Nasal Physiology

Noam Cohen, MD

Introduction

The nose and lungs are under constant attack from inhaled debris and microbes (viruses, bacteria and fungus). The respiratory system has developed several lines of defense to combat this continuous assault. One of the initial defenses is the mucus which is designed to trap inhaled particles (including microbes) that are subsequently cleared from the airways. The vast majority of mucus is propelled into the throat where it is swallowed and destroyed by the products of the stomach, or it is coughed up or sneezed out.

cilia
The mechanism by which mucus is propelled to the throat  involves the rhythmic beating of very small cellular projections, known as cilia, which line the airways.


Cilia continuously beat to drive the debris-laden mucus from the airways. Furthermore, ciliated cells have multiple sensors that allow the cell to respond to certain cues, such as changes in mucus viscosity and mucus loads to make their cilia increase the speed at which they beat. By accelerating the speed at which they beat, the cilia can generate more propulsive force and thus continue to clear the heavier mucus, or clear normal mucus at a faster rate.

While the ciliated cells respond to environmental cues, environmental insults can also affect cilia function in a detrimental manner. Many microbes that attack the airways produce toxins that rapidly alter cilia movement, ultimately paralyzing the cilia, stopping the movement of mucus, thus optimizing the conditions for infection. Infection generates a local inflammatory response and now it is becoming clear that even the inflammatory molecules our bodies produce to fight infection also have detrimental effects on cilia function thereby compounding the insult and further hindering mucus clearance. The combination of microbes and inflammation over a relatively short period can lead to loss of cilia.


This combination of microbial and inflammatory products is often found in upper airway of patients with chronic rhinosinusitis. The good news is that if the microbes can be removed and the inflammation controlled, the cilia can regenerate and resume proper movement of mucus.

conclusion
Why certain individuals can easily recover from an upper respiratory infection without developing chronic rhinosinusitis while others seem to always progress to a protracted course is not completely understood. What we do know is this: when it comes to the development of chronic rhinosinusitis many factors including anatomic variations, microbial exposure, as well as an individual’s inflammatory response play a role. Novel approaches are being developed to help combat sinonasal infection, improve removal of mucus, accelerate sinus healing, and control the inflammation.


Revised 8/2011
©American Rhinologic Society