Читать книгу Understanding Anatomy and Physiology in Nursing - John Knight - Страница 149

The nose functions as the primary inlet for air during inspiration. The upper, rigid section of the external nose is formed by the nasal bones and the frontal process of the maxilla (upper jaw bone); the lower and more flexible section is composed of hyaline cartilage. Air enters the nose through the nostrils (external nares) and passes into the nasal cavity which is divided into left and right portions by the nasal septum.

Within the nostrils, coarse hairs called vibrissae provide the first line of defence against larger airborne particles, e.g. soot, sawdust and small insects. The primary function of the nose and nasal cavity is to condition the inspired air by adding moisture (humidification) and progressively warming it so that it is closer to the inner (core) body temperature. The turbinates or conchae are bony structures which form shelf-like projections into the nasal cavities on both sides. As air enters the nose, it diverges into the left and right nasal cavities. On reaching the turbinates, airflow becomes turbulent (swirling movement), slowing its progress and allowing air to remain in contact with the warm respiratory epithelium for longer. The nasal cavities are lined by a pseudostratified epithelium, with microscopic hair-like structures called cilia projecting from the surface.

Mucus, produced by goblet cells, is secreted onto the epithelial surface to form a protective barrier, trapping pathogens and other particulate materials. The cilia move in a coordinated sweeping motion, shifting the mucus, and any trapped particulates, to the pharynx (throat) to be swallowed or expectorated. As well as acting as a physical barrier, mucus contains immune cells, secretory antibodies and an antimicrobial enzyme called lysozyme, which rapidly breaks down bacterial cell walls. A huge network of capillaries sits just below the nasal epithelium, facilitating rapid warming of air which reaches a temperature of approximately 34°C by the time it exits the nasal cavity at the nasopharynx.