The human body maintains a dynamic balance between water intake and elimination, and urination is the main way of elimination of body fluid. Normal human urine volume is about 1000-2000ml in 24 hours. If urine volume is less than 400ml in 24 hours or less than 17ml per hour, it is called oliguria; if urine volume is less than 100ml in 24 hours or no urine at all in 12 hours, it is called anuria; if urine volume exceeds 2500ml in 24 hours, it is called polyuria. The common causes of oliguria and anuria are: 1. Decreased blood volume in the body, such as shock, severe dehydration, hemorrhage, nephrotic syndrome and hepatorenal syndrome caused by various reasons; 2. Decreased ejection function of the heart, such as cardiac insufficiency caused by various reasons, severe heart rate arrhythmia, decreased blood flow to the kidneys caused by decreased blood pressure; 3. Kidney lesions, such as renal vascular stenosis, renal artery embolism, renal artery spasm, glomerular lesions caused by various reasons, acute tubular necrosis, etc.; 4, urinary tract obstruction, such as acute type of obstruction caused by kidney stones, blood clots blocking the urinary tract, and obstruction caused by prostate enlargement, tumor compression, and obstruction caused by neurogenic bladder, etc. Common causes of polyuria are: 1, endocrine abnormalities: such as reduced secretion of pituitary antidiuretic hormone resulting in reduced water reabsorption by the renal tubules, high sugar content in the urine of diabetic patients causing osmotic diuresis, etc.; 2, renal diseases: such as congenital or acquired defects in the distal tubules and collecting ducts of the kidney to reduce water reabsorption; reduced tubular concentrating function, seen in chronic nephritis, glomerulosclerosis, acute renal failure polyuric phase, etc.