| (1) |
In the nasal cavity the air is warmed and humidified. A turbulent airflow along the turbinates clears particles above 10 µm in diameter and pathogens from the inhaled air. |
| (2) |
Additionally, pharyngeal and laryngeal reflexes prevent aspiration of food or saliva. Cough, the most effective respiratory reflex clears large bronchiae or trachea from aspirated foreign bodies, fluid, or mucus. |
| (3) |
Small particels and bacteria are trapped in the mucus layer produced by the tracheobronchial epithelium. The mucus then is cleared by coordinated beats of the ciliae in rostral direction - the "mucociliary escalator". |
| (4) |
Small particles below 2 µm of size, however, may reach the alveolar system, where no ciliated epithelium is located. |
| (5) |
Here alveolar macrophages (AM), assisted by the pulmonary lymphatic system, form the second line of defense. They phagocytise foreign material, bacteria and they are able to start the inflammatory cascade. |
| (6) |
Invasion of pathogens is followed by an extended inflammatory reaction with increased capillary permeability, edema, enhanced mucus production and influx of inflammatory cells (granulocytes). |
| (7) |
Once alveolar macrophages have phagocytised bacteria or foreign material they are removed via the "mucociliary escalator", or by the interstitial lymphatic system. |
| (8) |
Lymphnodes containing large numbers of activated white blood cells contribute to host defense. These cells produce immunoglobulins and other substances to help fight the infection. |
