Changes

==Defense mechanisms==

==Defense mechanisms==

*Particle deposition  

===Particle deposition===

**Coiled nature of turbinates promotes turbulent airflow and impaction of large particles >10 μm in diameter onto the nasal mucosa

*Coiled nature of turbinates promotes turbulent airflow and impaction of large particles >10 μm in diameter onto the nasal mucosa

*Mucociliary escalator  

===Mucociliary escalator===

**Cilia on the respiratory epithelium beat in a co-ordinated manner

*Cilia on the respiratory epithelium beat in a co-ordinated manner

***Cilia beat in a caudal direction in nasal cavity

**Cilia beat in a caudal direction in nasal cavity

***Cilia beat in a cranial direction in trachea and lower airways

**Cilia beat in a cranial direction in trachea and lower airways

***Mucus is swallowed when it reaches the nasopharynx

**Mucus is swallowed when it reaches the nasopharynx

***Constant movement reduces chances that pathogens can adhere to the respiratory epithelium

**Constant movement reduces chances that pathogens can adhere to the respiratory epithelium

**Mucus

===Mucus===

***Produced by the goblet cells of the respiratory epithelium and the submucosal glands with contribution from lacrimal glands draining into the nose

**Produced by the goblet cells of the respiratory epithelium and the submucosal glands with contribution from lacrimal glands draining into the nose

***Traps particles for transportation away and subsequent swallowing

**Traps particles for transportation away and subsequent swallowing

***Physical barrier against mucosal damage

**Physical barrier against mucosal damage

***Prevents dessication of the mucosal epithelium

**Prevents dessication of the mucosal epithelium

***Contains antimicrobial substances

**Contains antimicrobial substances

***Immunoglobulin - IgA

**Immunoglobulin - IgA

****IgA produced by mucosal plasma cells

***IgA produced by mucosal plasma cells

****IgA can attach to specific pathogen antigens (viruses, bacteria) trapping them in the mucus for clearance

***IgA can attach to specific pathogen antigens (viruses, bacteria) trapping them in the mucus for clearance

***Lysosyme

**Lysosyme

****Direct action on bacterial cell walls

***Direct action on bacterial cell walls

****Lactoferrin

***Lactoferrin

*****Inhibits bacterial growth as sequesters iron, an essential co-factor for many bacteria

****Inhibits bacterial growth as sequesters iron, an essential co-factor for many bacteria

*Commensal bacteria

===Commensal bacteria===

***The normal bacterial flora of the nasal cavity, pharynx, larynx and proximal portion of the trachea compete with potentially pathogenic bacteria and help to prevent their colonisation (competitive exclusion).

***The normal bacterial flora of the nasal cavity, pharynx, larynx and proximal portion of the trachea compete with potentially pathogenic bacteria and help to prevent their colonisation (competitive exclusion).

***The airway environment distal to the mid-portion of the trachea is effectively sterile.   

***The airway environment distal to the mid-portion of the trachea is effectively sterile.   

*Reflexes

===Reflexes===

***Sneezing

***Sneezing

***Coughing

***Coughing