Medicine Notes Renal System Notes
These notes helped me achieve a mark of 78% in my renal system exam, which is the equivalent of a 1st. The notes are based on a series of lectures on the subject. This is a very good, thorough and in depth review of the nervous system. They are very clearly laid out and easy to follow. They cut out unnecessary information on the topic, making the notes very concise, and fast to get through. Anyone studying medicine, or any other subject requiring knowledge of the renal system (e.g. physiology or ...
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Lecture 5
Renal Function Test & Clearance
Renal function tests of urine
Visual examination
Colour, clarity (frothy can indicate PROTEINURIA)
Labstix analysis (normal)
Protein (trace/none)
Blood (none)
Free haemoglobin (none)
Glucose (none)
pH (variable- normal range ~4.5-8.5 cf plasma pH 7.4)
Osmolarity
Ability to concentrate and dilute urine
Normal range ~80-1,200mosm/L
Cf extracellular fluid osmolarity ~285mosm/L
Measurement of GFR
Equation
GFR= Ux x V/Px
Rate of filtration=rate of excretion (no tubular transport)
GFR= Glomerular filtration rate
Px= Plasma conc. of x (mg/ml)
Ux= Urinary conc. (mg/ml)
V= Urine output (ml/min)
Inulin clearance
Not endogenous, not metabolised/stored by kidney, not change GFR
Undergoes no tubular transport and is freely filtered
Accurate but not convenient
Example
UIN= 29mg/ml
V= 1.1 ml/min
PIN= 0.25mg/ml
GFR= 19 x 1.1/ 0.25= 129ml/min=184L/day
Creatinine (PREFERRED CHOICE OF TEST)
Endogenous (require no infusion, non-toxic CONVENIENT)
Freely filtered, not metabolised/stored by kidney, not change GFR
Plasma conc. does not vary with dietary intake (cf urea) or hydration (cf urea) so, in with normal renal function, serum creatinine stable
Creatinine clearance (CC) measured simply- patient takes 24hr urine, and blood sample take at any time in collection period
Not as accurate as inulin
Small amount involved in tubular transport into tubule
Ux (urinary conc) is a little high as creatinine is filtered
Px also a little too high (test picks up some non creatinine nitrogenous products in blood)
BUT two changes cancel each other out enough, so accurate
Serum creatinine
Any increase reflects impaired glomerular filtration
Less accurate
Canβt estimate GFR in early part of curve, only late RD
Good for rate of deterioration in late renal disease
CONVENIENT
Decreased GFR= inreased serum creatinine
Equivalent to number of functional nephrons
Donate kidney, GFR falls by half, serum creatinine still low
Blood urea level
Not accurate for renal disease
Other reasons for high results (e.g. high protein meal, dehydration)
Cr51 EDTA Elimination
Rate at which radioisotope is cleared from blood
Inject then test to see fall in levels in blood over period of time
BUT risk of injecting radioisotopes and expensive...
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These notes helped me achieve a mark of 78% in my renal system exam, which is the equivalent of a 1st. The notes are based on a series of lectures on the subject. This is a very good, thorough and in depth review of the nervous system. They are very clearly laid out and easy to follow. They cut out unnecessary information on the topic, making the notes very concise, and fast to get through. Anyone studying medicine, or any other subject requiring knowledge of the renal system (e.g. physiology or ...
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