Respiratory Anatomy & Physiology Lecture Notes

Upper Respiratory Tract (URT)
- Extends from the external nose → nasal cavity → pharynx → larynx.
- Key sub-regions & landmarks:
- Nose / external nares
- Nasal cavity
  - Contains conchae (increase surface area, create turbulence)
  - Lined with pseudostratified ciliated columnar epithelium (PCCE) → mucus production & particulate trapping
- Pharynx (posterior throat)
  - Sub-divisions: nasopharynx, oropharynx, laryngopharynx
- Larynx (voice box)
  - Sits between laryngopharynx & trachea
  - Hosts vocal cords → sound production during expiration
Lower Respiratory Tract (LRT)
- Begins below the larynx: trachea → primary bronchi → bronchial tree → bronchioles → alveoli.
- Primary (main) bronchi split:
- Right main bronchus: shorter, wider, more vertical → most common site of aspirated foreign bodies
- Left main bronchus: longer, more oblique due to heart position
- Lung asymmetry due to cardiac placement:
- Right lung: larger, 3 lobes (superior, middle, inferior)
- Left lung: smaller, 2 lobes (superior, inferior) + cardiac notch for heart’s apex

Conducting Zone (nose → terminal bronchioles)
- Function: move, warm, humidify, filter air; project sound
- Epithelia: predominantly PCCE with goblet cells (mucus producers) & cilia for mucociliary escalator
- Includes portions of both URT & early LRT but excludes alveoli
Respiratory Zone (respiratory bronchioles → alveolar ducts → alveoli)
- Function: gas exchange \Big(\text{O}2\ \leftrightarrow\ \text{CO}2\Big)
- Minimal/no mucus production (thick mucus would impair diffusion)

Goblet cells in conducting zone secrete mucus → traps debris
Cilia beat toward pharynx; swallowed or expectorated
Alveoli stay relatively free of mucus; any present generally migrated there from above

Pseudostratified ciliated columnar epithelium (PCCE) lines most conducting passages
Alveolar wall cells:
- Type I pneumocytes – thin simple squamous → primary diffusion surface
- Type II pneumocytes – secrete pulmonary surfactant → ↓ surface tension, prevent alveolar collapse (critical in premature neonates)
- Alveolar macrophages ("dust cells") – phagocytose debris & pathogens

Cystic Fibrosis (CF)
- Autosomal recessive defect in \text{CFTR} chloride channel → impaired \text{Cl}^- & water secretion
- Results: dehydrated, thick mucus in lungs, GI tract, reproductive ducts
- Consequences: recurrent pulmonary infections, airway obstruction, pancreatic duct blockage → pancreatitis, malabsorption; infertility
Asthma
- Reversible airway hyper-reactivity → bronchoconstriction, excess mucus, wheezing (esp. expiratory)
- Triggers: allergens, exercise (exercise-induced asthma)
- Treatments: inhaled beta-2 agonists (bronchodilators), corticosteroids
Pneumonia
- Infection of alveoli &/or interstitium with consolidation/exudate
- Types: typical, atypical, community-acquired (CAP), pediatric CAP, "walking" pneumonia (milder Mycoplasma form)
- Leading infectious cause of mortality worldwide
Otitis media linkage
- Nasopharynx connects to middle ear via auditory (Eustachian) tube → URT infections can spread to ear, causing pressure or infection

Nasolacrimal duct – drains tears → inferior meatus of nasal cavity; explains teary-nose linkage
Epiglottis
- Normally open to trachea → continuous airflow
- Swallowing reflex: epiglottis folds posteriorly over laryngeal inlet → food diverted to esophagus
Cricoid cartilage
- Only complete ring of cartilage in airway; landmark for emergency cricothyrotomy
- Palpation: locate thyroid cartilage (Adam’s apple) → slide inferiorly to soft space; incision here for airway access
Heimlich maneuver
- Performed when patient cannot speak (complete airway obstruction)
- Abdominal thrusts ↑ intra-thoracic pressure to expel object
Diaphragm mechanics
- Inspiration: diaphragmatic contraction → descends → thoracic volume ↑ → intrapulmonary pressure ↓ (air flows in)
- Expiration (quiet): diaphragm relaxes → elastic recoil → air passively exits
- Summary formula: \Delta P = P{atm} - P{alveoli}
Hilum of lung
- Medial indented region where bronchi, pulmonary arteries & veins, lymphatics, nerves enter/exit (root of lung)
- Visible on chest X-ray as central branching opacity; entire lung appearing uniformly black indicates collapse (no vascular markings)

Sound (voice) produced in larynx as air from lungs passes over vocal folds during expiration
Projection & resonance aided by URT structures (pharynx, nasal cavities, sinuses)
Conducting zone not only ventilates but also permits phonation; respiratory zone strictly gas exchange (silent)

Rhinorrhea – "runny nose"; may be infectious (viral/bacterial) or non-infectious (allergic rhinitis)
Tonsils (in nasopharynx/oropharynx)
- Immune surveillance; enlarged/infected → tonsillitis; markedly enlarged adenoids can obstruct nasal breathing in children
Walking Pneumonia – mild atypical pneumonia; patient ambulatory despite infection
Surfactant therapy – antenatal corticosteroids stimulate Type II cells in premature labor to ↓ risk of neonatal respiratory distress syndrome (RDS)