Effector is a muscle or gland which acts in response to a stimulus.
Endotherm controls body temperature within physiological levels and has homeostasis mechanisms to control body temperature, largely independent of external temperatures.
Response is a change in behavior or physiology as a result of a change in the environment.
Receptor is an organ or cell able to respond to external stimuli and transmit an electrical impulse to a sensory nerve.
Homeostasis is the maintenance of a stable internal environment.
Stimulus is a detectable change in the environment that causes a response.