Stimulus: Something that can elicit or evoke a response in a cell, a tissue, or an organism. It can be external or internal. Response: A reaction to a specific stimulus.
this talks about all the different types of processes and actions there are as well as what they are for.
Negative feedback is a key regulatory mechanism for physiological function in living things. This website gives you everything you need to know about negative feedback along with video to explain more.
Every body needs to maintain Homeostasis to keep the body regulated. This link above explains what exactly happens in Homeostasis.