[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Physiology](https://durgical.com/en/physiology/) › [Respiratory](https://durgical.com/en/physiology/#s-resp) › Airway defenses, cough and mucociliary clearance [Physiology](https://durgical.com/en/physiology/) · [Respiratory](https://durgical.com/en/physiology/#s-resp) # Airway defenses, cough and mucociliary clearance - Concept - For completeness The nose filters, mucus traps, cilia sweep upward and cough throws it out: that is how the lung stays clean. Updated 2026-11-01 Also called: Mucociliary escalator, Cough reflex **See it in 3D:** [Nasal cavity](https://durgical.com/en/anatomy/nasal-cavity/) · [Trachea](https://durgical.com/en/anatomy/trachea/) · [Main bronchi](https://durgical.com/en/anatomy/right-main-bronchus/) · [Segmental bronchi](https://durgical.com/en/anatomy/segmental-bronchus/) · [Epiglottis](https://durgical.com/en/anatomy/epiglottis/) · [Vocal folds](https://durgical.com/en/anatomy/vocal-fold/) ## Key points - Particle size: >10 µm stay in the nose; ≈2–10 µm in trachea and bronchi; - The turbinates make airflow turbulent: large particles hit the moist nasal mucosa and stick. - In trachea and bronchi, medium particles settle on the mucus by impaction and sedimentation. - Cilia beat in coordination in the periciliary layer and move the mucus sheet up to the larynx, where it is swallowed or expelled. - If something irritates the larynx or trachea, vagal receptors trigger cough: inspiration, glottic closure and expiratory contraction. - Intrathoracic pressure rises sharply; when the glottis opens, air leaves at high speed and drags out mucus and foreign material. - In the alveoli, macrophages engulf fine particles and microbes and move to the escalator or the lymphatics. ## When the defenses fail | Failure | Mechanism | Consequence | | --- | --- | --- | | [Smoking](https://durgical.com/en/conditions/chronic-obstructive-pulmonary-disease/) | Ciliary paralysis and loss, mucous gland hyperplasia | Chronic productive cough, COPD | | Cystic fibrosis | Periciliary layer dehydrated by faulty CFTR | Thick mucus, infections, bronchiectasis | | [Primary ciliary dyskinesia](https://durgical.com/en/conditions/bronchiectasis/) | Cilia that do not beat | Sinusitis, bronchiectasis, sometimes situs inversus | | [Weak cough or incompetent glottis](https://durgical.com/en/conditions/community-acquired-pneumonia/) | Neuromuscular disease, sedation, stroke | Aspiration and pneumonia | ## Clinical notes - Urban pollution and wood smoke in rural Colombia impair mucociliary clearance and cause COPD in non-smokers, especially women. - Stroke patient with dysphagia: weak cough and silent aspiration explain recurrent pneumonia. - Nursing: repositioning, hydration and chest physiotherapy help mobilize secretions. ## Memory aid Filter, stick, sweep, blow: nose, mucus, cilia, cough. ## Test yourself Think of the answer, then tap the question to see it. ## Why does bronchiectasis develop in cystic fibrosis if the cilia are normal? Faulty CFTR dehydrates the periciliary layer; cilia are trapped in thick mucus they cannot move, and chronic infection destroys the bronchial wall. ## Which step of the cough reflex fails in an intubated patient? Glottic closure: without it the high pressure before sudden opening cannot build, and cough is ineffective. ## Why do very fine particles, such as smoke, reach the alveoli? They are too small to impact on the mucosa or settle in the conducting airways; they ride the airflow to the alveoli, where macrophages must deal with them. ## Why can an ACE inhibitor cause a persistent dry cough? Angiotensin-converting enzyme also breaks down bradykinin; blocking it lets bradykinin build up and sensitize airway cough receptors. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/physiology/airway-defenses-cough-and-mucociliary-clearance/) ## See it in 3D The structures of Durgical's 3D anatomy where it happens. - [Nasal cavity](https://durgical.com/en/anatomy/nasal-cavity/) - [Trachea](https://durgical.com/en/anatomy/trachea/) - [Main bronchi](https://durgical.com/en/anatomy/right-main-bronchus/) - [Segmental bronchi](https://durgical.com/en/anatomy/segmental-bronchus/) - [Epiglottis](https://durgical.com/en/anatomy/epiglottis/) - [Vocal folds](https://durgical.com/en/anatomy/vocal-fold/) ## Related topics - [Airway resistance](https://durgical.com/en/physiology/airway-resistance/) - [Innate and adaptive immunity: overview](https://durgical.com/en/physiology/innate-and-adaptive-immunity-overview/) - [The physiology of inflammation](https://durgical.com/en/physiology/the-physiology-of-inflammation/) - [Swallowing and esophageal motility](https://durgical.com/en/physiology/swallowing-and-esophageal-motility/) ## Related conditions - [Bronchiectasis](https://durgical.com/en/conditions/bronchiectasis/) - [Chronic obstructive pulmonary disease (COPD)](https://durgical.com/en/conditions/chronic-obstructive-pulmonary-disease/) - [Community-acquired pneumonia](https://durgical.com/en/conditions/community-acquired-pneumonia/) - [Pulmonary tuberculosis](https://durgical.com/en/conditions/pulmonary-tuberculosis/) ## In Pharmacology - [ACE inhibitors](https://durgical.com/en/pharmacology/classes/ace-inhibitors/) - [Opioids and antagonists](https://durgical.com/en/pharmacology/classes/opioids-and-antagonists/) [← All of physiology](https://durgical.com/en/physiology/) Educational physiology content; not a diagnostic or treatment guide and no substitute for a health professional's advice. Values are approximate references. No doses are given. Sources: [22.1 Organs and Structures of the Respiratory System](https://openstax.org/books/anatomy-and-physiology-2e/pages/22-1-organs-and-structures-of-the-respiratory-system) (OpenStax (Rice University), 2022); [Anatomy, Thorax, Tracheobronchial Tree](https://www.ncbi.nlm.nih.gov/books/NBK556044/) (StatPearls (NCBI Bookshelf), 2026); [Bronchiectasis](https://www.ncbi.nlm.nih.gov/books/NBK430810/) (StatPearls (NCBI Bookshelf), 2026); Hall JE. Guyton and Hall Textbook of Medical Physiology, 13th ed. (ch. 38). Reference book used to check facts; its text and figures are not reproduced (Elsevier, 2016). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/physiology/airway-defenses-cough-and-mucociliary-clearance/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/physiology/airway-defenses-cough-and-mucociliary-clearance/