The first physiological response to high environmental temperature is
Sweating
Vasodilatation
Decreased heat production
Non-shivering thermogenesis
Under mechanisms activated by heat cutaneous vasodilation comes first followed by sweating increased respiration, decreased heat production, anorexia, apathy, and ineia. Ref: Ganong&;s review of medical physiology; 23rd edition; pg: 285; Table 18-4.
Nervous system