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Renal Physio > Tubular Transport > Flashcards

Flashcards in Tubular Transport Deck (57):
1

Changes in body Na content will result in

changes in the ECF volume

2

Na balance occurs when

Na input = Na output

3

(-) Na balance =

loss of Na content and loss in ECF volume

4

(+) Na balance =

increase in Na content and gain of ECF volume

5

a problem in Na balance would show up as a

altered ECF volume

6

What happens during Hyperaldosteronism

increased Na reabsorption, increased ECF volume, hypertension

7

Small changes in Na and H2O reabsorptive mechanisms result in

large changes in Na an dH2O excretion

8

Transport mechanisms for solutes

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

9

Solvent drag

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

10

Aquaporin-1

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

11

Aquaporin-2

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

12

Proximal tubule

main reabsorption of Na due to leaky epithelial junctions

13

Back-leak of Na

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)

14

Transporters

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

15

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

Tm = #of transporters x rate of transport

16

For reabsorption, if filtered load > Tm then

solute will appear in the urine

17

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

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

18

Na-glucose symport inhibitor will

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

19

SGLT2

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

20

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

glucose will be excreted to account for the difference

21

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

solute will be in the blood

22

Secretory transporters are non-specific for

organic anions, organic cations

23

Organic Anions compete for the same non-specific transporters

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

24

Organic cations compete for the same non-specific transporters

cimetidine, procainamide, histamine, and NE

25

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

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

26

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

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

27

Location of reabsorption

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

28

How does K differ from other solutes?

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

29

Transporters located in the early proximal tubule

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

30

What is reabsorbed in the late proximal tubule?

Cl and Na via paracellular pathway

31

What is reabsorbed in the proximal tubule?

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

32

Methods for Na reabsorption in the proximal tubule

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

33

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

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

34

How does the H+ secretion effect acid/base?

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

Transporters located in the thick ascending limb

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

36

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

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

37

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

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

38

What transporters are located in the early distal tubule?

Na/Cl symporter, Ca and Pi are also reabsorbed

39

Loop diuretics block

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

40

Thiazides block

Na/Cl symporter in the distal tubule

41

Aldosterone mechanism

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

Principal cells of the late distal tubule and collecting duct

reabsorb Na and H2O and secrete K

43

Intercalated cells if the late distal tubule and collecting duct

reabsorb K and secrete H or HCO3

44

Where is the main side of action for aldosterone?

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

45

How does aldosterone accomplish this effect on the principal cells?

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

46

Aldosterone is stimulated by

Ang II, high serum K, and plasma acidosis

47

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

CAP1 and SGK1

48

Amiloride diuretic acts by

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

49

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

positive; negative (allowing secretion of K)

50

Fractional excretion of Na (FENa) is the

fraction of the filtered Na load that is excreted

51

FENa =

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

52

FENa = ~

1%

53

FENa > 1

excreting more Na than expected

54

FENa < 1

retaining more Na than expected

55

FENa < 1 in acute renal injury means

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

56

FENa > 1 in acute renal injury means

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

57

Pre-renal causes of acute renal injury result from

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