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Hum Physiology II > urinary conc. and dilution, Lect 5 > Flashcards

urinary conc. and dilution, Lect 5 Flashcards

1
Q

when body fluids are hypoosmotic, the kidneys exrete urine. What is the limit?

A

a dilute urine, (as low as 50 mOsm/L - water diuresis)

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2
Q

when body fluids are hyperosmotic, the kidneys exrete urine. What is the limit?

A
  • water deficit
  • concentrated urine (to 1200 mOsm/L) - antidiuresis
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3
Q

are the kidneys able to regulate water excretion independently of solute excretion?

A

yes

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4
Q

how much sodium reabsorbtion and water reabsorbtion occur in the loop of henle? active or passive?

A
  • sodium: 25%, active
  • water: 15%, passive, solute linked
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5
Q

how much sodium reabsorbtion and water reabsorbtion occur in the distal and collecting tubule? active or passive?

A
  • sodium: 8%; active
  • water: 20%; passive
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6
Q

active Na2+ reabsorption in the distal and collecting tubule is regulated by

A

aldosterone

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7
Q

passive water reabsorption in the distal and collecting tubule is regulated by

A

ADH

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8
Q

what creates a large gradient in the instertitial fluid from the corticomedullary border to the top of the papilla by multiplying a small local gradient created by the epithelium of the loop of henle

A

the counter-current multiplier

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9
Q

what is the purpose of the osmotic gradient from cortex to medulla in the interstitial space

A

used to remove water from urine in the collecting duct

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10
Q

the descending limb is to water but to NaCL

A
  • very permeable to water
  • no active transport of NaCl
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11
Q

the ascending limb is to water but to NaCl

A
  • strucutre: thin to thick
  • active reabsorbtion to NaCl occurs (lumen looses NaCl)
  • impermeable to water
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12
Q

what happens to fluid as it flows down the descending limb

A

progressively concetrated

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13
Q

what happens to fluid as it flows up the ascending limb

A

progressively diluted

  • NaCl is actively reabsorbed from lumen into capillary
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14
Q

what is the largest osmotic gradient that can be maintained across the wall of the ascending limb?

A
  • you can only have a 200 mOsm/L difference between concentration in the tubule and that in the interstitial fluid
  • this is due to back diffusion; NaCl will flow back into the tubule (lumen) if greater than a 200 mOsm/L difference is created
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15
Q

which part of the nephron is described as the countercurrent multiplier

A

Loop of henle

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16
Q

sodium potassium ATPase is always on which side of the tubule cell

A

basolateral side -> towards interstitial fluid

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17
Q

what is the essential component of the countercurrent multiplier

A

active transport

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18
Q

Describe the NKCC2 transporter

A
  • Na2+, K+, 2 Cl- transporter on the luminal aspect of the tubule cell
19
Q

what stimulates NKCC2 transporter

A

ADH

20
Q

loop diuretics (furosemide (lasix)) has what effect on NKCC2 transporter

A
  • blocks this transporter
  • because of this kidney cant create corticopapillary gradient
21
Q

what is characterized by hairpin loops

A

vasa recta

22
Q

as blood flows down the capillary into papillary part of kidney, what happens to NaCl and water in the blood

A
  • NaCl diffuses in and H2O flows out
  • as blood flows up the capillary, the reverse occurs
23
Q

function of vasa recta and countercurrent exchanges

A

protect the ISF gradient (corticopapillary gradient)

24
Q

vasa recta and countercurrent exchanges is an active or passive process

A

entirely passive

25
Q

what is urea generated by

A

hepatic protein catabolism

26
Q

what is the importance of urea in the medullary interstitial fluid

A

contributes to hyperosmotic renal ISF and to concentration of the urine

  • people on low protein diets cannot concentrate urine as well (due to reduced urea formation)
27
Q

What happens to urea in the medulla of the kidney

A

it is recycled: reabsorbed and secreted

28
Q

permeability to urea of the unner medullary portion of the collecting duct is controlled by

A

ADH

29
Q

What transporters are present in the early distal convoluted tubule

A
  • the Na+, K+, 2Cl- transporter (NKCC2) is NOT present
  • there is a NaCl transporter (NCC) in the luminal membrane
    • symport
30
Q

describe what happens to NaCl and water in the early distal convoluted tubule

A
  • NOT permeable to water
  • has a transporter for NaCl (NNC)
  • thus referred to as a Diluting segment
31
Q

The NaCl transporter (NCC) in the early distal convoluted tubule is blocked by

A

Thiazide diuretics

32
Q

The Late distal tubule and collecting duct are composed of what two cell types

A
  • Principle cells
  • Intercalated cells (type A)
33
Q

what are the function of the Priniciple cells in the Late distal tubule and collecting duct

A
  • reabsorb Na+
  • secrete K+
    • reabsorb Na+ in exchange for K+
  • **site of aldosterone action
  • ***this depends on the Na+, K+-ATPase in the basolateral membrane and apical channels for both ions
34
Q

aldosterone acts on which cell types . MOA?

A
  • Principle cells in the Late distal tubule and collecting duct
  • MOA: increases the number of apical Na+ channels (ENaC) and Na+, K+ ATPase
35
Q

What is the function of the Intercalated cells (type A) in the Late distal tubule and collecting duct

A
  • secrete H+
    • via H+-ATPase
  • reabsorb K+
    • via H+, K+ ATPase
36
Q

water and urea permeability of the collecting duct is controlled by

A

vasopressin (ADH)

  • **the collecting duct is impermeable to water and urea in the absense of ADH
37
Q

MOA of ADH on water and urea permeability in the collecting duct

A
  • ADH causes the insertion of aquaporins into the apical membranes of collecting duct cells via cyclic AMP messenger system
  • ADH released when body fluids become concentrated: want to reabsorb water from urine
38
Q

is the collecting duct permeable to water in the absence of ADH

A

No

  • ADH create aquaporins
39
Q

fluid in the early distal tubule has what osmolarity

A

hyposmotic

  • no water reaborption
  • some NaCl reabsorption
40
Q

give osmolarity status of descending limp of LOH, ascending limb of LOH, early distal tubule

A
  • descending limp of LOH: hyperosmotic
  • ascending limb of LOH: hyposmotic
  • early distal tubule: hyposmotic
41
Q

why is the corticopapillary gradient strong when a person is dehydrated

A
  • ADH allows for Na, K+, 2Cl- transporter which gives the intersitium more ions
  • urea permability from lumen into interstitium
42
Q

When ADH is present, what determines the osmolarity of the urine in the collecting duct

A

the osmolarity of the interstitial fluid because water flows down concentration gradient

43
Q

when ADH is high, water is , and urine becomes

A
  • water reabsorbtion is high
  • urine becomes hyperosmotic
44
Q

when ADH is low, water is , and urine becomes

A
  • water is not reabsorbed
  • urine is hypoosmotic

Hum Physiology II (12 decks)

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