By Dr. Ashaq Hussain
Feeling thirsty is a sensation that everyone and every animal is familiar with and for an ordinary person the desire to drink water is called thirst. Yes, to fight dehydration on a hot summer day, you automatically crave the relief provided by a glass of water. But, have you ever put a thought that, how you sense the need for water, what generate the sensation of thirst, and then what leads you to drink water? You undoubtedly experience the feeling of thirst in the form of a slight itch in the back of your throat, a distracting urge to turn away from whatever you’re doing and find something to drink. It drives you to guzzle water on hot days and to drink something along with your meals. Our need for water is as omnipresent and critical as our need for food or oxygen–it’s an essential cog that keeps our bodies working normally. Although, it is an experience so common but still only a few of us give it a thought.
What makes us thirsty is altogether a scientific in nature. Scientifically, the desire to drink water, thirst, occurs for two reasons. One is linked to decreased volume of intermolecular fluid and other increased osmolarity in plasma. Our body is made up of countless cells. Cells are connected to each other but there is space between them called as extracellular space. This extracellular space is filled with a special type of liquid and when the volume of this liquid decreases there is a feeling of thirst. Secondly, when body starts to run low on water, there occurs a change in blood pressure, as the amount of salt and other minerals in body is staying constant while the volume of liquids decreases, their relative concentration increases. This increased concentration of particles in bodily fluids relative to the total amount of liquid is known as osmolarity, and it needs to be kept in a narrow range to keep the cells in your body functioning properly. The cells of our body are surrounded by a thin cell membrane which is semi permeable. If there is semi-permeable membrane barriers between the two solutions, the process of osmosis appear at work and the solvent travels from the low-concentration solution to the high-concentration solution, until the concentration of the two solutions is equal. The fluids in our body such as lymph and blood are called plasma which contains proteins and inorganic salts. As the amount of water in the plasma decreases, the concentration of proteins and salts increases leading to hypertonic osmolarity. When the osmolarity of the cells becomes hyper tonic, there is a feeling of thirst and the person normalizes the osmolarity of the plasma by drinking water or other beverages. It is the neurons in the lamina terminalis which actually respond to this physical act of swallowing liquids, even before there are any changes in the amount of water in the blood. This highly specialized part of the brain, lamina terminalis can sense when the body is running low on water and whether you’ve had anything to drink recently.
Drinking water does not immediately become part of our body. It takes time to absorb and normalize osmolarity. But the strange thing is that as soon as we take a certain amount of water down our throats, we feel that our thirst is quenched and we stop drinking water. Scientists believe that somewhere in the throat area of the esophagus there is a mysterious "meter" that controls the required amount of water. The existence of this "meter" and its performance is still a mystery however, it is believed, and that hypothalamus in the back of the brain controls many of our functions. The hormones released by it control hunger, thirst, sleep, breathing, etc. The pituitary gland also works under the influence of the hypothalamus. The hypothalamus is located near the area where the feeling of thirst is aroused produces compounds called Antidiuretic Hormone (ADH) also called as Vasopressin which stimulates the feeling of thirst. Similarly, the kidneys produce another vasopressin known as angiotensin. This stimulant also stimulates the hypothalamus to arouse the feeling of thirst. Under normal physical conditions, almost as much water is excreted as it enters the body, and a certain amount of water remains constant in the body. About 65% of our body is made up of water however; children have 75% water content. Two types of systems, Pituitary intake of water and discharge of water from the body in the form of urine regulate the amount of water in the body that makes one feel thirsty. Other control mechanisms also help in this process, such as the energy-regulating carbohydrate transfer mechanism and the sweat-releasing mechanism that controls body heat.
In short, understanding the mechanism of thirst is very important. It is the process of drinking water that eliminates dehydration in the body. In humans, the process of drinking water is more in control of habits and social requirements than the thirst mechanism. Man often drinks or is forced to drink unnecessary water, tea, coffee and other beverages. But no animal can be forced to water. There is a famous saying: "You can take a horse to the water but you cannot force it to drink water". You also have to quench your thirst in certain situations and occasions. To conclude with, thirst is governed by a sensory system, analogous to vision or hearing. Thirst is regulated by layers of signals that arise throughout the body and converge onto individual neurons in the forebrain. This convergence occurs at the first node in the thirst system and generates a real-time estimate of the body's need for water that downstream nodes use to dynamically adjust drinking. Too much of everything is harmful so is Excessive use of water which lead to hyperhydration , impair the ratio of water to salts in the body which adversely affect the functioning of various body processes. In relation to the survival of an organism, maintaining water balance in the body is incredibly important. A body that doesn’t take on fluids when it needs them will not be alive for long.
The Author Dr. Ashaq Hussain is Assistant Professor Chemistry (Selection Grade) at Govt. Degree College Chatroo and can be reached at [email protected]