Na+ Transport 1, 2

Front 1

What is tubular/luminal fluid analogous to?

Back 1

Urine

Front 2

Is the concentration of substance X in plasma [P]x assumed constant?

Back 2

YES

Front 3

What is SNGFR?

Back 3

Single Nephron GFR

Front 4

Do changes in concentration of substance X reflect tubular fluid or plasma?

Back 4

Tubular fluid. Plasma is assumed constant.

Front 5

What does it mean if [TF/P]x = 1

Back 5

The concentration of X in tubular fluid and plasma are the same. There has either a) Been no reabsorption or secretion or B) it's been reabsorbed in proportion to water.

Front 6

What does it mean if [TF/P]x < 1

Back 6

Tubular fluid concentration of X is less than plasma. There has been net reabsorption. Tubular fluid is reabsorbed more than water.

Front 7

What is an example of a substance with a [TF/P]x <1?

Back 7

Glucose. Special transporters remove it.

Front 8

What does it mean if [TF/P]x > 1

Back 8

Water is reabsorbed more than X. There is higher concentration of X in tubular fluid than in plasma. Could also mean X is secreted into tubular fluid.

Front 9

What's an example of a substance where [TF/P]x > 1?

Back 9

Without ADH, urea is not reabsorbed but water is.

Front 10

What is special about [TF/P]_inulin?

Back 10

Used to measure water reabsorption since inulin, after filtered, is neither reabsorbed nor secreted. So, the AMOUNT of inulin is the same along the tubule, but as the amount of water changes, the CONCENTRATION of inulin changes.

Front 11

What's the formula for the fraction of filtered water that's reabsorbed?

Back 11

1 - (1/[TF/P]_inulin)

Front 12

What is the double ratio? What's the significance?

Back 12

[TF/P]_X/[TF/P]_inulin

It's the fraction of the filtered load of a substance remaining.

Front 13

What is the proximal convoluted tubule permeable to?

Back 13

Na+ (and other solutes) and water

Front 14

What %age of Na+ is reabsorbed in the proximal convoluted tubule?

Back 14

About 66%

Front 15

What is the major force that drives reabsorption?

Back 15

Hi oncotic pressure of peritubular capillary blood

Front 16

What is glomerulotubular balance?

Back 16

Glomerular filtration is balanced by reabsorption --> constant fractional reabsorption of 2/3

Front 17

Which anion (Cl- or HCO3-) is preferentially absorbed as the counterpart to Na+ in the early proximal tubule?

Back 17

HCO3-

Front 18

Which anion (Cl- or HCO3-) is preferentially absorbed as the counterpart to Na+ in the <b>late </b>proximal tubule?

Back 18

Cl-

Front 19

What kinds of co-transporters are there in the early prox. tubule?

Back 19

Na-phosphate; Na-glucose; Na-amino acid. These all work by moving solute down Na's concentration gradient.

Front 20

There is a lumen (negative, positive) transepithelial potential difference in the early proximal tubule. Where does it come from?

Back 20

Negative. Comes from glucose-Na transporter (no counterpart negative ion)

Front 21

What part of the early proximal tubule solute movement uses ATP directly? (primary active transport)

Back 21

The Good Ol' Na+/K+ pump.

Front 22

What side of cell (blood or lumen) is the Na/K pump on?

Back 22

Blood

Front 23

What is the [TF/P]Na and [TF/P]osm in the proximal tubule? (both late and early)

Back 23

1.0 because it's absorbed in directly proportion with water. Isosmotic.

Front 24

What is the high luminal concentration of Cl- in the Late prox tubule caused by? What is the significance?

Back 24

The preferential reabsorption of bicarb for Cl- in early proximal tubule. Significance is Cl- gets reabsorbed by Cl-formate exchange (formate moves out, Cl- moves into cell)

Front 25

There is a lumen (negative, positive) transepithelial potential difference in the late proximal tubule. Where does it come from

Back 25

Positive. Created by Cl- diffusion

Front 26

What is the only place in the nephron where Cl- movement drives Na+ movement?

Back 26

The late proximal convoluted tubule. It occurs because [TF/P]Cl >1 because bicarb is preferentially removed in the early proximal tubule, which concentrates the Cl-.

Front 27

What %age of the the filtered Na+ does the thick ascending limb reabsorb?

Back 27

25%

Front 28

Why is the thick ascending limb called the diluting segment?

Back 28

Because it's impermeable to water. Solute moves out, but water doesn't --> tubular fluid is diluted.

Front 29

What are [TF/P]Na and [TF/P]Osm in thick ascending limb?

Back 29

Both <1.0, because water cannot move with solute

Front 30

What cotransporter is found in the lumen of the thick ascending limb? What type is it?

Back 30

The Na+/K+/2Cl- cotransporter. It's secondary active with energy come from Na+ moving down its gradient.

Front 31

There is a lumen (negative, positive) transepithelial potential difference in the thick ascending limb. Where does it come from?

Back 31

Positive. Although it seems like the Na+/K+/2Cl- cotransporter would be electroneutral, remember K+ can move back down its gradient, but Cl- can't. Thus, positive potential.

Front 32

What class of diuretics acts on the thick ascending limb?

Back 32

Loop diuretics (e.g., furosemide). Most powerful

Front 33

How do loop diuretics work?

Back 33

They inhibit the Na+/K+/2Cl- cotransporter, thereby inhibiting Na+ reabsorption (the basis of their diuretic action).

Front 34

Together, what %age of filtered Na+ do the distal tubule and collecting ducts reabsorb?

Back 34

8%

Front 35

What %age of filtered Na+ do the early distal tubule reabsorb?

Back 35

5%

Front 36

What %age of filtered Na+ do the collecting ducts/late distal tubule reabsorb?

Back 36

3%

Front 37

Like the thick ascending limb, cells of early distal tubule are ____________ to water.

Back 37

impermeable.

Front 38

What is the cortical diluting segment?

Back 38

The early distal tubule

Front 39

What are [TF/P]Na and [TF/P]Osm in early distal tubule?

Back 39

Both <1, water can't move with solutes.

Front 40

What diuretics class works on the early distal tubule?

Back 40

Thiazide diuretics.

Front 41

How do thiazide diuretics work?

Back 41

They block the Na+/Cl- cotransporter in the early distal tubule.

Front 42

Ca2+ reabsorption in the early distal tubule is (active, passive) and stimulated by _______ and ________.

Back 42

Active Parathyroid hormone (PTH) and thiazide diuretics

Front 43

What are the two cell types of late distal tubule/collecting ducts?

Back 43

Principal, Intercalated

Front 44

Which cell types of late distal tubule/collecting ducts reabsorb Na+?

Back 44

Principal

Front 45

What are the 3 functions of the principal cells?

Back 45

1) Reabsorb Na+ via ENaC.
2) Induce K+ channel to increase K+ secretion
3) Reabsorb water.

Front 46

What regulates changes in water reabsorption by principal cells of late distal tubule/collecting ducts?

Back 46

ADH.
In presence of ADH (V2 receptor), production of aquaporins (water channels) are stimulated.

Front 47

What is the site of action of K+ sparing diuretics?

Back 47

Principal cells of late distal tubule/collecting ducts

Front 48

What are the two functions of the intercalated cells?

Back 48

1) Can reabsorb K+ in low K+ diet
2) Secrete H+ (increased by aldosterone)

Front 49

What induces Na+ channels (ENaC) in the principal cells?

Back 49

Aldosterone

Front 50

Why is oncotic pressure of the peritubular capillaries so high?

Back 50

Lots of water and small solutes has been removed by filtration. However, large solutes and proteins DID NOT GO THRU THE GLOMERULUS INTO BOWMAN'S SPACE. This increases the oncotic pressure.

Front 51

What does an increase in GFR do to the capillary oncotic pressure?

Back 51

It increases it.

Front 52

What does increased capillary oncotic pressure (due to increased GFR) do to reabsorption in the proximal tubule?

Back 52

Increases it.