Doctors belong to a specialty (or specialties) that relates to the field of medicine that they are expert in e.g. paediatricians are paediatric specialists who are experts in the care of children and young people. Hospitals often use specialties as organisational units, a number of specialties may make up one directorate. For example NGH's Surgical directorate includes urology, vascular surgery, opthalmology, maxillo-facial surgery, oral surgery and Ear, Nose and Throat surgery and general surgery specialists. Tertiary centre A tertiary centre is a centre where patients may be tranferred to in order to receive specialist treatment for example a burns unit.