I've recently read a book on evolutionary-developmental biology for laymen, and it described how a fetus is progressively divided into more refined zones of genetic activity. These zones, kinda like GPS coordinates define which genes will be activated at which time and at which location.
What interests me is - after development to maturity, what defines how animals maintain their body shape? Is it the same "GPS" system that defines boundaries of an organism? Or is it something else within the specialized cells that tells them to grow in certain directions and avoid others?
To clarify the question with an example - lets take blood vessels - what prevents blood vessel lining from growing forever in all directions, taking up all available internal cavity space?