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Physiology Part 2 > Lec 43 Intro To Transport and Proximal Tubule Function > Flashcards

Lec 43 Intro To Transport and Proximal Tubule Function Flashcards

1
Q

What parts of nephron associated with vasa recta?

A
  • loop of henle

- collecting duct

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2
Q

What parts of nephron associated with peritubular capillary?

A
  • proximal and distal tubules
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3
Q

Equation for filtered load?

A

F.L. = Px * GFR

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4
Q

Equation of urinary excretion rate?

A

UEx = Ux * V.

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5
Q

Equation for tubular reabsorption rate?

A

TRx = FLx - UEx

= filtered load - urinary conc

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6
Q

Equation for tubular secretion rate?

A

TSx = UEx - FLx

= urinary conc - filtered load

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7
Q

Equation for fractional secretion?

A

FEx = UEx/FLx

= urinary excretion/filtered load

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8
Q

What is mech of transceullular transport?

A
  • through membrane through cell

- through channels, simple diffusion, or active transport

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9
Q

What is mech of paracellular transport?

A
  • between cells through tight junctions
  • no protein carriers
  • requires driving force
  • simple diffusion down electrochemical gradient
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10
Q

What are 3 forms of passive transport?

A
  • simple diffusion
  • facilitated diffusion
  • solvent drag
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11
Q

What are 2 forms of active transport?

A
  • primary active

- secondary active [cotransporter or countertransporter]

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12
Q

Is tight junction leaker in proximal tubule of ascending loop of henle?

A
  • very leaky in prox tubule for reabsorption

- very impermeable in ascending loop

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13
Q

How much of tubule content reabsorption occurs in proximal tubule?

A

2/3

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14
Q

How is Na transported in first half of proximal tubule?

A

on apical: Na couple transport into cell [Na-H, Na-gluc, or Na-AA, etc]
on basolateral: Na leaves via Na-K ATPase [2 K in, 3 Na out]

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15
Q

Describe Cl transport in first half of proximal tubule?

A

Cl trapped in lumen –> no Cl transport in early PT

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16
Q

What is predominant extracellular cation anion transported in first half of proximal tubule?

A

HCO3- goes to balance out charge of Na

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17
Q

What happens to Cl conc along early PT?

A
  • Cl conc increases as fluid moves down early PT since Cl trapped in lumen
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18
Q

What two types of Na transport in second half of proximal tubule?

A
  • paracellular: Cl driven Na reabsorption

- transcellular: Na-H exchanger

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19
Q

What is mech of Cl driven Na reabsorption in second half of proximal tubule?

A
  • Cl diffuses between cells into interstitium
  • driving force for Cl because of the increased conc from first half PT
  • causes +4 mV lumen positive potential
  • electrical gradient favors movement cations paracellular –> Na is most abundant cat so moves a lot
20
Q

What is mech of transcellular Na reabsorption in second half of proximal tubule?

A

apical:
- Na-H exchanger brings Na into cell
- Cl-anion exchanger brings Cl into cell [anion often formate]
- H and formate into lumen then re-transported back into cell to be used again
basolateral
- Na leaves via Na-K ATPase [3 Na out, 2 K in]
- Cl leaves via Cl-K cotransporter [1 K out, 1 Cl out]

21
Q

What is mech of HCO3 reabsorption in PT?

A
  1. filtered HCO3 trapped in lumen unless converted
  2. H comes out of cell into lumen via Na-H exchanger or H ATPase
  3. In lumen: HCO3 + H –> H2CO3 –> H20 + CO2 via luminal membrane bound carbonic anhydrase
  4. H2O and CO2 diffuse into cell
  5. CO2 and H2O converted back to HCO3 via intracellular carbonic anhydrase
  6. on basolateral HCO3 leaves by
    - – HCO3-Cl exchanger [1 HCO3 out, 1 Cl in]
    - – HCO3-Na cotransporter [3 HCO3 out, 1 Na out]
22
Q

What are the 2 ways HCO3 leaves epithelial cell basolateral membrane for reabsorption to capillary in PT?

A
  • – HCO3-Cl exchanger [1 HCO3 out, 1 Cl in]

- – HCO3-Na cotransporter [3 HCO3 out, 1 Na out]

23
Q

Is there net H secretion in HCO3 reabsorption in PT?

A

No – H is recycles back into cell via H2O and CO2

24
Q

How is glucose reabsorbed in PT?

A
  • in proximal tubule
  • if you saturate reabsorptive capacity in PT there is no downstream glucose transporter
  • apical: comes in by Na-glucose cotransporter
  • basolateral: leaves by Glut1/2
25
Q

How are proteins and AA reabsorbed in PT?

A
  • very little bit of protien filtered at glomerulus
  • degrades in lumen to peptide and AA

apical side:

  • peptide and small protein: endocytosed and degraded in cell to AA
  • AA: comes in via Na-AA cotransporter

basolateral side:
- via other AA transporters

26
Q

How is K reabsorbed in PT?

A
  • by solvent drag just goes along with water

- no specific transporter or driving force

27
Q

How is urea reabsorbed in PT?

A
  • not charged
  • diffuses into or out of lumen based on conc gradient
  • no cellular transporter
28
Q

How is Ca reabsorbed in PT?

A

80% via paracellular: combo of solvent drag and in late PT via electrochemical gradient from positive potential in lumen

20% via transcellular:

  • apical: Ca channel in
  • basolateral: Ca ATPase or Na-Ca exchanger [1 Ca out, 3 Na in]
29
Q

How is NH3/NH4 reabsorbed in PT?

A
  • glutaminase in PT cell activates glutamine –> NH3
  • NH3 + H –> NH4 from H+ HCO3 pool
  • HCO3 goes into circulation
  • NH4 goes into cell via Na-NH4 exchanger [1 NH4 out, 1 Na in]
  • allows you to excrete H+ without acidifying urine
30
Q

What happens to glutaminase if you are acidotic?

A

upregulated

31
Q

How is water reabsorbed in PT?

A
  • very leaky epithelium
  • Na dependent water reabsorption
  • thus anything you do to change Na reabsorption will change H2O reabsorption
  • oncotic pressure in PTC pulls water from interstitium into capillary to return to circulation
32
Q

Is fluid at end of PT hypo hyper or iso tonic?

33
Q

How does filtration fraction affect PT reabsorption?

A
  • high filtration fraction directly increases oncotic pressure in PTC
  • thus increases proximal tubule reabsoprtion
34
Q

What is glomerulartubular balance?

A
  • PT reabsorbs constant 2/3 of filtered material

- an increase in GFR will cause increase in amount of material reabsorbed in order to maintain this fraction

35
Q

What fraction of filtered material does PT reabsorb? How is that affected by GFR?

A
  • reabsorbs 2/3 of filtered material

- fixed fraction regardless of increase or decrease in GFR

36
Q

How does hydration status affect G-T balance?

A
  • when dehydrated or dehydrated we can reset that set point to higher or lower level
  • within shorter frame will maintain G-T balance around whatever the current set level is
37
Q

What percentage of filtered Na is reabsorbed in prox tubule?

38
Q

What percent of glucose reabsorbed in PT?

39
Q

What percent of protein reabsorbed in PT?

40
Q

What percent of AA reabsorbed in PT?

41
Q

What percent of urea is reabsorbed in PT?

42
Q

What percent of Cl reabsorbed in PT?

43
Q

What percent of HCO3 reabsorbed in PT?

44
Q

What percent of K reabsorbed in PT?

45
Q

What percent of Ca reabsorbed in PT?

46
Q

What percent of water reabsorbed in PT?

Physiology Part 2 (19 decks)

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