urolithiasis - stone disease in the urinary tract Flashcards
what are the commonest age group in which stones are seen?
30-50, unusual in children
males more than females
where are stones of the upper urinary tract?
renal stones
ureteric stones
where are stones of the lower urinary tract?
bladder
prostatic
urethral
why do people get stones?
anatomical factors - both congenital and acquired
urinary factors
infection
give some examples of anatomical factors that influence whether people get stones
congenital: spina bifid horseshoe kidney duplex kidney PUJO -Pelvi-ureteric junction obstruction
acquired:
- obstruction related to previous radiotherapy or previous surgery or stones from before
- trauma to the urinary tract can result in a changed anatomy
- reflux
give examples of urinary factors that can cause stones
- metastable urine ie a stage of saturation of the urine where crystals can form
- imbalance of stone promotors and inhibitors
- presence of high levels of calcium, oxalate, urate, cystine
- dehydration
what substances in the urine are stones made from?
oxalate
calcium
urate
cystine
explain the mechanism of stone formation with reference to a theory
nucleation theory - states that stones form from crystals in supersaturated urine
so dehydration plays a significant role
solubility point is where the solute and solvent are present in a metastable state as in you naturally have certain stone inhibitors which prevent solutes and solvents from making stones, but when you have supersaturated crystals in urine ie the formation point, this is when you make stones and crystals form due to pH and lack of inhibitors
Kfp - formation point
Ksp - solubility point
what are the most common types of crystals made from?
calcium based eg calcium oxalate and calcium phosphate
how do uric acid stones appear on KUB XR?
lucent ie not seen
what is another name for infection stones?
struvite stones
How do infection stones form?
these are potentiated by bacterial infection that hydrolyses urea to ammonium and raises urine pH to alkaline values (eg Proteus, Pseudomonas, Klebsiella, S. aureus and mycoplasma)
struvite crystals form in alkaline urine
what is the cause of cystinuria?
Cystinuria is an inherited autosomal recessive disease that is characterized by high concentrations of the amino acid cysteine in the urine, leading to the formation of cystine stones in the kidneys, ureter, and bladder.
Cystinuria is caused by gene mutations which prevent proper reabsorption of basic, or positively charged, amino acids: Cystine, lysine, ornithine, arginine. (COLA) Under normal circumstances, this protein allows certain amino acids, including cystine, to be reabsorbed into the blood from the filtered fluid that will become urine
how can we prevent the formation of stones?
overhydration - 3.5-3L per hour low ssalt diet normal dairy intake healthy protein intake reduce BMI
why is a low sodium diet needed to prevent the formation of stones?
a high sodium diet increases the amount of calcium in the urine
why is a normal amount of protein recommended?
eating too much protein increases the level of uric acid so causes uric acid crystals to develop
what happens if you eat too little calcium?
oxalate levels build up in the blood
why should a pt reduce their BMI to prevent stone formation?
as this reduces uric acid levels in the blood
what are the specific preventative measure for someone who keeps getting uric acid stones?
they only form in acid urine, so deacidify urine to pH 7-7.5
