Lecture 3- Renal Transport

Question 1

How much fluid does the kidney filter per day?

Answer 1

180 L

Question 2

> 99% of filtered

Answer 2

water, Na, Cl, and HCO3

Question 3

100% of filtered

Answer 3

glucose are reabsorbed

Question 4

Facilitated diffusion

Answer 4

• passive movement of solute

- i.e. glucose transport

Question 5

Coupled transport

Answer 5

• movement of two solutes. couples
• cotransport: solutes move in same direction (Na/glucose cotransporter)
• antiport: solutesmove in opposite direction (Na/H antiporter)

Question 6

active transport

Answer 6

movement of solute up a concentration gradient

• require input of energy
• Na/K ATPase

Question 7

endocytosis

Answer 7

invagination of region of plasma membrane

• captures material in extracellular space
• internalize material w/in endosome then traffic to lysosome for degradation

Question 8

transcellular

Answer 8

through apical surface; through cell into basolateral surface

Question 9

paracellular

Answer 9

between cells via junction (i.e. water and solutes – solvent drag)

Question 10

Transport in the proximal tubule

Answer 10

67% of Na, Cl, and water is reabsorbed into PT
-reabsorption is iso-osmotic since reabsorption of water follows uptake of solutes
-primary driving force for transport = Na/K ATPase
(low cytoplasmic Na concentration in tubular cells)

Question 11

First Half of the Proximal Tubule

Na+ Reabsorption Coupled to HCO3- Reabsorption

Answer 11

1. Na+ crosses apical membrane via Na+/H+ antiporter
2. Lumenal H+ facilitates HCO3- uptake
3. Cytoplasmic CO2 converted to H+ and HCO3- by carbonic annhydrase (CA)
4. Cytoplasmic HCO3- crosses basolateral membrane via Cl-/HCO3- exchanger and Na+/HCO3- cotransporter
5. CA inhibitors at as diuretics

Question 12

First Half of the Proximal Tubule

Na+ Reabsorption Coupled to Sugar and Amino Acid

Answer 12

1. Low cytoplasmic Na+ drives uptake of sugars and amino acids across apical membrane via Na+-coupled cotransporters
2. Sugars and amino acids cross the basolateral membrance via passive transport

Question 13

Cystinuria

Answer 13

caused by loss of a Na-coupled amino acid transporter (characterized by kidney stones)

Question 14

Second Half of the Proximal Tubule

Answer 14

1. Na+ moves across apical membrane via Na+/H+ antiporter
2. H+ re-enter from lumen by combining with anions (i.e. formate)
3. Anions recycled to lumen via Cl-/anion exchanger (also allows for Cl- uptake)
4. Cl- crosses basolateral membrane via K+/Cl- cotransporter
5. Cl- also leaves lumen by paracellular pathway: transepithelial membrane potential (lumen positive); additional Na+ reabsorption

Question 15

Thin Descending portion of loop of Henle

Answer 15

HIGHLY permeable to WATER

allows extensive water reabsorption

Question 16

Thick Ascending portion of loop of Henle

Answer 16

IMPERMEABLE to water but permeable to Na and Cl (allows salt reabsorption)

Question 17

Thick Ascending Loop of Henle

Answer 17

Na/K+/Cl- transporter

• driven by Na gradient
• electroneutral
• inhibited by furosemide (loop direutic)
• K+ exits lumen, creating lkumen positive trans epithelial potential that drives paracellular uptake of cations

Question 18

High ADH

distal and CD

Answer 18

high water permeability > extensive reabsorption of water > concentrate urine

Question 19

Low ADH

distal and CD

Answer 19

low water permeability > extensive excretion of water > dilute urine

Question 20

Early Part of Distal Tubule

Answer 20

• Impermeable to water
• Na+ and Cl- reabsorbed via Na+/Cl- cotransporter (inhibited by thiazide diuretics)
• Na+ crosses basolateral membrane via Na+/K+ ATPase
• Cl- crosses basolateral membrane via Cl- channels

Question 21

Principal Cells

Answer 21

absorb Na+ via apical Na+ channels

Question 22

Principal Cells of Late Distal Tubule and CD

Answer 22

• Na+ channels inhibited by amiloride diuretics
• Principal cells have K+ channels, allowing secretion into lumen
• Principal cells have ADH-sensitive water channels that help w/ reabsorption

Question 23

Liddle’s Syndrome

Answer 23

mutation in Na+ channel > ↑ reabsorption > ↑ BP

Question 24

Diabetes Insipidous

Answer 24

no ADH response

Question 25

Intercalated cells of Late Distal Tubule and CD

Answer 25

• a-intercalated cells have apical proton pump (V-ATPase) that pumps H+ into the lumen
• a-intercalated cells also have basolateral HCO3-/Cl- exchanger

Question 26

vacuolar H+ ATPase (V-ATPase)

Answer 26

Responsible for H+ secretion into a-intercalated cells in DT and CD

Question 27

renal tubule acidosis

Answer 27

Responsible for H+ secretion into a-intercalated cells in DT and CD
Genetic defects in renal specific isoforms of certain subunits

Question 28

Agents that Increase NaCl and/or Water Reabsorption by the Renal Tubule

Answer 28

LOOK AT CHART

Question 29

antidiruretic hormone (ADH)

Answer 29

stimulated by: low BP/volume or increased plasma osmolarity
Site: DCT/CD
no effect on NaCl
increases water reabsorption

Question 30

starling forces

Answer 30

Movement of water (and solutes) into blood is favored by Pi and (pi)c and opposed by Pc and (pi)I

Question 31

increase GFR

Answer 31

increase filtration of blood = increase protein concentration in blood in peritubular capillaries= increased movement of water (and solutes) into blood and decreased backleak into tubular fluid

prevents large changes in Na excretion when GFR changes