Hypothalamus is a part of the brain which controls many important functions of the body by producing hormones.
When the amount of water gets reduced in the blood, it leads to a change in the osmolarity which can be easily detected by the osmorecpetors present in the neurons of the hypothalamus.
In response, neurons secrete Anti-diuretic hormone in the blood which acts in the tubules of the kidney where they help in re-absorption of the water from the body.
The Law of Conservation of Mass tells us that matter is neither created nor destroyed during a chemical reaction. Atoms can be rearranged to form new compounds, but the total mass of the system remains constant.
