Chemical Pathology - Renal Physiology Flashcards
What is the normal glomerular filtration rate?
120ml/hr
What is the approximate age-related decline of renal function (GFR) per year?
1ml/hr/yr
What is renal clearance?
The volume of plasma that can be completely cleared of a marker substance in a unit of time
What is GFR (glomerular filtration rate)?
Clearance, if a marker is not bound to serum proteins, freely filtered by the glomerulus + not secreted/reabsorbed by tubular cells
What is the gold standard measure of GFR and what does it rely on?
Inulin
- Requires steady state infusion
What causes insensible water loss?
- High surface area
- High skin blood flow
- High metabolic/resp rate
- High transdermal fluid loss
What causes fluid overload?
- Bronchopulmonary dysplasia
- Necrotising enterocolitis
What causes hypernatraemia?
- Intraventricular haemorrhage
- Sodium bicarbonate when treating acidosis
What causes hyponatraemia?
- Congenital adrenal hyperplasia
- Caffeine/theophylline when treating apnoea
What type of marker is creatinine?
An endogenous marker
What is creatinine used for in clinical practice?
To measure renal function
How is creatinine used in clinical practice to measure renal function, and why?
- Monitor trend + use it to look for changes over time
- Very variable between individuals
What is creatinine a by-product of?
- Muscle turnover
= muscular individuals have higher creatinine than others
How is a single sample of urine examined?
- Dipstick testing
- Microscope examination
- Proteinuria quantification (PCR - protein:creatinine ratio)
How is a 24-hour collection of urine examined?
- Proteinuria quantification (superseded by PCR)
- Creatinine clearance estimation
- Electrolyte estimation
- Stone forming elements
What are the different elements observed on urine micropscopy and what do they signify?
- Crystals (stones)
- Red blood cells (stones, UTI)
- White blood cells (UTI, glomerulonephritis)
- Casts (glomerulonephritis)
- Bacteria (UTI)
What is an AKI defined as?
- Rise in serum creatinine >26 within 48hr
- 50% or great rise in serum creatinine known or presumed to have occurred within the past 7 days
- Fall in urine output to less than 0.5mL/kg/hr for more than 6hrs
What is an AKI defined as?
- Rise in serum creatinine >26 within 48hr
- 50% or great rise in serum creatinine known or presumed to have occurred within the past 7 days
- Fall in urine output to less than 0.5mL/kg/hr for more than 6hrs
What are pre-renal AKIs?
- Reduced renal perfusion with no structural abnormality of the kidney; can become renal if ischaemia leads to necrosis
- Responds to volume replacement
What are renal AKIs?
- Vascular, glomerular, tubular or interstitial
What are post-renal AKIs?
- Characterised by obstruction to urinary flow, glomerular filtration requires pressure gradient
- Reversal can lead to scarring + permanent renal impairment
What are 5 indications for dialysis?
AEIOU:
1. Acidosis
2. Electrolyte disturbance (e.g. refractory hyperkalaemia)
3. Intoxication (e.g. lithium, aspirin)
4. Overload (fluid) (e.g. pulmonary oedema)
5. Uraemic encephalopathy
What are the different stages of chronic kidney disease and their approximate GFRs?
- Kidney damage with normal GFR (>90)
- Mild GFR (60-89)
- Moderate GFR (30-59)
- Severe GFR (15-29)
- End-stage kidney failure (<15 or dialysis)
What are the commonest causes of chronic kidney disease?
- Diabetes
- Atherosclerotic renal disease
- Hypertension
- Chronic Glomerulonephritis
- Infective or obstructive uropathy
- Polycystic kidney disease
What are the consequences of chronic kidney disease?
- Progressive failure of homeostatic function
- Acidosis
- Hyperkalaemia - Progressive failure of hormonal function
- Anaemia (loss of EPO synthesis)
- Renal bone disease (secondary to hyperparathyroidism due to low Vit D) - Cardiovascular disease
- Vascular calcification + subsequent atherosclerosis (biggest mortality in CKD)
- Uraemic cardiomyopathy - Uraemia + death
What are the two types of dialysis?
- Haemodialysis
- Peritoneal dialysis
What are the features of haemodialysis in terms of renal replacement therapy?
- Done via tunneled central line (TESSLO LINE) / ARTERIOVENOUS FISTULA
- Usually done ~3x/wk depending on patient’s circumstances
- Not ideal for ppl still working as time-consuming + hooked up to machine
What are the features of peritoneal dialysis in terms of renal replacement therapy?
- Undertaken via TENCKOFF CATHETER
- Uses peritoneum as dialysis membrane, insert dialysate through catheter, leave for a few hrs + then drain
- Can be done at home
- Increased risk of peritoneal infections
What are some features of a renal transplant in terms of CKD?
- Only definitive cure
- Requires lifelong immunosuppression with agents like tacrolimus/ciclosporin
- Transplanted kidney usually in RIF (Rutherford Morrison = hockey stick scar; right mesocolon not fixed + therefore easier to access iliac vessels to connect transplant
