Final answer:
The hypothalamus is the brain structure that triggers feelings of hunger and thirst by regulating homeostatic processes related to appetite and fluid intake.
Step-by-step explanation:
The brain structure that played a key role in triggering feelings of hunger and thirst is the hypothalamus. This part of the brain regulates a number of homeostatic processes, which includes the control of appetite and thirst signals. When the body needs food or fluids, the hypothalamus responds to various signals, including hormone levels and the stretch of the stomach, and triggers the sensation of hunger or thirst respectively. The hypothalamus integrates these signals and determines when to initiate feeding behavior, acting as an interface between the nervous system and the endocrine system for this regulation.