Alveoli Function: Gas Exchange, Not Speech Production

Alveoli are microscopic air sacs (~300 million) at the terminal ends of the bronchial tree. Their sole primary function is gas exchange—not speech production.

Alveolar Structure for Gas Exchange

• Single-cell epithelium (type I pneumocytes = 95% of surface area)
• Surfactant (type II pneumocytes) → reduces surface tension, prevents collapse
• Dense capillary network (1,400 km total length)
• Blood-gas barrier: 0.2–0.5 μm → rapid O₂/CO₂ diffusion
• Surface area: ~70 m² (tennis court)

Speech Production Apparatus

Speech requires coordinated action of:

• Respiratory system: Lungs (air supply), diaphragm/intercostals (pressure generation)
• Larynx: Vocal folds (phonation — vibration → sound source)
• Articulators: Tongue, lips, teeth, hard/soft palate, jaw (filtering → phonemes)
• Resonators: Pharynx, oral/nasal cavities (timbre)
• Neural control: Broca's area (motor planning), motor cortex, cranial nerves (V, VII, IX, X, XII)

Alveoli's Indirect Role

Alveoli enable sustained phonation by providing efficient O₂/CO₂ exchange for the respiratory muscles powering speech. But they produce no sound, articulate no phonemes, and have no motor innervation for speech.

Clinical Pearl

Alveolar disease (ARDS, fibrosis, edema) → dyspnea → reduced speech duration/volume. This is respiratory limitation, not primary speech pathology.