Biochemistry Flashcards
What are the cons to using inulin to measure eGFR?
It isn’t endogenous
It’s difficult to measure
What makes up the urea in the urea cycle?
Endogenous ammonia
Ammonia in the portal circulation
How much urea is excreted by the kidney?
75%
Where does the urea that isn’t excreted by the kidney go?
Into the blood
What do ureases and proteases do?
Breakdown urea and proteins respectively into ammonia
Where do blood proteins come from?
Diet
Bacteria
Cells
What can happen to blood ammonia?
Enters portal circulation
Changed into ammonium ion (which can then enter the portal circulation or be excreted in stool)
What percentage of ammonia/urea in the portal circulation enters the systemic circulation?
15%
Where does the majority of the urea cycle occur?
In the cell cytosol
What step in the urea cycle occurs in the mitochondrial matrix?
Ornithine conversion to Citrulline by the addition of Carbamoyl Phosphate
What forms Carbamoyl Phosphate?
Carbon Dioxide and Ammonium (with 2ATP molecules)
When is urea produced in the urea cycle?
When Arginine is converted to Ornithine
What is the chemical formula of urea?
CO(NH2)2 (ie. Diaminomethanal)
When is Fumarate produced in the urea cycle?
During the conversion of Arginosuccinate to Arginine
What step in the urea cycle requires the addition of Asparate?
Conversion of Citrulline to Arginosuccinate
What are the cons of using urea to estimate GFR?
Doesn’t appear at a constant rate
It is reabsorbed in the renal tubule
It undergoes extra-renal elimination
What does Creatine Kinase do? What else does this conversion require?
Converts Creatine -> Phosphocreatine:
- Requires ATP
Where can creatinine come from?
Muscle turnover
Creatine
Phosphocreatine
How much creatinine is filtered out at the glomerulus?
90-95%
Is any creatinine secreted in the renal tubules?
Yes:
- 5-10% in the DCT
What is the only con of using creatinine as a measure of eGFR?
It is secreted in the DCT
When is the use of creatinine useless for calculating eGFR?
If GFR >60ml/min
How is creatinine clearance calculated?
[Creatinine]urine x Urine Volume
Divided by
[Creatinine]plasma x Duration of collection
What is the rough creatinine clearance in young, well-built people?
Arround 120ml/min
What proteins are seen in overflow proteinuria?
Bence Jones Proteinuria (in myeloma)
Myoglobinuria (in Rhabdomyolysis)
What type of proteins are seen in glomerular proteinuria?
Albumin
What proteins are seen in tubular proteinuria?
β₂ microglobulin
α₁ microglobulin
What protein is seen in secreted proteinuria?
Tamm-Horsfall protein (most commonly excreted protein in normal urine)
How does hypoalbuminaemia result in oedema?
Results in decreased capillary oncotic pressure:
-> Water loss from vessels in ECF
What is a normal ACR?
What is microalbuminaemia defined as?
PCR 45-149mg/mmol
ACR:
- 2.5-30 (Men)
- 3.5-30 (Women)
What PCR defines nephrotic syndrome?
> 450 mg/mmol
What volume is filtered by the kidneys every day?
180L
What is the urine sodium in pre-renal failure?
What is the urine/serum urea ratio in pre-renal failure?
> 10:1
What is the urine/serum osmolality ratio in pre-renal failure?
> 1.5:1
What is the urine sodium in intrinsic renal damage?
> 40nmol/L
What is the urine/serum urea ratio in intrinsic renal damage?
What is the urine/serum osmolality ratio in intrinsic renal damage?
