Introduction

Infections of the upper respiratory system are the most common type of infection.

Pathogens that enter the respiratory system can infect other parts of the body.

Structure and Function of the Respiratory System

The upper respiratory system consists of the nose, pharynx, and associated structures, such as the middle ear and auditory tubes.

Coarse hairs in the nose filter large particles from air entering the respiratory tract.

The ciliated mucous membranes of the nose and throat trap airborne particles and remove them from the body.

Lymphoid tissue, tonsils, and adenoids provide immunity to certain infections.

Upper Respiratory System

The lower respiratory system consists of the larynx, trachea, bronchial tubes, and alveoli.

Lower Respiratory System

The ciliary escalator of the lower respiratory system helps prevent microorganisms from reaching the lungs.

Microbes in the lungs can be phagocytized by alveolar macrophages.

Respiratory mucus contains IgA antibodies.

Normal Microbiota of the Respiratory System

The normal flora of the nasal cavity and throat can include pathogenic microorganisms.

Nasal Cavity:

• Diphtheroids

• Staphylococci

• Micrococci

• Bacillus species

Throat:

• Streptococcus pneumoniae

• Haemophilus influenzae

• Neisseria meningitidis

The lower respiratory system is usually sterile because of the action of the ciliary escalator.