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Physiology > Renal 4 - Tubular Reabsorption and Secretion > Flashcards

Renal 4 - Tubular Reabsorption and Secretion Flashcards

1
Q

describe tubular reabsorption

A

-high capacity and variable
-very selective
- many electrolytes and nutrients almost completely reabsorbed
- most waste products poorly reabsorbed

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2
Q

describe tubular secretion

A

-variable
- important for certain electrolytes such as K+ and H+, drugs, toxins

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3
Q

what are the 2 different ways solute can be reabsorbed

A

-paracellular
-transcellular

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4
Q

how does fluid in the ISF enter the peritubular capillaries

A

bulk flow

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5
Q

what is the normal rate of peritubular capillary reabsorption

A

124 ml/min

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6
Q

what percentage of filtered sodium is reabsorbed

A

greater than 99%

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7
Q

what ways are sodium reabsorbed

A

transcellular and paracellular

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8
Q

describe transcellular sodium reabsorption

A

passive across apical membrane and active across basolateral membrane

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9
Q

what type of active transport might Na+ be on the apical membrane

A

secondary active and tied to the reabsorption of another substance

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10
Q

what is the TEPD

A

-transepithelial potential difference
- charge difference across epithelial cell
-negative charge in lumen

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11
Q

describe the secondary active transporters in the apical membrane and what are they

A

-Sodium glucose symporter
- sodium H+ antiporter
- both exhibit saturation, specificity, and competition

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12
Q

what molecules move through facilitated diffusion across the basolateral membrane

A

glucose, amino acids

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13
Q

what exhibits maximum rate that some substances can be transported across the epithelium

A

absorption or secretion

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14
Q

what is the renal threshold

A

the plasma concentration that saturates the carrier - tubular load

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15
Q

what happens when the transport maximum is reached for all nephrons

A

further increases in tubular load are not reabsorbed or excreted

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16
Q

what substances reach a transport maximum

A

glucose, amino acids, phosphate, sulfate, urate, creatinine, PAH

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17
Q

as [glucose]plasma increases what happens to [glucose]filtrate and glucose tubular load

A

[glucose]filtrate increases and glucose tubular load increases

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18
Q

what effect does Na+ reabsorption have on water

A

creates gradient for H2O reabsorption via osmosis

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19
Q

what area of the nephron is highly permeable to H2O

A

proximal tubule

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20
Q

what happens as H2O moves via osmosis

A

-carries other solvents along = solvent drage
- creates gradients for the passive reabsorption of other solute such as Cl- and urea

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21
Q

what area of the nephron is impermeable to water

A

ascending limb of loop of henle

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22
Q

what part of the nephron is water permeability regulated and what regulates it

A

collecting duct - ADH

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23
Q

Proximal tubule reabsorption of Na+, Cl-, urea and H2O exhibit _____

A

gradient-time transport

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24
Q

if water is reabsorbed to a greater extent than the solute, the solute will become ______ such as____

A

more concentrated in the tubule; creatinine and inulin

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25
Q

if solute is reabsorbed to a greater extend than water, the solute will become _____ such as

A

less concentrated in the tubule; glucose, amino acids

26
Q

what is the order of regional tubular transport

A

-early PCT and late PCT
- loop of henle: thin descending limb, thin ascending limb, thick ascending limb
-early distal tubule
- late distal tubule and cortical collecting duct
- medullary collecting duct

27
Q

describe the cells in the proximal tubule

A

-high capacity for active and passive reabsorption
- large number of mitochondria
- large surface area on both apical and basolateral membranes
- large number of membrane proteins
- high permeability for H2O

28
Q

what makes up the proximal tubule

A

proximal convoluted tubule and proximal straight tubule

29
Q

what does the proximal tubule reabsorb

A
  • 65% of filtered Na+, Cl-, HCO3- and K+
  • all filtered glucose and amino acids
30
Q

what does the proximal tubule secrete

A
  • metabolic waste products such as H+, organic acids, and bases such as bile salts, oxalate, urate and catecholamines
    -drugs or toxins
  • PAH
31
Q

what is the transport mechanism for Cl- reabsorption in the early proximal tubule

A

-paracellular
-passive down electrochemical gradient
- solvent drag

32
Q

what is the transport mechanism for Cl- reabsorption in the late proximal tubule

A
  • transcellular: apical secondary active via formate/Cl- antiporter and basolateral facilitated diffusion
  • paracellularly
33
Q

what transporters for glucose are located on the apical and basolateral membrane for glucose in the early and late proximal tubule and what is their affinity and capcity

A

-SGLT2 on apical in early PT; low affinity, high capacity
- GLUT2 on basolateral in early PT; low affinity, high capacity
- SGLT1 on apical in late PT; high affinity, low capacity
- GLUT1 on basolateral in late PT; high affinity, low capacity

34
Q

what inhibitors are used in the treatment of type 2 DM

A

SGLT2 inhibitors

35
Q

what percentage of glucose is absorbed in each the early PT and late PT

A

-90% in early PT
-10% in late PT

36
Q

how much Na+ and H2O are reabsorbed in PT

A

an isotonic solution

37
Q

how much glucose, amino acids, and HCO3- are reabsorbed in the PT

A
  • all glucose and amino acids
  • 65% HCO3-
38
Q

what portion of the PT reabsorbs Cl- and urea

A

distal portion

39
Q

describe creatinine reabsorption in the PT

A

not actively reabsorbed

40
Q

what percentage of filtrate is reabsorbed by the end of proximal tubule

A

70% (126 L/day)

41
Q

describe the permeability of the thin descending limb

A
  • high H2O permeability via AQP-1: major role in concentration/dilution of urine
    -20% filtered load of water
  • no active solute transport
  • urea secretion via facilitated diffusion
42
Q

describe the permeability of the thin ascending limb

A
  • does not reabsorb significant amounts of any solutes
  • impermeable to water
  • urea secretion via facilitated diffusion
43
Q

describe the permeability of the thick ascending limb

A

-impermeable to H2O and urea
- major site of Na+, Cl-, K+ reabsorption (25% filtered load) and H+ secretion

44
Q

by the end of the loop of henle, is more solute reabsorbed or water

A

more solute

45
Q

what portion of the loop of henle forms part of the JGA

A

the distal end of the TAL

46
Q

what transporter is characteristic of the TAL

A

Na+ 2Cl- and K+ secondary active co transporter

47
Q

what percentage of filtrate is reabsorbed in the end of the loop of henle

A

20% 36 L/day

48
Q

what does the early distal tubule do

A

-impermeable to H2O and urea
- reabsorbs 5% of Na+ and Cl-
-further dilutes filtrate

49
Q

what is the early distal tubule known as

A

the diluting segment

50
Q

what transporters are in the apical and basolateral membrane of the early distal tubule and what do they do

A
  • Na+ Cl- co transporter in apical membrane moves Na+ and Cl- into cells from lumen
  • Na+ K+ ATPase transports Na into interstitium on basolateral membrane
  • Cl- diffused into ISF though Cl- channel in basolateral membrane
51
Q

what are the 2 cell types in the late distal/cortical collecting duct

A

-principle cells
- intercalated cells

52
Q

what percentage do principal cells make up in the late distal/CCD

A

60-70%

53
Q

what do principle cells do

A

-site of aldosterone and ADH action
- reabsorb Na+ and H2O
- secrete K+
- impermeable to urea

54
Q

what identifies a principal cell

A

-Na+ K+ ATPase and K+ leak channel on apical membrane
- Na+ leak channel and K+ leak channel on basolateral membrane

55
Q

what do alpha intercalated cells do

A

-function important during acidosis
- secrete H+
- reabsorb K+ and HCO3-
- primary active transport of H+ across apical membrane can secrete H+ against a great concentration gradient

56
Q

how do you identify alpha intercalated cells

A

-H+ ATPase and Cl- leak channel and H+ K+ ATPase on apical membrane
- HCO3- Cl- antiporter and K+ leak channel on basolateral membrane

57
Q

what is the function of beta intercalated cells

A

-function important during alkalosis
- secrete K+ and HCO3-
- REabsorb H+

58
Q

how do you identify a beta intercalated cell

A

-HCO3- Cl- antiporter and K+ leak channel on apical membrane
- H+ ATPase and H+ K+ ATPase and Cl- leak channel on basolateral membrane

59
Q

what does the medullary collecting duct do

A

-processes less than 10% of Na+ and water but very important
-site of aldosterone and ADH action
- urea reabsorbed via facilitated diffusion
- secretes H+ using same mechanism as alpha intercalated cells

60
Q

what percentage of filtrate is reabsorbed at the end of the collecting duct

A

9% 16.5 L/day

Physiology (41 decks)

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