Regulation of tubular transport

Question 1

Why regulation is important

Answer 1

Water follows solutes
Need to ensure a constant delivery of fluid to the tight, distal epithelium
Intrinsic and extrinsic factors to control this

Question 2

Ingestion of excess salt

Answer 2

Increase in osmotic potential
Modulate ADH, more ADH release to dilute body fluids
More water reabsorbed to dissolve excess salt
Causes volume expansion

Question 3

Increase in ECV

Answer 3

Increase Na+ excretion to remove excess water

Reduce angiotensin/ aldosterone and increase ANP

Question 4

Proximal tubule fluid regulation

Answer 4

Glomerulotubular balance
Hormones
Nerves
- Not major site of regulation because of leaky epithelium

Question 5

Glomerulotubular balance

Answer 5

Proximal tubule reabsorbs a constant fraction of filtrate, even if the GFR changes so absorption is load-dependent
Increase transport of carriers, sodium coupled transporters
Uptake/backflux: changes in pressure affects the Starling forces, efferent arteriole dilation reduces GFR -> increases amount of backflux

Question 6

Regulation of transport in Loop

Answer 6

Na+ absorbed is proportional to load delivered
NKCC activated by hormones
If flow rate increases, more NaCl stays in lumen which feeds back to macula densa

Question 7

Tubuloglomerular feedback

Answer 7

Changes in NaCl reaching macula densa
Release of renin from granular cells in afferent arteriole wall
Macula densa acts as a flow rate sensor
Increase in flow rate causes decrease in GFR and renin

Question 8

Distal nephron segments regulation

Answer 8

NCC in DCT inhibited by amiloride, regulated by angiotensin/aldosterone
Collecting duct: reabsorb Na+ through amiloride sensitive channels, increased by aldosterone and ANP

Question 9

ANP action

Answer 9

Increases sodium excretion
from atria in the heart, antagonises renin cascade
Increases GFR, reduces ADH release (more sodium and water excretion)

Question 10

Distal nephron segments regulation

Answer 10

NCC in DCT inhibited by amiloride, regulated by angiotensin/aldosterone
Collecting duct: reabsorb Na+ through amiloride sensitive channels, increased by aldosterone and ANP

Question 11

ANP action

Answer 11

Increases sodium excretion
from atria in the heart, antagonises renin cascade
Increases GFR, reduces ADH release (more sodium and water excretion)