotic)

36
Q

What are the late DT and CCD/MCD variable based about?

A

Amount of ADH present

37
Q

What does maximal ADH cause?

A

Reabsorb water and cause hyperosmotic filtrate

38
Q

What does the absence of ADH cause?

A

No water reabsorption, hypoosmotic filtrate

_Physiology Exam 5 (10 decks)

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