kidney function 2 Flashcards
what is the definition for clearance ?
the volume of plasma that is cleared of a substance in a given time
how is renal clearance calculated ?
(conc in urine x volume of urine/min ) divided by conc of plasma
why is the clearance of inulin used to measure GFR ?
- it is freely filtered
- not reabsorbed
- not secreted
- not metabolised
- easily measured
why isnt inulin used clinically to measure GFR ?
what is used instead ?
has to be adminstered via IV
use creatinine instead but isnt exact
what does para-aminohippuric acid show ?
renal plasma flow
how is renal blood flow calculated ?
renal plasma flow divided by plasma % in blood
what is osmolality ?
what is it measured in ?
a measure of water conc. higher the solution osmolality = the lower the water conc
mosm/kg
what is osmolarity ?
what is it measured in ?
a measure of water conc. the higher the solution osmolarity the lower the water conc
what word is used to describe physiological fluids ?
osmolality + osmolarity can be used interchangeably
osmolality is preferred because it is independent of temp
what are the 3 types of urine that the kidney can make ?
- dilute
- iso-osmotic
- concentrared
what is the main osmotically active solute in plasma ?
sodium
what is the average sodium plasma conc ?
135-145 mmol/l
how can you calculate the amount of sodium filtered ?
plasma Na conc x GFR
how can you calculate the amount of sodium filtered ?
plasma Na conc x GFR
how is sodium reabsorbed in the loop of Henle
- none absorbed in descending limb
- passive in thin ascending limb
plasma is electroneutral how is this maintained ?
by the Na + Cl conc
where is the main site of Na reabsorption
how much is reabsorbed here ?
proximal tubule
65%
how is Na absorbed in proximal tubule ?
- Na/K ATPase pump : actively pumps Na into interstitial fluid
- Na/H exchanger (NHE3) : drives Na out of lumen into cell
- Na nutrient symporter : Na moves into cell via conc gradient
how is Na absorbed in the thick ascending limb ?
what % of Na is absorbed here ?
25 %
- Na/K ATPase pump : Na into interstitial fluid
- Na/K/2Cl cotransporter : Na pumped into cell
how is Na absorbed in distal tubule ?
how much is reabsorbed ?
2-5%
- Na/K ATPase pump
- Na/Cl cotransporter
how is Na reabsorbed in collecting duct ?
what % is reabsorbed ?
5%
- Na/K ATPase pump
- ENa channel : pumps Na in via its conc gradient
what are the 2 cell types in ion transport ?
- principal cells ( Na transport )
- intercalated cells ( H transport)
what does water reabsorption depend on ?
- osmosis
- sodium reabsorption
- tubule permeability
how is filtrate volume reduced but osmolality kept the same ?
coupling of water reabsorption to sodium reabsorption in proximal tubule
how can urine that is more concentrated than plasma be produced ?
- separate Na + water reabsorption
- have renal medulla interstitial fluid with high osmolality = water reabsorption
where does water separation from sodium occur ?
loop of Henle
how is water separated from Na ?
- have counter current flow in loop
- leads to different absorptions of salt to water
- only salts absorbed in ascending limb + only water absorbed in descending limb
how does the loop of Henle make a renal medulla interstitial fluid with high osmolality ?
- sodium gradient of increasing osmolality
- countercurrent multiplier
- vasa recta
what does it mean when the loop of Henle is referred to as a counter-current multiplier ?
it increases the osmotic gradient between the tubular filtrate + the medullary interstitial fluid
what is a benefit of the vasa recta ?
supplies blood without washing away the gradient loop of Henle created
what 2 components contribute to the renal medulla interstitial fluid ?
- urea
- sodium
what are the stop of urea handling in the kidney ?
- freely filtered in renal corpuscle
- passively reabsorbed in proximal tubule
- secreted via urea transporters in loop of Henle
- reabsorbed via urea transporters in collecting duct
what is urea recycling ?
refers to the secretion + reabsorption of urea
how is urea reabsorption controlled ?
hormonally
what are the functions of the loop of Henle ?
- separate sodium + water
- reabsorb more sodium than water
- create a gradient of increasing osmolality inn the medullary interstitial fluid
what is water reabsorption at the collecting duct dependent on ?
anti-diuretic hormone (ADH)
describe the action of ADH on collecting duct :
- ADH released from pituatry gland
- bind to v2 receptor on collecting duct
- this cause AQP2 to move towards edge of collecting duct (by using cAMP)
- AQP2 opens + allows water in
what effect does ADH have on urine ?
makes it more concentrated
what does concentrated urine depend on ?
- high osmolality of renal medulla interstitiual fluid
- permability of collecting duct
