Respiratory System Anatomy: From Nose to Alveoli

Upper Airway

• Nose/Nasal Cavity: Nostrils, vestibule, conchae (turbinates), septum, olfactory epithelium. Functions: filter, warm, humidify, smell.
• Pharynx: Nasopharynx (adenoids, Eustachian tubes), oropharynx (palatine tonsils), laryngopharynx.
• Larynx: Thyroid, cricoid, arytenoid cartilages; epiglottis; true/false vocal cords; glottis.

Lower Airway

• Trachea: 16–20 C-shaped cartilage rings; carina at T4/T5.
• Bronchi: Right (wider, shorter, vertical) and left main bronchi → lobar (3 right, 2 left) → segmental bronchi.
• Bronchioles: No cartilage; terminal → respiratory bronchioles → alveolar ducts → alveolar sacs.
• Alveoli: ~300–500 million; type I (gas exchange), type II (surfactant), macrophages. Barrier: epithelium + basement membrane + capillary endothelium.

Thoracic Pump

• Diaphragm: Primary inspiratory muscle (innervated by phrenic nerve C3–5).
• Intercostals: External (inspiration), internal (forced expiration).
• Accessory: Scalenes, SCM, pecs, abdominals.

Control

Medullary (DRG/VRG) and pontine (pneumotaxic, apneustic) centers; chemoreceptors (central: CSF pH; peripheral: carotid/aortic bodies).