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It is well known that when we are thirsty, the mouth and throat feel exceptionally dry and parched. It is apparent, though, that the sensations commonly associated with thirst do not arise simply from dryness of the mouth and throat. If this were true, chewing gum or wetting the mouth and throat would fully relieve thirst, and obviously this is not the case. When we are unusually thirsty, we continue to drink, even though the mouth and throat tissues may be saturated with water.
In an effort to discover the physiological basis of thirst, Adolph (1941) showed that water placed directly in an animal’s stomach would relieve thirst. This investigator observed that if water was placed directly in a dog’s stomach, and the dog was immediately given the opportunity to drink, it would do so. However, if restrained from drinking for several minutes after the water was placed in the stomach, the animal would refrain from drinking. These findings indicate that apparently the water must be absorbed into the animal’s tissues for the thirst drive to be satisfied.
The conclusion to which many investigators have come is that the physiological basis of thirst appears to be cellular dehydration. Some investigators believe that cellular dehydration stimulates secretion of a pituitary hormone that may have a regulatory function in relation to water consumption.
Some investigations indicate that the thirst drive is at least partially regulated by a specific part of the brain. The thirst center is located in the region of the anterior hypothalamus. It has been found that if a salt solution is directly injected into this area, animals will drink an excessive drinking does not occur.
Other studies have explored the possibility that the septal area is involved in thirst motivation. Harvey and Hunt, for example, produced septal lesions in laboratory rats and found and this increased water consumption. More research is needed, however, before we can specify the exact physiological mechanisms in thirst.
Like hunger, the thirst drive may be modified by various social factors. We learn to prefer certain liquids to satisfy the thirst drive, and in many cases the things we drink are not directly related to satisfaction of the thirst drive at all. We are all familiar with the fact that the French consume large quantities of wine. It is part of the cultural heritage of France that wine is preferred by most of plain water. Also, while it is relatively easy to modify the drinking habits of people initially, once these habits are established, they are in some cases difficult to alter. We may recall attempts in France to reduce wine consumption and the great resistance to these efforts.
Unlike other animals, human often drink when they are not thirsty at all. They drink for social reasons in many cases, and like the hunger motive, drinking often must be done in special places with special people. Human watering places bear little resemblance to those of other animals.
Sources:
http://arjournals.annualreviews.org/doi/pdf/10.1146/annurev.ps.14.020163.000421
