Final answer:
Rectangular/envelope shaped crystals in urine typically indicate the presence of kidney stones, which consist of crystalized compounds like calcium salts, and can lead to severe health issues if they block the urinary tract.
Step-by-step explanation:
When rectangular/envelope shaped crystals are found in urine after the ingestion of a substance, it is typically indicative of the formation of kidney stones. These stones are comprised of compounds that crystalize and build up on the kidney walls, potentially leading to severe pain and health complications if they obstruct the urinary tract.
Kidney stones are largely composed of sparingly soluble calcium salts such as Ca(O₂CCO₂) H₂O and Ca3(PO4)2. A microscopic study of urine can reveal the presence of such compounds, along with other elements like proteins, red blood cells, and bacteria. Substances that can lead to the formation of kidney stones include calcium, oxalate, and phosphorus.
Certain types of kidney stones, such as cystine stones, occur due to genetic conditions like cystinuria and result in accumulation of cystine in the urine. Symptoms of kidney stones can range from colicky pain to hematuria, which is the presence of blood in the urine.