Control Of Volume

Question 1

What is the majorly osmotically effective solute in the ECF?

Answer 1

Na+

Water in the ECF depends on Na content

Question 2

Sodium transporters in the apical membrane of the proximal tubule? what are these transporters driven by? What percent of glucose, AA, water and Na is reabsorbed here?

Answer 2

67% Na reabsorption PCT
Na-H antiporter 
Na-glucose (symporter) -all uptake of glucose PCT
Na-AA co-transporter 
Na-Pi 
Cl-anion antiporter 

Driven by 3Na2KATPase at basal membrane into interstitium so keeps conc grad from lumen to cell

Also driven by Cl- paracellular (through interstitium) movement which leaves transepithelium positively charged (tubular cells) so helps drive Na+ out via paracellular route

100%AA
65% water reabsorption

Question 3

Na transporters in the loop of Henle ascending limb apical membrane?

Answer 3

NaKCC (symporter)
Na, K, Cl, Cl cotransporter into cell

K+ transporters out of cell into lumen (ROMK) renal outer-medullary potassium channel

Question 4

Transporters in basal surface of ascending limb of LOH?

Answer 4

K+ and Cl- symporter, K+ transporter, Cl- transporter, 3Na out- 2K in ATPase (all into interstitum bar K in ATPase)

Question 5

Transporter on apical surface of DCT?

Answer 5

early: Na and Cl symporter active

Late and CT: ENaC (epithelial Na channels)

Cyctosolic calcium immediately bound by calbindin which shuttles it to basolateral side of DCT cell (and then transported out by NaCa exchanger)

Question 6

Transporters on basal membrane of DCT?

Answer 6

3Na2KATPase
K transporter

Sodium calcium exchanger (NCX)

Question 7

What drives diffusion through channels on the apical membrane of the nephron?

Answer 7

The active 3Na2KATPase pump on the basal membrane into interstitium

Question 8

What percent of the renal blood gets filtered through in the glomerulus?

Answer 8

20%

Question 9

What forces drive the uptake of fluid into the capillaries from the interstitium?

Answer 9

Hydrostatic and oncotic forces

Question 10

What happens to NaHCO3 in the lumen of the nephron in the PCT?

Answer 10

Breaks down into Na and HCO3

(Na antiported our with H+ coming in)

HCO3 then joins the H+ to make H2CO3

H2CO3 breaks down into H2O and CO2 which diffuse into the cell join again to make H2CO3 which breaks down to form H+ (transported out) and HCO3 which moves into interstitium though HCO3 - Cl- antiport

Question 11

How does amiloride work?

Answer 11

It’s a diuretic which inhibits the ENaC (apical epithelial Na channel) in DCT

but also blocks the Na+/H+ antiporter in PCT = stopping 80% of action of angiotensin2 (prevents it from increasing BP)

So Amiloride is used to decrease BP

Question 12

What is ordinate?

Answer 12

Tubular fluid to plasma concentration ratio (TF/P)

When TF/P= 1 for a substance that is the same concentration in the tubular fluid and plasma (freely filtered at the glomerulus so 100% gets through)

Question 13

What type of transport can occur at the late stages of the PCT?

Answer 13

Diffusion through tight junctions

Of Na and Cl from lumen into interstitium

All chloride driven transport

Question 14

Where does amino acid get reabsorbed? How much of it and through what?

Answer 14

PCT

100%

Sodium dependent AA transporters (co-transporter 3Na and 1AA) on apical membrane - 7+ types

& then passive AA transporters on basal membrane

Question 15

How does transport of Na change in the ascending limb of LOH and why?

Answer 15

Goes from passive in thin lower part (as deeper in medulla where the tubule is more hypertonic) to active transport out (when the the tubule becomes hypotonic to interstitium)

Question 16

How do loop diuretics work? Give an example. What’s a problem with this? How can we prevent this problem? Where else do loop diuretics work in the nephron?

Answer 16

Block the NaK2Cl co-transporter on the apical membrane in thick ascending limb LOH

E.g. furosemide

While the renal outer medullary potassium channel keeps the K+ gradient but K+ now isn’t getting reabsorbed so can lead to hypokalaemia

Can use K+ sparing diuretics e.g. spironolactone blocks both NaKCC and ROMK

Loop diuretics also work at macula densa cells of the DCT as they too have NaKCC channels to detect NaCl conc and constrict AA if too high (too high GFR) SO keeps filtrate flowing through kidneys and diuretics working

Question 17

How doo thiazides work?

Answer 17

Block NCCT channel (active Na2Cl symporter) on apical membrane DCT

Question 18

How does calcium transport at the DCT work?

Answer 18

Cytosolic calcium bound by calbindin which shuttles calcium to basolateral aspect of DCT

Then transported out by Na Ca exchanger (NCX)

Tightly regulated PTH (increases) and 1,25-dihydroxyvitamin D/ calcitriol (increases)

Question 19

What are the two cell types of the collecting duct and where are they found?

Answer 19

Principle 70% and intercalated cells found in cortical CD

Question 20

Principle cells function

Answer 20

Cortical CD

Reabsorption Na through ENAC at apical membrane and then 3Na2KATPase at basolateral is driving force

Produces a negative lumen charge so driving force for Cl- uptake via paracellular route

Variable water uptake through aquaporins dependent on ADH

Question 21

Intercalated cell function

Answer 21

Cortical Cd

Secrete H+ Iona or HCO3- ions

Type A: H+ATPase (H into lumen) and HKATPase (H into lumen) apical membrane
And ClHCO3 exchanger at basolateral (HCO3 into interstitium)