A critical element in the mentoring relationship is a mutual respect between you and your mentor. For example, the publisher of one of my books told me that he had a mentor when he first joined a large publishing company. Once a month, I had lunch with my mentor, a senior vice president in the company. I learned more about the publishing industry and how the company really worked at those lunches than I could have in years if I had to discover all of it myself. The coach is more of a tutor, observing your work and actions, providing comments on execution, and teaching skills which may be lacking.
Coaches can come from many sources.
A coach can be a colleague, a manager, or an employee, and doesn't have to come from the same function or division in which you work. For example, a coach may come from the company's personnel or training function. Some senior executive hire an outside consultant to act as their coach. It is critical in the coaching relationship for the coach to have opportunities to observe your work and for you to respect the coach and be open to feedback. These two roles, whether performed by one person or two, are an essential ingredient in your career development.