Renal plasma clearance Flashcards
Describe inulin
An inert polysaccharide, MW ~5,000
Filters freely through the glomerular membrane
Not absorbed, secreted or metabolised
How to find urine flow rate?
dividing the urine volume collected by the duration in minutes of the collection period.
urine volume/collection time
What is P(in)
Plasma inulin
P(in)x GFR =
U(in)xv
Renal clearance definition
Renal clearance of a substance is the volume of plasma that is completely cleared (excreted into urine) of the substance by the kidney per unit of time, (expressed in ml/min)
Inulin is freely filtered by the glomerulus and is neither reabsorbed or secreted.
what does this mean
all that is filtered will end up in the urine, no more (as I is not secreted), no less (as I is not reabsorbed).
Name some drawbacks to the inulin method:
- prolonged infusion
- repeated plasma samples
- difficult routine clinical use
What is used for clinical GFR management?
creatinine
Advantages of Creatinine
- An intrinsic inert substance
- Released at ~steady level in plasma from skeletal muscle
- No infusion needed
- Freely filtered
- Not reabsorbed in the tubule
Disadvantages of Creatinine
Some secreated into tubule
What does trimethoprim do?
competitively inhibits renal tubular creatinine secretion and may cause an artificial increase in serum creatinine, particularly in patients with a pre-existing renal insufficiency; however, GFR is unchanged;
Despite creatinine secretion why is it still accurate for GFR?
there’s usually slight error in estimation of plasma [creatinine] these 2 errors cancel each other out and creatinine clearance provides a reasonable estimate of GFR
Where is the majority of Creatine found?
MUSCULAR TISSUES
The muscles have almost no creatine synthesising capacity, how is it taken up from blood?
Cr has to be taken up from the blood against a large concentration gradient by a saturable, Na+- and Cl−-dependent Cr transporter that spans the plasma membrane.
How does trimethoprim inhibit crn secretion?
Competes with Crn for same transporters that secrete from Crn from tubular blood into urine
How is the daily demand for creatine met?
intestinal absorption of dietary Cr or by de novo Cr biosynthesis.
Does conversion of Pcr / Cr to Crn require enzymes
nO
In which 3 ways does Cr supplementation improve muscle performance?
- by increasing the muscle stores of PCr
-ccelerating PCr resynthesis
-depressing the degradation of adenine nucleotides
What is eGFR?
Estimated glomerular filtration rate
Equation using blood tests, age ex, and other info to measure GFR
What is the current equation for GFR
CKD-EPI
How many stages of CKD are there?
There are five stages but kidney function is normal in Stage 1, and minimally reduced in Stage 2
How is CKD estimated?
mainly based on measured or estimated GFR.
Which substances have transport maximums?
- All amino acids
- Ca+/Na+/PO42-/Mg2+
- Water-soluble vitamins
These are all actively reabsorbed
What are bence-jones proteins?
Small antibody fragments
