The epiglottis is a leaf-shaped flap of tissue located in the throat, situated at the junction between the pharynx and the larynx. It rests behind the tongue, above the opening to the larynx. This structure acts as a valve, remaining upright during breathing to allow air into the trachea and lungs. When a person swallows, the epiglottis rapidly changes position to divert food and liquid away from the airway and into the esophagus, preventing aspiration.
The Core Material: Elastic Cartilage
The epiglottis is constructed almost entirely from elastic cartilage. This specialized cartilage provides a skeletal framework that is both firm for support and extremely flexible. The matrix contains a dense network of elastin fibers, which gives the tissue a yellowish color and a springy texture.
This composition differs from hyaline cartilage, the more common, rigid type found in the trachea and most of the larynx, which contains predominantly collagen fibers. Elastic cartilage’s high concentration of elastin allows it to be repeatedly bent and deformed during swallowing without suffering structural damage. Chondrocytes, the cells maintaining the cartilage matrix, are embedded within this network, ensuring the structure’s resilience and ability to snap back to its original, upright shape after each movement.
Protective Layers and Supporting Tissue
The flexible cartilage core is enveloped by a mucous membrane, which provides outer protection and lubrication. The two surfaces of the epiglottis are lined with different types of epithelium, reflecting the distinct environments they face. The forward-facing, or lingual, surface is covered by stratified squamous non-keratinized epithelium, which provides a durable layer similar to the lining of the mouth.
Conversely, the back, or laryngeal, surface is lined with pseudostratified ciliated columnar epithelium, typical of the respiratory tract. This lining contains mucus-secreting goblet cells that trap small foreign particles and move them away from the lungs. Seromucous glands in the underlying lamina propria provide moisture, aiding in the smooth passage of a food bolus. The epiglottis is held in place by the thyroepiglottic ligament, which anchors it to the thyroid cartilage, and the hyoepiglottic ligament, which attaches it to the hyoid bone.
Structure and Its Role in Preventing Aspiration
The structural elements of the epiglottis facilitate its precise and rapid movement during swallowing. Coordinated muscular action causes the larynx and the attached hyoid bone to lift and shift forward. This movement creates a space beneath the epiglottis and causes the back of the tongue to exert pressure on the flap.
This pressure, combined with the movement of the larynx, passively forces the epiglottis to fold backward and downward. The folding action creates a tight seal over the glottis, the entrance to the trachea. The food or liquid bolus is then deflected over the lubricated surfaces of the epiglottis and directed into the esophagus.