Air enters the upper respiratory tract through the nasal cavity and mouth, which both lead to the pharynx . The upper respiratory tract is colonized by an extensive and diverse normal microbiota, many of which are potential pathogens.

The respiratory tract is divided into upper and lower regions at the epiglottis The lower respiratory tract extends from the larynx into the trachea before branching into the bronchi , which divide further to form the bronchioles , which terminate in alveoli , where gas exchange occurs

upper respiratory tract — colonized by an extensive and diverse normal microbiota, many of which are potential pathogens. infected tissues; these conditions — given names ending in -itis , such as rhinitis , sinusitis , otitis , pharyngitis , and bronchitis. respiratory tract — divided into upper and lower regions at the epiglottis.

Be able to describe the major anatomical features of the upper and lower respiratory tract; describe the normal microbiota of the upper and lower respiratory tracts; explain how microorganisms overcome defenses of upper and lower respiratory-tract membranes to cause infection.