Water and salt

Too much salt is not good for us, which is well known to most of us. The same is also true for too much water, a shortage of salt or a shortage of water. Most of the salt comes from our diet. Besides the salt that we add ourselves on our food, there is too much salt in the food such as ready-to-eat products. We drink water, but water is also present in solid foods. In addition, our body produced water with various processes.

For water- and salt balance, it is important that the daily excretion corresponds to the daily intake. This is mainly regulated by the renal tubules. Our kidneys filter blood and produce 180 liter of pro-urine per day, a mixture of water and dissolved salts. The vast majority of water and dissolved substances, including sodium, are then reabsorbed into the blood by the cells of the renal tubules.

The tuning of the renal water excretion is controlled by the hormone vasopressin or ADH which is produced in the brain. If the kidneys do not respond well to this hormone, they cannot reabsorb water and urinate too much water. This is for instance the case with the condition is diabetes insipidus. As a result, these patients are prone to dehydration. Also, the salt concentration in the blood can rise too much (hypernatremia). If there is too much ADH, too much water is reabsorbed by the kidneys. This is the case with SIADH (Syndrome of Inappropriate which is inappropriate ADH release), whereby the salt content in the blood can be dangerously low (hyponatremia).

The salt excretion itself is also regulated mainly by the kidneys. In various parts of the kidney tubules, transport proteins can reabsorb sodium into the blood. Due to an increase or decrease in the function of these transport proteins, patients will excrete too little or too much salt in their urine. This usually does not lead to changes in the salt concentration in the blood, but rather to a high or low blood pressure. This is because the regulation via ADH will ensure that the sodium level is stable within certain limits, by adhering more or less water.

For a description of specific syndromes in which there may occur a disorder of water and / or salt balance, see the links.

Links
o    Bartter syndrome
o    Gitelman syndrome
o    Pseudo hypoaldosteronism type I
o    Pseudo hypoaldosteronism type II (Gordon syndrome)
o    Nephrigenic diabetes insipidus
o    Liddle syndrome