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Renal Physio > Tubular Transport > Flashcards

Tubular Transport Flashcards

1
Q

Changes in body Na content will result in

A

changes in the ECF volume

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2
Q

Na balance occurs when

A

Na input = Na output

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3
Q

(-) Na balance =

A

loss of Na content and loss in ECF volume

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4
Q

(+) Na balance =

A

increase in Na content and gain of ECF volume

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5
Q

a problem in Na balance would show up as a

A

altered ECF volume

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6
Q

What happens during Hyperaldosteronism

A

increased Na reabsorption, increased ECF volume, hypertension

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7
Q

Small changes in Na and H2O reabsorptive mechanisms result in

A

large changes in Na an dH2O excretion

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8
Q

Transport mechanisms for solutes

A

active, diffusion (transcellular or paracellular), facilitated diffusion (transporter)

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9
Q

Solvent drag

A

H2O reabsorption allows solutes dissolved in the H2O to be reabsorbed via paracellular diffusion (Na, K, Cl, Mg, Ca)

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10
Q

Aquaporin-1

A

present in the proximal tubule, allows H2O to move rapidly from the tubule to the interstitium

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11
Q

Aquaporin-2

A

present in the collecting duct; under control of vasopressin (ADH)

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12
Q

Proximal tubule

A

main reabsorption of Na due to leaky epithelial junctions

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13
Q

Back-leak of Na

A

in the proximal tubule, Na can leak out or back into the tubule decreasing the amount of Na reabsorbed (always a net reabsorption of Na)

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14
Q

Transporters

A

transporters can become saturated, and therefore there is a maximum rate of transport for that solute

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15
Q

Maximum transport of a solute via a transporter protein (Tm)

A

Tm = #of transporters x rate of transport

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16
Q

For reabsorption, if filtered load > Tm then

A

solute will appear in the urine

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17
Q

Na-Glucose symport in the proximal tubule has a Tm of 375

A

if GFR = 100 and plasma [glucose] = 4 than filtered load FL= 400; meaning that 25mg/min of glucose would appear in the urine

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18
Q

Na-glucose symport inhibitor will

A

decrease the reabsorption of glucose by decreasing the Tm of the symporter, increasing excretion of glucose in urine

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19
Q

SGLT2

A

Na-glucose symporter in the proximal tubule; targeted inhibition for treatment of Type II diabetes

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20
Q

When filtration of glucose exceeds the transporters ability to transport Tm then

A

glucose will be excreted to account for the difference

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21
Q

If delivery of solute to the peri-tubular capillaries > Tm of secretory transport proteins, then

A

solute will be in the blood

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22
Q

Secretory transporters are non-specific for

A

organic anions, organic cations

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23
Q

Organic Anions compete for the same non-specific transporters

A

penicillin, PAH, probenecid, diuretics (furosemide and acetazolamide)

24
Q

Organic cations compete for the same non-specific transporters

A

cimetidine, procainamide, histamine, and NE

25
Q

Co-administration of 2 drugs that compete for the same secretory transporter will

A

increase the plasma concentration and time for excretion drastically for both drugs, may result in drug toxicity

26
Q

the Na/K ATPase sets the stage for ALL solute transfer in the proximal tubule

A

all solutes are carried by the passive movement of Na into the tubular cells down its gradient

27
Q

Location of reabsorption

A

67% in proximal tubule, 20% in thick ascending limb, veyr little “fine-tuned” in distal and collecting duct

28
Q

How does K differ from other solutes?

A

K can be SECRETED in the distal tubule if there is elevated intake of K

29
Q

Transporters located in the early proximal tubule

A

Na-H+ antiport, Na-solute (glucose, aa, lactate, phosphate) symport

30
Q

What is reabsorbed in the late proximal tubule?

A

Cl and Na via paracellular pathway

31
Q

What is reabsorbed in the proximal tubule?

A

Na, Cl, aa, glucose, lactate, and phospahte

32
Q

Methods for Na reabsorption in the proximal tubule

A

Na/H antiport, Na/solute symport, passive diffusion of Na and Cl, and solvent drag

33
Q

What is the osmolarity of the filtrate at the end of the proximal tubule?

A

isotonic to plasma (300), even though 67% of the Na and H2O have been reabsorbed

34
Q

How does the H+ secretion effect acid/base?

A

The more H+ that leaves the more CO2 + H2O that is converted into HCO3 and H+ and the more HCO3 is reabsorbed. Decreasing the acidity

35
Q

Transporters located in the thick ascending limb

A

Na/K ATPase, Na/K/2Cl symport, Na/H antiport

36
Q

Methods of Na reabsorption in the thick ascending limb of Loop of Henle

A

Na/Cl/K symport, Na-H antiport, Na paracellular diffusion

37
Q

The rate of the Na transport in the thick ascending limb is __________

A

LOAD-DEPENDENT; more Na delivered, more Na reabsorbed (constant Na arrives at distal tubule)

38
Q

What transporters are located in the early distal tubule?

A

Na/Cl symporter, Ca and Pi are also reabsorbed

39
Q

Loop diuretics block

A

Na/K/2Cl symporter in the thick ascending limb

40
Q

Thiazides block

A

Na/Cl symporter in the distal tubule

41
Q

Aldosterone mechanism

A

increased Na reabsorption in the thick ascending limb, distal tubule, and principal cells of distal tubule and collecting duct; by increasing Na/K ATPase, Na/K/Cl symporters, and Na/Cl

42
Q

Principal cells of the late distal tubule and collecting duct

A

reabsorb Na and H2O and secrete K

43
Q

Intercalated cells if the late distal tubule and collecting duct

A

reabsorb K and secrete H or HCO3

44
Q

Where is the main side of action for aldosterone?

A

principal cell of late distal tubule and collecting duct where Na is reabsorbed and K secreted

45
Q

How does aldosterone accomplish this effect on the principal cells?

A

synthesis of ENaC proteins or Na/K ATPase, cell signaling, increased ENaC conductance (via CAP1) and increased # of ENaC channels on surface (SGK1)

46
Q

Aldosterone is stimulated by

A

Ang II, high serum K, and plasma acidosis

47
Q

What 2 signalling molecules increase the conductance of ENaC due to Aldosterone?

A

CAP1 and SGK1

48
Q

Amiloride diuretic acts by

A

blocking the ENaC channel in the distal tubule and collecting duct to prevent Na reabsorption

49
Q

The charge in the tubular lumen is ______ in the thick ascending limb and __________ in the distal tubule

A

positive; negative (allowing secretion of K)

50
Q

Fractional excretion of Na (FENa) is the

A

fraction of the filtered Na load that is excreted

51
Q

FENa =

A

Na excreted / Na filtered = ((Una x Pcreat) / (Ucreat x PNa))

52
Q

FENa = ~

A

1%

53
Q

FENa > 1

A

excreting more Na than expected

54
Q

FENa < 1

A

retaining more Na than expected

55
Q

FENa < 1 in acute renal injury means

A

retaining more Na - reabsorptive function is intact, may mean decreased RBF and GFR = ischemia called PRE-RENAL

56
Q

FENa > 1 in acute renal injury means

A

excreting more Na than expected, reabsorptive function is impaired and INTRA-RENAL

57
Q

Pre-renal causes of acute renal injury result from

A

derangement in hemodynamics; volume depletion, decreased RBF (hemorrhage, vomiting, diarrhea, CHF)

Renal Physio (8 decks)

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