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38 Cards in this Set

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Interpret: [TF/P]x = 1.0
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
Interpret: [TF/P]x < 1.0
x is reabsorbed more than water

ex. glucose in proximal tubule (glucose reabsorbed more than water here)
Interpret: [TF/P]x > 1.0
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)
What does the [TF/P]inulin measure?
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
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?
2.0
What are inulin's 3 functions?
1) ECF marker
2) measures GFR (Cinulin)
3) measures water reabsorption
What does the "double ratio" tell us?
fraction of the filtered load of a substance remaining in the nephron at any point
Interpret a double ration for Na+ of 0.33 and a [TF/P]Na of 1.0. Where would this happen?
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.
What is the MOST IMPORTANT function of the kidneys?
Na+ regulation
How much Na+ is ingested/excreted per day?
about 150 mEq of Na+
If the kidneys excrete more Na+ than is injecsted, what kind of 'balance' is the body in?
negative Na+ balance
Give the % of Na+ reabsorption by location in the nephron.
proximal tubule - 67%
thick ascending limb - 25%
early distal tubule - 5%
late distal tubule and collecting duct - 3%
(<1% is excreted)
What are the 9 main features of the EARLY proximal tubule?
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
What are the 7 main features of the LATE proximal tubule?
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
What happens to the isosmotic reabsorption process if more Na+ is filtered?
nothing - isosmotic reabsorption is maintain by increasing Na+ reabsorption
What is glomerulotubular balance?
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!
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.
volume expansion = dilution = decrease in oncotic press in peritubular cap blood = decrease in Na/water reabsorption
Can the % of Na reabsorbed in the proximal tubule change?
yes - if ECF volume changes
What happens to the amount of Na+ reabsorbed in the prox tubule in ECF volume expansion?
fractional reabsorption is decreased (due to decreased oncotic press in PT capill), and excretion is increased
What happens to the amount of Na+ reabsorbed in the prox tubule in ECF volume contraction?
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
What is unique about the thick ascending loop of henle?
it is impermeable to water
(but DOES reabsorb solute)

*this is why it is called the Diluting Segment
How much of Na+ is reabsorbed in the Thick ascending limb?
25%
What is [TF/P]Na and [TF/P]osm in the TAL?
<1.0

(because tubular fluid is more dilute than plasma)
What transporters are located in the TAL?
Na/K/2Cl- in luminal membrance, and Na/K ATPase on basolateral membrane
What hormone specifically stimulates Na+ reabsorption in the proximal tubule?
Angiotensin II
What is an example of a loop diuretic, and how does it work in the TAL?
furosemide - inhibits the Na/K/2Cl- cotransporter by binding to the Cl- binding site thus inhibiting Na+ reabsorption
(is a weak acid)
What is important about the luminal potential pressure here?
it is (+), and drives the reabsorption of Ca2+ and Mg2+ between cells
(IMPORTANT BECAUSE LOOP DIURETICS ABOLISH THE (+) LUMINAL POTENTIAL)
Is the 3-ion cotransporter in the TAL electrogenic?
yes -- some K+ diffuses back into the tubular lumen giving the lumen a net (+) charge
What is the [TF/P]Na and [TF/P]osm in the TAL?
<1.0
What characterizes the early distal tubule?
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
Which is stronger between loop diuretics (furosemide working in TAL) or thiazide diuretics (working in the early distal tubule)?
loop diuretics
Which cells in the late distal tubule and collecting ducts reabsorbs Na+?
principal cells
What 2 hormones work in the late distal tubule and collecting duct areas?
1) ADH
2) Aldosterone
What are the 3 functions of principal cells?
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)
What are the 2 functions of intercalated cells?
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)
What are aldosterone's 3 actions? IMPORTANT!!!
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
What is responsible for "fine tuning " Na+ reabsorption in the nephron?
the principal cells
Which cells do spironolactone and amiloride (K-sparing diuretics) affect?
the principal cells - by blocking Na+ channels