Only the organs specifically used for the excretion are considered a part of the excretory system. In the narrow sense, the term refer to the urinary system. However, at excretion involves several functions that are only superficially related, it is not usually used in more formal classifications of anatomy or function.
As most healthy functioning organs produce metabolic and other wastes, the entire organism depends on the function of the system. Breaking down on one of more of the systems is a serious health condition, like renal failure.