Renal function tests and urinalysis Flashcards
The amount of urine excreted through the urethra each day
1.5 litres
Glomerulus function
non-selective filtration across the semi-permeable membrane of capillary
All substances with low mw (
Proximal convuluted tubule (PCT) function
reabsorption
control/response to acid-base homeostasis by H+, HCO3- reabsorption
remove waste product: urea, creatine
Loop of Henle
concentrate/dilute urine
descending limb: highly permeable to water, passive reabsorption, concentration of urine occurs here
ascending limb: impermeable to water, active NaCl reabsorption, dilution of urine occurs here
Distal Convoluted Tubule (DCT)
homeostatic regulation and secretion of waste/toxic substances from bloodstream into tubules
control/response to acid-base homeostasis
Collecting ducts
direct urine flow into renal pelvis
responsive to hormones ADh and aldosterone
stimulates ADH secretion from posterior pituitary gland causing the DCT to reabsorb water
aldosterone stimulates sodium reabsorption and secretion of K+
Functions of the kidney
- Remove waste and toxins from the body
- Regulation of homeostasis
- Synthesize hormones
Acute vs chronic kidney disease
Acute: result of injuries: post renal, renal, and pre-renal causes
Chronic: result of long-term disease, abnormalities of kidney structure or function present for >3 months with implications for health
Azotemia
an elevated concentration of urea in the blood
Uremia
high concentration of urea accompanied by renal failure
Urease
hydrolyses urea to liberate ammonium ions
can be measured spectrophotometrically
Chemical method for urea measurement
spectrophotometric measurement of coloured product as a result of reaction of urea with diacetyl monoxamine in presence of strong acid
Increased urea is a sign of
increased protein intake
decreased kidney function
dehydration
Decreased urea is a sign of
Decreased protein intake
decreased liver function
Creatinine
a breakdown product of creatine phosphate in muscle
a good renal marker as it is produced at a fairly constant rate depending on body mass
shows little-no response to dietary changes
also a product of muscle function (confounding)
Jaffe reaction
Creatinine + Alkaline Picrate –> orange red chromogen
lacks specificity
inexpensive, rapid, easy to perform
Creatinase
catalyses the conversion of creatine –> creatinine
has potential to replace jaffe reaction as most widely used
less interference
Clinical significance of creatinine
- Increased serum creatinine –> impaired renal function
2. Decreased glomerular filtration rate results in less creatinine being filtered causing increased serum creatinine
Uric acid
end product of purine metabolism by the liver
readily filtered by the glomerulus but undergoes a complex cycle of reabsorption and secretion by the tubules
Caraway method
measuring uric acid
PTA reduction by uric acid
lacks specificity
Enzymatic method using Uricase
measuring uric acid
measures H2O2 produced in primary step
Clinical significance of Uric acid
increased uri acid production –> increased nucleic acid turnover , genetic enzyme defects, gout
decreased uric acid excretion: defetive reabsorption, overtreatment, decrease in renal functional mass
Gout
monosodium urate (MSU) preceppitates form a supersaturated body fluid into joint fluid –> gouty arthritis
Clearance test
the amount of plasma cleared of a substance per minute
