& lt produce urine and keep water balance >
This is the main function of the kidney. When blood flows through the glomerulus, due to the pressure, it will filter out a liquid that is the same as plasma but does not contain protein. This liquid is called "protourine". When the original urine passes through the renal tubule, the renal tubule reabsorbs most of the water, all the sugar and some salt and sends them back to the blood, but most of the nitrogen is not absorbed back. The remaining concentrated solution containing residual substances is urine, accounting for about 65438 0% of the original urine. The urine volume of normal people 1 day is 1000 ~ 2000 ml, generally light yellow, and the specific gravity is between 1.003 ~ 1.030. Too high, too low or fixed specific gravity, too much or too little urine all indicate the possibility of renal insufficiency.
[Trilogy of Urine Generation]
Filtration: The blood flow of normal people through the kidney per minute is about 1200ml. When human blood flows through the glomerulus, some components in plasma can be filtered out of the glomerulus and enter the renal capsule.
Re-absorption: filtered liquid enters renal tubules and collecting ducts through renal capsules, and many substances that can be used by the body are re-absorbed into the blood.
Secretion: Epithelial cells of renal tubules and collecting ducts can secrete some components in the surrounding capillaries and all substances produced by these cells into the lumen of renal tubules and collecting ducts.
When blood flows through glomerular capillaries, except blood cells and macromolecular proteins, water, electrolytes and small molecular organic substances (including small molecular proteins) in plasma can enter the glomerular capsule through glomerular filtration membrane. This liquid is called filtrate. After the glomerular filtrate enters the tubule, it is called tubule fluid. When the tubule fluid flows through the renal tubule and collecting tube, the water and various solutes in it will be completely or partially reabsorbed back into the blood.
& lt Urine excretion, metabolism of wastes, poisons and drugs & gt；;
The human body is undergoing metabolism all the time. Kidney excretes harmful substances such as creatinine, urea, uric acid and other nitrogen-containing substances, phosphate and inorganic sulfate through urine metabolism, so that these wastes will not accumulate in the body. Similarly, the kidneys can also excrete toxic substances and drugs that enter the human body.
& lt maintain body fluid balance and acid-base balance >
The kidney has a high reabsorption rate of water. If the reabsorption rate of water by renal tubules and collecting tubes changes slightly, the urine volume will change greatly. For example, when the reabsorption rate of water is reduced by 1%, the urine output can be increased by 1 time. Therefore, the urine volume mainly depends on the reabsorption speed of water by renal tubules and collecting tubes. This reabsorbed water can be divided into two parts. Part of it is reabsorbed in the proximal tubule, and it is absorbed with the absorption of solute components in plasma filtrate, regardless of whether there is water shortage in the body. The other part is reabsorbed in the distal tubule and collecting duct, which can be adjusted according to whether there is water shortage in the body, and plays a vital role in maintaining the balance of human body fluids.
In addition, normal people need to excrete 3 ~ 5 grams of sodium salt from urine every day, which plays an important role in maintaining the relative stability of extracellular sodium concentration and osmotic pressure.
Acid-base balance is another important factor to maintain the stability of human internal environment. The kidney has a strong function of maintaining acid-base balance in the body. Renal acid excretion consists of three parts, namely ammonia excretion, titratable acid excretion and carbonate reabsorption. The sum of the three parts is called "net acid discharge". In addition, there are many factors, including systemic factors (such as the change of acid-base balance and body fluid volume) and local factors (such as the change of small tubular blood flow, the change of small tubular fluid composition and pH value). ), as well as some humoral factors and polypeptide hormones, have a certain impact on the acidification function of the kidney.
& lt regulate blood pressure >
Renin secreted by the kidney can raise blood pressure. When sodium intake is limited or insufficient, it will lead to the decrease of plasma volume and renal perfusion pressure; When standing upright, cells secrete renin, which can depsipeptide angiotensinogen in plasma into angiotensin ⅰ, and then become angiotensin ⅱ through the action of invertase. Through the action of angiotensin ⅱ and aldosterone, blood pressure can be increased.
At the same time, prostaglandin secreted by the kidney has the effect of lowering blood pressure. Prostaglandins can reduce blood pressure by increasing renal cortical blood flow, promoting diuresis and sodium excretion, reducing peripheral vascular resistance, and finally dilating blood vessels.
& lt secretes renin >
Renin is a proteolytic enzyme with a molecular weight of 40,000, which is mainly synthesized, stored and secreted by the periglomerular cells of the periglomerular organs. The role of renin is:
Vascular contraction and vascular smooth muscle cell division.
Enhance myocardial contraction and promote myocardial hypertrophy.
Participate in the regulation of renal dynamics and increase the sodium reabsorption capacity of renal tubules.
Promote the increase of adrenal aldosterone secretion.
Promote the production of other vasoactive substances such as peptides.
The action center produces thirst and promotes the release of catecholamine.
& lt secretes prostaglandin >
Prostaglandin is named after its earliest discovery in prostate. Later, prostatic cord was found in almost all tissues and cells of human body, such as seminal vesicle, lung, kidney, brain, stomach and intestine. Its main functions are:
Effects on renal blood circulation: Prostaglandin E2 and prostacyclin can dilate renal blood vessels, while thromboxane A can contract renal blood vessels.
Effect on sodium chloride excretion: Prostaglandin E2 and prostacyclin can excrete sodium from urine.
Effect on water excretion: Prostaglandin can increase water excretion. When there is a problem with renal function, prostaglandin secretion decreases, which is an important factor leading to high filtration and high perfusion of kidney and one of the important reasons leading to renal hypertension.
& lt promote erythropoiesis >
The kidney can secrete erythropoietin, which acts on the hematopoietic system of bone marrow and promotes the differentiation and maturity of primitive red blood cells; Promote the absorption of iron by bone marrow and accelerate the production of hemoglobin and red blood cells; Promote the release of bone marrow reticulocytes into the blood. In a certain period of time, the degree of anemia is directly proportional to the degree of renal failure, and erythropoietin in blood and urine decreases. At this time, renal anemia can be corrected if exogenous erythropoietin is supplemented.
& lt Promote the Activation of Vitamin D>；;
Vitamin D must be converted into 1, 25-dihydroxy vitamin D3 through the kidney to play its physiological role. Renal cortical cells contain 1 hydroxylase, and vitamin D is first converted into 25- hydroxyvitamin D3 under the action of liver 25 hydroxylase. Under the action of kidney 1 hydroxylase, it is converted into 1, 25 dihydroxy vitamin D3, that is, active vitamin D3. Can promote the absorption of calcium and phosphorus in gastrointestinal tract; Promote bone calcium transfer; Promote bone growth and cartilage calcification; Promote the reabsorption of phosphorus by renal tubules and reduce urinary phosphorus excretion; Inhibit the secretion of parathyroid hormone.
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