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+ CAPS 301: Respiratory, Renal, GI, Endocrinology, Reproduction > Renal Transport > Flashcards

Renal Transport Flashcards

1
Q

Describe the polarity of epithelial cells.

A

(functionally distinct sides)

  • apical membrane
  • basolateral membrane
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2
Q

Where are tight junctions, and what do they do?

A

near apical surface

segregate membrane surfaces (and associated proteins) from one another – this determines function of epithelium (transport directionality)

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3
Q

Where are there transepithelial potential differences?

A

across peritubular/interstitial space (0 mv) and tubular lumen

  • interstitial space is always used as the references (0)
  • tubular lumen can be electronegative, neutral, or electropositive – has implications for ECs in terms of what types of transport is being favoured
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4
Q

What is the brush border?

A

membrane folding and villi on renal epithelial cells that amplify/enhance the apical surface area

  • greater SA for transport to occur across
  • especially important in proximal tubule, where bulk of transport occurs
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5
Q

Na+ Reabsorption

Where does the bulk of Na+ reabsorption occur?

A

proximal tubule

~2/3 reabsorbed by the time we reach the end of PT

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6
Q

Na+ Reabsorption

Where does regulation of Na+ reabsorption occur?

A

collecting duct

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7
Q

Na+ Reabsorption

What is the filtered load?

A

amount of Na+ in ultrafiltrate per day

GFR x [Na+]plasma

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8
Q

Na+ Reabsorption

What is fractional reabsorption?

A

fraction of Ma+ that has been successfully reabsorbed

1 - [Na+]tubular/[Na+]ultrafiltrate

where [Na+]tubular is the % of Na+ remaining along nephron
where [Na+]ultrafiltrate is the % of Na+ remaining in Bowman’s space (100%)

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9
Q

Na+ Reabsorption

What is fractional excretion?

A

how much Na+ being lost vs. how much has been filtered – amount of excretion is quite low compared to how much is filtered

excretory rate of Na+ / filtered load of Na+
= [Na+]urinary x V / GFR x [Na+]ultrafilitrate

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10
Q

Na+ Reabsorption

What is Na+ transport dependent on?

A
  • available transporters
  • regional permeability (regulated by tight junctions)
  • composition of the delivered tubular fluid (changes based on flow rate through nephron)
  • transepithelial voltage gradient (helps favour come types of transport)
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11
Q

Na+ Reabsorption

How much Na+ is reabsorbed (beginning from proximal tubule to collecting duct)?

A

almost 100% of the Na+ that gets filtered from glomerulus into the tubule

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12
Q

Na+ Reabsorption

Proximal Tubule – Mechanism

A

see notes

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13
Q

Na+ Reabsorption

Thin Descending Limb – Is the thin descending limb permeable to NaCl?

A

NO

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14
Q

Na+ Reabsorption

Thin Ascending Limb –Is the thin ascending limb permeable to NaCl?

A

YES – some/minimal passive Na+ reabsorption occurs (not much transport proteins contributing here)

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15
Q

Na+ Reabsorption

Thick Ascending Limb – Mechanism

A

see notes

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16
Q

Na+ Reabsorption

Distal Tubule – Mechanism

A

see notes

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17
Q

Na+ Reabsorption

Distal Tubule – Does the composition of proteins change along the tubule?

A

YES – composition of proteins (especially found on apical membrane) varies depending on part of distal tubule

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18
Q

Na+ Reabsorption

Distal Tubule – How can hypertension be reduced?

A

reduced amount of Na+ transport, paired with reduced H2O absorption

19
Q

Na+ Reabsorption

Distal Tubule – What are thiazides?

A

diuretics – help get rid of excess H2O, and slightly reduces blood presure

20
Q

Na+ Reabsorption

Distal Tubule – What are the principal cells?

A

DCT1 and DCT2

21
Q

Na+ Reabsorption

Collecting Duct – Mechanism

A

see notes

22
Q

What is the last portion of the nephron where fluid in the tubule is still modifiable?

A

collecting duct

23
Q

Na+ Reabsorption

Collecting Duct – Why is this part of the tubule so important?

A

regulates Na+ reabsorption

more fine tuning and regulation of the final composition of fluid

24
Q

Na+ Reabsorption

Collecting Duct – Mechanism

A

see notes

25
Q

Where does bulk K+ reabsorption occur?

A

proximal tubule

26
Q

Where is K+ reabsorption the same for all K+ levels? Where is it different?

A

PT and TAL reabsorption is same for all K+ levels

CD reabsorption is different for normal/elevated vs. low K+ levels

27
Q

Where does regulation of K+ reabsorption/secretion occur?

A

collecting duct

28
Q

What happens if there is normal/elevated K+ levels in the collecting duct?

A

secretion predominates – K+ leaves blood, and going to be excreted

29
Q

What happens if there is low K+ levels in the collecting duct?

A

reabsorption predominates – excrete < 1% of K+ filtered

30
Q

What does K+ concentration determine in the collecting duct?

A

direction of transport – secretion vs. reabsorption

31
Q

K+ Reabsorption

Proximal Tubule –Mechanism

A

see notes

32
Q

What does transport do?

A

alters tubular fluid composition and decreases flow rate

33
Q

What is the TF/P ratio?

A

ratio of concentration of solute (x) in tubular fluid to solute (x) in plasma at a given distance along PT

  • describes how composition of tubular fluid is changing compared to fluid in plasma
34
Q

What is the filtrate in the glomerulus very similar to?

A

composition to plasma – EXCEPT there is no protein in filtrate

35
Q

What is used as the reference point when observing TF/P ratios? Why?

A

inulin

  • substance is freely filtered at glomerulus, and is NOT reabsorbed/secreted – therefore, amount of inulin in tubular fluid is constant
  • use as reference to observe how other things in PT fluid are changing
36
Q

What decreases TF/P?

A

reabsorption of valuable substances – such as glucose, amino acids, HCO3-

37
Q

What increases TF/P?

A

reabsorption of Na+ (less) and Cl- (more)

38
Q

From beginning to end of proximal tubule, how does fluid composition resemble?

A

goes from closely resembling plasma (without protein) to becoming essentially NaCl

39
Q

In the proximal tubule why is transepithelial potential (PD) inegative at beginning, but then becomes positive?

A

initially negative because there is very little Cl- movement

later movement of Cl- makes it positive

40
Q

How does proximal tubular fluid flow rate change along the tubule?

A

decreases progressively – result of bulk H2O reabsorption into bloodstream

41
Q

K+ Reabsorption

Thick Ascending Limb – Mechanism

A

see notes

42
Q

K+ Secretion

Distal Convoluted Tubule – Mechanism

A

see notes

43
Q

K+ Handling

Collecting Duct – Mechanism

A

see notes

44
Q

Where does bulk K+ reabsorption occur?

A
  • PT

- TAL – paired with Na+ reabsorption

+ CAPS 301: Respiratory, Renal, GI, Endocrinology, Reproduction (32 decks)

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