Question

Why do we break the body into "systems" when discussing it? Why don't we just talk about the entire body all at once?

Answer 1

Because each system has many intricate and detailed parts and functions. Breaking it up part by part ensures that you learn sufficiently each system and gather all of the information you need. 

Answer 2

While discussing about the body, it is broken down into simpler component to understand it better. The body is a complex mechanism of all the systems present in it. Studying or considering body at once would make more complex to study.

Each system present in the body have its specific function. The specific function of each system is not shared by other systems in the body,so, by studying different system in the body, we can easily interpret the whole mechanism of body functions.