See also: diuretic foods - draining herbal tea - kidney and hydrosaline balance
What is Diuresis?
The term urine formation in the kidney is defined as diuresis . Over the course of 24 hours, an adult individual produces a urinary volume of around 1, 000 - 2, 000 ml; however, diuresis can vary significantly based on various factors, such as the type of diet and environmental conditions.
Changes in Diuresis
Oliguria and Poliuria
These changes in diuresis can be benign or result of particular pathologies; polyuria, for example, is among other things a characteristic symptom of various forms of diabetes, while oliguria is typical of nephritis, renal colic and all the diseases that cause dehydration (such as those that result in diarrhea, for example viral gastroenteritis).
Anuria
In anuria, diuresis falls below 100 ml in 24 hours; we are therefore talking about a pathological condition characterized by severe impairment of kidney function.
Nocturia and other alterations
In addition to quantitative alterations, there are other forms. The nocturia, for example, leads the patient to urinate especially at night; it is a typical problem of patients with heart failure, caused by the nocturnal reabsorption of edema. This alteration of diuresis is also typical of men with prostate problems, in which it is often accompanied by rather annoying disorders, such as burning or pain during urination, and the sense of incomplete emptying of the bladder, with consequent need to urinate often .
Recall that urination is the physiological act that leads to the expulsion outside of the urine contained in the bladder.
Regulation of diuresis
Diuresis is conditioned by:
1) renal blood flow: represents the amount of blood that reaches the kidneys, equal to about 700 ml per minute;
2) glomerular filtrate: amount of filtered plasma per unit of time; the glomeruli filter about 80% of the blood that reaches the renal level, so roughly 150 ml of plasma per minute for a total of around 180 liters a day. This liquid is called preurine and under normal conditions contains all the substances present in the blood, with the exception of cells (white blood cells, red blood cells, platelets etc.) and larger plasma proteins.
3) Tubular reabsorption: without fluid reabsorption by the kidney diuresis would be equal to 180 L per day. Naturally the body cannot afford to waste such a precious element, so it reabsorbs the vast majority of the glomerular filtrate and the nutrients it contains. 90% of this reabsorption is independent of hormones (it occurs for osmotic reasons, linked to the reabsorption of sodium), while the resorbable percentage of the remaining 18 liters is regulated at the endocrine level. In particular, the regulating hormone of diuresis par excellence is known as vasopressin, ADH or antidiuretic hormone. As the name suggests, ADH reduces diuresis. Not surprisingly, in his absence we speak of diabetes insipidus, a disease that if not accurate can be accompanied by the conspicuous release of urine, up to 18 liters / day in cases of total hormone deficiency or failure to respond to its action.
According to the above, the secretion of vasopressin increases in the conditions of dehydration, since in similar circumstances it is necessary to retain as much water as possible in the body. Urinary losses can and should instead increase when the individual drinks too much and in this case ADH secretion decreases. Directors of this fine regulatory mechanism are the hypothalamic cells of the thirst center, which act as osmoceptors; as such, they are able to capture variations in the osmolarity of the blood (ie if it is more or less concentrated), inducing or inhibiting the secretion of vasopressin at the level of the posterior pituitary (neurohypophysis) as needed.
Another very important hormone in the regulation of diuresis is aldosterone. Produced by the adrenal gland, this steroid hormone (derived from cholesterol) increases sodium reabsorption in the distal tubule and in the collecting duct, while accelerating the elimination of potassium and hydrogenions. Substantially, it therefore has an inhibiting effect on diuresis, mediated also by its stimulus on the release of the antidiuretic hormone.
Among the hormones with diuretic effect we remember the atrial natriuretic peptide; it is a peptide secreted by specialized cells of the myocardium following an excessive increase in blood volume (high blood pressure). Given that the pressure increases as the volume of blood increases, in similar conditions it is necessary to deprive it of part of its liquid component; this result is obtained by simply increasing the diuresis.
Most diuretic drugs, as well as some commonly used foods (those containing xanthines, such as coffee, tea, cocoa and derivatives), stimulate diuresis acting not so much as hormones, but rather as inhibitors of mineral reabsorption, which for osmotic reasons they attract water by increasing diuresis.
