Epiglottis

Structure

The epiglottis is leaf-like elastic cartilage. Its narrow base is called the stalk (petiolus) and it is attached to the laryngeal prominence of the thyroid cartilage via an elastic ligamentous band called the thyroepiglottic ligament. The lateral margins of the epiglottis are connected with the arytenoid cartilages of the larynx via the aryepiglottic folds. Each fold contains the aryepiglottic muscle, which plays an important role in the movements of the epiglottis. The upper end of the epiglottis is free and it projects posterosuperiorly from the stalk, passing anterior to the laryngeal inlet and behind the body of hyoid bone and the base of the tongue.

The epiglottis has two surfaces; lingual (anterior) and laryngeal (posterior).

• The lingual surface of the epiglottis is covered by the mucosa of the oral cavity. More specifically, by the non-keratinized stratified squamous epithelium, which usually contains some taste buds as well. The mucosa of the lingual surface reflects onto the lateral pharyngeal walls and the pharyngeal surface of the tongue, forming the two lateral glossoepiglottic folds and a median glossoepiglottic fold, respectively. This creates a shallow depression on each side of the median and lateral glossoepiglottic folds, called the epiglottic vallecula. The inferior part of the lingual surface of the epiglottis lies posterior to the hyoid bone and thyrohyoid membrane. The space between this surface and the thyrohyoid membrane is called the pre-epiglottic space and it is filled with adipose tissue and lymphatics. The hyoepiglottic ligament connects the lingual surface with the superior margin of the hyoid bone. 
• The laryngeal surface, however, has the same epithelial covering as the respiratory system; the ciliated pseudostratified columnar epithelium. It makes up the anterior wall of the laryngeal vestibule.

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Innervation and blood supply

The epiglottis and its taste buds are sensory innervated by the internal laryngeal branch of superior laryngeal nerve, which is a branch of the vagus nerve (CN X).

The epiglottis is vascularized by the superior laryngeal artery, a branch of the superior thyroid artery. The lymphatic drainage of this area happens via the deep cervical lymph nodes.

Test your knowledge on the histology of the tongue and epiglottis with this quiz.

Function

The function of the epiglottis is to seal the laryngeal inlet during swallowing and so to prevent the aspiration of the food and liquid into the lungs. The movements of the epiglottis are regulated by the passive movements of the tongue and hyoid bone and by the actions of the aryepiglottic muscles.

• In the initial stage of swallowing, the tongue pushes the food towards the oropharynx. During this process, the base of the tongue puts the pressure upon the epiglottis, bending it posteriorly.  
• The suprahyoid muscles pull the hyoid bone anterosuperiorly. The hyoid bone, then, due to its attachment to the epiglottis via hyoepiglottic ligament, pulls the stalk of epiglottis in the same direction. This results in further moving of the free end of the epiglottis in the opposite direction, i.e. posteriorly towards the laryngeal inlet.
• Finally, the aryepiglottic muscles which attach to the lateral margins of the epiglottis, pull the epiglottis towards the larynx and seal the laryngeal inlet. They perform this action in synergy with the oblique arytenoid and transverse arytenoid muscles.

Once the deglutition is over, the base of the tongue and suprahyoid muscles relax, and so do the aryepiglottic muscles. This leads to returning the epiglottis into its initial position and to re-establishing the patency of the respiratory airways so that the breathing can be continued.

Some authors suggest that the aryepiglottic muscle contraction isn’t enough to move the epiglottis and that this process is facilitated by the physical pressure of food that leans onto the posterior surface of the epiglottis.

Histology

The mucosa of the lingual surface of the epiglottis (as well as half of the laryngeal surface) is continuous with that of the laryngopharynx. It is lined with stratified squamous non keratinized epithelium (lingual mucosa), while the other half of its laryngeal surface is lined by pseudostratified ciliated columnar epithelium. Deep within the lamina propria of the mucosa are seromucous glands.

Elastic cartilage in the center of the epiglottis provides scaffolding for the overlying mucosa. Both surfaces of the epiglottis are equipped with diffuse lymphoid tissue and taste buds.