Renal 5: Tubular Functions Along Nephron

Question 1

In the proximal nephron, there is high/low volume, high/low gradient pumping of solutes and water.

Answer 1

high, low

Question 2

How much of a filtered load is typically reabsorbed in the proximal nephron?

Answer 2

2/3

Question 3

What is the primary mechanism for reabsorption int he proximal tubule

Answer 3

Na+, K+, ATPase in basolateral membrane

Question 4

What transporters exist in the apical membrane in the first half of the proximal tubule?

Answer 4

Na+/H+ antiporter : couples entry of Na+ with extrusion of H+ (H+ secretion also leads to sodium bicarb reabsorption)
Na+/Glucose symporter (SGLT2)

Question 5

What transporters exist in the basolateral membrane in the first half of the proximal tubule?

Answer 5

Na+/K+ ATPase.
HCO3- transporter,
Glucose transporter (GLUT2)

Question 6

How is Na+ mainly reabsorbed in the second half of the proximal tubule?

Answer 6

With Cl- both transcellular and paracellularly

Question 7

What transporters exist in the apical membrane in the second half of the proximal tubule?

Answer 7

Parallel
Na+/H+ Antiporters
Cl-/anion antiporters
SGLT1 Na/glucose symporter (difference is 2Na per 1 glucose)

Question 8

What happens to the H+ and anion in the tubular fluid of the second half of the proximal tubule?

Answer 8

Combine and reenter the cell

Question 9

What transporters exist in the basolateral membrane in the second half of the proximal tubule?

Answer 9

Na+/K+ ATPase- Na+leaves cell and enters blood
K+/Cl- symporter- Cl- leaves cell and enters blood
GLUT1 glucose transporter

Question 10

In what part of the proximal tubule is the Na/K ATPase located?

Answer 10

basolateral membrane, both halves

Question 11

In what part of the proximal tubule is the SGLT2 located?

Answer 11

apical membrane, first half

Question 12

In what part of the proximal tubule is the GLUT1 located?

Answer 12

basolateral membrane, 2nd half

Question 13

In what part of the proximal tubule is the Na/H antiporter located?

Answer 13

apical membrane, both halves

Question 14

In what part of the proximal tubule is the anion/Cl- antiporter located?

Answer 14

apical membrane, 2nd half

Question 15

In what part of the proximal tubule is the K+/Cl- symporter located?

Answer 15

basolateral membrane, 2nd half

Question 16

In what part of the proximal tubule is the SGLT2 symporter located?

Answer 16

apical membrane, 1st half

Question 17

In what part of the proximal tubule is the GLUT2 transporter located?

Answer 17

basolateral membrane, 1st half

Question 18

In what part of the proximal tubule is the HCO3- transporter located?

Answer 18

basolateral membrane, 1st half

Question 19

Isosmotic Reabsorption

Answer 19

water reabsorption occurs in equal proportion wiht reabsorbed solutes

Question 20

How is the driving force for osmotic reabsorption of water across the proximal tubule established?

Answer 20

Via transport of solutes into lateral interceullar space, causing the osmolality of this compartment to increase

Question 21

How does the movement of solutes across the proximal tubule membranes affect osmosis?

Answer 21

It increases osmolarity on the basolateral side, favoring water transport to that side.

Question 22

What is an important consequence of osmotic water flow in the proximal tubule regarding potassium and calcium ions?

Answer 22

They are entrained in the reabsorbed fluid and thereby reabsorbed by the process of solvent drag.

Question 23

How much of filtered protein is reabsorbed in the proximal tubule?

Answer 23

100%

Question 24

What are the 2 causes of complete protein reabsorption in the proximal tubule?

Answer 24

enzymatic degradation of proteins to amino acids

encapsulation of proteins by pinocytic processes

Question 25

What causes proteinuria?

Answer 25

saturation of the transport process results in protein appearing in the urine.

Question 26

What happens to organic cations and anions in the proximal tubule?

Answer 26

actively secreted.

Question 27

What effect does cimetidine have on procainamide plasma concentration?

Answer 27

Increases (vice versa as well)

Question 28

Why is drug toxicity a danger for the cations of cimetidine and procainamide?

Answer 28

They elevate the plasma concentration of each other

Question 29

In the distal nephron, the kind of pumping that occurs is low/high volume and low/high gradient.

Answer 29

low, high

Question 30

What fraction of filtered loads is typically reabsorbed in the distal nephron?

Answer 30

1/3

Question 31

What conditions indicate the urine/plasma osmolality ration in the distal nephron being < 1

Answer 31

low ADH, dilute pale urine

Question 32

What conditions indicate the urine/plasma osmolality ratio in the distal nephron being >1

Answer 32

high ADH, concentrated dark urine

Question 33

Is the tubular lumen potential in the distal nephron strong or weak? What does this mean in regards to tight junctions there?

Answer 33

strong(-40 mV), tight junctions don't leak

Question 34

What is reabsorbed in the thin descending limb of the loop of Henle?

Answer 34

water

Question 35

What is reabsorbed in the thin ascending limb of the loop of Henle?

Answer 35

Na+ and Cl-

Question 36

What is not reabsorbed in the thin descending limb of the loop of Henle?

Answer 36

Na+ and Cl-

Question 37

What is not reabsorbed in the thin ascending limb of the loop of Henle?

Answer 37

water

Question 38

What is the prime mover in the loop of Henle?

Answer 38

Na+/K+ ATPase

Question 39

What channels are on the apical membrane in the thick ascending loop of henle?

Answer 39

K+ channel (ROMK) 1Na+-1K+-2Cl- Symporter (NKCC2) Na+/H+ Antiport

Question 40

What channels are on the basolateral membrane in the thick ascending loop of henle?

Answer 40

Cl- Channel (C1CNKB) Na/K ATPase K+/Cl- Symporter

Question 41

What is Bartter's syndrome caused by?

Answer 41

mutation in channels of ascending loop of henle?

Question 42

What channels are located in the early segment of the distal tubule?

Answer 42

apical: Na/Cl symporter basolateral: Na/K ATPase, Cl channel

Question 43

what channels are located in principle cells of the distal tubule?

Answer 43

Apical: Na channels inward, K channels outward Basolateral: Na/K ATPase, K channel outward

Question 44

What channels are located in intercalated cells of the distal tubule?

Answer 44

apical: H+ ATP pump, H/K ATPase Basolateral: Cl-/ HCO3- channel (out)

Question 45

What happens to salt and water reabsorption and the RAA system when extracellular volume decreases?

Answer 45

v ECV --> ^RAA system --> ^AT-II --> ^H2O, Na+, H+, Cl- reabsorption in proxmal tubule

Question 46

What happens to salt and water reabsorption and the RAA system when extracellular volume increases?

Answer 46

^ ECV --> v RAA system --> v AT-II --> v H2O, Na+, H+, Cl- reabsorption

Question 47

How does aldosterone regulate salt and water reabsorption

Answer 47

^ AT-II or ^ plasma K+ => ^ Aldosterone => ^ reabsorption of Na+ and Cl- in thick ascending loop of Henle, distal tubule, and collecting duct

Question 48

``` What is the effect of atrial natriuretic peptide on the following? natriuresis total peripheral resistance Na+ reabsorption ADH ```

Answer 48

increase decrease decrease decrease

Question 49

How does ANP and Urodilatin regulate salt and water reabsorption

Answer 49

^ ECFV or ^ Blood Volume => atrial stretch => ^ ANP => ^ natriuresis => v total peripheral resistance and v reabsorption of Na+, Cl- and v ADH

Question 50

What happens to sympathetic nervous activity and Na+ reabsorption with decreased ECV?

Answer 50

v ECV => ^ symp. activity => ^ NE and E => ^ Na+ and Cl- reabsorption in proximal and distal nephron

Question 51

What happens to Na+ reabsorption with increased dopamine?

Answer 51

decreased

Question 52

What happens to dopamine activity and Na+ reabsorption with increased ECV?

Answer 52

^ ECV => ^ dopamine => v Na+ and Cl- reabsorption in PT

Question 53

How does increased GFR affect Na+ reabsorption?

Answer 53

^ GFR => ^ filtered load of glucose and AAs => ^ H2O and Na+ reabsorption in PT

Question 54

What happens to Na+ reabsorption with increased antidiuretic hormone?

Answer 54

Nothing. Reabsorbs water in collecting duct with no effect on Na+/Cl- excertion

Question 55

What happens to peritubular cap reabsorption when glomerular cap filtration increases?

Answer 55

Increases

Question 56

What is meant by glomerulotubular balance?

Answer 56

Despite variations in GFR, a constant fraction of Na+ and H2O are still reabsorbed from the proximal tubule.

Question 57

What are the 3 routes of water transport across the proximal tubule?

Answer 57

1. solutes and water reabsorbed across apical membrane And then 2 paths: 2. solute and water cross the lateral cell membrane. 3. remainder enters interstitial space and flows into capillary.