The nose is the organ for respiration and smell perception or olfaction. It also performs several functions that we are little aware of. Let’s take a look at what these functions are and how the nose performs them.
Respiration and the Nose
Both inhaled and exhaled air must pass through the nose on their way in and out of the lungs. In fact, the nose is the natural pathway for respiration and we only acquire mouth breathing by learning it. Newborn babies can only breathe through their noses.
But the nose does more than just act as pathway for inhaled air. It acts as an air-conditioner for the lungs by regulating the temperature and humidity of inspired air. How does the nose do this?
The temperature of air we breathe in can range from +50°C to –50°C depending on the local climate. But by the time this air reaches the post nasal space, the space within the airway located just behind the nose, its temperature becomes 30°C, close to the body temperature. This phenomenon largely occurs due to the mucosa inside the nose and the large number of blood vessels running just beneath it.
The inside of the nose has several projections called ‘turbinates’. These structures serve to dramatically increase the surface area inside the nose, so the air inhaled is exposed to a much larger area of nasal mucosa. A large number of blood vessels or ‘sinusoids’ are located just below the mucosa and play an important role in raising or lowering the temperature of the air we breathe in, bringing it close to the normal body temperature.
The nose also adds water vapour to air, adjusting its relative humidity to 75%. Humidity is very important for the proper functioning of the respiratory system.
The Nose and Protection of the Lower Airway
While the function of preventing foreign bodies from entering the trachea and lungs is largely performed by the larynx, the nose plays its part, too. Short hairs located just inside the nostrils, called ‘vibrissae’, serve to trap dust particles present in air. While these hair filter larger particles at the entrance of the nose, finer particles tend to adhere to mucus secretions inside the nose.
Secretions of the nose tend to completely drape the inside of the nasal cavities forming a kind of film covering its surface. Fine dust particles between 0.5 and 3μm in size settle on this film. The entire mucus blanket moves like a conveyor belt, carrying bacteria and dust particles entrapped in it. Secretions of the nose also contain Immunoglobulin A (IgA), a surface antibody that combats bacteria that enter the nose.
Another protective mechanism that the nose is endowed with is the sneeze reflex. This reflex is triggered off by dust particles entering the nose and coming into contact with its mucosal covering. Expiratory air is immediately propelled with great force through the nasal airway so that the foreign body or irritant is expelled.
The Nose and the Sense of Smell (Olfaction)
The nose is the organ for olfaction, one of the five senses. Situated on the roof of the nose is a small amount of tissue comprised of special cells that are capable of perceiving odours. This region is called the olfactory epithelium. These cells give rise to nerve fibres that run through the skull bone above and join to form the olfactory nerve, the nerve for the sense of smell.
Air currents that we breathe in carry odours to the olfactory epithelium. These cells recognize the odour or fragrance and transmit the information as an electrical impulse along the fibres of the olfactory nerve to the olfactory area of the brain, the part of the brain designated for identification of odours.
In addition to the aforementioned functions, the nose also provides resonance to one's voice. All of these functions are hampered when infections or other diseases affect the nose.
Sources
- Gleeson, Michael J. "Scott-Brown's Otorhinolaryngology: Head and Neck Surgery" (Oxford University Press; 7 Edition, 2008).
Lakshmi Ananth - Lakshmi Ananth is a practising ENT, head and neck surgeon and has faculty position at a medical college. She is specially interested in ...
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