The theory of formation of urine

The most common filtration-reabsorbtsionno-secretory theory of the formation of urine. According to this theory, in the renal corpuscles per day filtered around 180 l primary (provisory) Urine, that concentrated in the tubules of nephrons. This tubular epithelium reabsorbs some of the elements of blood in urine. Processes of reabsorption may occur actively, with the participation of enzymes and energy costs, and by simple passive diffusion. Besides, epithelium of the tubules in the nephrons secretes certain substances (drugs, acid, alkalis).

Filtration is carried out through complex structural formations glomerular capillary wall. Filtered liquid part of the blood flows through the small window of the endothelium, layers of basement membrane and the gap between the pedikulami podocytes into the lumen of the glomerular capsule. Most important in the basal membrane filtration has. Filtering is faster, higher or lower blood colloid osmotic pressure. The pressure in the glomerular capillaries - 9,3-10,7 kPa (70-80 Mm Hg. Art.), and colloid osmotic pressure of plasma proteins - 3,3-4,0 kPa (20-30 Mm Hg. Art.). Reducing the pressure in the glomerular capillaries below 6,7 kPa accompanied by a breach of filtration processes. The pressure in the glomerular capillaries and resulting reduction in regulated abductor arterioles.

Primary urine identical protein-free plasma and contains glucose, phosphate, Urea, uric acid, creatine and occasionally other fine proteins with a molecular weight below 70 000 (to 0,15- 0,2 g / l). Relative density of the primary urine-1.01, pH - 7,4.

The tubules of nephrons primary urine undergoes reabsorption, in which the blood comes back into the body substances necessary for (glucose, amino acids, gidrokarʙonatы, fine proteins, salt, water). Some elements of the filtrate (Creatine, inulin and some other polysaccharides) do not reabsorbed. Urea, uric acid, phosphates are absorbed partly due to simple diffusion.

Substances, undergoing active reabsorption, called high-threshold. Glucose fully reabsorbed, if its concentration in plasma does not exceed a threshold (9,99 mmol / l). When the concentration of glucose in the blood it is partially excreted in the urine. Proved, that through the channels kistochkovoy border epithelial proximal tubules of the nephron is reabsorbed and the filtrate protein accumulates in the apical part of the cell vacuoles. When interacting with the mitochondria of the protein are formed hyaline droplets, which are further digested with the participation of enzymes cell.

The mechanism of release of various substances studied, determining factor of their cleansing and comparing it with the cleaning ratio of inulin taken as a measure of the value of filtration. Inulin, consisting of large molecules, released only by filtration and reabsorbed. Established, that if the rate of purification of a substance above, purification than the coefficient of inulin, this material was isolated by filtration not only, but secretion. If the coefficient of purification of the studied material factor other cleansing inulin, it is not only filtered, and reabsorbed. The coefficients of purification of various substances range from 0 to 700 ml / min.

Purification factor is glucose 0.

Uric acid, sodium chloride, ascorbic acid, and many other substances have relatively low coefficient of purification (largely reabsorbed in the tubules of the nephron). Due to a significant diffusion of urea in the tubules of nephrons cleaning ratio below its coefficient of purification of inulin. The coefficient of purification of exogenous creatinine ratio cleansing inulin (index of active secretion of creatinine in the tubules). Endogenous Creatinine is filtered only, so the cleaning ratio of endogenous creatinine and inulin same.

In honor of the proximal nephrons kanalʹcev water reabsorbiruetsâ constantly deux, together with other active substances reabsorption, creating izoosmiyu urine. The distal portion of the tubular reabsorption of water is regulated by the pituitary antidiuretic hormone and therefore impermanent.

Sodium reabsorption in the proximal tubule is active and constant, and distal - fickle and regulated by aldosterone. In the absence of this hormone reabsorption of sodium is not carried out and developed hyponatremia.

Thus, through the epithelium of the proximal tubules of the nephron actively absorbed from the filtrate all useful substances for the body. The distal tubular portion occurs mainly regulating the osmotic pressure and acid-base balance. Absorption takes place independently of the osmotic gradient. The epithelium of the distal tubules of the nephron setserniruet not only hydrogen ions, and potassium (potassium inulin clearance above).

The acid-base status It is regulated by the exchange of sodium ions into hydrogen ions, setseriiruemye distal tubular part, with the participation of carbonic anhydrase. Reabsorption of sodium is accompanied by a change in the reaction of urine to the acid side, the body maintains the level of alkaline reserve. Inhibition of carbonic anhydrase diuretics inhibits the secretion of hydrogen ions. Besides, the allocation of the distal part of the tubular ammonia (it is formed from glutamine under the influence of the enzyme glutaminase) It contributes significantly to the preservation of the body alkaline reserves.

Urine is very important in the diagnosis of kidney damage, urinary tract, and diseases of other organs.

For the study take all morning urine, collected in a clean dry the dishes after the toilet of genitals. Sometimes urine catheter obtained (catheterization increases shedding cells of the urethra and bladder). If you want to explore the daily amount of urine stored in its collection period in the refrigerator. Application Express greatly simplifies the research methods, since a drop of urine is applied to the finished dry reagent (tablet or paper, propytannuyu reagent). The appearance of a certain color indicates the chemical composition of the investigated urine. For the diagnosis of PKU can explore dried on filter paper a drop of urine.

Urinalysis includes a determination of its physical properties, chemical and microscopic examination.

Back to top button