(7) Renal Transport Mechanism: NaCl and Water Absorptions Along the Nephron (Walker)

Question 1

What are the 5 barriers something must cross to be reabsorbed?

Answer 1

5 distinct barriers

1. Leave tubular fluid, cross luminal membrane of tubular cell
2. Pass through cytosol from one side of tubular cell to the other
3. Cross the basolateral membrane of the tubular cell to enter the interstitial fluid
4. Diffuse through the interstitial fluid
5. Penetrate the capillary wall to enter the plasma

*This is referred to as TRANS EPITHELIAL TRANSPORT

Question 2

Where are glucose and a.a. 100% reabsorbed in the nephron?

Answer 2

Proximal convoluted tubule

Question 3

Describe the Overview of reabsorption in the nephron

Answer 3

Question 4

The proximal tubule reabsorbs aproximately

__ - __ % of filtered water, Na+, Cl-, K+ and other solutes

Answer 4

65- 70%

Question 5

The proximal tubule reabsorbs virtually ALL of the ________ and ________ filtered by the glomerulus

Answer 5

Glucose

Amino acids

Question 6

What is the key element that is responsible for the properties of the proximal tubule?

Answer 6

Na-K ATPase pump

Question 7

Explain this graph

Answer 7

As you travel further down the proximal tubule, the amount of various solutes changes

Question 8

Diffusion:

Define

Transcellular

Paracellular

Answer 8

Transcellular = Through the cell membrane

Paracellular = Between cells

Question 9

Facilitated Diffusion:

Two types?

*Notable fact about FD?

Answer 9

Symport: coupled transport of two or more solutes in the same direction

Antiport: coupled transport of two or more solutes in the opposite direction

*At least one of the solutes is transported AGAINST its electrochemical gradient

Question 10

Na+/K+ ATPase pump

How many Na out?

How many K in?

Answer 10

3 Na out

2 K in

Question 11

How much Na+ is filtered and reabsorbed per day?

Answer 11

aprox. 25,000 mEq/day

Question 12

Describe how the Sodium/Hydrogen exchanger works

Answer 12

Question 13

More _____ than ______ is reabsorbed in the first half of the proximal tubule, and this causes the ____ concentration in tubular fluid to rise along the length of the proximal tubule

Answer 13

More __water___ than ___Cl-___ is reabsorbed in the first half of the proximal tubule, and this causes the __Cl-__ concentration in tubular fluid to rise along the length of the proximal tubule

Question 14

Chloride moves

Paracellularly? Intracellularly?

Answer 14

Paracellularly

Question 15

Paracellular movement is determined by the presence or the absence of….

Answer 15

Tight junctions b/w cells

(they retard water movement)

Question 16

Where are there a ton of tight junction proteins?

Answer 16

Thick ascending limb

&

Collecting duct

Question 17

What two aquaporin channels do we care about?

Answer 17

Aquaporin-1 (AQP-1)

Aquaporin-2 (AQP-2)

Question 18

Where is aquaporin-1 (AQP-1) found?

Answer 18

Proximal tubule

Question 19

Where is aquaporin-2 (AQP-2) found?

Answer 19

Collecting duct

Question 20

What two factors determine the water permeability of the renal tubule?

Answer 20

1. Presence/absence of tight junctions
2. Presence of aquaporin channels

Question 21

Aquaporin II is regulated by…

Answer 21

ADH

Question 22

At what point in the renal tubule does it become IMPERMEABLE to water?

Answer 22

Thin ascending limb

Question 23

The _______ part of the distal tubule is 0% permeable to water

Answer 23

Early

Question 24

SGLT2

Location?

How much glucose does it reabsorb?

Answer 24

S1/early part of PCT

90%

Question 25

SGLT1

Location?

How much glucose does it reabsorb?

Answer 25

S3/Distal part of PCT

10%

Question 26

What is an effective pharmacologic intervention for diabetes?

Answer 26

Inhibit the SGLT2 transporters

This will reduce the amount of glucose being reabsorbed into the bloodstream

Question 27

Describe the major characteristics of the loop of henle

Answer 27

H2O permeable

Solutes impermeable

Question 28

Describe the major characteristics of the Thin and Thick Ascending Loop

Answer 28

Permeable to NaCl (35-40 %) is reabsorbed here

IMPERMEABLE to water

Question 29

Where do your loop diuretics target?

Answer 29

Na-K-2Cl co transporter

on the THICK limb of the ascending limb

Question 30

Describe the countercurrent multiplier

Answer 30

Question 31

What type of transporter?

The THICK ASCENDING LIMB has:

The DISTAL TUBULE has:

Answer 31

The THICK ASCENDING LIMB has: Na-K-2Cl transporter

The DISTAL TUBULE has: Na-Cl transporter

Question 32

The collecting ducts are ________ to water in the absence of ADH

Answer 32

impermeable

Question 33

Function of aldosterone in the collecting duct?

Answer 33

“Fine-tunes” reabsorption of the remaining Na+

Question 34

Aldosterone aka

Answer 34

“Salt-retaining hormone”

Question 35

Goals of aldosterone?

Answer 35

• Acts on thick segment of nephron loop, DCT and cortical portion of collecting duct
• Net effect = body retains NaCl and water
• Urine volume is reduced
• Urine has elevated K+ concentration

Question 36

Major stimulus, Nephron site of action, effect on transport?

Answer 36

Question 37

What are the three major classes of diuretics?

Answer 37

Thiazide diuretics

Loop Diuretics (Furosemide)

K+ Sparing Spironolactone

Question 38

Thiazide Diuretics

Mode of action?

Answer 38

Inhibits the reabsorption of

Na+ and Cl-

In the cortical diluting segment of the DCT

DECREASES BLOOD VOLUME AND PRESSURE

Question 39

Loop Diuretics (Furosemide)

Mode of action?

Answer 39

Inhibits Na-K-2Cl cotransporter in the thick ascending limb

Decreases reabsorption of Na+, K+ and Cl-

Increased urine output

Question 40

K+ sparing Spironolactone

Mode of action?

Answer 40

Aldosterone-dependent potassium sparing diuretics

INHIBITS Na+/K+ exchange in the distal tubule and collecting duct

PROMOTES K+ retention and Na+ and water loss

HYPOTTENSIVE effect