Respiratory System Anatomy & Physiology: Complete Guide

The respiratory system conducts air, conditions it, and exchanges gases.

Conducting Zone (No Gas Exchange)

1. Nose/nasal cavity: Filter, warm, humidify; olfaction.
2. Pharynx: Air/food crossroads; tonsillar immune tissue.
3. Larynx: Voice box; vocal folds; epiglottis protects airway.
4. Trachea: C-shaped cartilage rings; ciliated pseudostratified epithelium (mucociliary escalator).
5. Bronchi (R/L): Branch into lungs; cartilage plates.
6. Bronchioles: No cartilage; smooth muscle controls caliber; terminal → respiratory bronchioles.

Respiratory Zone (Gas Exchange)

• Alveolar ducts → alveolar sacs → alveoli: 300M sacs, 70 m² surface; type I (gas exchange), type II (surfactant) pneumocytes.
• Capillary network: 0.5 μm barrier — O₂ diffuses in, CO₂ out.

Key Functions

1. Ventilation: Bulk air movement (diaphragm, intercostals).
2. External respiration: Alveolar-capillary gas exchange.
3. Gas transport: Hb (O₂), bicarbonate/Hb (CO₂).
4. Internal respiration: Capillary-tissue exchange.
5. pH regulation: CO₂/HCO₃⁻ buffer; respiratory compensation.
6. Phonation: Vocal fold vibration.
7. Defense: Mucociliary, macrophages, IgA, cough/sneeze reflexes.