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Physiology Exam 3 > Urine concentration and Dilution > Flashcards

Urine concentration and Dilution Flashcards

1
Q

How much urine can the kidneys excrete a day? What is the lowest osmolarity of the urine?

A

20 L/ 50 mOsm

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2
Q

What are the two portions of the nephron that are involved with the excretion of dilute urine?

A

Ascending thick limb of Henle and th eLAte distal convoluted tubule

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3
Q

Describe the ascending thick limb of Henle

A
  • absorbs sodium, potassium, and chloride
  • impermeable to water
  • more dilute as it flows up the tubule
  • ADH does not effect
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4
Q

Describe the late distal convoluted tubule

A
  • reabsorb sodium chloride

- impermable to water in the absence of ADH

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5
Q

What is the maximum urine concentration that the kidney can produce?

A

1200-1400 mOsm

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6
Q

What are the two requirements for forming concentrated urine?

A
  • presence of ADH

- high osmolarity of renal medullary interstitial tubule (establishes gradient)

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7
Q

Why is there an obligatory volume of excreted urine of 0.5 L a day?

A

Because the maximum osmolality of the urine is about 1200 and the average human must secrete 600 mOsm of solute a day to get rid of the waste

600/1200=0.5 L/day
to get rid of the basic metabolic wastes that would otherwise be problematic

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8
Q

Where in the kidney are most of the filtered electrolytes absorbed?

A

proximal tubule reabsorbs about 65%

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9
Q

Describe the proximal tubule

A

65% of electrolytes
highly permeable to water
300 mOsm

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10
Q

Describe the descending loop of Henle

A

-highly permeable to water
-less permeable to sodium chloride and urea
osmolarity increases to 1200 mOsm/L with high ADH

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11
Q

Describe the thin ascending loop of Henle

A
  • impermeable to water
  • reabsorbs sodium chloride
  • tubular fluid is more dilute
  • urea diffuses into the ascending limb
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12
Q

Describe the thick ascending loop of henle

A
  • impermeable to water
  • large amounts of sodium chloride, potassium, and other ions are transported in
  • tubular fluid is dilute (100 mOsm)
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13
Q

Describe the early distal tubule

A
  • similar to the thick ascending loop of henle

- fluid is more dilute

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14
Q

Describe the late distal tubule and cortical collecting tubule

A

osmolarity depends on ADH

urea is not permeant

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15
Q

Describe the inner medullary collecting duct

A

osmolarity of the fluid depends on the ADH and surrounding intersititium osmolarity

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16
Q

What are the portions of the nephron that are impermeable to urea?

A

Ascending thick limn of Henle and the distal cortical collecting tubule

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17
Q

What happens in the cortical collecting tubule if ADH is increased?

A

water is reabsorbed and urea is not very permeant here and becomes more concentrated

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18
Q

What happens in the medullary collecting duct if ADH is increased?

A

More water is reabsorbed form the medullary collecting duct
higher concentration of the urea
-diffusion of urea into the interstitial fluid

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19
Q

What are the ADH activated transporters?

A

UT-A1 and Ut-A3

20
Q

What helps to maintain the high concentration of urea in the tubular fluid?

A

simultaneous movement of water and urea in and out of the inner medullary collecting duct

21
Q

What happens to the urine concentration if the ADH levels are low?

A

diluted urine

22
Q

What happens to the urine concentration if the ADH levels are high?

A

concentrated urine

23
Q

What prevents the medullary hyperosmolarity from being dissipated?

A

Vasa recta

24
Q

Describe the osmoreceptor-ADH feedback mechanism

A
  • controls the extracellular fluid sodium concentration and osmolarity
  • ADH is formed in the magnoceullluar neurons
  • osmoreceptor cells
25
Q

What happens if there is and increased extracellular fluid osmolarity?

A

There is a shrinking of the osmoreceptor cells in the anterior hypothalamus which leads to increased action potentials which causes the release of ADH

This increases water permeability in the distal nephron segment and the urine will be concentrated

26
Q

Where is ADH formed in the magnocellular nephron?

A

supraoptic nuclei and the paraventricular nuclei

27
Q

Where are the osmoreceptor cells?

A

In the vicinity of the AV3V region (anterior region of the third ventricle

28
Q

Describe the osmoreceptor feedback mechanism

A
  1. water deficit
  2. increased extracellular osmolarity
  3. ADH secretion form the posterior pituitary
  4. increased in the plasma ADH
  5. Increased H2O permeability in the distal tubules and the collecting ducts
  6. increased H2O reabsorption
  7. decreased water is excreted
  8. Concentrated urine
29
Q

Describe what happens to osmolarity and volume in isotonic volume depletion

A

osmolarity stays the same and volume decreases

30
Q

Describe what happens to osmolarity and volume in isovolumetric osmotic increase

A

volume is the same but the osmolarity increases

31
Q

What are the steps of the countercurrent multiplier system?

A
  1. concentration in the loop of henle is the same
  2. concentration is reduced because of the activation of an active ion pump pulling out solutes
  3. concentration in the descending limb reaches osmotic equilibrium because of osmosis
  4. hyperosmotic fluid flows into the ascending limb
  5. More ions are pumped out fo the ascending limb (dilutes more)
  6. Repeat steps 4-6 over and over again until we reach
  7. equilibrium
32
Q

Which tubules are permeable to water?

A

descending

33
Q

Which tubules are impermeable to water?

A

ascending

34
Q

What is the overall role of ADH?

A

To make the tubules permeable to water by inserting aquaporins into the cellular membranes

ALSO inserts urea transporters

35
Q

What is reabsorbed in the proximal tubule?

A

Water, NaCl and urea

36
Q

what is reabsorbed in the descending loop of henle when ADH is high

A

water

37
Q

What is reabsorbed in the ascending loop of Henle when AHD is high

A

NaCl

38
Q

What is reabsorbed in the medullary area when ADH is high?

A

Water, NaCL, urea

CONSERVING WATER

39
Q

What is reabsorbed in the proximal tubule when the ADH levels are low?

A

NACl and H2O

40
Q

What is reabsorbed in the descending loop when the ADH levels are low?

A

H20

41
Q

What is reabsorbed in the medullary region when the ADH levels are low?

A

NaCl, urine will be diluted

42
Q

Where does the urea that is reabsorbed from the medullary region go?

A

Goes to the loop of henle and is recycled into the tubular fluid

43
Q

What are the vasa recta?

A

Capillaries that parallel the loop of henle; water leaves the descending portion and inserts into the ascending limb

help to maintain the equilibrium of the interstitial concentration differences

44
Q

True or false: the main purpose of the vasa recta is to supply blood to the nephron

A

False, they help to maintain the equilibrium of the concentration gradient

45
Q

Where is most of the change in the concentration of the urine occurring when there is increased ADH?

A

In the collecting tubule in the medullary region and the urine

46
Q

Does blocking the aldosterone system have an effect on the sodium intake and extracellular sodium concentrations relationships?

A

Nah

Physiology Exam 3 (9 decks)

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