| How does the impaction within the nasal cavity defend against respiratory pathogens in the upper airways? | The nasal cavity has a structure that promotes the warming and ‘scrubbing’ of inhaled air. Bony projections (conchae) increase the surface area of the nasal cavity. Inhaled air bounces along the nasal epithelium known as the ciliated epithelium. |
| How does the cough reflex defend against respiratory pathogens in the upper airways? | There are three phases of Cough Inspiratory phase – rapid inhalation of up to 2.5L of air. Compression phase – closure of epiglottis and larynx, combined with contraction of the chest wall, diaphragm and abdominal muscles. This generates intrathoracic pressure of >100mmHg. Expiratory phase – the larynx and epiglottis suddenly open, resulting in a high expiratory flow. Rapidly moving air carries dislodged mucus and removes any foreign matter. |
| How does the mucociliary defence defend against respiratory pathogens in the upper airways? | The motion of cilia (10-20 Hz) moves mucus approx. 1cm/min upwards towards the pharynx (down from the nose, upwards from bronchi) Mucus consists of mucins secreted by the epithelial cells and submucosal glands of the airways. |
| How do the cellular mechanisms defend against respiratory pathogens in the upper airways? | Alveolar macrophages are considered the resident immune cell responsible for cellular indigestion of inhaled pathogens (phagocytosis) as they synthesise and secrete an array of pro-inflammatory cytokines and chemokines. |
| How can respiratory cilia protect against respiratory pathogens? | In the respiratory passageways, cilia project 2-4μm from the cell surface. Ciliary movement describes the ‘whip like’ action of cilia on the respiratory surfaces. Effective for the removal of particles <10 microns from the trachea and main bronchi. |
| How can humoral immune mechanisms protect against respiratory pathogens? | Immunoglobin A (IgA) Synthesised in submucosal areas and binds to antigens to prevent their attachment to epithelial cells. Agglutinates microorganisms, leading to easier removal of mucociliary transport. Immunoglobin B (IgB) Enhances macrophage handling of bacteria, agglutinates microparticles and activated complement |
| How can lymph nodes protect against respiratory pathogens? | Lymph nodes exist through the respiratory tract and contain lymphocytes, including B and T cells. Lymphoid tissue of mucosal areas is known as Mucosal-Associated Lymphoid Tissue (MALT). Primarily found in the conducting airways In the lungs, it’s known as Bronchus-Associated Lymphoid Tissue (BALT – provides an initial line of defence through induction of IgA |
| Describe the innate and acquired immune response against respiratory pathogens in the lower airways. | Adaptive immunity in the lungs is primarily involved in mounting a response in the presence of pathogens. B-cell immunity – B lymphocytes produce antibodies. T-cell immunity – activated lymphocytes Dendritic cells – involved in capture, process and presentation of antigen to T cells |
