Functions of the Nose: Breathing, Smell, Speech, and Facial Structure

1. Respiration (Primary)

• Filtration: Nasal hairs (vibrissae) trap large particles; mucociliary blanket catches smaller ones.
• Conditioning: Turbinates (conchae) increase surface area → warm air to 37°C, humidify to 100% RH.
• Airflow regulation: Nasal cycle (alternating congestion) balances workload.

2. Olfaction

• Olfactory epithelium (superior turbinate/septum) contains ~5–6 million receptor neurons.
• Odorants bind G-protein-coupled receptors → cAMP cascade → signal to olfactory bulb → piriform cortex, amygdala, orbitofrontal cortex.
• Integrated with taste (flavor = taste + smell + trigeminal sensation).

3. Speech Resonance

• Nasal cavity acts as resonating chamber for voiced sounds (m, n, ng).
• Velopharyngeal closure directs air orally for non-nasal sounds.
• Hypernasality (velopharyngeal insufficiency) or hyponasality (obstruction) alters speech quality.

4. Facial Aesthetics and Identity

Central facial landmark; contributes to profile, symmetry, and recognition. Rhinoplasty alters both form and function.

5. Immune Defense

Mucosal IgA, lysozyme, lactoferrin, defensins; lymphoid tissue (Waldeyer's ring) samples antigens.

Clinical Correlates

• Nasal obstruction → mouth breathing → sleep apnea, dental malocclusion, facial growth changes (adenoid facies).
• Anosmia → safety risk (gas, smoke), nutrition decline, depression; early marker in Parkinson's, Alzheimer's, COVID-19.