In the past few years, use of the nasal cavity as an alternative route for drug delivery has attracted great interest in the pharmaceutical industry, especially for systemic delivery of drugs that possibly can be delivered only through injection. The nasal route is favored for drugs that are given in small doses and require rapid onset of action, have extensive GI and hepatic degradation, and are used chronically.106,107 The nasal route of delivery is advantageous because of its rich blood supply, accessibility, noninvasiveness, low risk of overdose, and possibility of self-medication.108,109

Nasal anatomy and physiology. The nose is the first organ of the respiratory tract. The structure of the nasal cavity is shown in Fig. 2.8.

Nasal cavity. The nasal cavity has a volume of 15 to 20 cm3 and a surface area of 150 to 180 cm2.110,111 The human nasal cavity is divided into two halves by the midline septum.45,107 Each cavity consists of three regions: (1) vestibules, which are the anterior sections of the nasal cavity, (2) respiratory region, consisting of turbinates or chonchae (superior, middle, and inferior), and (3) olfactory region, which constitutes about 10 percent of nasal area.45,107

The nasopharynx plays an important role in optimizing the temperature and moisture content of the inhaled air. It also protects the body from particles and microorganisms by filtering the particulate matter in the inhaled air to prevent it from reaching the lower airways.107 The nasal turbinates divide the nasal passageway into narrow slits, resulting in a turbulent airflow, which helps in warming and humidifying the


air, and an increased surface area.

Nasal epithelium. The nasal cavity superior to the nostrils (vestibule) is covered by skin containing hair follicles and sebaceous and sweat glands. The skin is continuous with the inner nasal mucosa. Posteriorly, the epithelium is a pseudostratified ciliated columnar epithelium that covers the respiratory regions (formed by the maxilloturbinates).45,107,110

The superior turbinate (also called the ethmoturbinate) is lined by a thicker mucosa consisting of olfactory receptors and supporting cells.45,110

Sphenoidal sinus

Sphenoidal sinus

Frontal sinus Frontal bone

Olfactory Superior Middle turbinate Inferior turbinate Vestibule Maxilla

Figure 2.8 Structure of the nasal cavity.

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