tubular function 2 Flashcards
define osmolarity
measure of the osmotic pressure exerted by a solution across a perfect semi-permeable membrane
calculating osmolarity
depends on the number of particles not the nature of the particles
all the conc of different solutes added together - each ion counted separately
define the minimum and maximum urine osmolarity in humans
50-1200mosmol/l
change massively - depends on how much of the solutes you’re excreting
water reabsorption in descending loop
passive
followed by Na and K
because osmolarity of interstitial fluid is high
ascending limb reabsorption
chloride is actively reabsorbed
Na passively reabsorbed - because actively pumped out on the other side
bicarb is reabsorbed
impermeable to water - no aquaporins, TJ
tubular fluid at end of loop of henle
85% water and 90% na has been reabsorbed
fluid leaving is hypoosmolar
loop diuretics
block the Na/K/2Cl transporter into the cell
Na is not reabsorbed despite the conc grad made by the Na/K ATPase
What happens to water when there is high salt in the cell
Water enters the cell
What happens to water when there is low salt in the cell
Water leaves the cell
Regulation of salt and water
They are interrelated
If you increase the salt you also have to increase the water
What determin3s the ability to produce concentrated urine
The ratio of medulla:cortex
Higher = more conc urine - larger length of nephron
Also depends on how active the system is
permeability of the collecting duct
ascending us impermeable to water
descending limb - permeable to water
how can you concentrate urine above normal plasma osmolarity
produce hyperosmolar interstitial fluid
explain the mechanisms that lead to the development of the countercurrent multiplier
ascending tubule pump out Na - increase osmolarity of the interstitial fluid
gradient of 200
descending tube recognises this and water moves out of tubule by osmosis - increasing osmolarity of teh descending limb
tubule fluid moves round and the system repeats
less able to create such a high osmolarity at top because there is already a lower osmolarity in the tubule
this forms the osmolarity gradient throughout the medulla
effect of urea on the osmolarity gradient
bottom of collecting duct is permeable to urea
it enters the interstitial fluid down conc grad
increase the osmolarity to max
bottom of loop also permeable to urea so it enters here
significance of counter current mechanism
allows you to create highly concentrated urine
position of urea transporters
UT-A1 - collecting duct
UT-A2 - DCT
UT-A3 - collecting duct
UT-B1 - blood vessel
UT-A1/3 KO
reduced urea in medulla - cant leave the CD
cant conc urine
increased intake by 20%
cant reduce water output either
UT-A2 KO
very mild phenotype
visible on low protein diet
UT-B KO
don’t cycle urea into bv
increased urine production
reduced urine conc ability
weight loss
urea transporter mutations in humans
UT-A2 point mutations observed - get rid of more fluid
loss of function in UT-B - reduction in conc ability
why doesn’t the blood flow eliminate the gradient
blood flow is another counter-current
vasa recta
permeable to water and solutes
water out, solute in of descending - more concentrated
reverse in ascending limb
oxygen and nutrients are delivered w/o loss of gradient
synthesis of vasopressin
in hypothalamus and packaged into granules
secreted form neurohypophesis
where dies vasopressin act
bind to the specific receptors - V2 on basolateral mem of principle cells in cd
