Well, that question is quite vaque, since there are myriad types of physicians bearing the "M.D." or "D.O." title.
General internists (specialists in internal medicine) cover all internal findings of the body that is non-surgical. There are sub-specialties of internal medicine dealing with specific organ-systems, such as: gastro-enterologists ("GI" digestive), cardiologists (heart and vessels), immunologists (allergies, lymphatic/immune disorders), nephrologists (urogenital/kidneys), pulmonologists (lungs), hepatologists (liver/gall bladder), rheumatologists (bone and autoimmune disorders), oncologists (cancers).
Then, amongst surgical sub-specialties there are: neuro-surgeons, plastic surgeons (hands, genitals, skin, breasts, etc.), orthopedic surgeons (bone and joints), spinal surgeons, vascular surgeons (blood vessels), cardio-thoracic (CT) surgeons (heart, chest, lungs), craniofacial (skull and face), general abdominal surgeons (digestive, liver, spleen, gallbladder, pancreas, appendix, kidneys, etc.), ophthalmologist/ eye surgeons (blepharo/oculoplastic/retinal/corneal, etc.), ear, nose, and throat (ENT) surgeons, urologists (urethra, ureters, bladder, prostate, testes, vas deferens, scrotum, etc.).
And there are their own individual specialties outside of surgery or internal medicine: Obstetrics-Gynecology (OB-GYN) covering pregnancy and female genitalia, ovaries, uterus, cervix, fallopian tubes, vulva, vagina; Pediatrics (babies and children) which has pediatric subspecialties in most internal subspecialtites and surgical subspecialties, including neonatalogy
(newborns); Dermatology (skin); Neurology (non-surgical nervous system disorders); Psychiatry (mental, behavioral, and emotional disorders)
SO THERE ARE QUITE A FEW ROLES FOR DIFFERENT "PHYSICIANS"!!!
