Mechanisms to Adjust Urine Concentration Flashcards
proximal tubule Na?
50-55% of reabsorption
- cotransport with glucose, amino acids, phosphate
- countertransport with H+
+2 mV
thick ascending limb Na?
Na/H/2Cl contransport
+10mV
early distal tubule Na?
5-8%
Cl cotransport
-70 mV
because Cl left over at greater rate because it can’t passive flow with the Na
late distal tubule Na and collecting duct Na?
2-3%
luminal Na channels
-70mV
water reabsorption
always passive
paracellular or transcellular
follows sodium
chloride reabsorption
always linked to Na reabsorption
-further down tubule, chloride can’t get across membrane
so thats why we have a negative luminal potential
descending limb of loop
permeable to water
ascending limb of loop
always impermeable to water
thin - NaCl reabsorption mechanisms unknown
thick - active Na/K/2Cl cotransport
thick ascending limb potential?
around +6
because of K+ leak channels
pushes Na, K, Ca, Mg, NH2 transcellularly
distal convoluted tubule first half?
Na/K ATPase
K leak channels
Na/Cl cotransporter (reabsorption)
-action of thiazide diuretics
aldosterone
stimulates Na reabsorption, K and H secretion
-in late DCT and collecting duct
ANP
inhibits Na reabsorption in medullary collecting duct
ADH
stimulates water reabsorption
-aquaporins in collecting duct
late distal tubule cation transport
large negative luminal potential
-driving force for H and K secretion by principal cells
aldosterone mechanism
in principal cells
- increased sodium channels
- increased Na/K ATPase in basolateral membrane
well-hydrated individuals
collecting duct impermeable to water
-low level aquaporins
dehydrated individuals
collecting duct permeable to water
-high level of aquaporins
ADH mechanism?
increase water permeability of late distal tubule and collecting duct
-via V2 receptors - leads to aquaporin
too high of a blood flow in kidney?
will wash out concentration gradient
countercurrent multiplier mechanism?
3 component:
descending and ascending limb of henle
vasa recta capillaries
collecting ducts
vasa recta?
flows at slow rate, so it equilibrates with interstitium
too fast, washes out medullary interstitial gradient
- pulls out solutes
- due to increases renal blood flow
what establishes medulla concentration gradient?
loop of henle
urea recycling
ADH causes urea reabsorption increase (dehydrated patient)
- from inner medullary collecting duct**
- recycled to vasa recta and loop of henle
vasa recta importance?
maintain solute gradient
- water and NaCl exchanged between descending and ascending limb
- solute gradient maintained while small amounts of NaCl and water are returned to systemic circulation
antidiuresis?
high ADH
makes collecting duct highly permeable to water and urea
-increase urea reabsorption allows even stronger gradient to pull out more water
low volume, concentrated urine
ascending limb of henle?
diluting segment
with ADH present
stronger medullary interstitial gradient
early distal tubule?
very low osmolarity
as you go down collecting duct
- pull out water and urea
- concentrated urine
diuresis?
low ADH
-no urea recycling (half gradient washed out)
as you go down collecting duct, not permeable to water
also have increased flow through collecting duct
have high volume of dilute urine
lower concentration in medullary interstitium**
obligatory urine volume
have to put this much urine out to get rid of bodies waste
clearance
U x V / P
can calculate osmolar clearance
C-osm = U-osm x V / P-osm
free water clearance?
C-H2O = V - C-osm
total volume - osmolar clearance
negative - pure water retained
positive - pure water cleared from body
U-osm vs. P-osm?
U < P pure water cleared (dilute urine)
U > P pure water retained (concentrated urine)
fractional excretion
fraction of filtered load excreted in urine
Fex = ? ***
U:x x P:cr / P:x x U:cr ***
of sodium - below 1% prerenal and AGN (glom)
above 2% ATN (tub), renal
creatinine clearance
approximation of GFR
