Cellular Anatomy and Physiology

The nasal cavity, turbinates, and paranasal sinuses are lined with mucosa comprised of four distinct nasal epithelium populations: olfactory epithelium (OE), stratified squa-mous epithelium (SE), respiratory epithelium (RE), and nonciliated cuboidal/columnar epithelium (NCE), also known as transitional epithelium. Each type has its own unique cell populations and distribution throughout the nasal cavity. SE lines the external nares and vestibule of the nose, RE covers most of the nasoturbinates, maxiloturbinates, septum, and maxillary sinus cavities, OE lines the ethmoid turbinates, and NCE is found in narrow zones of transition between each type (Harkema, 1992; Herbert, 1999). In studies involving rats, Gross et al. (1982) showed the percentage of these epithelium types to be 7% for SE, 46% for RE, and 47% for OE. When compared to humans these values would shift, as OE in humans is restricted to a very small area covering the mid-dorsal aspect of the nasal cavity. Additionally, rodents only possess maxillary and ethmoid sinus cavities, as opposed to the four found in humans.

The external nares and vestibule are completely lined by SE. In rats and mice there are

Figure 1.2. Histological analysis of murine sinuses in a model of acute invasive fungal sinusitis. The arrow indicates hyphal A. fumigatus becoming invasive in the right maxillary cavity. Tissue invasion has occurred in addition to the necrotic tissue surrounding the mass. et = ethmoid turbinates; hp = hard palate; M = maxillary sinus cavity; s = septum.

Figure 1.2. Histological analysis of murine sinuses in a model of acute invasive fungal sinusitis. The arrow indicates hyphal A. fumigatus becoming invasive in the right maxillary cavity. Tissue invasion has occurred in addition to the necrotic tissue surrounding the mass. et = ethmoid turbinates; hp = hard palate; M = maxillary sinus cavity; s = septum.

predominantly basal cells along the basal lamina and several layers of squamous cells, which become progressively flatter toward the luminal surface. This group contains the largest quantity of cells in S phase of the cell cycle, meaning it possesses larger cellular turnover. There are no mucociliary mechanisms in this population as the region most likely functions to protect the subsequent tissues and physiology.

Respiratory epithelium, the predominant cell type in humans, covers most of the turbinates (except for the ethmoid region) as well as the septum and maxillary sinus cavities. In rodents the principle cell types found within the RE are cuboidal cells, goblet cells, brush cells, basal cells, and ciliated and non-ciliated columnar cells. The lamina propria of the RE contains collagen fibers, nerves, mucus, and serous glands, as well as venous sinuses, which dilate to alter the airflow through the passageway (Harkema, 1992).

The OE in humans is limited to a small portion of the nasal cavity and lines the eth moid nasal turbinates. In rodents the epithelium is pseudo-stratified and consists of three primary cell types including supporting cells, olfactory neurons, and basal cells. The lamina propria of OE has blood vessels, unmyeli-nated nerve bundles, and Bowman's glands responsible for the secretion of mucus to moisten the surrounding tissue. Microvilli are present on the epithelium and help move mucus around the region (Herbert, 1999).

Lastly the NCE lies in the transitional zones between different regions, primarily between the SE and RE. It consists of microvilli-covered epithelium, nonciliated cubodial/columnar cells, and basal cells (Harkema, 1992).

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