Tubular Transport

Question 1

Changes in body Na content will result in

Answer 1

changes in the ECF volume

Question 2

Na balance occurs when

Answer 2

Na input = Na output

Question 3

(-) Na balance =

Answer 3

loss of Na content and loss in ECF volume

Question 4

(+) Na balance =

Answer 4

increase in Na content and gain of ECF volume

Question 5

a problem in Na balance would show up as a

Answer 5

altered ECF volume

Question 6

What happens during Hyperaldosteronism

Answer 6

increased Na reabsorption, increased ECF volume, hypertension

Question 7

Small changes in Na and H2O reabsorptive mechanisms result in

Answer 7

large changes in Na an dH2O excretion

Question 8

Transport mechanisms for solutes

Answer 8

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

Question 9

Solvent drag

Answer 9

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

Question 10

Aquaporin-1

Answer 10

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

Question 11

Aquaporin-2

Answer 11

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

Question 12

Proximal tubule

Answer 12

main reabsorption of Na due to leaky epithelial junctions

Question 13

Back-leak of Na

Answer 13

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)

Question 14

Transporters

Answer 14

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

Question 15

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

Answer 15

Tm = #of transporters x rate of transport

Question 16

For reabsorption, if filtered load > Tm then

Answer 16

solute will appear in the urine

Question 17

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

Answer 17

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

Question 18

Na-glucose symport inhibitor will

Answer 18

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

Question 19

SGLT2

Answer 19

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

Question 20

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

Answer 20

glucose will be excreted to account for the difference

Question 21

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

Answer 21

solute will be in the blood

Question 22

Secretory transporters are non-specific for

Answer 22

organic anions, organic cations

Question 23

Organic Anions compete for the same non-specific transporters

Answer 23

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

Question 24

Organic cations compete for the same non-specific transporters

Answer 24

cimetidine, procainamide, histamine, and NE

Question 25

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

Answer 25

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

Question 26

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

Answer 26

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

Question 27

Location of reabsorption

Answer 27

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

Question 28

How does K differ from other solutes?

Answer 28

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

Question 29

Transporters located in the early proximal tubule

Answer 29

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

Question 30

What is reabsorbed in the late proximal tubule?

Answer 30

Cl and Na via paracellular pathway

Question 31

What is reabsorbed in the proximal tubule?

Answer 31

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

Question 32

Methods for Na reabsorption in the proximal tubule

Answer 32

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

Question 33

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

Answer 33

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

Question 34

How does the H+ secretion effect acid/base?

Answer 34

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

Question 35

Transporters located in the thick ascending limb

Answer 35

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

Question 36

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

Answer 36

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

Question 37

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

Answer 37

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

Question 38

What transporters are located in the early distal tubule?

Answer 38

Na/Cl symporter, Ca and Pi are also reabsorbed

Question 39

Loop diuretics block

Answer 39

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

Question 40

Thiazides block

Answer 40

Na/Cl symporter in the distal tubule

Question 41

Aldosterone mechanism

Answer 41

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

Question 42

Principal cells of the late distal tubule and collecting duct

Answer 42

reabsorb Na and H2O and secrete K

Question 43

Intercalated cells if the late distal tubule and collecting duct

Answer 43

reabsorb K and secrete H or HCO3

Question 44

Where is the main side of action for aldosterone?

Answer 44

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

Question 45

How does aldosterone accomplish this effect on the principal cells?

Answer 45

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

Question 46

Aldosterone is stimulated by

Answer 46

Ang II, high serum K, and plasma acidosis

Question 47

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

Answer 47

CAP1 and SGK1

Question 48

Amiloride diuretic acts by

Answer 48

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

Question 49

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

Answer 49

positive; negative (allowing secretion of K)

Question 50

Fractional excretion of Na (FENa) is the

Answer 50

fraction of the filtered Na load that is excreted

Question 51

FENa =

Answer 51

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

Question 52

FENa = ~

Answer 52

1%

Question 53

FENa > 1

Answer 53

excreting more Na than expected

Question 54

FENa < 1

Answer 54

retaining more Na than expected

Question 55

FENa < 1 in acute renal injury means

Answer 55

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

Question 56

FENa > 1 in acute renal injury means

Answer 56

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

Question 57

Pre-renal causes of acute renal injury result from

Answer 57

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