Mechanisms to Adjust Urine Concentration

Question 1

proximal tubule Na?

Answer 1

50-55% of reabsorption

• cotransport with glucose, amino acids, phosphate
• countertransport with H+

+2 mV

Question 2

thick ascending limb Na?

Answer 2

Na/H/2Cl contransport

+10mV

Question 3

early distal tubule Na?

Answer 3

5-8%
Cl cotransport

-70 mV
because Cl left over at greater rate because it can’t passive flow with the Na

Question 4

late distal tubule Na and collecting duct Na?

Answer 4

2-3%
luminal Na channels

-70mV

Question 5

water reabsorption

Answer 5

always passive
paracellular or transcellular

follows sodium

Question 6

chloride reabsorption

Answer 6

always linked to Na reabsorption
-further down tubule, chloride can’t get across membrane

so thats why we have a negative luminal potential

Question 7

descending limb of loop

Answer 7

permeable to water

Question 8

ascending limb of loop

Answer 8

always impermeable to water

thin - NaCl reabsorption mechanisms unknown

thick - active Na/K/2Cl cotransport

Question 9

thick ascending limb potential?

Answer 9

around +6
because of K+ leak channels

pushes Na, K, Ca, Mg, NH2 transcellularly

Question 10

distal convoluted tubule first half?

Answer 10

Na/K ATPase
K leak channels

Na/Cl cotransporter (reabsorption)
-action of thiazide diuretics

Question 11

aldosterone

Answer 11

stimulates Na reabsorption, K and H secretion

-in late DCT and collecting duct

Question 12

ANP

Answer 12

inhibits Na reabsorption in medullary collecting duct

Question 13

ADH

Answer 13

stimulates water reabsorption

-aquaporins in collecting duct

Question 14

late distal tubule cation transport

Answer 14

large negative luminal potential

-driving force for H and K secretion by principal cells

Question 15

aldosterone mechanism

Answer 15

in principal cells

• increased sodium channels
• increased Na/K ATPase in basolateral membrane

Question 16

well-hydrated individuals

Answer 16

collecting duct impermeable to water

-low level aquaporins

Question 17

dehydrated individuals

Answer 17

collecting duct permeable to water

-high level of aquaporins

Question 18

ADH mechanism?

Answer 18

increase water permeability of late distal tubule and collecting duct

-via V2 receptors - leads to aquaporin

Question 19

too high of a blood flow in kidney?

Answer 19

will wash out concentration gradient

Question 20

countercurrent multiplier mechanism?

Answer 20

3 component:
descending and ascending limb of henle
vasa recta capillaries
collecting ducts

Question 21

vasa recta?

Answer 21

flows at slow rate, so it equilibrates with interstitium

too fast, washes out medullary interstitial gradient

• pulls out solutes
• due to increases renal blood flow

Question 22

what establishes medulla concentration gradient?

Answer 22

loop of henle
urea recycling

ADH causes urea reabsorption increase (dehydrated patient)

• from inner medullary collecting duct**
• recycled to vasa recta and loop of henle

Question 23

vasa recta importance?

Answer 23

maintain solute gradient

• water and NaCl exchanged between descending and ascending limb
• solute gradient maintained while small amounts of NaCl and water are returned to systemic circulation

Question 24

antidiuresis?

Answer 24

high ADH

makes collecting duct highly permeable to water and urea
-increase urea reabsorption allows even stronger gradient to pull out more water

low volume, concentrated urine

Question 25

ascending limb of henle?

Answer 25

diluting segment

Question 26

with ADH present

Answer 26

stronger medullary interstitial gradient

Question 27

early distal tubule?

Answer 27

very low osmolarity as you go down collecting duct - pull out water and urea - concentrated urine

Question 28

diuresis?

Answer 28

low ADH -no urea recycling (half gradient washed out) as you go down collecting duct, not permeable to water also have increased flow through collecting duct have high volume of dilute urine lower concentration in medullary interstitium**

Question 29

obligatory urine volume

Answer 29

have to put this much urine out to get rid of bodies waste

Question 30

clearance

Answer 30

U x V / P can calculate osmolar clearance C-osm = U-osm x V / P-osm

Question 31

free water clearance?

Answer 31

C-H2O = V - C-osm total volume - osmolar clearance negative - pure water retained positive - pure water cleared from body

Question 32

U-osm vs. P-osm?

Answer 32

U < P pure water cleared (dilute urine) | U > P pure water retained (concentrated urine)

Question 33

fractional excretion

Answer 33

fraction of filtered load excreted in urine

Question 34

Fex = ? ***

Answer 34

U:x x P:cr / P:x x U:cr *** of sodium - below 1% prerenal and AGN (glom) above 2% ATN (tub), renal

Question 35

creatinine clearance

Answer 35

approximation of GFR