5 Renal Tubular Function 2

Question 1

What is the key function of the thick ascending limb?

Answer 1

to create a hyperosmolar interstitial space in the medulla to drive water loss from the descending limb and cortical collecting duct

Question 2

What is the descending limb permeable to?

Answer 2

water, which passes paracellularly passively

Question 3

How does Na+ leave the filtrate in the ascending limb?

Answer 3

apical cotransporter
takes K+, Na+ and 2x Cl-
NKCC2

basolateral 3x Na+ / K+ exchanger

Question 4

Why do we need a pump and not a channel to facilitate Na+ reabsorbtion in the ascending limb?

Answer 4

because it’s against its’ electrochemical gradient

Question 5

Why does K+ reenter the filtrate after reabsorption in the ascending limb?

Answer 5

we have more Na+ than K+ in the filtrate, so reabsorbing Na+ and K+ 1:1 will cause us to run out of K+ in the filtrate

letting K+ out stops this from happening

Question 6

What is the osmotic gradient, maintained by the ascending limb?

Answer 6

200 mOsm.kg-1

Question 7

What does Furosemide do?

Answer 7

blocks the NKCC2 co-transporter in the ascending limb
causes water and sodium loss

acts as a diuretic

Question 8

Why is Furosemide so useful?

Answer 8

it is very potent, so can be given in a wide range of doses to give effects of varying degrees

Question 9

When is furosemide used?

Answer 9

cardiac and renal failure

types of volume overload

Question 10

What is the major side-effect of furosemide, and what exacerbates this?

Answer 10

K+ loss (hypokalaemia), leading to cardiac dysrythmias

Digoxin coadministration

Question 11

Name 3 minor side-effects of furosemide

Answer 11

hypovolaemia
mild metabolic alkalosis
Mg2+ and Ca2+ loss

Question 12

What might people on Furosemide be told to do by their doctor?

Answer 12

eat a banana

or just some KCl tablets lol

Question 13

How does a loop contribute to ion reabsorption?

Answer 13

takes it from 70% if it were a straight tube to 93%

Question 14

What is the osmolality of the filtrate at different points of the loop of Henle?

Answer 14

285 as it enters
1200 in deep medulla
85 as it leaves

Question 15

What happens to ions and water in the loop of Henle?

Answer 15

ions leave the ascending loop into interstitial space

water leaves descending loop into interstitial space

this hence causes osmolality change

Question 16

How is Sodium reabsorbed in the distal tubule?

Answer 16

Na+ and Cl- cotransport

Question 17

What do Thiazides do?

Answer 17

diuretics inhibiting Na+ and Cl- absorption on the apical membrane of the DCT

Question 18

What are thiazides used as?

Answer 18

antihypertensives, although they’re being phased out for thiazide-like alternatives with fewer side-effects (endapomide)

Question 19

What is different about Na+ reabsorption along the collecting duct?

Answer 19

we usually use the Na+ electrochemical gradient to drive the movement of other stuff, but here we need to separately regulate Na+

Question 20

How is Na+ reabsorbed in the collecting duct?

What happens to K+?

Answer 20

Na+ channel, influx, Na/K ATPase on basolateral membrane

K+ efflux through ion channel on apical membrane

Question 21

On the whole, what does the kidney do to K+ and Na+ levels and why?

Answer 21

It sees a lot of Na+ and little K+

to maintain this, the kidney has to reabsorb more Na+ and secrete more K+ to maintain whole body homeostasis

Question 22

Name 2 hormone anti-diuretics

Answer 22

ADH

Aldosterone

Question 23

How does Aldosterone work?

Answer 23

increases expression of epithelial sodium channel (ENAC) and sodium potassium ATPase

Question 24

Name 2 pharmacological diuretics

Answer 24

Amiloride

Spironolactone

Question 25

How does Amiloride work?

Answer 25

inhibits Na+ channels

Question 26

How does Sprinolactone work?

Answer 26

inhibits receptors for aldosterone, indirectly inhibiting sodium reabsorption

Question 27

What inadvertent effect does Sprinolactone cause, why might this be useful?

Answer 27

reduces K+ secretion, so we maintain potassium in our blood

we can hence use it with Furosemide!

Question 28

What is sprinolactone used for?

Answer 28

heart failure (as it’s a K+ sparing diuretic)

Question 29

Name 3 side-effects of Sprinolactone

Answer 29

inhibits other steroid receptors (androgens)
causes feminising in men (gynaecomastia)
menstrual disorders in women

Question 30

What is the process of Urea cycling

Answer 30

reabsorbed into blood by UT-A1 transporters

this increases the osmolality in the interstitial space, facilitating water reabsorption

some then goes back into the kidney in the descending loop of Henle (UT-A2)