All people feel thirsty at one point whether they are healthy or not. The thirst sense is guarded by a negative feedback loop which links brain with all the other organs in the body. Unfortunately, in the age of 50 and above this loop gets weaker and weaker and it is very risky situation for the body. By extensive research of the complexity of the thirst instinct mechanism, scientists are trying to develop better cure for people who have lost their sense of thirst.
Many researches have confirmed that the body’s primary “thirst center” is hypothalamus and it is located in brain. Hypothalamus is the cavernous arrangement and its function is to control body temperature, hence it is functioning as the body thermostat and it performs some extra task like controlling sleep and appetite. Sensory neurons in hypothalamus continuously observe the blood’s levels of sodium. It can also receive messages from the sensors which are present in the blood which mainly controls mineral levels and blood pressure. Anytime the blood volume or pressure decreases due to factors as diarrhoea, bleeding or severe sweating, or when blood sodium increases to very high levels from consuming foods snacks or due to some diseases, the urge to drinking water is generated by the hypothalamus.
The reaction to take water due to thirst can be described to as a result of negative feedback which then stimulates the positive feedback which is the reverse. In positive feed back the strong urge to replace or create water or fluid balance forces the brain to command the necessary organs through the nervous system as hand muscles the eyes and others to respond to the thirst stimulus. Here the stimulus is the thirst instinct which gives the brain the message that the fluid levels need to be adjusted to maintain healthy metabolism, the brain then sends messages to the muscles and other organs as eyes to recognize water and generate sliding force to deliver water to the mouth. The brain also alerts the mouth muscles to accept the incoming fluid and swallow it (Halliday, 1998).
The sliding filament theory explains the function which is responsible for contacting and expanding of the muscles. It describes that wide and thin thread in the sarcomere slide with each other and this sliding decreases the length of sarcomere which merely depend on the signals transmitted by neurotransmitters. Sliding happens when myosin heads act together with fibres and actin together with ATP, bends past the actin.
Water is swallowed in the mouth (buccal or oral cavity) and goes down through the oesophagus to the stomach, then to the small intestines through the duodenum, after that it goes to the colon or large intestines, where it is absorbed into the blood vessels through the activity of the osmotic gradient. The water in the blood vessels is then taken to organs in the body; starting with the liver, heart, lungs, the heart, and then through the aorta to the kidneys where it is processed. At this point the water is in urine form; it is collected in the kidney and released into the ureter then to the gall bladder where it accumulates to be later excreted through the urethra to the outside.
Water forms the largest component of blood and acts as the medium for most of the body metabolism hence any shortage is lethal to the body operations. Water shortage will lead to poor air supply to organs, problems in digestion, insulin imbalance and many other problems that will eventually lead to death.
References
Halliday, T.(1998).The Senses and Communication (Biology: Brain and Behaviour). New York: Springer.