See also: hunger, what do hunger attacks depend on?
What is thirst and what it depends on
Thirst is not a simple sensation, but a very important physiological stimulus that has the purpose of keeping the quantity of water present in the organism in balance.
In an adult man, water constitutes about 60% of body weight, a little less in the female body (about 50%) due to a higher percentage of adipose tissue.
From a purely physiological point of view, the thirst reflex is triggered in the presence of an imbalance between the water and the salts circulating in the blood; the reduction of plasma volume (the liquid part of the blood) or the increase in the concentration of salts in dissolved, it represents a clear alarm signal; in these conditions it is essential to ensure an adequate supply of liquids from the outside.
The research and the intake of water is presided over by a particular hypothalamic region, known as the thirst center and sensitive to the aforementioned stimuli. In this anatomical site there are specific receptors, called osmoreceptors, which trigger the thirst reflex when the plasma osmolarity exceeds the standard values. The same reflex is inhibited, that is, slowed down (absence of thirst) in conditions opposite to the previous ones.
In addition to hypothalamic control, various local factors contribute to regulating fluid intake, such as the dryness of the oral and pharyngeal mucosa.
It is interesting to note that the act of drinking is in itself sufficient to quench thirst, at least temporarily. We realize this when we suck on an ice cube and manage, despite the modest quantities of liquids introduced, to calm a particularly stubborn thirst. The dilatation of the gastric wall also helps to quench the thirst stimulus, avoiding an excessive decrease in osmolarity following an exaggerated intake of liquids.
But thirst, similar to hunger or better to appetite, is not the result of simple physiological factors. The human being, in fact, is inclined to drink even in the absence of a real thirst stimulus, for example due to certain habits cultural and social.
Thirst and health
It is important to remember, first of all, that the stimulus of thirst diminishes in the elderly. Hence the recommendation to drink at least one and a half liters - two liters of water every day, regardless of the perception of this stimulus.
The feeling of thirst is abolished as a result of brain injury and loss of consciousness. An increase in this impulse occurs instead in conditions of untreated diabetes and in the presence of a major hemorrhage, due, respectively, to the increased loss of fluids with the urine (polyuria induced by hyperglycaemia) and the decrease in plasma volume.
As per common experience, thirst increases greatly when you practice a "expensive physical activity, especially if carried out in hot environments. In this regard it is good to remember that if the subject replaces the lost fluids with water with a low fixed residue, the plasma volume but not its salt concentration, which is even diluted, aggravating even more the electrolyte deficit (hyponatremia). many drinks enriched with mineral salts. Saline supplements in powder form are also available on the shelves of supermarkets or in specialized shops, which must always be added to drinks in the dosages indicated on the label. When these are exceeded, in fact, the high salt concentration at intestinal draws liquids by osmotic gradient, subtracting them from the plasma, causing d and aggravating the state of body dehydration.
