The functions of the Nose
April 27th, 2011 | 
Author: The nose acts as a respiratory pathway, through which air becomes warmed, humidified and filtered, as the organ of olfaction and as a resonator in speech. There is a strong inborn reflex to breathe through the nose. This is natural to the survival of babies during suckling. As a result, nasal obstruction may cause gross discomfort; thus, packing the nose after surgery may cause restlessness upon emergence from on anaesthetic, and choanal atresia may cause cyanosis in the newborn.
The natural expiratory resistance of the upper airways is in the order of 1–2 cmH2O and can be increased subconsciously to provide a natural form of continuous positive airway pressure (CPAP). Intubation of the trachea decreases this natural expiratory resistance. Air passes through the nose, not directly along the inferior meatus, but in a curve through the upper reaches of the nasal cavity. The vascular cavernousplexuses, arranged longitudinally like so many radiator pipes, increase the temperature of the air to that of the body by the time it reaches the nasopharynx.
Water, derived partly from the mucous and serous glands, partly from the goblet cells, but mainly by exudation from the mucous surfaces, produces nearly 100% saturation of the inhaled air. Filtration is effected by the blanket of mucus covering the nasal cavity and its related sinuses. The mucus is swept towards the pharynx like a sticky conveyor belt by the action of the cilia and then swallowed. Reflex sneezing also helps rid the nose of irritants.
The blood supply to the nasal mucosa is under reflex control. General warming of the subject produces reflex hyperaemia whereas general cooling results in vasoconstriction. Hence the well-known observation that one’s stuffy nose in a hot room clears on going out into the cold air. A part of the Horner’s syndrome produced in a cervical sympathetic block is blockage of the nasal passage on that side as a result of paralysis of sympathetic vasoconstrictor fibres to the nasal mucosa.