Final answer:
The three types of doctors are cardiologists, orthopedists, and dermatologists, each specializing in areas concerning the heart, musculoskeletal system, and skin, respectively, and requiring extensive training and certification.
Step-by-step explanation:
The three types of doctors mentioned in the given content are cardiologists, orthopedists, and dermatologists. A cardiologist is a medical doctor specializing in the heart and its diseases, requiring extensive training, including medical school, residency, cardiology training, and board certification. An orthopedist focuses on the musculoskeletal system, dealing with disorders and injuries that may require surgery or other treatments. Dermatologists specialize in skin disorders, offering treatments ranging from medication to cosmetic procedures, and must be licensed and board-certified to practice.