What are the physiologic functions of the nose?

Updated: Nov 04, 2019
  • Author: Samuel J Lin, MD; Chief Editor: Arlen D Meyers, MD, MBA  more...
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Answer

 

The nasal physiologic functions, such as warming and humidification, are vital for upper airway function. An adult inspires up to an estimated 10,000 liters of air daily. [1] Filtration of environmental particles occurs first in the nasal cavity. The largest particles are filtered by vibrissae. Nasal resistance is an important factor in considering airway resistance, contributing up to half of the total airway resistance observed in adults. [1] Through heat exchange, the nasal mucosa maintains the nasal cavity at a range of 31–37° C. [1]

One theory regarding the efficiency of heat exchange relates to the location of the sphenopalatine artery. This vessel courses anteriorly in the nasal cavity over the turbinates, whereas air flows in a posterior direction, forming a countercurrent exchange. [1] Thus, the two opposing motions create a more efficient heat exchange process. (Lending further support to this theory, computational simulation of gradual inferior turbinate resection demonstrates a stepwise reduction in air-warming capacity. [2] ) However, this process remains imperfect, and as much as 10% of heat loss occurs in the nose.

Humidification is another important process of nasal physiology. [1] Vascular mucosa increases relative humidity to 95% before air reaches the nasopharynx. Physiologic nasal fluids and ciliary function are vital to maintain immune defense through normal mucociliary flow. A number of nasal neurovascular reflexes occur as well. The nasopulmonary reflex suggests that pressure on one nasal sidewall causes ipsilateral pulmonary congestion. [1]

The nose may serve as a contributing factor in voice modification. Previous authors have noted that nasal aerodynamics may have a role in modifying high-frequency sounds and consonants. [1] Such aerodynamics also contribute to the olfactory system. [3] The active process of sniffing allows environmental particles to reach the olfactory system, which is located at the skull base. Moreover, in-vivo models have demonstrated that the frequency of sniffing can attenuate scents, acting as a rheostat to modulate smell. [4]

A study by Li et al indicated that a larger airflow vortex—its size likely influenced by the width-to-height ratio of the external nose and the nasal vestibule notch index—improves olfactory sensitivity to odors with high mucosal solubility. In addition, according to the report, a narrower vestibule region appears to intensify the airflow vortex toward the olfactory region, further contributing to such sensitivity. [3]

Ciliary flow is a vital component of normal sinonasal function. [5] The ciliary structure in the nose, consisting of two layers, provides an important immunologic defense mechanism. Resting on a pseudostratified ciliated cell layer, mucociliary flow occurs throughout the nose and paranasal sinuses. [6]

The nasal cycle is an additional feature of normal nasal physiology. This cycle causes turbinate hypertrophy to periodically alternate airflow between the two sides of the nose, resulting in intermittent unilateral obstruction approximately every 3 hours. Age, sleep, and posture are among the many physiologic factors that have been shown to modify the nasal cycle. [7]  A computational nasal air-conditioning model developed by White et al indicated that during the nasal cycle, the airway that conducts most of the airflow, and with it, most of the transfer of heat and water mass, undergoes some airway surface liquid dehydration, while the other airway maintains enough hydration to allow continuous mucociliary clearance. [8]


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