Nasal Anatomy And Physiology Anatomy

The human nose consists of two nasal cavities separated by the septal wall, the narrowest section being the nasal valve near the front of the nose. Each nasal cavity opens onto the face through the nostril and extends posteriorly to the nasopharanyx with a length of approximately 10 cm. The combined surface area of both cavities is approximately 150 cm2 and the volume approximately 15 mL. The vestibular area serves as a baffle system whose surface is covered by a common pseudostratified epithelium and long hairs, to provide filtering of airborne particles. Found in the posterior region of the nose are the inferior, middle, and superior turbinates (Fig. 1), which combined with the nasal blood vessels play an important role in the humidification and temperature regulation of inspired air (17), a prime function of the human nose. Breathing through the mouth can sustain life, but without the air conditioning effect the air flow is both unpleasant and potentially harmful. In one inspiration via the nose, room temperature air (23°C) at 40% humidity is conditioned to 32°C at 98% humidity (18), suited to conditions required by the lungs. Under normal conditions, respiration predominantly occurs via one side of the nose, with the other side becoming congested, a cycle which alternates every 3-7 h (9,19). There is also a diurnal variation, with reduced nocturnal secretion rate (18) when the clearance of secretion is also markedly reduced (20).

The olfactory region, the area responsible for the detection of smell is situated in the posterior of the nose, near the top of the nasal cavity. It has been suggested that absorption directly to the central nervous system (CNS) is provided by formulations which can be administered directly to the olfactory region (21,22). This is of interest for the administration of drugs for conditions such as Parkinson's disease (23), which tend to have a high incidence of side effects that may be reduced by the lower doses

3. Nasal vestibule

2. Turbinate

1. Olfactory region

Figure 1 The nasal cavity.

3. Nasal vestibule

2. Turbinate

1. Olfactory region

Figure 1 The nasal cavity.

required for direct CNS delivery, or centrally acting analgesics such as morphine (24).

The majority of the nasal mucosa is composed of ciliated columnar cells, which are further covered in microvilli, providing an ideal large surface area for absorption. Secretions from the mucosal and submucosal glands form the mucus layer of the nose, which covers the mucosa and functions in conjunction with the cilia to trap foreign particles and remove them from the nose.

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