thirst

1 a physiological need to drink

2 strong desire for something (not food or drink); "a thirst for knowledge"; "hunger for affection" [syn: hunger]

1 feel the need to drink

2 have a craving, appetite, or great desire for [syn: crave, hunger, starve, lust]

English

Etymology

Old English þurst

Pronunciation

• Rhymes: -ɜː(r)st

Noun

thirst

1. A sensation of dryness in the throat associated with a craving for liquids, produced by deprivation of drink, or by some other cause (as fear, excitement, etc.) which arrests the secretion of the pharyngeal mucous membrane; hence, the condition producing this sensation.
2. Fig.: A want and eager desire after anything; a craving or longing; — usually with for, of, or after; as, the thirst for gold.

Translations

Thirst is the craving for liquids, resulting in the basic instinct of humans or animals to drink. It is an essential mechanism involved in fluid balance. It arises from a lack of fluids and/or an increase in the concentration of certain osmolites such as salt. If the water volume of the body falls below a certain threshold, or the osmolite concentration becomes too high, the brain signals thirst.

Continuous dehydration can cause myriad problems, but is most often associated with neurological problems such as seizures, and renal problems. Excessive thirst, known as polydipsia, along with excessive urination, known as polyuria, may be an indication of diabetes.

There are receptors and other systems in the body that detect a decreased volume or an increased osmolite concentration. They signal to the central nervous system, where central processing succeeds. Some sources therefore distinguish "Extracellular thirst" from "intracellular thirst", where extracellular thirst is thirst generated by decreased volume and intracellular thirst is thirst generated by increased osmolite concentration. Nevertheless, the craving itself is something generated from central processing in the brain, no matter how it is detected.

Detection

There are different receptors for sensing decreased volume or an increased osmolite concentration.

Decreased volume

Further reading: Hypovolemia

• Renin-angiotensin system

Hypovolemia leads to activation of the renin angiotensin system (RAS) and a decrease in atrial natriuretic peptide. These mechanisms, along their other functions, contribute to elicit thirst, by affecting the subfornical organ.. For instance, angiotensin II, activated in RAS, is a powerful dipsogen (ie it stimulates thirst) which acts via the subfornical organ.

• Other
  • Arterial baroreceptors sense a decreased arterial pressure, and signals to the central nervous system in the area postrema

In addition, there are visceral osmoreceptors. This is also a result of the renin-angiotensin system activation.

Senior Citizens

For adults over age 50, the body’s thirst sensation diminishes and continues diminishing with age, causing many to suffer symptoms of dehydration.

Central processing

The area postrema and nucleus tractus solitarius signal, by 5-HT, to lateral parabrachial nucleus, which in turn signal to median preoptic nucleus. In addition, the area postrema and nucleus tractus solitarius also signal directly to subfornical organ.

Thus, the median preoptic nucleus and subfornical organ receive signals of both decreased volume and increased osmolite concentration. They signal to higher integrative centers, where ultimately the conscious craving arises. However, the true neuroscience of this conscious craving is not fully clear.

In addition to thirst, the organum vasculosum of the lamina terminalis and the subfornical organ contribute to fluid balance by vasopressin release.

Preventing subtle dehydration

For optimal health, experts recommend that humans get 8-10 servings of about 8-ounces of water (in total, approximately 2 litres) per day to maintain hydration. This figure does vary according to ambient temperature, movement and physical size. Being that water is essential to the general function of the human and all animal bodies, eight servings is widely regarded as the minimum for the body to function optimally. However, water can be obtained from many sources, such as foods and other beverages containing water. Getting enough water from your diet and staying hydrated is key to your overall health, including urinary tract and digestive tract health. When getting your daily water intake, it's important to not rely heavily on caffeinated beverages, as they actually work as a diuretic. Further, moderate or excessive alcohol consumption can lead to dehydration, thus it's important to maintain hydration when drinking caffeinated and alcoholic beverages.

See also

• Hunger
• Dehydration

References

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