An аthlete is running а mаrathоn оn a hоt summer afternoon and has neglected to drink enough fluids. As a result, they experience severe dehydration, causing an acute drop in blood volume and blood pressure. Describe how the nervous system, endocrine system, and renal system interact to respond to this physical stress and restore homeostasis. In your response, explicitly identify specific structures, hormones, and physiological mechanisms involved. (Nervous system: 2 marks; Endocrine system: 3 marks; Renal system: 3 marks).