Renal tubular acidosis

Kidneys are the main organs that ensure the removal of excess nonvolatile acids from the body. This is their vital homeostatic function, aimed at maintaining the consistency of the pH of blood and other fluids. In the kidneys as a result of the dissociation of water, H + and OH-ions are formed. The hydrogen ion is secreted into the lumen of the renal tubule. OH ion participates in the formation of an anion of carbonic acid( HCO3-), which undergoes reverse absorption in the renal tubules. Such mechanisms and maintains the constancy of the pH of the internal environment of the body due to the fact that the H + anion provides a shift in pH to the acid side, and OH-anion - in the main. The kidneys play a major role in regulating the constant relationship between these anions in the human body, which keeps the pH of blood and other fluids in the body constant, thus ensuring optimal conditions for the functioning of all organs and systems of man. For example, the pH of the blood is 7.34.The shift of the pH of this biological fluid by 0.4 in one direction or the other is already incompatible with life.

There are renal tubular acidosis of proximal and distal type. Renal tubular acidosis of the proximal type is associated with impaired reabsorption of the anion of carbonic acid in the proximal tubules. Distal renal tubular acidosis is caused by a defect in the secretion( excretion) of H + ions in the distal sections of the nephron. The first signs of renal tubular acidosis are manifested in the first year of life and consist in reducing appetite until complete refusal of food intake( anorexia), the allocation of much more than the norm of the amount of urine( polyuria), increased thirst( polydipsia), weakness. Children begin to lag behind in physical development. At the end of the first year of life, rachitis-like deformations of the skeleton( frontal and parietal tubercles, "rosary", "bracelets", deformities of the lower extremities), marked decrease in muscle tone, sometimes reaching the degree of paralysis. Later, nephrocalcinosis( kidney stones) can be detected.

X-ray changes in bone tissue do not have specific features and resemble in their picture the disorders found in the de Toni-Debreu-Fanconi disease( systemic osteoporosis, tubular bone deformities, disruption of the structure of growth zones).

The following biochemical abnormalities are characteristic of renal tubular acidosis: metabolic acidosis( shift of the pH of the internal environment of the organism to the acidic side), hypophosphatemia( decrease in the amount of phosphates in the blood serum), hypocalcemia( decrease in the amount of calcium in the blood serum), increased activity of alkaline phosphatase, low levelexcretion of acids in the urine, a high pH of the urine( a shift in the main side), a significant decrease in the concentration function of the kidneys( a decrease in the relative density of urine).In some cases, the appearance of protein and white blood cells in the urine( proteinuria and leukocyturia, respectively).When carrying out special research methods( excretory urography), almost all people with this pathology are diagnosed with multiple kidney stones( nephrolithiasis and nephrocalcinosis).

Renal tubular acidosis is inherited in an autosomal recessive manner. There are descriptions of autosomal dominant inheritance, sporadic cases due to primary mutations are possible.

Patients with proximal tubular acidosis often display other defects of the proximal tubule function: the appearance of amino acids and glucose in the urine( aminoaciduria and glucosuria, respectively).Some authors suggest a third type - combined failure of proximal and distal tubules. The disease is characterized by an early onset, expressed by a rachitis-like syndrome, the formation of kidney stones, sometimes an increase in the protein content in the blood.