The human urinary system has a cleansing function, aimed at getting rid of unnecessary metabolic products from the body and maintaining acid-base, water-electrolyte balance, thus regulating blood pressure. Learn about the structure and functions of the urinary system!
Contents:
- Urinary system: kidneys
- Urinary system: urine formation
Urinary system , apart from cleansing the urinary system, it has an endocrine function - it produces erythropoietin, is involved in vitamin D metabolism, and produces substances with vasopressor and vasodilating properties. The urinary system consists of: kidneys, ureters, bladder, urethra.
Urinary system: kidneys
The kidneys are a paired bean-shaped organ located retroperitoneally. Normal kidney of an adult is approx. 12 cm long, weight 125-170 g in men, 115-155 g in women. The left kidney is located at the height of the Th12-L3 vertebrae, and the right one is 1-3 cm lower and is smaller.
The kidneys are made up of two parts: the cortex and the core of the kidney.
The cortex of the kidney , lying on the outside, consists of pyramids (4-18 in number), conical-shaped structures placed with their bases on the outside. The tops of the pyramids face the renal pelvis, formingrenal papillae , which are the outlet of the collecting tubules.
Kidney pillars (Bertin's columns) run between the pyramids, and the spinal rays (Ferrein) penetrate from the base of the pyramids towards the cortex.
Renal nipplesgo into the (smaller) calyces, which combine into groups to form the greater kidney calyces and into the renal pelvis. The pelvis becomesureterconnecting the kidney with the bladder.
There is a valve at the entrance of the ureter to the bladder to prevent the return of urine.
The urine then goes to the urethra, which is the last part of the urinary tract.
The urethrain its initial section is surrounded by the bladder sphincter muscle, which holds the urine in the bladder. The female urethra ends near the vestibule of the vagina, is about 6 cm long, the male is 18-20 cm long, and ends at the tip of the penis.
The functional and structural unit of the kidney isnephron . Each kidney has approx.million nephrons, and each nephron consists of the glomerulus, the proximal urethra, and the distal urethra (tubules).
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Renal glomerulusconsists of a network of capillaries, has a vascular pole (the place where the afferent arterios enter and where the efferent arteriole leaves), and the urinary pole (where the glomerulus connects with the proximal urethra). In addition, its structure includes:
- endothelial cells (they form the first layer of the filtration barrier, permeable to water and small molecules);
- podocytes (they adhere to the basal membrane by projections, between which there are gaps covered with a filter membrane, they synthesize enzymes);
- basement membrane (mostly covers the loops of glomerular vessels, is located between endothelial cells and podocytes, creates a barrier for molecules with a specific mass and electric charge);
- mesangium (fills the space between the loops of the glomerulus capillary). The glomerulus is surrounded by Bowman's purse, forming the corpuscle of the kidneys.
The proximal coilconsists of a 1st degree spiral coil, a section of the thick descending arm of the Henle loop, and a section of the thin Henle loop.
Distal coilfrom the thick section of the ascending limb of the Henle loop, the 2nd degree tortuous coil and the collecting coil.
The glomerular apparatusis an organ that performs a receptor-secretory function. It is located between the vascular pole of the glomerulus and the distal convoluted tubule of the same nephron. It consists of a dense spot, external mesangium and granular cells.
Granular cellsact as baroreceptors that respond to changes in pressure gradients between the afferent artery and interstitial fluid.
Under the influence of pressure drop and reduction of sodium reabsorption (reabsorption), they secrete the hormone renin, the action of which reduces diuresis and increases blood pressure.
Dense macular cellsare an element of the distal urethra, they act as a chemoreceptor for sodium concentration in the urethral fluid. As a result of increasing the concentration of this electrolyte, the secretion of renin is also increased through a series of reactions.
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Urinary system: urine formation
In the first step, the plasma is seeping across the barrierfiltration, where blood morphotic elements, large mass particles are retained, and less mass products (metabolic products) and some substances necessary for the body are removed, which will be reabsorbed at a later stage.
Glomerular filtration rate per minute (GFR) is 80-120ml / 1.73m2body surface area. About 150 liters of glomerular filtrate are produced per day, 99% of which is reabsorbed in the renal tubules, and 1% is excreted as final urine.
Nephron is divided into specialized sections, each of which has a specific task. In the proximal tubules, the reabsorption of glucose, amino acids, phosphates, bicarbonates, and some of the electrolytes filtered in the glomeruli takes place. At this stage, the substances are reabsorbed in large amounts, the regulation is not precise. The main function of the Henle Loop is to concentrate and dilute the urine.
In the distal coil, sodium, potassium and calcium balance are precisely regulated. The final urine concentrating and fine regulation of hydrogen and bicarbonate excretion take place in the collecting tubule in the presence of vasopressin (an antidiuretic hormone).