Upper respiratory system

The respiratory system is a gas exchange system that can be divided into two main parts: The upper respiratory system (including nasopharynx, olfactory epithelium, larynx and trachea) and the lung (bronchus and the lung). The system starts at the nostrils and then leads on to the two nasal passages, which are the channels for air through the nose and are coated with respiratory mucus membranes that help move mucus to the throat. Olfactory epithelium is a special epithelial tissue in the nasal cavity, which is responsible for directly detecting odors. The larynx is an organ located below the pharynx, involving in breathing, generating sounds and protecting the trachea from inhaling food. The trachea is the extension from larynx that branches into the two primary bronchi. The porcine trachea is notably longer and more cartilaginous than the human trachea.

The nasopharynx and olfactory epithelium histologically consists of three main layers:

• The mucosa, consisting of epithelium, which is the most superficial, and lamina propria, which forms the tissue beneath the epithelium.
• The submucosa, a connective tissue layer.
• The adventitia, the deepest layer separating the nasopharynx and olfactory epithelium from the surrounding tissues.