Physiology 3120 Lecture Notes - Lecture 3: Epithelial Sodium Channel, Ion, Symporter
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25 Feb 2017
School
Department
Course
Professor
Renal Physiology
Lecture 3
GFR Measurements
Difficult to physically measure the fluid moving into Bowman’s capsule without
being invasive
BUT: can measure urine easily
Is measuring total urine production sufficient to determine how much fluid was
filtered in a day?
o NO
o You only produce 2L of urine per day but filter 180L of blood per day
Excretion [sub X] = Filtration [sub X] – Reabsorption [sub X] + Secretion [sub X]
If substance X isn’t reabsorbed and isn’t secreted, then the rate that substance X is
excreted equals the rate that it was filtered
To select the correct substance X, what characteristics should it have?
o Shouldn’t be reabsorbed
o Nothing secreted in
o Something that actually filters
o Pick a waste product! (product body makes & filter and want to get rid of)
i.e. Creatinine – reabsorbed a little but good
How to Measure GFR
Renal Handling
Once it is known what an individuals GFR is, it can be determined how much of each
of solute is filtered into the capsular space (filtered load)
[substance X]urine
Urine volume
[substance X]plasma
o Vary in the waste products we
produce
o i.e. creatine is produced in skeletal
muscles. So if you have lots of
muscle, produce more of this and
will have high conc in blood
o Therefore excrete more creatinine
If 1L of blood is filtered and 1mg of
creatinine is filtered through into capsule
If we have 1mg of creatinine we can
determine that 1L of blood was filtered
through
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