Overview
- Lecture covers Respiratory System (Blossom 22.1–22.2), relevant for final exam.
- Focus: anatomy, histology, zones of respiration, gas exchange, lung gross anatomy, common pathologies.
- Emphasis on connections with cardiovascular and lymphatic systems.
Major Divisions And Pathway Of Air
- Air enters via external nares (nostrils) into nasal cavity or oral cavity.
- Nasal cavity → nasopharynx → oropharynx → laryngopharynx → glottis → larynx → trachea.
- Trachea bifurcates at the carina into right and left primary bronchi.
- Bronchi → secondary (lobar) bronchi → tertiary bronchi → bronchioles → terminal bronchioles → respiratory bronchioles → alveolar ducts → alveolar sacs (alveoli).
Conducting Zone Versus Respiratory Zone
- Conducting Zone:
- Function: airway passage, warming, humidifying, filtering air; olfaction in nasal region.
- Structures: nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles (until terminal bronchioles).
- Epithelium: pseudostratified ciliated columnar (respiratory epithelium) with goblet cells and cilia.
- No gas exchange occurs here.
- Respiratory Zone:
- Function: gas exchange (O2 in, CO2 out).
- Structures: respiratory bronchioles, alveolar ducts, alveolar sacs, alveoli.
- Epithelium: simple squamous for thin diffusion barrier.
Nasal Anatomy And Functions
- Key parts: nares (nostrils), nasal bones (bridge), cartilage (majority of nose), nasal septum (perpendicular plate of ethmoid + vomer).
- Conchae (superior, middle, inferior) create meatuses to increase surface area.
- Floor: hard palate (palatine bones) + soft palate; uvula marks inferior limit of nasopharynx.
- Functions: humidify/warm air, filter particulates (mucus + cilia), olfaction via CN I through cribriform plate.
- Paranasal sinuses (frontal, sphenoidal, ethmoid, maxillary): produce mucus, lighten skull, add resonance to voice.
Pharynx And Tonsils
- Pharynx regions: nasopharynx (to uvula), oropharynx (uvula to epiglottis), laryngopharynx (below epiglottis).
- Histology:
- Nasopharynx: pseudostratified ciliated columnar (respiratory epithelium).
- Oropharynx & laryngopharynx: stratified squamous non-keratinized (protects against food abrasion).
- Tonsils: pharyngeal (adenoid), palatine, lingual — lymphatic tissue that samples pathogens.
- Eustachian (pharyngotympanic) tube opens in nasopharynx; connects to middle ear (risk for otitis media).
Larynx And Voice Production
- Larynx cartilage: epiglottis, thyroid cartilage (largest; contains laryngeal prominence/Adam’s apple), cricoid cartilage.
- Hyoid bone: floating bone above larynx.
- Vocal structures:
- Vestibular folds (false vocal cords) — superior, protective.
- Vocal folds (true vocal cords) — inferior; ligaments that vibrate to produce sound.
- Pitch related to vocal fold thickness and length (thicker → lower pitch).
Trachea And Bronchial Tree
- Trachea: 16–20 C-shaped hyaline cartilaginous rings (C-rings); posterior side has trachealis muscle adjacent to esophagus.
- Carina: bifurcation point stimulating cough reflex if foreign material contacts it.
- Right primary bronchus wider and more vertical than left → more likely foreign body lodgment; right lung has three lobes, left has two (cardiac notch).
Bronchi Versus Bronchioles
- Bronchus: cartilage present in airway wall (primary, secondary, tertiary).
- Bronchiole: no cartilage; smooth muscle only — site vulnerable to constriction (asthma).
- Branching ~20–25 generations (respiratory tree) ending in alveoli.
Alveoli And Gas Exchange
- Alveolar sac: clusters of alveoli; each alveolus surrounded by capillary beds.
- Respiratory membrane: alveolar simple squamous epithelium + capillary endothelium (thin double layer + fused basement membranes) for diffusion.
- Cell types in alveoli:
- Type I cells: simple squamous epithelial cells (majority; gas exchange).
- Type II cells: secrete surfactant (reduces surface tension; prevents alveolar collapse).
- Alveolar macrophages (dust cells): phagocytose particulates reaching alveoli.
- Estimated ~300 million alveoli; total surface area ~a doubles tennis court.
Pulmonary And Bronchial Circulation
- Pulmonary arteries/arterioles: carry deoxygenated blood (blue in lung diagrams) to alveolar capillaries.
- Pulmonary veins/venules: carry oxygenated blood back to heart.
- Bronchial arteries (systemic circulation): supply oxygenated blood to lung tissues; bronchial veins return systemic blood.
- Note: color coding flips in pulmonary circuit (arteries blue, veins red).
Pleura, Lung Mechanics, And Innervation
- Pleura:
- Visceral pleura: adherent to lung surface.
- Parietal pleura: lines thoracic wall and superior diaphragm.
- Pleural cavity contains serous fluid for lubrication and allows lungs to be “vacuum sealed” to thoracic wall.
- Intercostal muscles and diaphragm expand thoracic cavity, pulling lungs open (inhalation).
- Pneumothorax: puncture allows air into pleural cavity → lung collapse.
- Pleurisy / pleural effusion: fluid or inflammation in pleural cavity, impairing lung expansion.
- Innervation: pulmonary plexus (autonomic). Parasympathetic → bronchoconstriction; sympathetic → bronchodilation.
Histology Highlights
- Respiratory epithelium: pseudostratified ciliated columnar with goblet cells and mucous production.
- Mucociliary escalator: coordinated upward ciliary movement moves mucus/particles toward pharynx to be swallowed.
- Alveoli: simple squamous epithelium for minimal diffusion distance.
Common Disorders Covered
- Asthma:
- Chronic inflammatory airway disease primarily affecting bronchioles (no cartilage).
- Features: bronchoconstriction, mucus buildup, smooth muscle spasm.
- Treatments: inhalers/nebulizers (bronchodilators, often beta-agonists mimicking epinephrine), mucolytics.
- Emphysema (COPD type):
- Destruction of alveolar walls → fewer, larger air spaces → decreased total surface area for gas exchange.
- Result: decreased oxygen uptake, breathing difficulty.
- Lung cancer:
- Smoking major risk factor; can disrupt pleural integrity and present as pneumothorax.
- Segmental lung resections possible because of lobar/segmental organization.
Key Terms And Definitions
| Term | Definition / Note |
| Conducting Zone | Airway passages that warm, humidify, and filter air; no gas exchange. |
| Respiratory Zone | Structures where gas exchange occurs: respiratory bronchioles, alveoli. |
| Conchae / Meatuses | Bony shelves creating turbulent airflow and increasing mucosal surface area. |
| Carina | Tracheal bifurcation point where trachea splits into primary bronchi. |
| Alveolus | Microscopic air sac where gas exchange occurs. |
| Respiratory Membrane | Combined alveolar and capillary simple squamous layers for diffusion. |
| Surfactant | Substance from Type II cells that reduces alveolar surface tension. |
| Mucociliary Escalator | Upward beating of cilia moving mucus and debris to pharynx. |
| Pneumothorax | Air in pleural cavity causing lung collapse. |
| Bronchial Arteries | Systemic arteries supplying lung tissue (not involved in gas exchange). |
Action Items / Next Steps (For Students)
- Watch assigned videos on: nasal anatomy, mucociliary escalator, vocal cord visualization, paranasal sinuses.
- Complete end-of-section questions and vocabulary for 22.1 and 22.2.
- In lab: identify nasal conchae, pharynx regions, laryngeal cartilages, tracheal C-rings, bronchial branching, pleura.
- Review connections with cardiovascular system (hemoglobin transport, pulmonary circulation) and lymphatic/immune tissues (tonsils, alveolar macrophages).
- Understand clinical relevance: asthma mechanisms and treatments, emphysema effects on surface area, pneumothorax and pleural conditions.