Tubulopathy

The term " tubulopathy " combines a fairly diverse group of diseases, based on the violation of tubular transport processes( transport of substances in the renal tubules), reabsorption( backward absorption) and secretion( excretion in the urine) of various substances - protein, organicconnections. Most often, these disorders are the reabsorption of these compounds from the glomerular apparatus of the kidneys with the formation of primary urine in them, as well as tubular secretions.

The cause of primary( hereditary) tubulopathies can be associated with such tubular defects as:

1) a change in the molecular structure of the proteins that make up the epithelium of the renal tubules;

2) fermentopathy - a hereditary conditioned deficiency of enzymes involved in the active transfer of substances through the membrane of the renal tubules;

3) changes in the structure and functions of the receptor apparatus of the tubules, which leads to a decrease in their sensitivity to hormones;

4) a change in the overall structure of tubular cells and their membranes - dysplasia at the tissue level.

The main clinical manifestations of tubulopathy are determined by the localization of the primary defect during the renal tubules. The structural and functional unit of renal tissue is nephron. It is arranged as follows: first there is a renal glomerulus formed by a dense network of capillaries;From the glomerulus, the proximal( proximal to the glomerulus) convoluted tubule departs;then comes the loop of Henle, consisting of the descending and ascending renal tubules;after it is located the distal convoluted tubule( far from the glomerulus).The entire structure ends with a collecting tube that flows into the renal pelvis. The primary urine passes through this whole system of tubes, the volume of which can reach 120 liters per day.

In all the above tubules from the primary urine, water and various chemicals such as protein, sugar( glucose), potassium, sodium, chlorides, phosphorus are absorbed back into the blood, resulting in the formation of final urine. At the same time, in each of the tubules, there is a reverse absorption of strictly defined substances, which determines the clinical picture in the lesion of any part of the nephron. In the proximal convoluted tubules, reabsorption( backward absorption) of amino acids, glucose, inorganic phosphates takes place, and their defeat is characterized by the appearance of the listed substances in the urine( hyperaminoaciduria, glucosuria, hyperphosphaturia), as well as a violation of the acid-base equilibrium in the body,shift it to the acid side( metabolic acidosis is noted).A full range of such disorders is characteristic of the disease and the de Toni-Debreu-Fanconi syndrome. In addition, defects in individual transport systems are possible, which can manifest only either glucose- or phosphaturia( the appearance of glucose or phosphorus in the urine, respectively), metabolic acidosis. Henle's loop and distal convoluted tubules provide regulation of homeostasis - constancy of ionic composition and osmotic pressure of blood and body fluids. Here, processes of water saving and release of excess( secretion) of osmotically active substances, secretion of excess hydrogen and sodium ions, saving or secretion of potassium ions are carried out here. Therefore, manifestations of defects of the distal nephron are mainly characterized by disturbances of homeostasis - renal tubular acidosis, dehydration - loss of body fluid( renal diabetes mellitus), loss of salt or hypokalemia( decrease in the amount of potassium to the blood).

Increased urinary excretion of organic and inorganic substances is often caused not only by damage to the kidney tubules, but by a general metabolic disorder in the body, when the concentration of these substances rises in the blood and, accordingly, in the glomerular ultrafiltrate( in the primary urine).Therefore, in order to diagnose the renal origin of metabolic or homeostatic disorders, it is necessary to conduct a study of the content of the relevant substances not only in the urine, but also in the blood plasma.

In addition, defects in transport systems may be identical in the kidneys and in the intestines( although not always), so in the clinic special studies are being carried out, which make it possible to establish the possibility of joint involvement of the intestinal and kidney transport systems in the pathological process.