General information: 1, the general structure and main functions of the kidneys The kidneys are a pair of internal organs very similar to the bean-shaped, it is in the posterior abdominal cavity on both sides of the spine, in front of the intestinal tube in the abdominal cavity, followed by strong lumbar muscles. In adult men, each kidney weighs about 120-170 grams and has a size of about 11х6х2.5 cm, which is about the size of the head of the palm I hold. The inner middle of the kidney is recessed and open, called the hilum, which contains the renal pelvis, blood vessels, lymphatic vessels and nerve plexus, from which they enter the kidney. If the kidney is cut open from the longitudinal axis, two layers can be seen. The outer layer is about 1 cm thick and contains many tiny red dotted particles called the renal cortex, and those red particles are the glomeruli. The inner layer is about 2.5 cm thick, dark red in color, and contains many tiny stripes, which is called the renal medulla, and those tiny stripes are the tubules. The glomerulus is connected to the renal tubules, called the renal unit. The most important function of the kidney is to form urine. First of all, we need to know the structure of the glomerulus. After the artery at the renal portal enters the renal parenchyma, it gradually divides into many tiny arteries by branching and then connects with the glomerulus, and when you look at the glomerulus with a microscope, it is a composed of many very fine vessels, i.e. capillaries, and then look at these capillaries with an electron microscope, it has many holes on it, just like a sieve. When the blood flows through the renal artery and enters the glomerulus, the large components, such as red blood cells, white blood cells, platelets, proteins, etc., cannot pass through these sieve holes, so they remain in the blood vessels and return to the body; while the small components, such as water, sodium, chloride, urea, sugar, etc., are filtered out through these sieve holes and flow into the renal tubules, at which time the filtered liquid is called primary urine. The original urine contains many nutrients, such as sugar and amino acids, etc. When it flows through the renal tubules, all these nutrients are reabsorbed into the body, and 99% of the water is also absorbed, at which time only the metabolic wastes of the body and very little water remain, and they form urine. After entering the renal pelvis, urine flows through the ureter into the bladder and is excreted when it is retained to a certain amount. Each kidney in the human body has about 1.3 million glomeruli, which filter out about 180 liters of raw urine every day and form about 1.8 liters of urine, which contains the waste products metabolized by the body The kidneys have another important function, which is the endocrine function. The so-called endocrine function is that the kidneys synthesize and secrete some substances to regulate the function of the body. For example, erythropoietin, when synthesized by the kidneys, stimulates bone marrow hematopoiesis to produce red blood cells, and when the kidneys are seriously ill, they cannot be synthesized and become anemic. Another example is active vitamin D3, the kidney synthesis, it enters the intestinal canal, can make the intestinal canal absorption of calcium increased, human bones will be stronger, when the kidney has a serious disease, can not be synthesized, children will produce rickets, adult bones will become weak, and even pain, fractures. In addition, the kidneys are also the site of breakdown inactivation of a variety of endocrine substances. For example, insulin stays in the blood significantly longer in renal failure, and diabetic patients should adjust their insulin dosage in renal failure. 2, the quality of urine and the relationship between kidney function How do the kidneys excrete urine? Urine is formed by blood flowing into the kidney, filtered out by glomerular capillaries, and then reabsorbed and excreted by the renal tubules. The concentration of metabolic wastes, such as creatinine and urea, is much higher in urine than in plasma. Through the production and excretion of urine, the body can excrete metabolic wastes that are harmful to the body, while maintaining the water and electrolyte balance and acid-base balance in the body. If a person drinks a lot of water or a lot of soup, then he will excrete a lot of urine, and vice versa without water, the amount of urine is significantly reduced, and this phenomenon is regulated by the kidneys. In general, the urine volume of a normal person is about 2,000 milliliters per day, light yellow, transparent, with ammonia taste, pH about 6.5 specific gravity between 1.015-1.025, its composition is water and metabolic waste such as urea, uric acid and creatinine produced in the metabolic process. If the urine volume >3000 ml is called polyuria, urine volume <400 ml is called oliguria and urine volume <100 ml is called anuria. If the kidney is diseased and the glomerular filtration function decreases, the excess water and metabolic products and waste products in the body cannot be excreted well, and a series of clinical symptoms will occur. During the period of decreased renal reserve (i.e., glomerular filtration rate is 35%-70% of normal), the excretory function of the kidney can maintain the stability of the body's internal environment. In the azotemia phase (i.e., glomerular filtration rate of 20%-35% of normal), the ability to maintain the stability of the body's internal environment is impaired, there is mild impairment of renal concentrative function (polyuria and nocturia), and there may be mild anemia. If infections, nephrotoxic drugs (such as gentamicin), and insufficient blood volume occur during this period, the patient may rapidly develop renal failure or even uremic symptoms, i.e., swelling, low urine output, hypertension, nausea and vomiting, loss of appetite, and anemia. If the patient does not receive good treatment for kidney disease and does not pay attention to the changes in the quality and quantity of urine, the kidney function will gradually deteriorate to the point of renal failure ( The glomerular filtration rate is 10%-20%), and in the uremic stage (the glomerular filtration rate is less than 10% of the political party), dialysis or kidney transplantation will be needed eventually. The main indicators of kidney function: The main function of the kidney is to produce urine. The production of urine first passes through glomerular filtration, and then through reabsorption and secretion of renal tubules to produce concentrated urine. Therefore, the kidneys eliminate metabolic wastes and excess biochemical substances and harmful substances such as drugs from the body through urination, retain substances useful to the organism and adjust the volume of body fluids. In other words, the kidneys have the function of removing what is left and keeping what is needed. Once this function is impaired, the metabolic wastes of the body will accumulate and have toxic effects on the organism, and the internal environment will be out of balance, and then a series of manifestations of renal insufficiency will appear. The main indicators of glomerular function are blood creatinine and urea nitrogen. Blood creatinine is released by the metabolic process of muscles. It is now accepted in the medical community that blood creatinine is the best indicator of glomerular function when considered in conjunction with the patient's age and weight. The following formula is commonly used by clinical doctors and to calculate creatinine clearance from serum creatinine. Creatinine clearance (ml/min) = [(140 - years) x kg body weight] ÷ [[72 х creatinine (mg) In the case of women, the value obtained from the above formula, multiplied by 0.85 The creatinine clearance of each individual varies according to gender, age and weight. Creatinine clearance in adult men is about 120 mlmin, and as age increases, creatinine clearance gradually decreases, and by the age of 70, it is only 50% of that in young people. Both blood creatinine and urea nitrogen are end products of the metabolism of nitrogen-containing organic substances and proteins. Under normal conditions, these substances are filtered from the glomerulus, so doctors often use them as diagnostic and screening indicators of glomerular filtration function. However, urea nitrogen is actually a very inaccurate indicator and is influenced by many factors. For example, eating more meat, fish and eggs with high protein, various infections such as sepsis, high fever and gastrointestinal bleeding can increase urea nitrogen. Ms. Li's mother's increased blood urea nitrogen is due to infection, fever, and enhanced tissue breakdown. As the infection is controlled and the body temperature returns to normal, the urea nitrogen will also return to normal. Unfortunately, there are still some doctors who still mistakenly believe that urea nitrogen is an accurate glomerular function test. In fact, blood creatinine is a more accurate indicator of glomerular function, but of course it is better to calculate creatinine clearance according to the formula.