The kidneys are the main filter of our body. Thanks to their daily work, our blood is cleansed of toxins and waste products, excess water and salts. And the kidneys maintain blood pressure and synthesize important hormones. Just like the heart, the kidneys work around the clock without breaks and weekends, passing through 1500 liters of blood daily. Let’s find out how our filter works and why it should be protected.
The structure of the kidney
Having analyzed the structure of the kidney, we will understand how this paired organ performs its complex and important functions.
The kidneys are located behind the peritoneum on both sides of the lumbar spine. The right kidney lies at the level of the XII thoracic – III lumbar vertebra, the left-slightly higher, at the level of the XI thoracic-and the upper edge of the III lumbar vertebra.
The kidneys are surrounded by membranes – a dense capsule and a fat layer that protect the organ from mechanical damage.
The kidney consists of the cortical (outer) and cerebral (inner) layers. There is a cavity inside the kidney, or the renal pelvis, where the urine is released. The renal pelvis passes into the ureter.
The kidney has a small depression called the kidney gate. At the gate of the kidney, the arteries enter, the veins exit, the lymphatic vessels and the ureter, from which the urine enters the bladder.
We turn to the microscopic structure. The structural and functional unit is the nephron. It is a system of convoluted tubules and blood vessels covered with a capsule. At the level of the nephron, the main functions of the kidney are performed – blood filtration, the formation of urine and its excretion. In total, there are more than a million nephrons in the kidneys.
Arterial blood enters the nephron through the arteriole, which is divided into many small — caliber vessels-capillaries. They are woven in the form of a glomerulus (glomerula). The glomerulus of the vessels is surrounded by a capsule that looks like a bowl. The capsule tapering forms a canaliculus. In the cortical layer, it is convoluted, and when it passes into the brain layer, it becomes straight. This is the proximal division (descending division) of the tubule. In the brain layer, the canal makes a bend, turning 1800 in the direction of the cortical layer. This section is called the Henle loop. Next, the canal passes into the ascending part, and then into the distalpart , which has a wider lumen compared to the proximal part. In the cortical layer of the kidney, the distal tubule makes several bends and flows into the excretory ductsthat follow to the renal pelvis.
The total length of the renal tubules is about 200 km
From the center of the renal glomerulus comes the outputting arteriole, which again breaks up into a network of capillaries. They twist around the tubules of the nephron all over and go into the venules. Then they combine and eventually pass into the renal vein.
Thus, the blood enters the renal glomerulus through the bringing arteriole, and exits through the carrying one. At the same time, the diameter of the first one is larger and the muscle wall is better developed, which creates conditions for blood to enter the glomerular capillaries.
The blood supply to the kidney is quite intense. In one minute, a quarter of the blood released by the heart into the aorta enters the kidneys. The features of the blood supply allow you to maintain the optimal pressure in the glomerulus, which is necessary for blood filtration.
Juxtaglomerular apparatus of the kidneys
An important role in the regulation of blood pressure is played by the so-called juxtaglomerular apparatus, which is located in the triangle between the bringing and carrying out arterioles and the ascending part of the Henle loop.
The juxtaglomerular apparatus is represented by special cells that can record changes in blood pressure and secrete the hormone renin, which is necessary to maintain blood pressure.
Kidneys are a unique filter. As we can see, the structure of the nephron is much more complex than the filters we know. Let’s see how the blood is filtered and urine is formed in the kidneys.
So, the blood enters the fetal arteriole from the renal artery. The pressure in the arteriole is high-60-70 mm Hg. For comparison, the average pressure in small-caliber vessels in our body is about 30-40 mm Hg.
Once in the vessels of the glomerulus under high pressure, the blood begins to filter – its liquid part (plasma) exits through the microscopic holes of the glomerular capillaries. At the same time, blood cells and proteins remain in the blood, since they have a large molecule. Together with the plasma, carbohydrates, water, amino acids, salts, urea, hormones and vitamins are released. This is the primary urine. In fact, it is a blood plasma without protein, which flows into the tubule of the nephron, containing both useful and harmful substances.
Part of the blood is not filtered in the glomerulus, and goes out into the outflow arteriole, which, as we remember, breaks down into small arterioles. These capillaries entwine the tubules and perform an important function. The fact is that in the primary urine there are useful substances that need to be left in the blood. Therefore, they pass through the walls of the tubules and capillaries, returning to the blood. This process is called reabsorption or reabsorption.
Some substances, such as potassium ions, hydrogen, ammonia, uric acid, antibiotics and other drugs, dyes and X-ray contrast agents can not pass through the wall of the blood vessel and enter the urine. Nevertheless, you need to display them. There is another mechanism for removing large molecules, using tubular secretion. These compounds enter the cells of the renal tubules from the interstitial fluid, and then, with the help of active transport, they are released into the lumen of the tubule.
Stages of blood filtration and urine formation:
- Themucus that enters the kidney is filtered in the glomerulus. In the first stage, it loses all the molecules that can pass through the capillary wall.
- Then useful substances-vitamins, hormones, ions and part of the water, are selected in the renal tubules by reverse reabsorption.
- In the urine, harmful substances, potassium and hydrogen ions, which cannot pass through the capillary barrier, are released from the cells of the tubule wall. The elimination of hydrogen ions is a way to reduce the acidity of the blood.
- From the tubules, urine enters the renal cups, then the renal pelvis.
- From the renal pelvis, urine passes through the ureter into the bladder, which is its reservoir.
With a normal drinking regime, about 1.5 liters of urine are formed per day. It consists of 95% water and includes compounds to be removed from the body – urea, uric acid, urobilin, urochrome, creatinine, potassium, sodium, phosphates, sulfates and harmful substances. Urine can contain more than 150 components.
The kidneys are involved in the regulation of blood pressure. If it needs to be increased, the kidneys reduce the intensity of filtration and reabsorption. To reduce blood pressure, the activity of the kidneys increases, which leads to an increase in the amount of urine. Thus, the blood volume decreases, which leads to a decrease in blood pressure.
Another mechanism of pressure regulation is the work of the juxtaglomerular apparatus. When blood pressure decreases, cells secrete the hormone renin, which activates angiotensinogen and triggers the renin-angiotensin-aldosterone system (RAAS).
In addition to renin, the kidneys synthesize another hormone – erythropoietin, which stimulates the formation of new red blood cells and prevents their death. The stimulus for the production of erythropoietin is a lack of oxygen.
The kidneys are directly involved in the activation of vitamin D. Regardless of the way this vitamin enters the body, it must undergo certain processing in the liver, and then in the kidneys. You can take as much useful vitamin D as you want and at the same time have signs of its deficiency in the case of impaired kidney function.
Another important aspect of kidney function is participation in protein metabolism, the end product of which is urea. The kidneys are the only organ that can remove urea from the body. When their work is disrupted, the amount of urea in the blood increases, which slows down the process of protein assimilation.
So, we got acquainted with the main functions of the kidneys in the body. Let’s sum it up.
The task of the kidneys:
- Filtration of blood and elimination of body waste products and toxic substances.
- To maintain an optimal volume of liquid.
- Regulation of salt metabolism.
- Regulation of blood pressure.
- Regulation of blood acidity.
- Participation in the synthesis of red blood cells.
- Activation of vitamin D.
- Participation in protein metabolism.
Causes of kidney failure
The kidneys are a fairly vulnerable organ, which can lead to a violation of their work:
- Intoxication with drugs and poisons
- Autoimmune diseases
- Increased blood pressure
- Diabetes mellitus and other metabolic disorders
Recently, we have received more and more advice on increasing the amount of drinking water in the diet. In this matter, it is important to know the measure. An excess amount of fluid increases the volume of blood, which puts an additional load on the nephrons of the kidney. In this case, the capillaries of the glomeruli stretch, the filtration process is disrupted. Fortunately, the kidneys have a significant reserve. If some of the nephrons fail, then others begin to perform their function. It’s no secret that a person can live with one kidney. Moreover, it is proved that even a part of the nephrons of one kidney can completely cover the needs of the body. However, the reserve of kidneys is exhausted, and this should be remembered. Violation of the kidneys leads to sad consequences and no artificial filter can replace them.
The kidneys are a complex mechanism that performs a number of important functions, treat them carefully!