Do you know the kidneys?7 The normal human kidneys look like fava beans and are located on either side of the spine at the waist. Each kidney is about 9 to 12 cm long, 5 to 6 cm wide, 3 to 4 cm thick, and weighs 120 to 150 grams. The shape, size and weight of the two kidneys are roughly similar, generally speaking, the left kidney is slightly larger than the right kidney, while the female kidney is slightly lighter than the male kidney. The kidneys have a smooth, reddish-brown surface and a deep depression on the inside called the hilum, through which the blood vessels, nerves, lymphatic vessels and ureters of the kidneys enter and exit. There is a small adrenal gland on the upper end of each kidney. The kidneys are mainly fixed to the posterior peritoneal wall by the renal fascia. The kidneys have two protective membranes: the outer layer is the renal fat capsule and the inner layer is the renal fibrous membrane. Inside these two protective membranes is the renal parenchyma. If you cut the kidney into sections, you can see two parts: the outer part is called the cortex and the inner part is called the medulla. From the medulla to the hilum, you can see a flat funnel-shaped cavity, which is the renal pelvis. Why is the kidney easily “injured”? This has to do with its structure and function. The basic structures of the kidney are the glomerulus, the tubules, the collecting ducts and the renal pelvis. When human blood flows through the glomerulus, large components, such as red blood cells, white blood cells, platelets, proteins, etc., cannot pass through the glomerulus screen, so they remain in the blood vessels; while some small components, such as water, sodium, chloride, urea, sugar, and some of the body’s metabolic waste, such as urea, uric acid, creatinine, etc., can be filtered out through the glomerulus screen, forming “primary urine”. This results in “primary urine” flowing into the renal tubules. The renal tubules have the function of reabsorption, and when the original urine flows through the tubules, 99% of the water is absorbed back into the body, and almost all of the useful substances filtered out by the glomerulus, such as sugar, amino acids, small molecules of protein and salt, and other small amounts of nutrients, are also reabsorbed. At this point, only metabolic waste and very little water remain in the original urine, forming the “final urine”, which is the urine we normally see and eliminate from the body. Each kidney has about 1.3 million glomeruli, which filter out about 180 liters of primary urine and form about 1.8 liters of final urine every day. When there is too much or not enough water in the body, the kidneys regulate the amount of urine and maintain the water balance in the body. In addition to the function of reabsorbing useful substances, the renal tubules also secrete certain harmful metabolites and work together with the glomerulus to play a role in regulating the electrolyte and acid-base balance in the human body. The collecting ducts and renal pelvis, which are mainly urine discharge lines, are also involved in the regulation of water balance in the body. The kidney is not only an excretory organ, but also a very important endocrine organ that produces a variety of hormones and biologically active substances that play an important role in blood pressure, water-electrolyte balance, red blood cell production and calcium-phosphorus metabolism in the human body. For example, the kidneys secrete renin and prostaglandin, which regulate blood pressure. Renin mainly raises blood pressure, while prostaglandin lowers it, and together they maintain blood pressure stability. People with renal vascular lesions or renal patients with blood flow affecting the kidneys often have high blood pressure because the lesions affect the normal secretion of renin by the kidneys for this reason. At the same time, the kidneys produce a kind of erythropoietin. Erythropoietin promotes bone marrow hematopoiesis and the production of red blood cells. The kidneys produce 90% of the total erythropoietin in the body, so when the kidneys are diseased, the production of erythropoietin is low and anemia will occur. In addition, the kidney also converts active vitamin D precursors into active vitamin D, regulates calcium and phosphorus metabolism in the body; participates in the degradation and inactivation of various endocrine hormones, regulates hormone metabolism, and so on. Because the human body is metabolizing every moment, and in this process, some unwanted and even harmful wastes will be produced, and the kidneys have to excrete these wastes from the body, so as to maintain the normal physiological activities of the human body. In addition, because of the need to maintain the balance of water and salt, as well as the elimination of metabolic waste, about one-fifth of the blood discharged through the heart has to pass through the kidneys, and once the blood contains fine or toxic substances, or metabolic waste exceeds the load that the kidneys can withstand, it will often damage the kidneys and cause damage. At the same time, because the kidneys are very sensitive to changes in blood pressure and ischemia, large fluctuations in blood pressure or acute blood loss can also cause damage to the kidneys. It is because of the above factors that the kidneys are particularly vulnerable to injury.