The Respiratory System
The respiratory system's primary function is gas exchange: delivering oxygen to the blood and removing carbon dioxide. Air enters through the nose and mouth, passes through the pharynx, larynx, trachea, bronchi, and bronchioles, and finally reaches the alveoli — tiny air sacs where diffusion occurs. Respiratory medicine includes conditions from asthma and COPD to lung cancer and respiratory failure.
Learning Objectives
- 1Trace the pathway of air from the nose to the alveoli
- 2Identify key combining forms for respiratory anatomy
- 3Describe the mechanics of breathing (ventilation)
- 4Recognize common respiratory diseases and their terminology
- 5Interpret pulmonary function tests and procedures
1Upper Respiratory Tract
Air enters through the nose (nasal cavity) or mouth → pharynx (throat) → larynx (voice box, contains vocal cords and epiglottis) → trachea (windpipe)
The epiglottis is a flap of cartilage that covers the larynx during swallowing to prevent food/liquid from entering the airway.
The sinuses (frontal, maxillary, ethmoid, sphenoid) are air-filled cavities in skull bones that lighten the skull, warm/humidify air, and resonate voice.
Upper respiratory infections (URI): Common cold, sinusitis, pharyngitis, laryngitis
2Lower Respiratory Tract
Trachea → Right and left main bronchi → Lobar bronchi → Segmental bronchi → Bronchioles → Terminal bronchioles → Respiratory bronchioles → Alveolar ducts → Alveoli
The right lung has 3 lobes; the left lung has 2 lobes (the heart occupies the cardiac notch on the left).
Alveoli are surrounded by pulmonary capillaries — site of gas exchange by diffusion:
3Respiratory Diseases
COPD (Chronic Obstructive Pulmonary Disease): Umbrella term
Asthma: Chronic inflammation + bronchospasm + mucus hypersecretion → airway obstruction (reversible)
Pneumonia: Lung infection (bacterial, viral, fungal) → consolidation
Pulmonary embolism (PE): Blood clot in pulmonary artery — life-threatening
Lung Cancer: #1 cancer killer; non-small cell (NSCLC) most common
Tuberculosis (TB): *Mycobacterium tuberculosis*; tested with PPD/Mantoux
4Procedures and Tests
Pulmonary Function Tests (PFTs):
Bronchoscopy: Flexible scope → bronchi; biopsy, BAL, remove foreign bodies
Chest X-ray (CXR): First-line imaging
CT chest: More detailed; used for PE (CT angiography), tumors
Pulse oximetry: Non-invasive O₂ saturation (SpO₂); normal 95–100%
ABG (Arterial Blood Gas): pH, PaO₂, PaCO₂, HCO₃—; assesses respiratory/metabolic status
Clinical Connections
- ►COPD is the 3rd leading cause of death worldwide and is largely caused by smoking
- ►COVID-19 primarily attacks type II pneumocytes in alveoli, causing severe respiratory failure
- ►Asthma affects 1 in 13 Americans; peak attacks occur between 10 PM and 2 AM