@indigomoth - It really depends on the hospital. In the better kinds of hospitals, nurses will get a wide range of duties and have opportunities to try different positions and get professional development so that they can eventually take up new duties.
But, other hospitals might not worry about that and just keep all their nurses in limited positions without the chance to try anything new. It's very important to look at the nursing job description before you accept it and to ask other people working at that hospital what the professional development is like and what opportunities they are given.
Some places are almost always going to end up hiring outside the workplace rather than promoting people within it, and those are not the places that you want to work (at least, not if you're hoping to rise through the ranks).