1, generate urine and maintain water balance: The glomerulus is like a sieve, when the blood flows through the glomerulus, the components of large volume, such as red blood cells, white blood cells, platelets, proteins, etc. cannot pass through the sieve, so they cannot be filtered out from the glomerulus and remain in the blood vessels; while the components of small volume, such as water, sodium, chloride, urea, sugar, etc., can pass through the sieve, filter out through the glomerulus and flow into the renal tubules, and these liquids are called “proto-urine”. When the original urine flows through the renal tubules, the tubules have a reabsorption function, 99% of the water is absorbed back into the body, and almost all of the nutrients are reabsorbed; at this point, only the body’s metabolic waste and very little water remain, forming urine (called “final urine”). Each kidney in the human body has about 1.3 million glomeruli, which filter out 180 liters of raw urine every day, forming about 1.8 liters of urine. When there is too much or too little water in the body, the kidneys regulate the volume of urine to maintain the balance of water in the body. 2.Discharge of metabolites and toxic substances: When human body metabolizes, it will produce some metabolic wastes, such as urea, uric acid and creatinine, etc. The kidneys discharge these wastes from urine through glomerular filtration and tubular secretion to maintain normal physiological activities. In acute and chronic renal insufficiency, the glomerular filtration function is reduced, and the accumulation of metabolic waste in the body will occur, causing disorders of normal physiological functions of the body. 3.Regulate electrolyte and acid-base balance: Through glomerular filtration, renal tubular reabsorption and secretion, the kidney excretes excess water from the body, regulates electrolyte and acid-base balance, and maintains the stability of the internal environment. 4, secretion of erythropoietin (EPO): promote bone marrow hematopoiesis, the production of red blood cells; renal insufficiency, erythropoietin synthesis is reduced, it will cause anemia. 5.Produces active vitamin D: converts 25(OH)2 vitamin D3 into 1,25(OH)2 vitamin D3, regulates calcium and phosphorus metabolism in the body, maintains the normal structure and function of bones, and is also involved in the regulation of immune function. Insufficient active vitamin D is caused by renal insufficiency. 6, secretion of vasoactive substances: secretion of renin, angiotensin, prostaglandins, etc., play an important role in the regulation of blood pressure. In chronic kidney disease, the above vasoactive substances can become dysregulated, causing an increase in blood pressure. 7. Degradation and inactivation of hormones: The kidney is also the site of degradation and inactivation of many hormones, such as insulin, parathyroid hormone, glucagon, calcitonin and many other hormones, all of which are degraded in the proximal tubular cells of the kidney. When renal insufficiency occurs, the biological half-life of these hormones is significantly prolonged, leading to accumulation in the body and causing metabolic disorders. In addition, the kidney secretes a variety of cytokines-growth factors that play an important role in regulating vital activities.