Lecture 7 - Renal Clearance Flashcards
Define flow rate?
feed of fluid in ml/min
What is GFR?
glomerular filtration rate - amount of fluid going into bowman’s capsule per unit of time.
What is usually the normal GFR?
100-130 ml/min
using GFR we can estimate what?
we can estimate the amount of dissolves molecules of electrolytes, glucose and amino acids that are entering bowmans capsule.
It is not universally true, for example we can’t calculate glucose, only specific molecules. Like inulin (fructose polymer) we inject it in, and its not normally present in the body.
normal urine flow rate?
1-3 ml/min
Explain each variable?
TL - Tubular load which is the amount of solute delivered into the tubule
Ps - Plasma concentration
GFR - Glomerular filtration rate
Why isn’t TL necesarrily high just because Ps is high?
because of filtration rate, therefore only molecules that are freely filtired would be true for this.
WHat is Tm or transport max?
essentially when transporters are shuttling solutes, the rate of shuttling has a maximum
What happens when solutes present (Tl) exceed the amount that can be transported (Tm)?
You pee it out, it will show up in the urine
When one nephron reaches its transport maximum what happens?
tiny amounts of the solutes will appeak in the urine.
As more nephrons reach their transport maximum, ……… appears in the urine
more solute
What is threshold?
Appearance of solute in the urine before you reach the overall Tm of the kidney.. Essentially, the plasma concentration at which a substance begins to appear in the urine.
What is the benefit and negative of measure renal clearnace?
measure both left and right at the same time.
Measures the ability of the kidney to handle solutes and water.
What is renal clearance?
Compares the filtration rate of a substance to the rate of its appearance in the urine. Essentially the amount filitred vs the amount excreted.
Why is renal clearance limited?
Measure all nephrons at once and so we cannot give info on specific regions of the nephron or on individual nepherons.
the clearance value of a certain substance is the ……. which is cleared of this substance by the kidney into urine.
volume of plasma
In order to measure renal clearance we need to measure what?
V - volume of urine
U - concentration of substance in urine
P - concentration of substance in plasma
What is the maximum and minumum concentration in the plasma?
min - 0
max - 600-750
What can we use renal clearance for ?
- measurement of glomerular filtration rate
- measurement of the renal plasma flow rate (from thre renal blood flow rate )
- Determine the renal handling of the different substances, whether or not the substance is reabsorbed or secreted by the renal tubules.
A = V + U
Arterial input (amount going in) = Venous output + urine output
What is the formula for clearance?
C = (U X V) / P
c- clearance
u - urine output
v - venous output
p - plasma concetration
What is the clearance of PAH and why?
It is 100 % cleared beause it is freely filtered, not metabolises, not reabsorbed and freely secreted.
What is the clearance of inulin and why?
Filtration rate = excretion rate
because it is freely filtered, not metabolised, not reabsorbed and not secreted.
fully excreted
What is inulin used for?
used experimentally to measure GFR
What is creatinine used for and what does it indicate?
It is secreted to a small extent about only 10 % and so an elevated Pcr is an indicator of reduced GFR.
What does Clearence of over and under 125 mean?
over - reabsorption
under - secretion
