S2 Bsf Exam 4: Renal Handling Of Ions

Front 1

Na+:
How much (mEq/day) is filtered?
excreted?
reabsorbed?

Back 1

filtered- 25,200
excreted- 150
reabsorbed- 25,050 (99.4%)

Front 2

Describe transcellular Na+ transport

Back 2

apical border- passive via chemical gradient

basolateral side- active via Na+K+ pump (establishes electrochemical gradient ^)(3 Na+ out, 2 K+ in, uses majority of energy in kidney)

Front 3

Descibe paracellular Na+ transport

Back 3

via electrochemical gradient & solvent drag
- decreased conductance w/ distance along nephron

tight junctions allow leaking (leaking varies)

Front 4

The difference in tight junction "leakiness" between segments is due to what?

Back 4

different claudins isotypes

Front 5

Where is most Na+ absorbed?

Back 5

proximal tubule (PT)

Front 6

The PT's (-) electrochemical gradient allows Na+ to be used for what?

Back 6

secondary active transport (driving transcellular reabsorption of other solutes across apical border)

Front 7

In the thick ascending limb (TAL), how is the (+) lumen medullary potential established?


What solute is recycled back into the lumen?

Back 7

Na+K+2Cl- (NKCC2) secondary active electroneutral symporter


K+ (via K+ channel)

Front 8

In the distal convoluted tubule (DCT) the ONLY type of movement is via (paracellular/transcellular)


Via what mechanism?

Back 8

transcellular ONLY


via Na+Cl- (NCC) cotransporter
(no water permeability = solute dilution)

Front 9

Na+ transport in the connecting tubule (CNT) & cortical collecting tubule (CCT) is mediated by what?


This results in a (+/-) lumen charge

Back 9

principal cells*

(transcellular via epithelial Na+ channel, ENaC)

(-) charge (partially offset by K+ in apical membrane)

Front 10

Cl-:
How much (mEq/day) is filtered?
excreted?
reabsorbed?

Back 10

filtered- 18,000
excreted- 150
reabsorbed- 17,850 (99.2%)

Front 11

How is Cl- transported in PT?

Back 11

paracellular-
in early PT, driven by (-) lumen & solvent drag
in late PT, driven by [Cl-] gradient (opposing + lumen)

transcellular-
in late PT, tertiary active transport

Front 12

In the TAL & DCT, Cl- is ONLY transported (paracellular/transcellular)

What is the mechanism?

Back 12

transcellular ONLY

TAL- via NKCC2 (apical) & Cl- channel (basolateral)
DCT- via Na+Cl- channel (apical) & Cl- channel (basolateral)

Front 13

How is Cl- transported in CCT?

Back 13

paracellular-
(-) lumen electrical gradient

transcellular-
Cl-HCO3- exchanger (apical B-intercalated cells)
Cl- channel (basolateral)

Front 14

T/F
alpha-intercalated & principal cells are NOT involved in Cl- reabsorption

Back 14

TRUE

(only B-intercalated)

Front 15

K+:
How much (mEq/day) is filtered?
excreted?
reabsorbed?

Back 15

filtered- 720
excreted- 100
reabsorbed- 620 (86.1%)

Front 16

PT reabsorbs a large portion of K+ via ______________

Back 16

paracellular route
(early- solvent drag, late- electro gradient)

Front 17

In low dietary intake, K+ is _________________ in distal segments of nephron

Back 17

conserved by further net absorption

Front 18

In high dietary intake, K+ is _______________ in distal segments of nephron

Back 18

excreted by net secretion

Front 19

In low or high dietary intake, _________filtered K+ remains in tubule at end of TAL

Back 19

10%

Front 20

In low dietary intake, where is K+ reabsorbed?

Back 20

DCT
CNT
ICT
CCT
MCD

Front 21

In high/normal dietary intake, where is K+ secreted?

Back 21

ICT
CCT
MCD (proximal part)

Front 22

Describe K+ trapping in juxta-medullary nephrons

Back 22

stationary [K+] gradient in interstitial medulla leads to K+ cycling from lumen back out to interstitium (back and forth):
tDL secretes
tAL reabsorbs
TAL reabsorbs
MCD reabsorbs

Front 23

Which of the following reabsorbs via paracellular & transcellular routes ?
tDL
tAL
TAL
MCD

Back 23

TAL ONLY


(rest act through paracellular route only, tDL secretes)

Front 24

Describe TAL K+ reabsorption

Back 24

paracellular-
(+) transepithelial lumen (favorable K+ gradient)

transcellular-
NKCC2 (apical)
high K+ permeability--> passive leakage (basolateral)

Front 25

______________ cells are responsible for active reabsorption if K+ in ICT, CCT, & MDC

Back 25

alpha intercalated cells


(also active H+K+ exchanger imports & K+ channels extrude (apical side))

Front 26

_____________ cells are responsible for K+ secretion in CNT & ICT

Back 26

principle cells


(also Na+K+ pump imports & K+Cl- symporter moves into lumen)