Na+ Transport I And Ii

Front 1

Interpret: [TF/P]x = 1.0

Back 1

x is not reabsorbed or secreted
OR
x is reabsorbed in proportion to water
ex. all freely filtered items in Bowman's space and Na+ in proximal tubule

Front 2

Interpret: [TF/P]x < 1.0

Back 2

x is reabsorbed more than water

ex. glucose in proximal tubule (glucose reabsorbed more than water here)

Front 3

Interpret: [TF/P]x > 1.0

Back 3

x is reabsorbed less than water
OR
x is secreted
ex. urea in cortical collecting ducts in the presence of ADH (water reabsorbed and urea not reabsorbed)

Front 4

What does the [TF/P]inulin measure?

Back 4

water reabsorption

* amount of inulin is constant in the tube, but the concentration of inulin in the tube varies based on amount of water reabsorbed

Front 5

If the tubular inulin conc is 1.0, and 50% of the water is reabsorbed, what is the new conc of inulin in the tubular fluid?

Back 5

2.0

Front 6

What are inulin's 3 functions?

Back 6

1) ECF marker
2) measures GFR (Cinulin)
3) measures water reabsorption

Front 7

What does the "double ratio" tell us?

Back 7

fraction of the filtered load of a substance remaining in the nephron at any point

Front 8

Interpret a double ration for Na+ of 0.33 and a [TF/P]Na of 1.0. Where would this happen?

Back 8

At the end of the proximal tubule 67% of Na+ has been reabsorbed (33% still in nephron), and it has been reabsorbed in the same proportion as water.

Front 9

What is the MOST IMPORTANT function of the kidneys?

Back 9

Na+ regulation

Front 10

How much Na+ is ingested/excreted per day?

Back 10

about 150 mEq of Na+

Front 11

If the kidneys excrete more Na+ than is injecsted, what kind of 'balance' is the body in?

Back 11

negative Na+ balance

Front 12

Give the % of Na+ reabsorption by location in the nephron.

Back 12

proximal tubule - 67%
thick ascending limb - 25%
early distal tubule - 5%
late distal tubule and collecting duct - 3%
(<1% is excreted)

Front 13

What are the 9 main features of the EARLY proximal tubule?

Back 13

1) isosmotic reabsorption
2) Na+ glucose cotransporter (Na+ phosphate and Na+ aa also)
3) Na+/H+ exchange on luminal membrane and Na+/K+ ATPase on basolateral membrane
4) lumen has (-) transepithelium difference due to Na+/glucose transport
5) [TF/P]Na and [TF/P]osm = 1.0
6) preferential reabsorption of HCO3- over Cl-
7) reabsorb most vital nutrients here!
8) reabsorb 33% of Na
9) Na/P cotransport inhibited by PTH

Front 14

What are the 7 main features of the LATE proximal tubule?

Back 14

1) isosmotic reabsorption
2) 33% of Na reabsorbed here
3) high [Cl-] in lumen
4) Cl- moves into cells and between cells down conc grad, and also via Cl-/formate exchange on luminal membrane
5) lumen (+) transepith pot diff created by Cl- diffusion
6) [TF/P]Na and [TF/P]osm = 1.0
7) still have Na+/H+ exchange and Na+/K+ ATPase on basolateral membrane

Front 15

What happens to the isosmotic reabsorption process if more Na+ is filtered?

Back 15

nothing - isosmotic reabsorption is maintain by increasing Na+ reabsorption

Front 16

What is glomerulotubular balance?

Back 16

a regulatory feature of the proximal tubule - filtration of Na+ balanced by reabsorption -> constant fractional reabsorption of 67% (normally) -> ECF Na+ content and volume are maintained
THE ONCOTIC PRESSURE OF THE PERITUBULAR CAPILLARY MAINTAINS THE GT BALANCE!

Front 17

Explain what happens to the oncotic pressure of the peritubular capill blood and to the proximal tubule reabsorption of Na+ and water when ECF volume INCREASES.

Back 17

volume expansion = dilution = decrease in oncotic press in peritubular cap blood = decrease in Na/water reabsorption

Front 18

Can the % of Na reabsorbed in the proximal tubule change?

Back 18

yes - if ECF volume changes

Front 19

What happens to the amount of Na+ reabsorbed in the prox tubule in ECF volume expansion?

Back 19

fractional reabsorption is decreased (due to decreased oncotic press in PT capill), and excretion is increased

Front 20

What happens to the amount of Na+ reabsorbed in the prox tubule in ECF volume contraction?

Back 20

fractional reabsorption is increased because of:
1)increase in oncotic press of PT capill
2) decrease in Pa, increase in sympathetics
3) decrease in Pa, increase in RAA, increase in AII, increase in Na/H cotransport

Front 21

What is unique about the thick ascending loop of henle?

Back 21

it is impermeable to water
(but DOES reabsorb solute)

*this is why it is called the Diluting Segment

Front 22

How much of Na+ is reabsorbed in the Thick ascending limb?

Back 22

25%

Front 23

What is [TF/P]Na and [TF/P]osm in the TAL?

Back 23

<1.0

(because tubular fluid is more dilute than plasma)

Front 24

What transporters are located in the TAL?

Back 24

Na/K/2Cl- in luminal membrance, and Na/K ATPase on basolateral membrane

Front 25

What hormone specifically stimulates Na+ reabsorption in the proximal tubule?

Back 25

Angiotensin II

Front 26

What is an example of a loop diuretic, and how does it work in the TAL?

Back 26

furosemide - inhibits the Na/K/2Cl- cotransporter by binding to the Cl- binding site thus inhibiting Na+ reabsorption
(is a weak acid)

Front 27

What is important about the luminal potential pressure here?

Back 27

it is (+), and drives the reabsorption of Ca2+ and Mg2+ between cells
(IMPORTANT BECAUSE LOOP DIURETICS ABOLISH THE (+) LUMINAL POTENTIAL)

Front 28

Is the 3-ion cotransporter in the TAL electrogenic?

Back 28

yes -- some K+ diffuses back into the tubular lumen giving the lumen a net (+) charge

Front 29

What is the [TF/P]Na and [TF/P]osm in the TAL?

Back 29

<1.0

Front 30

What characterizes the early distal tubule?

Back 30

1) impermeable to water
2) "cortical diluting segment"
3) Na/Cl cotransporter in luminal membrane
4) 5% of Na+ reabsorbed here
5) thiazide diuretic works here (by inhibiting Na/Cl- cotransporter)
6) Ca2+ reabsorption stimulated by PTH
7) [TF/P]Na and [TF/P]osm <1.0

Front 31

Which is stronger between loop diuretics (furosemide working in TAL) or thiazide diuretics (working in the early distal tubule)?

Back 31

loop diuretics

Front 32

Which cells in the late distal tubule and collecting ducts reabsorbs Na+?

Back 32

principal cells

Front 33

What 2 hormones work in the late distal tubule and collecting duct areas?

Back 33

1) ADH
2) Aldosterone

Front 34

What are the 3 functions of principal cells?

Back 34

1) Na+ reabsorption (thru Na+ channels induced by aldosterone)
2) K+ secretion (thru K+ channels on luminal side induced by aldosterone)
3) water reabsorption (thru AQP2 channels induced by ADH)

Front 35

What are the 2 functions of intercalated cells?

Back 35

1) K+ reabsorption (thru H+/K+ ATPase - same transporter that secretes acid from parietal cells in the stomach)
2) H+ secretion (thru H+ ATPase upregulated by aldosterone)

Front 36

What are aldosterone's 3 actions? IMPORTANT!!!

Back 36

1) induces Na+ channels - increase Na+ reabsorption in the principal cells
2) adds K+ channels - increases K+ secretion in principal cells
3) stimulates H+ secretion in intercalated cells

Front 37

What is responsible for "fine tuning " Na+ reabsorption in the nephron?

Back 37

the principal cells

Front 38

Which cells do spironolactone and amiloride (K-sparing diuretics) affect?

Back 38

the principal cells - by blocking Na+ channels