Respiratory system host defense 2025

Vocabulary flashcards covering key terms from the lecture on respiratory system host defense.

Oropharynx

The part of the pharynx behind the oral cavity; source of lung bacteria in healthy lungs.

Oropharyngeal colonization

Bacterial colonization of the oropharynx that can seed the lungs and lead to pneumonia.

Microbiome

Community of microorganisms in the oropharynx and lung that helps set immune tone and responses.

Microaspiration

Passive transfer of microbes from the oropharynx into the lower respiratory tract.

Dysbiosis

Abnormal Upper Respiratory Tract microbiota associated with disease or impaired defense.

Mechanical protection

Physical barriers (airways, mucus, cilia, cough) that protect against infection.

Upper airway

Nose to larynx; major site of initial mechanical defenses.

Nasal hairs

Filtration of large particles at the entrance of the nasal cavity.

Turbinates

Nasal structures that create turbulence to trap particulates.

Rhinorrhea

Nasal mucus discharge; part of the protective response.

Epiglottis

Flap that helps prevent food and liquids from entering the trachea during swallowing.

Glottis

Opening between vocal folds; contributes to airway protection.

Cough reflex

Reflex to clear the airway of irritants and pathogens.

Respiratory mucus

Mucus layer that impedes bacterial adherence and helps trap particles.

Mucociliary clearance

Cilia and mucus work together to move debris out of the airways.

Cilia

Hair-like projections beating to propel mucus; ~200 per cell, 12–15 beats/second.

Bronchial branching

Extensive branching from trachea to alveolar ducts; influences particle deposition.

Cross-sectional area

Increased total airway cross-sectional area reduces particle forward velocity.

Particles 5–10 µm

Size range effectively deposited in the conducting airways.

Ventilator-associated pneumonia

Pneumonia occurring in intubated patients due to bypassed upper airway defenses.

Endotracheal intubation

Insertion of a tube through the mouth/nose into the trachea; risk factor for VAP.

Tracheostomy

Surgical airway opening; associated with risk of VAP in long-term cases.

Aspiration pneumonia

Pneumonia arising from aspiration of oropharyngeal contents.

Lung abscess

Localized pus collection in the lung often from aspiration or infection.

Cystic fibrosis

Inherited disease with defective mucociliary clearance leading to mucus stasis and infection.

Bronchiectasis

Bronchial dilation from chronic infection/inflammation; can be diffuse or focal.

Post-obstructive pneumonia

Pneumonia surrounding an airway obstruction (tumor/foreign body).

Pattern Recognition Receptors

Innate immune receptors that detect microbial components to trigger defense.

Toll-like receptors

A class of PRRs that recognize conserved microbial components.

Collectins

Soluble PRRs (e.g., surfactant collectins) that aggregate and opsonize microbes.

SP-A

Surfactant protein A; collectin involved in lung innate defense.

MBL

Mannose-binding lectin; collectin that promotes opsonization and complement activation.

Complement

Plasma protein system that mediates lysis, opsonization, and chemotaxis.

Defensins

Antimicrobial peptides produced by airway epithelia with broad microbicidal activity.

Pneumocystis jiroveci

Fungal organism causing Pneumocystis pneumonia in immunocompromised hosts.

Mycobacterium tuberculosis

Tuberculosis pathogen; disease pattern depends on immune status.

HIV/AIDS

HIV infection leads to progressive loss of CD4 T cells and immune deficiency.

Encapsulated bacteria

Bacteria with capsules (e.g., S. pneumoniae, H. influenzae, N. meningitidis) high risk with humoral deficiency or asplenia.

Asplenia

Absence or dysfunction of the spleen; increases risk of encapsulated bacterial infections.

Hypersensitivity pneumonitis

Immune-mediated lung disease from inhaled antigens, involving IgE and other pathways.

Oropharyngeal flora

Bacterial community of the oropharynx that can influence lung infections.

Aerosolization

Process by which particles become suspended in air and can be inhaled.

SARS-CoV-2

Virus that infects the upper respiratory tract and can invade the lungs.

Mucus clearance

Removal of mucus from the airways as part of innate defense.

Opsonization

Coating of microbes with antibodies or complement to enhance phagocytosis.

APC (antigen-presenting cell)

Cells (e.g., lung macrophages, dendritic cells) that present antigens to T cells.

MHC II

Molecule on APCs presenting antigen to CD4 T cells.

CD4 T cells

Helper T cells coordinating adaptive immune responses.

CD8 T cells

Cytotoxic T cells that kill infected cells.