Location of the kidneys: The kidneys are located on both sides of the spine, close to the posterior abdominal wall, and reside behind the peritoneum. The upper end of the left kidney is level with the lower edge of the 11th thoracic vertebra and the lower end is level with the lower edge of the 2nd lumbar vertebra. The right kidney is half a vertebra lower than the left kidney. The left 12th rib is oblique over the middle of the back of the left kidney, and the right 12th rib is oblique over the upper part of the back of the right kidney. It is shaped like a broad bean. There is one on each side: the right kidney is slightly lower than the left bone because of the liver on it. Each kidney weighs 120-150 grams, is 10-12 cm long, 5-6 cm wide, and 3 cm thick, and is usually smaller in women. Kidney structure: The kidney structure is divided into two parts, the lateral layer of the renal cortex and the medulla medullaris, when viewed in longitudinal section. The tip of the renal medulla forms a papilla shape connected to the calyces. The urine formed in the kidney reaches the bladder from the papillary part of the kidney through the calyces, renal pelvis, and ureter, passes through the urethra, and is excreted from the body. The basic working unit of the kidney is called the “renal unit”. Each kidney is made up of more than one million kidney units. The renal unit: The renal unit consists of a renal tubule and a connected tubule. The renal tubules are located in the cortical part of the kidney. Each renal tubule consists of a glomerulus and a capsule surrounding it. The core of the glomerulus is a network of capillaries that is connected at both ends to the small input and output arteries, respectively. The glomerulus is surrounded by a capsule. The epithelium of the dirty layer of the capsule and the epithelium of the wall of the capsule are continuous with the epithelium of the renal tubules. The lumen of the capsule communicates with the renal tubules. The renal tubules are divided into proximal tubules, medullary tubules and distal tubules, which finally converge into the collecting duct. The function of the renal unit is mainly to produce urine, including the filtration of the glomerulus and the reabsorption and secretion of the renal tubules. Although the collecting duct is different from the renal unit in terms of occurrence and structure, it is closely related to the renal tubules in terms of function and plays an important role in the process of urine production, especially for urine concentration. The glomerulus and tubules each have different physiological roles: the glomerulus is responsible for filtration and is located within the cortical layer; the tubules are responsible for reabsorption and secretion. Renal functions: Waste products in the body are transported through the blood circulation to the kidneys, where they are filtered and excreted into the urine. In fact, the kidneys are responsible for excreting nitrogenous waste products produced by the body’s daily protein metabolism, in addition to their regulatory, synthetic and metabolic roles. Electrolytes such as water, sodium and potassium in the human body need to be regulated by the kidneys in excess or deficiency in the body to keep the quantity and quality of the body solutions (body fluids) normal, and also have the role of maintaining a certain acidity (PH) of the blood. The kidney is an important organ for the synthesis and secretion of hormones in the body, and is related to the production, activity, and breakdown of hormones and vitamins needed to regulate blood pressure, bone metabolism, glucose metabolism, and the hematopoietic system, and is especially close to the production of erythropoietin (EPO) and active vitamin D3; and is also involved in regulating endocrine operations. Since the blood flow of the kidney accounts for 1/5 to 1/4 of the blood output of the heart, the complexity and importance of the physiological functions of the kidney are closely related to its abundant blood flow. The kidney is one of the most important organs in the human body and has many important functions, which are briefly summarized as follows: 1) formation of urine; 2) regulation of fluid and electrolytes; 3) regulation of blood pressure; 4) other metabolic and endocrine functions; 5) regulation of blood acid-base balance.