Regulation of effective circulating volume Flashcards
describe permeability of Proximal tubule?
Active NaCl transport —> +++
Water permeable —-> +++
NaCl permeable —> +
Urea permeability —> +
describe thin descending limb permeability ?
0 active NaCl transport
Water permeable
NaCL permeable
Urea permeable
describe permeability of thin ascending limb?
0 active NaCl transport
0 water permeability
Nacl permeable
Urea permeable
describe thick ascending limb permeability ?
Active NaCl transport
0 water permeability
0 NaCl permeability
0 urea permeability
describe Distal tubule permeability ?
Active NaCl transport
Water permeable depend on ADH
0 NaCl permeability
0 urea permeability
Describe cortical collecting tubule permeability?
Active NaCl transport
Water permeability depend on ADH
0 NaCl permeability
0 urea permeability
describe inner medullary collecting duct permeability?
Active NaCl transport
Water permeability depend on ADH
0 NaCl permeability
Urea permeability depend on ADH
describe corticopapillary osmotic gradient ?
kidneys generate hyperosmolarity gradient in the medullary of interstitium through Countercurrent multiplication system in the loop of henle but the ability to reabsorb water is based on ADH
while your moving from cortex to medulla to papilla = osmolarity of intersitital fluid increases ( High conc of solutes )
What solutes contribute to gradient?
Na, CL, urea
what mechansms maintain corticopapillary osmotic gradient ?
Countercurrent multiplication : Function of loops
Urea recycling : Function of inner medullary collecting ducts
what does countercurrent multipplication depend on?
NaCl deposition in medullary interstitium
describe hyperosmotic renal medullary interstitium ?
active transport of Na ions and co-transport of potassium chloride and other ions from thick ascending limb of loop of henle into the medullary interstitium
Active transport of ions from the collecting ducts into interstitium
Facilitated diffusion of urea from inner medullary collecting into interstitium
Diffusion of small amounts of water from medullary tubules into interstitium
all these causes hyperosmotic
describe countercurrent multiplier system in loop of henle?
Step 1 : initial condition :
Loop of henle is filled with fluid at 300 which is the same conc as that leaving proximal tubule
Step 2 : Active ion pumping in the ascending limb :
Thick ascending limb actively pumps out Na and CL into surrounding interstitial fluid while water cant follow forming CONCNETRATNED INTERSTITIAL FLUID
-This creates 200 concentration gradient difference between tubular fluid at Interstitial fluid
-becomes more concentrated 400 near the loop, ascending limb
Step 3 : OSMOTIC EQUILIBRIUM in descending limb :
water moves out the descneding limb due to osmosis making tubular fluid in descending limb more concentrated up to 400, movement of water occur to reach equilibrium between interstitum and tubular fluid , water keeps getting reabsorbed until reaches 400 in tubular fluid now the tubular is more conce that it was initially
Step 4: Fluid movement from proximal tubule :
New fluid from proximal tubule enters descending limb pushing the conce fluid toward the ascending limb
Step 5 : More ion pumping
Ascending limb continues to actively pump ions into interstitium , increasing osmolarity in deeper regions
Step 6 : water moves out to balance osmolarity
Interstitium becomes more conc and water moves out of the descending limb to establish osmotic equilibrium
Step 7: maximal conc in medulla :
cycle repeats leading to progressively increasing osmolarity gradient (up to 1200 in medulla )
this allows the kidney to concentrate urine effectively
net effect of countercurrent multiplier ?
More solute than water is added to renal medulla –> solutes trapped in medulla
fluid in ascending loop is diluted
Horizontal gradient of solute concentration established by active pumping NaCl is multiplied by countercurrent flow of fluid
factors required to maintain countercurrent multiplier?
Active Na Cl transporter in the thick ascending part
Continuous fluid flow into the PCT
U-shaped structure of loop of henle
Counter current mutliplication dependence ?
Size of corticopapillary gradient is dependent on SIZE OF LOOP OF HENLE
humans bend of loop of henle it reaches 1200 max
in desert rodents it can each 3000
describe recirculation of urea absorbed from medullary collecting duct into interstitial fluid ?
Urea contributes of osmolarity 500-600
Urea is passively reabsorbed
When ADH is high urea is reabsorbed from inner medullary collecting duct through urea transporters UT-A1 and UT-A3 activated BY ADH ( 1 and 3 for reabsorption in Medullary)
Passive secretion of urea in THIN loop of henle by UT-A2 ( 2 is secretion in thin loop )
Urea recirculates through the tubular system several times before being excreted
** thick boundary from thick ascending segment , distal tubule and collecting ducts shows that these areas not very permeable to urea
UTA1 AND UTA3 activated by ADH = reabsorption in medullary CD
UTA2 = secretion in thin loop of henle
describe vasa recta preserve hyperosomlarity of renal medulla?
Vasa recta serve as counterrecurrent exchangers
minimizing wash out of solutes
Vasa recta blood flow is low , sluggish , blood minimizes solutes loss from medullary interstitium
U shaped of vasa recta prevents loss of large amount of solutes from renal medulla
Even with maximal levels of ADH , urine concnetration ability will be reduced if medullary blood flow increases enough to reduce hpyerosomolarity in renal medulla
Vasodilators can increase the medullary blood flow and wash out solutes , this will reduce urine conc ability to nephrons
Vasa recta do not create the medullary hyperosmolarity but they do prevent it from being dissipated
describe mechanism of formation of concentrated urine ?
Continue electrolyte reabsorption
Increase water reabsorption
by :
Increase ADH
High osmolarity of renal medulla
Countercurrent flow of tubular fluid
describe mechanism of formation of dilute urine?
Continue electrolytes reabsorption
Decrease water reabsorption
by :
Decrease ADH release
describe obligatory urine volume?
minimum urine volume in which the excreted solutes can be dissolved and excreted
example :
If max urine osmalirty is 1200 and 600 of solutes must be excreted each day to matinain electrolyte balance the obligatory urine volume is :
600/1200 = 0.5
