I totally agree with you now, I really didn't think much about the word vitality, And since English isn't my first language, I didn't consider the other contexts this word may have, and that can contribute to making the word vague. It's just that I couldn't find the appropriate word to express (being alive) or (being a living thing). maybe I should have just said "life". However, the whole thing (my post) wasn't meant to be about my choice of the word that expressed possessing the property of life -not saying that it's ok to use vague or obscure words-, But what I mainly questioned about the definition in the original post, was the overall idea; whether we can say physiology studies the mechanisms and processes that occur in the body of an organism?.
I had someone telling me that "studying mechanisms of living" was far from any possible definition of physiology. and that physiology on the other hand was "studying the functions of parts of the body". I couldn't see much difference between the two definitions. So I decided to ask online.
I hope it doesn't seem like i'm so caught up in semantics.