Anatomical and Histological Factors Affecting Intranasal Drug and Vaccine Delivery

The aim of this review is to provide an understanding of the anatomical and histological structure of the nasal cavity, which is important for nasal drug and vaccine delivery as well as the development of new devices. The surface area of the nasal cavity is about 160 cm(2), or 96 m(2) if the microvilli are included. The olfactory region, however, is only about 5 cm(2) (0.3 m(2) including the microvilli). There are 6 arterial branches that serve the nasal cavity, making this region a very attractive route for drug administration. The blood flow into the nasal region is slightly more than reabsorbed back into the nasal veins, but the excess will drain into the lymph vessels, making this region a very attractive route for vaccine delivery. Many of the side effects seen following intranasal administration are caused by some of the 6 nerves that serve the nasal cavity. The 5(th) cranial nerve (trigeminus nerve) is responsible for sensing pain and irritation following nasal administration but the 7(th) cranial nerve (facial nerve) will respond to such irritation by stimulating glands and cause facial expressions in the subject. The first cranial nerve (olfactory nerve), however, is the target when direct absorption into the brain is the goal, since this is the only site in our body where the central nervous system is directly expressed on the mucosal surface. The nasal mucosa contains 7 cell types and 4 types of glands. Four types of cells and 2 types of glands are located in the respiratory region but 6 cell types and 2 types of glands are found in the olfactory region.