Physiological Pharmaceutics

200 Physiological PharmaceuticsANATOMY AND PHYSIOLOGYThe nose is a prominent structure located on the face between the eyes. The externalopenings are known as nares or nostrils which open at the back into the nasopharynx andlead to the trachea and oesophagus. The nose is the primary entrance to the respiratorytract, allowing air to enter the body for respiration. It conditions inspired air by filtering,warming, and moistening it. The nose also contains the olfactory organ, essential for thesense of smell.The nasal cavity is an irregularly-shaped space in the front of the head extending fromthe bony palate upwards to the cranium (Figure 9.1). The bony framework of the nasalcavity is formed by the fusion of seven bones (Figure 9.2). It produces a chamberapproximately 7.5 cm long by 5 cm high, subdivided into the right and left halves by acartilaginous wall, the nasal septum. The septum consists of the anterior septal cartilage andposteriorly, the vomer and perpendicular plate of the ethmoid bone. It terminates at thenasopharynx.The floor of the nose and the roof of the mouth are formed by the hard palatine boneand the soft palate, a flap of tissue. The soft palate extends back into the nasopharynx andduring swallowing is pressed upward, so that food cannot lodge at the back of the nose,blocking the airway. The ability to breathe through the mouth as well as the nose isextremely beneficial, although the air inspired through the mouth is not humidified, heatedand filtered to the same extent as the nose breathed air.The forward section of the nasal cavity, which is within and above each nostril, iscalled the vestibule. Behind the vestibule and along each outer wall are three thin, scrollshapedbony elements forming elevations, the conchae or turbinates, which generally runfrom front to rear. Each turbinate hangs over an air passage and they serve to increase thesurface area of the cavities. The superior, middle and inferior turbinates form flues throughwhich the air flows. The flues are quite narrow, and cause the air to flow in such a way thatno part of the airstream is very far from the moist mucous blanket lining the air spaces. Theturbulent airflow through this region, and the changes in direction caused by the turbinates,encourage inertial impaction of suspended particles. The width of the air spaces is adjustedby swell bodies in the septum and turbinates. Heating and humidification of inhaled air areimportant functions of the nose, which are facilitated by the abundant blood flow throughFigure 9.1 Cross section through the nose