Thirst: Function, Tasks, Role & Diseases

What is thirst, how does thirst arise and what is the significance of thirst for humans? Already in Greek mythology, thirst is considered one of the most severe torments. For example, the furious Zeus imposed on his son Tantalus the punishment of thirsting and starving because he had betrayed divine secrets. Tantalus stood up to his knee in clear water, but when he tried to drink, it escaped. Above him hung many juicy fruits, but as soon as he wanted to pick them, they moved away with the wind. Thirst, eternal thirst, Tantalosqualen says for centuries.

What is thirst?

Thirst is a feeling triggered when the salt concentration of body fluids increases – whether as a result of a lack of water, for example, after heavy sweating and after diarrhea, or after ingestion of overly salted meals. If we now ask a physiologist what thirst really is, he will answer as follows: Thirst is a feeling that is triggered when the salt concentration of the body fluids increases – whether as a result of a lack of water, for example after heavy sweating and diarrhea or after eating overly salted meals. The term body fluid covers not only blood, but also the tissue fluid that is found between and within the cells. In addition to the nutrients important for cell metabolism, various minerals are dissolved in it, such as sodium, potassium, magnesium, calcium, chlorine, etc., all of which are in exact proportion to each other and are involved in the undisturbed functioning of almost all the body’s functions. This salt level is not a product of chance, but must always be kept at the same level by the cooperation of several organs. First and foremost are the kidneys. From their activity depends the changing amount and concentration of urine, which are adapted to the water and mineral content of the body. The functioning of the skin, lungs and intestines also influence the fluid and mineral stock of the organism. At any change of the same, no matter how small, regulations are immediately set in motion to prevent the salt concentration from fluctuating. Therefore, it is essential to replace any loss of fluid. Thirst is therefore a feeling that we experience when something is wrong in our water-mineral balance. You could compare it to the red indicator light on a machine. We can only judge for ourselves how great our thirst is. Objectively, we only register the salt content of the blood with the help of complicated apparatus.

Functioning of the sense of thirst

When we speak of thirst, which makes us aware of profound changes in the water and mineral balance, or of the organs by whose function the salt concentration of the blood is kept constant, we must also ask ourselves where the center for regulations is located, which registers deviations from the normal and transmits impulses to the organs. In addition to other vital centers responsible, for example, for the functioning of heat balance and sleep, the so-called water center is also located in the diencephalon. It sends its impulses either via the pathways of the autonomic part of the nervous system, i.e., the part that is independent of our will, or it gives impulses to the pituitary gland, whose posterior lobe secretes the hormone adiuretin when the body’s water level threatens to drop below normal. The adiuretiri slows down the excretion of water by the kidneys and in this way helps to keep the fluid level of the organism constant. In addition, the water and mineral balance is regulated by the activity of the hormones of the adrenal cortex. Thirst is inserted into this system insofar as it makes us aware of the change in the body’s juices and prompts us to take active remedial action. In general, however, habits and ideas regulate our fluid intake by way of conditioned reflexes, without thirst being felt every time. As a result, the amount of fluid drunk does not always correspond to the organism’s real need for fluid. Mostly, even during the feeling of thirst, more liquid is taken in than the organism needs. This is easy to understand when one knows that thirst is not extinguished until the water is absorbed by the intestines. It happens all too often that on hot summer days we feel great thirst after heavy sweating, but for some reason we have no way to quench it immediately.

Complications of fluid deficiency

Our relative well-being shows that this has not yet caused serious changes in the composition, of the bodily fluids. This is due to the fact that the body has fluid reserves in its subcutaneous tissue, which can be mobilized very quickly in an emergency and bring about a balance. At the same time, the kidneys – as already mentioned above – adjust their activity to the new conditions, i.e. they produce less, but more concentrated urea. In this case, however, the release of fluids through the skin cannot be throttled, since the constant evaporation of moisture on the skin draws heat from the body and thus regulates the temperature of the organism. Thirst is particularly agonizing when working under high temperature, such as in the summer in the sun, in kitchens and bakeries or in steel processing. Due to increased perspiration, one is inclined to drink indiscriminately and is surprised that thirst is not quenched despite the abundant supply of fluids. How can this be explained? With sweat we excrete not only water, but also common salt – sodium and chlorine – whose function is, among other things, to retain water in the organism. If we do not return these substances to our body with the liquid, i.e. if we only consume tap water, cola or coffee, this leads to a salt depletion in the organism. As a result, the absorbed water is immediately excreted again. Therefore, people are thirsty because they drink too much water. For this reason, on hot days or at the above-mentioned workplaces, we should consume mineral water or a slightly more saline meal. It should be emphasized, however, that more salted food should not become a habit for health reasons. How long can a person live without hydration? Experiments have shown that death occurs when the body loses 15 percent of its water. How quickly this point is reached depends, among other things, on the organism’s water reserves, on the air temperature and humidity, and on whether heavy physical work is being done at the same time. What is certain is that we are able to survive the state of thirst for only a few days. Adults can survive 24 hours without drinking, but infants can suffer from life-threatening disorders. Water, like any other food or food in general, we can not do without for several days. This is only too understandable if we consider that our body consists of 60-70 percent water. In the case of newborns, this figure is as high as 75 percent. If we assume a body weight of 70 kilograms, this alone amounts to 48 kilograms of water. Muscle accounts for the largest proportion of this, at 50 percent, and fatty tissue for 15 percent of the total fluid content. The great importance of water also results from the fact that the function of the body’s cells is tied to the aqueous solution of nutrients. The excretion of metabolic waste products by the kidneys is also impossible without water, and digestion is equally unthinkable without fluid. Approximately 8 liters of digestive juices are secreted into the intestines daily. These are normally largely reabsorbed in the large intestine. However, large fluid losses can occur in diarrheal diseases if reabsorption is disturbed as a result of inflammation of the intestinal mucosa. While too little fluid is imperative, the body can tolerate too much within certain limits because we have several excretory organs, such as the kidneys, the skin, the lungs and the intestines. Every day we excrete about 2.5 liters (1500 ml of urine, 500 ml of sweat, the rest is the moisture content of the feces and exhaled air). In a healthy adult, this amount can increase to 5 liters or more if the person has drunk beyond thirst.