renal 3 Flashcards
initial filtrate is ___mmol –> solutes and water and reabsorbed ___ (when fluid enters loop of henle, it is ___ mmol) –> it is the ___ that is responsible for setting up the mechanism of concentrating the urine… –> in collecting duct, urine that leaves to go to bladder can be as high as ___ mmol (anywhere b/w ___ and ___, depends on mechanisms)
300 mmol
equally
300
long loop of Henle - more concentrated as it goes down descending limb (water laves), becomes more dilutes as it travels back up (NaCl leaves)
1200 mmol, b/w 70-1200
concentration & dilution of urine: if final fluid is less than ___, it is diluted (if more, it is concentrated)
300 mmol
the loop os Henle acts as the ____ since it starts the overall mechanism to decide whether urine is diluted or concentration
name the 3 characteristics
countercurrent mulitplier
countercurrent flow/exchange
selective permeability in diff parts of loop
has active transport
countercurrent flow/exchange of LOH =
2 diff fluids moving in opposite directions over a common exchange surface and exchange(diffusion) will occur from fluid with higher conc of substance (donor fluid) to fluid with the lower conc of substance (receiving fluid)
countercurrent exchange is highly ___, compare concurrent & countercurrrent flow
efficient
concurrent: diffusion occurs from water to blood, initial high rate of diffusion, but as soon as reach 50%, conc in both fluids are equal and diffusion will stop (get the average b/w the 2 concentrations, it is reached quickly, so only part of the exchange surface is used for that transfer and the other isn’t - so not efficient)
countercurrent: ensures the lowest conc of your donor fluid is going to equilibrate with the lowest conc of receiving fluid; and the highest conc of donor fluid is going to equilibrate with highest conc of receiving fluid –> as the 2 fluids move across each other in opposite directions, always going to be small exchange, nothing goes to waste, conc gradient exists across entire exchange surface – when receiving fluid leaves exchange surface, it’s fully equilibrated with donor fluid – very efficient
countercurrent flow exists b/w loop of Henle and ____…
blood of the vasa recta portion of paratubular
fluid flows down descending limb as vasa recta blood is flowing up
selective permeability & active transport
what is the descending limb of LOH permeable to?
membrane is permeable to water, but completely impermeable to salts & urea (lose water and retain salts)
fluid enters LOH at 300 mmol, as it goes down, loses water b/c very permeable to it (water gets carried away by countercurrent exchange with vasa recta), conc of fluid gets higher and higher as fluid moves down (as high as 1200 mmol) b/c not permeable to salts or ureea
selective permeability & active transport
what is ascending limb of LOH permeable to?
impermeable to water, in thin section of ascending limb: passive reabsorption of NaCl (thru epithelial sodium channels, EAC, and Cl follows b/c of charge) –> in thick section, active reabsorption/transport of Na and Cl thru sodium pump and Na/Cl cotransport
losing salts but retaining water –> as fluid goes up, becomes more dilute (can leave ascending at 100 mmol or less)
selective permeability & active transport?
what is collecting duct permeable to?
urea
describe concentration gradient involving salt and urea around ascending limb & collecting duct
salt begins to accumulate in interstitial fluid that surrounds ascending limb and collecting duct as it goes down thru renal medulla –> NaCl builds up & creates conc gradient that surrounds the loop and collecting duct and increases as you go from renal cortex down to deep parts of renal medulla
also lots of urea moving from collecting duct accumulating in interstitial fluid (can become very concentrated in deeper parts of renal medulla also)
can start with 300 mmol in collecting duct –> as it goes further down, loses more and more water –> can keep becoming more concentrated, increasing all the way down and get as high as 1200 mmol due to water pulled out into interstitial fluid
what channel does water move thru in the nephron?
aquaporin (not gated, so permeability of collecting duct membrane depends on number of aquaporin channels in membrane at a given time)
what controls the number of aquaporin channels in the membrane?
under control of the hormone, ADH (aka vasopressin)
over 99% of the water that our kidney filters gets ___
what controls this?
reabsorbed and stays in blood stream
reabsorption regulated at collecting duct mechanism by ADH
what is the signal for ADH?
dehydration, osmotic concentration (conc of NaCl in blood) goes up to abnormal levels, also get signals from BP
increased salt conc and decreased BP is signal for ADH production
the signal to produce ADH is received by the ___ –> this sends signal to ___ —> ___ secretes ADH –> ADH acts on ___ of kidney –> ADH binds to receptor and activates ___ pathway, which activates ___ –> that phosphorylates a reserve supply of ____….
hypothalamus
posterior lobe of pituitary gland
posterior pituitary gland
collecting duct
cyclic AMP pathway
protein kinase A
aquaporin protein channels –> causes aquaporin to be inserted into apical membrane of collecting duct –> more water channels, greater permeability to water and water is reabsorbed across big conc gradient –> brings BP back up and NaCl levels back down to normal, rehydrated
