Diuretics are medications that promote diuresis.
These drugs are used mainly for:
• edema syndrome;
• their effect to reduce arterial pressure in case of arterial hypertension;
• elimination of toxic substances from the body.
Nephron is the main structural unit of the kidney. Low molecular weight compounds (sodium bicarbonate, sodium chloride, glucose, amino acids, etc.) are filtered in nephron glom-eruli from blood plasma to become primary urine; afterwards, they are significantly or completely reabsorbed by means of a transport systems located in the apical portion of renal tubular epithelium. Sodium ions return from urine to blood plasma by means of a heterogeneous system of specific transporters. A block of thistransport system destroys reabsorption of sodium ions, thus leading to an increase in-osmotic pressure in the renal tubule lumen and subsequent re-absorption of water. Diuretics inhibiting sodium reabsorption systems in different portions of nephrons are referred to as saliuretics (natriuretics).
In proximal tubules, Na+, Cl- ions, and water associated with them are reabsorbed; the osmotic pressure of the filtrate is the same as osmotic pressure of blood plasma.
In the descending portion of the loop of Henle, only water is reabsorbed; osmotic pressure of the filtrate does not increase. There are two mechanisms of water reabsorption in the nephron: through aquaporins and paracellular transport pathway.
In the thick ascending limb of the loop of Henle, co-reabsorption (co-transport) of Na+, K+, 2Cl- as well as Ca2+ and Mg2+ takes place. Water is not reabsorbed in this segment, and osmotic pressure of the filtrate decreases.
In the initial portion of the distal tubules, Na+ and Cl- are reabsorbed; water is not reabsorbed, and osmotic pressure of the filtrate becomes lower than that of blood plasma.