Our need to drink triggers a sensation virtually everyone recognizes as being "thirsty". It is actually the end result of an elaborate and interesting sequence of events that is explained below.

The thirst reflex occurs as a response to changes in the body's fluid (water) balance. It is a physiological (functional) mechanism that stimulates a sensation of thirst, leading to the desire for and consumption of fluids. 

The process of thirst has the following steps:

1. Dehydration or increased osmolality: When the body's fluid levels decrease (from excessive sweating, excessive urination, fever, fast breathing, fasting) or the concentration of solutes (salts, sugars) in the blood increases (from intake of excess salts, excess sugars), the osmolality (concentration of particles in a fluid) rises. This change is detected by specialized cells called "osmoreceptors" or "osmotic sensors" which are primarily located in a special part of the brain called the "hypothalamus".

2. Stimulation of osmoreceptors: The osmoreceptors in the hypothalamus sense these changes in osmolality and send signals to the area of the brain responsible for water intake called the "thirst center", located in the hypothalamus.

3. Activation of the thirst center: The thirst center, upon receiving signals from the osmoreceptors, triggers the sensation of thirst. This stimulates the feeling of needing to drink fluids.

4. Release of antidiuretic hormone (ADH): At the same time, the hypothalamus sends messages or signals to another part of the brain called the "pituitary gland" to release a special compound called "Antidiuretic Hormone" (ADH), also known as vasopressin. ADH acts on the kidneys, reducing water loss through urine and promoting water reabsorption in the body to help conserve fluid. This leads to the formation of the dark-coloured urine that we sometimes see on days and times when we sweat heavily without drinking enough water to stay hydrated.

5. Drinking to quench thirst: The sensation of thirst motivates a person to seek and consume fluids, typically water. Drinking water helps restore the body's fluid balance.

6. Monitoring fluid intake: After consuming fluids, the body's osmolality decreases, and the osmoreceptors detect these changes. As osmolality returns to normal, the signals to the thirst center gradually diminish, leading to the sensation of thirst being alleviated.

It is important to note that the thirst reflex might not always accurately reflect the body's actual hydration level. However, it is essential to pay attention to the body's signals and drink fluids regularly, even before feeling excessively thirsty, to maintain proper hydration.

P.S. The increased water intake associated with the consumption of food such as beans is because the products of their digestion following absorption lead to an increase in the osmolality of blood and sets in motion all the series of events described above that lead to increased water intake.

Author: Dr. Yeibake, Weriwoyingipre Silver.

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