Urinary organs are the main group of excretory organs of the body. By removing water and mineral salts, the urinary organs maintain the water and salt balance of blood and tissues at a certain level. The main product of urinary excretion is organic matter: uric acid salts and urea, which are the product of protein decay, sodium chloride and others; they are all excreted in dissolved form (urine).
The urinary organs consist of two (right and left) kidneys located in the lumbar abdomen on the sides of the spine (at the level from the 11th thoracic to the 2nd lumbar vertebrae). The kidneys are organs in which the flowing blood is freed from toxins. Urine secreted by the kidneys collects in their cavities – renal pelvis .
Long channels coming from each of the pelvis – ureters — extend along the posterior surface of the abdominal cavity down into the small pelvis; front covered with peritoneum. The ureters are a paired tubular organ through which urine outflows from the kidneys to the bladder. They come from each side to the base of the bladder and open holes in it – the mouth. The length of the ureters is on average 30-35 cm, diameter 4-6 mm in the narrowest and 7-9 mm in the widest part. The ureters are lined with mucous membranes. The smooth muscles of the ureters ensure the movement of urine into the bladder at any position of the body.
The bladder is a hollow muscle organ with an average capacity of 750 cm 2 , but when stretched, the bladder can hold much more urine. The bladder is a reservoir in which urine accumulates and from time to time, as it accumulates, is discharged through the urethra.
Mochespuskatelny channel – terminal urinary tract. The urethra is a tube consisting of an internal – mucous – membrane, surrounded by a layer of muscle tissue.
The urethra in men begins from the lower anterior section of the bladder – its neck, passes through the prostate gland, penetrates the so-called urogenital diaphragm under the pubic joint and enters the cavernous body of the penis, opening at the top of its head with an external opening. The length of a man’s urinary canal is about 20 cm, diameter is about 7 mm.
The female urethra is much shorter than the male urethra (about 5cm) and has an almost straight course, opening with an external opening in the vestibule of the vagina. The initial part of the urethra in the bladder is surrounded by an annular muscle layer. Its walls are in a collapsed state and stretch only with the passage of urine.
In the place where the urethra in men passes through the prostate, the mouths of the vas deferens and the prostate open . Thus, in men, the urethra serves to excrete urine and semen. The mucous membrane of the urethra contains glands.
In addition to the urinary organs, the organs performing the function of removing from the body the products of reverse metabolism (dissimilation) and water, are the sweat glands, lungs, intestines.
WATER-SALT EXCHANGE.
For the normal functioning of the body requires a constant composition of the internal environment: blood and intercellular fluids. The ability of individual cells and the whole organism as a whole to maintain the constancy of its liquid phase with the help of numerous physiological and biochemical reactions is one of the most amazing features of living matter.
Maintaining constancy (within certain limits) of the internal environment of the body is called homeostasis. An important role in maintaining homeostasis is played by the excretory organs – the kidneys, sweat glands, intestines, as well as the liver and lungs, which are involved in the removal of the final metabolic products from the body. Excretory organs work no less intensely than the heart, brain, and other vital systems of the body.
The degree of purity of blood, cells and tissues from toxins largely determines the well-being of the body. On the other hand, even a short delay in unnecessary substances in the body causes various disturbances, while their long accumulation can be the cause of numerous chronic diseases.
ABOUT THE STRUCTURE AND FUNCTIONS OF KIDNEYS.
The kidneys perform important and complex functions in the body.
• play an important role in cleansing the body, removing metabolic products;
• regulate water-salt metabolism, including the exchange of sodium, potassium, chlorine, phosphorus ;
• synthesize biologically active substances (for example, renin, heparin),
• having a great influence on the level of blood pressure, blood coagulation, protective properties of the body, etc.
The kidneys are located on the sides of the spine behind the peritoneum. Short powerful vessels connect them to the abdominal aorta lying on the spine and the inferior vena cava. Each kidney consists of two layers: cortical and cerebral. The kidneys have a very developed vascular network. All the blood circulating in the arteries and veins passes through the kidneys every 5-10 minutes, and in 24 hours more than 700 liters of blood flows through them.
The kidney consists of approximately 1 million functional units – nephrons involved in the formation of urine. The composition of each nephron includes the glomerulus and tubule .
The glomerulus is a filtering apparatus, it is a plexus of capillaries supplied with blood from the renal arteries. The walls of the glomerular capillaries are very thin, they are penetrated by numerous holes that are so small that they can only be seen with an electron microscope. Unlike the capillaries of other organs, the glomerular capillaries, uniting together, form not veins, but small efferent arteries – arterioles, which again disintegrate into a second network of capillaries surrounding the tubules.
The tubular capillaries form a vein through which blood, having twice passed through the capillaries (glomerulus and tubule), is directed back to the heart.
The glomerulus of capillaries is located in a small capsule in the shape of a bowl. This capsule is a hollow double-walled bag of cells. The cavity between the walls of the capsule gives rise to the tubule, which first has a convoluted shape, then is stretched out by a loop, after which, again wriggling, passes into the collecting tube. Both branches of the loop lie close to each other, and the fluid moves in them in opposite directions. The total length of the tubule of one nephron is 35–53 mm, while the length of all tubules of both kidneys reaches 70–100 km. The collecting tube merges with the neighboring tubes and flows into the renal pelvis, from where urine passes through the ureters into the bladder.
Passing through the capillaries of the glomerulus, the blood gives water and various mineral and organic substances into the cavity of the capsule. The total surface of the walls of the capillaries of one glomerulus, through which the filtration of water and the substances dissolved in it, also has quite impressive dimensions – about 5-8 m 2 . Analysis of the fluid entering the capsule showed that its only important difference from blood plasma is the absence of protein molecules.
This fluid is called primary urine, in a day its amount reaches 150-180 liters. The amount of urine excreted during the day is approximately 1.5 liters. This suggests that over 99% of the fluid entering the nephron is absorbed back into the blood. Re-absorption ( reabsorption ) of water and small molecules occurs in the tubules.
The kidneys reliably protect the constancy of the internal environment, changing within a wide range the composition of the fluid ejected from the body. For example, if the amount of sugar (glucose) in the blood does not exceed normal values, then all glucose that is filtered in the glomerulus undergoes complete reverse absorption and remains in the body. If the concentration of glucose in the blood is abnormally high, as is the case with diabetes or after consuming too many sweets, part of it is retained in the tubules and excreted in the urine. So the body is freed from excess sugar.
The kidneys are the main tool for removing protein breakdown products from the body. Healthy kidneys have an inhibitory effect on the blood coagulation system. The kidneys are actively involved in the regulation of blood pressure. They form a special vasoconstrictor factor, called renin ( ren – the Latin name for the kidney). The kidneys also contribute to lowering blood pressure by the formation of certain vasodilating substances.