Each person has two kidneys, shaped like fava beans, located behind the peritoneum immediately behind the abdominal wall on both sides of the lumbar spine. A single kidney is about 10-12cm long, 5-6cm wide, 3-4cm thick, and weighs about 100-140g. The functions of the kidneys are mainly urinary and endocrine functions: 1. Urinary function: The kidneys complete the production of urine through three links, namely glomerular filtration, tubular reabsorption and tubular secretion. When blood passes through the glomerulus, the plasma filtered out from the glomerulus is proto-urine, all or most of its substances are reabsorbed, water and electrolytes are partially reabsorbed, while creatinine and urea nitrogen, etc. are hardly reabsorbed, and the remaining un-reabsorbed part is what we know as urine, through which we excrete useless waste from the body and maintain the balance of the body’s internal environment. 2, endocrine function: The renal parietal cells can secrete renin, which is finally converted into angiotensin II, which has a strong vasoconstrictive effect. Overproduction of angiotensin II is one of the main mechanisms of hypertension generation, in addition to being one of the main factors causing the loss of renal function. The glomerular paracellular apparatus produces erythropoietic factor, which promotes the maturation of red blood cells. The lack of this factor in renal failure results in renal anemia.