L54

Question 1

What layer of the kidney contains the glomeruli?

Answer 1

Cortex

Question 2

What is the basolateral transporter for Na reabsorption in the prox tubule?

Answer 2

3Na out (into blood) // 2K into cell ATPase
Active transport

Question 3

What limits the amount of Na that is reabsorbed in the PCT?

Answer 3

Glomerulotubular balance - reason limited effectiveness of PCT diuretics
As you pull off volume, you incite this mechanism
Not about the increase in bicarb in the urine due to carbonic anhydrase inhibitors

Question 4

How reabsorb bicarb at PCT?

Answer 4

Freely filtered - PCT impermeable to bicarb
Carbonic anhydrase in the brush border: bicarb -> CO2
CO2 diffuses across
CO2 + H2O = bicarb + H
Bicarb reabsorbed, H secreted into urine
HCO3- absorption = H secretio n

Question 5

Explain the mechanism + effects of carbonic anhydrase inhibitors. Name the drug you need to know.

Answer 5

Acetazolamide

Lose bicarb in urine -> non-gap metabolic acidosis

Question 6

What are the PCT organic acid transporters? How do you measure if they are working or not?

Answer 6

OCT = cation
OAT = anion
Para-amino-hippurate = 100% secreted into urine via transporters

Question 7

Name + explain the drug that targets PCT organic acid transporters.

Answer 7

Probenecid - inhibits OAT 1
1ary use for gout - keeps uric acid in urine
Also extend life of antibiotics elim in the urine

Question 8

What is the fxn of the descending limb of the LOH?

Answer 8

H2O perm + imperm to electrolytes = concentrating

Question 9

What is the fxn of the ascending limb of the LOH?

Answer 9

H2O imperm + perm to electrolytes = diluting

Question 10

Why is the thick ascending loop thick?

Answer 10

Cells have ↑mitochondria (v metabolically active)

Question 11

What is the apical vs basal Na transporter in the thick ascending LOH?

Answer 11

Apical = Na/K/2Cl
Low [Na] in cells, moves down [ ] to get inside, pushed out via:
Basal = N/K ATPase

Question 12

What happens to K in the thick ascending LOH?

Answer 12

Cycles into urine via ROM K

Question 13

Explain how Na is reabsorbed paracellularly in the thick ascending LOH.

Answer 13

Bringing Cl into cells via 2Cl/Na/K
Hyperpolarizes the BL membrane
Drives reabsorption of Na between cells

Question 14

Mechanism of loop diuretics

Answer 14

Direct: X 2Cl/Na/K
Indirect: elim trans-tubular potential from Cl that drives paracell absorption Na
1. Can't [ ] urine
2. Large volume output 
"Can't concentrate or dilute your urine"

Question 15

What the Uosm on loop diuretics?

Answer 15

Isosthenuria = same as plasma

Question 16

Where is the macula densa? How does it work?

Answer 16

End of thick ascending LOH
Senses [Cl-] in urine as determinant of flow
Low -> release renin (thinks low flow = underprofused)

Question 17

What is the role of DCT?

Answer 17

1. Final dilution = H2O imperm while reabsorbing NaCl
2. Ca reabsorption
   - Apical = Ca channel
   - BL = Ca/3Na transporter

Question 18

Explain the mechanism of diuretics that work at the DCT

Answer 18

Thiazides
X apical NaCl cotrans
↑Ca reabsorption
Can no longer dilute urine - lose salt AND water

Question 19

Where and how does aldosterone act in kidney?

Answer 19

Cortical CD
↑ENAC - water follows
Have to excrete K into urine this way to keep charge neutral

Question 20

3 factors that det K excretion rate

Answer 20

1. Lumen (-) due to Na absorption
2. Fluid flow rate - determines [K] in the urine
3. Aldosterone via ENAC

Question 21

What 2 diuretics directly block ENAC

Answer 21

Amiloride

Triamterene

Question 22

What diuretic blocks aldosterone directly

Answer 22

Sprionolactone

Question 23

What diuretic blocks the aldosterone receptor

Answer 23

Eplerenone

Question 24

What diuretic works at the medullary CD?

Answer 24

V2 antagonists = vaptans

Block ADH action - no water reabsorption

Question 25

How does ADH increase with water deprivation vs vol depletion?

Answer 25

Water deprivation: LINEAR ↑ADH

Vol depletion: EXP ↑ADH