Also called kidney stones, they are formed by the accumulation of certain substances – calcium, uric acid, oxalate (a salt) or cystine (an amino acid) – inside the kidneys or in the urinary tract. “It is important to emphasize that this problem occurs mainly in those who have a defect in the metabolism, caused by heredity. The person must already be predisposed to develop stones, because their body excretes these substances in excess, which accumulate there”, says nephrologist (kidney specialist) Fernanda Carvalho, from the State University of São Paulo (Unesp). In addition to this natural tendency to the problem, there are other factors that can cause the appearance of stones: low water intake (especially in summer) or a diet that is very high in salt and red meat.
Inside the kidneys, there are about 1 million structures called nephrons, which work as filters, discarding what is not useful for the body and reabsorbing what is beneficial, mainly water. “When there is little fluid intake, there is a greater concentration of the substances that can form the calculus. When we ingest salt, the kidneys exchange the sodium present in it for calcium, releasing a greater amount of this substance, which is the cause of about 50% of these stones. In the case of red meat, its proteins reduce the ability of the kidney to dissolve the substances inside it”, says Luis Cuadrado Martin, also a nephrologist at Unesp.
Substances taken from the blood can block the kidney1. Blood reaches the kidney through the renal artery to be filtered2. After that, the blood returns to the body through the renal vein3. Filtering takes place in thousands of structures called nephrons. What is beneficial to the organism is retained; the rest is eliminated along with excess water, forming urine
4. When there is little water, the concentration of these substances increases, facilitating the agglomeration of the particles that form the stone.
5. If we eat too much salt, the kidneys absorb the sodium contained in it and, in exchange, release calcium, the main cause of stones.
6. The stone can remain inside the kidney or go down the channel that takes urine to the bladder, called the ureter.
7. Both cases cause severe pain – either when the stone moves inside the kidney, or when the channel contracts trying to push urine into the bladder.