a. Urolithiasis is the presence of stones in the urinary system.

These stones are formed by the deposit of crystalline substances excreted in the urine.

(1) Variations in sizes range from sand-like granules to stones the size of a baseball.

(2) Most stones are combinations of calcium and phosphate.

(3) Different stone compositions develop in association with the pH of the urine. For example:

(a) Phosphate, oxalate, and carbonate stones form in alkaline urine.

(b) Uric acid, urate, and cystine stones form in acid urine.

b. Factors that precipitate stone formation include:

(1) Infections.

(2) Urinary stasis.

(3) Excess calcium.

(4) Vitamin deficiencies (especially vitamin A).

(5) Dehydration.