The correct answer is a) hypothalamus.
The hypothalamus, a small region at the base of the brain, plays a crucial role in regulating many bodily functions, including thirst. It contains osmoreceptors that detect the concentration of solutes in the blood. When these receptors sense an increase in solute concentration, indicating dehydration, they trigger the sensation of thirst. This prompts the individual to drink fluids and restore the body’s balance.
In contrast, the kidneys help regulate water levels in the body, but they do not control the sensation of thirst. The medulla oblongata primarily manages autonomic functions such as breathing and heart rate, while the mouth and stomach are involved in the intake and processing of food and drink but do not serve as thirst centers.