Complex sentence: An emergency physician must be on duty anytime, and a specialized physician can be called anytime depending on the specific pathology (i.e. on duty in the hospital, not in the emergency service).
Split into simpler sentences: An emergency physician must always be "on-call," and a specialized physician can be called anytime. This depends on the specific pathology of the patient, (i.e. in the hospital, not in the emergency service).