Our canine companions are composed of a number of organs and systems. This is another way of saying that a lot of parts go into making the whole that is your dog! Ideally these parts all function together as a well-oiled machine. To understand your dog's health, it helps to know about the different systems and the main organs that make up each one, as well as some of the more common problems that occur with each. These organs and systems must all work properly on their own and also interact in order to keep your dog in top condition.