This document discusses upper respiratory tract infections (URTIs). It begins by outlining the protective mechanisms of the respiratory tract, such as hair, mucus, cilia, and lymphoid tissues that prevent pathogen attachment. It then describes the main types of URTIs like rhinitis, sinusitis, pharyngitis, and their typical symptoms. It lists the most common viral and bacterial causes for each. The document concludes with discussing laboratory diagnosis of URTIs through microscopy, culture and serology, and treatment approaches including symptomatic relief and antibiotics when indicated.