Read this text about HOSPITAL HIERARCHY I in Great Britain.
DOCTORS
At present, in Great Britain, an undergraduate, after five years as a successful medical student, receives the title of MBBS (Bachelor of Science) or MBBCh. (Bachelor of Surgery). In the USA, the title is MD (Medical Doctor). The new doctor can then provisionally register with the General Medical Council (GMC).
As a post-graduate, s/he then becomes a House Officer (HO) (USA intern) for one year, at the end of which full registration with the GMC is permitted.
At this point, those doctors who wish to become family doctors, working in General Practice, leave hospital and spend three years as GP trainees with the Royal College of General Practitioners. (RCGP)
Doctors who decide for a career in hospital then progress to Senior House Officers 
(SHO) (USA residents), but still have to train for a further two years. For those choosing careers as surgeons – neurosurgeons, urologists, etc. – the final examination qualifies them as MRCS /AFRCS (exams of the Royal College of Surgeons). For those wishing to follow a career as physicians – dermatologists, endocrinologists, etc. – the final examination is an MRCP (exam of the Royal College of Physicians). For those intending to become anaesthetists the final examination is FRCA (exam of the Royal College of Anaesthetists).
This qualification allows them all to become Specialist Registrars, which includes 5 or 6 years of Higher Training and a final examination which leads to a Certificate of Completion of Specialist Training (CCST).
At this point, surgeons are no longer referred to as ‘Doctor’, but the more prestigious title of ‘Mr’ and their names are written in the GMC’s specialist register.
The last step in the hierarchical ladder is as a Consultant, the head of department, and a doctor usually maintains this position until retirement.