Epiglottis

The epiglottis is a leaf-shaped flap of cartilage located at the root of the tongue that plays a crucial role in protecting the airway during swallowing. It is composed primarily of elastic cartilage and is covered by a mucous membrane. The epiglottis acts as a movable lid that helps direct food and liquids away from the trachea and into the esophagus during swallowing.

Location

The epiglottis is located at the upper part of the larynx (voice box), just above the glottis and behind the tongue. It sits at the level of the C3 to C6 vertebrae in the neck. The epiglottis is connected to the thyroid cartilage and extends upward toward the pharynx.

Structure and Anatomy

The epiglottis is a crucial anatomical structure within the larynx that functions as a protective barrier during swallowing. Its anatomical design allows it to function efficiently within the respiratory and digestive systems. Below is a detailed description of the epiglottis’ anatomy.

Shape and Structure

• The epiglottis is leaf-shaped and consists primarily of elastic cartilage. It is broad at the top and tapers toward the bottom, resembling the shape of a leaf or spoon. This structure provides the epiglottis with the flexibility and durability it needs to move and cover the laryngeal inlet during swallowing.
• The outer surface of the epiglottis is covered by a layer of mucous membrane, which helps protect it and aids in its smooth movement during the swallowing process. The mucosa covering the epiglottis is a stratified squamous epithelium on its upper surface, which transitions into pseudostratified columnar epithelium in the lower regions.

Cartilaginous Composition

The epiglottis is composed mainly of elastic cartilage, which gives it a flexible yet sturdy structure. Unlike hyaline cartilage, elastic cartilage can bend and return to its original shape without damage, which is essential for the epiglottis’ repetitive movements.

Elastic Cartilage: This type of cartilage allows the epiglottis to perform its function of bending backward to cover the glottis during swallowing and then returning to its upright position to open the airway after swallowing.

Attachments

• Thyroid Cartilage: The epiglottis is anchored to the inner surface of the thyroid cartilage at its inferior end via the thyroepiglottic ligament. This attachment allows it to pivot backward and forward as it covers or uncovers the airway.
• Hyoid Bone: The epiglottis is also connected to the hyoid bone via the hyoepiglottic ligament, which helps hold it in place and provides structural support during movement.
• Base of the Tongue: The upper part of the epiglottis is connected to the base of the tongue through the median glossoepiglottic fold and lateral glossoepiglottic folds. These folds create the small depressions on either side of the epiglottis known as the valleculae, which are important anatomical landmarks during swallowing.

Mucosal Surface

The surface of the epiglottis is covered by a mucous membrane that varies depending on its location:

• Anterior Surface: The anterior (or lingual) surface of the epiglottis, facing the tongue, is covered by stratified squamous epithelium, which provides protection from mechanical abrasion caused by food or other objects passing through the pharynx.
• Posterior Surface: The posterior surface of the epiglottis, which faces the laryngeal inlet, transitions into pseudostratified columnar epithelium with cilia, particularly in its lower portion, which helps move mucus and debris away from the airway.

Muscles Associated with the Epiglottis

The movement of the epiglottis is indirectly controlled by several muscles associated with the larynx and pharynx, which elevate or depress it during the swallowing process.

• Suprahyoid Muscles: These muscles, which include the mylohyoid, geniohyoid, and digastric muscles, raise the hyoid bone during swallowing. Since the epiglottis is attached to the hyoid bone via the hyoepiglottic ligament, elevation of the hyoid bone indirectly raises the epiglottis.
• Aryepiglottic Muscles: These muscles, part of the intrinsic laryngeal muscles, assist in pulling the epiglottis backward to cover the laryngeal inlet during swallowing, helping to protect the airway from ingested food and liquids.

Blood Supply

The epiglottis receives its blood supply from branches of the superior laryngeal artery and the superior thyroid artery.

• Superior Laryngeal Artery: A branch of the superior thyroid artery, this artery supplies blood to the upper part of the larynx, including the epiglottis.
• Superior Thyroid Artery: A branch of the external carotid artery, this artery provides oxygenated blood to the laryngeal structures, including the epiglottis.

Innervation

The sensory innervation of the epiglottis is provided by the internal branch of the superior laryngeal nerve, a branch of the vagus nerve (cranial nerve X).

Sensory Function: The internal branch of the superior laryngeal nerve provides sensory innervation to the mucous membrane of the epiglottis. This innervation is essential for triggering the swallowing reflex and the gag reflex when the epiglottis or surrounding structures are stimulated.

Lymphatic Drainage

The lymphatic drainage of the epiglottis flows to the deep cervical lymph nodes and prelaryngeal nodes. These nodes help filter lymph and prevent infections from spreading to the surrounding tissues.

• Deep Cervical Nodes: These lymph nodes are part of the network that drains lymph from the laryngeal structures, including the epiglottis.
• Prelaryngeal Nodes: These lymph nodes are located around the larynx and receive lymphatic drainage from the surrounding areas, including the epiglottis.

Function

The epiglottis serves as a critical structure within the respiratory and digestive systems, functioning primarily to protect the airway during swallowing and to aid in regulating airflow during breathing and speech. Below is a detailed explanation of its functions.

Airway Protection During Swallowing

The most important function of the epiglottis is to prevent food, liquids, and foreign objects from entering the airway during swallowing.

• Swallowing Reflex: When food or liquid is swallowed, the epiglottis automatically folds down to cover the opening of the glottis (the space between the vocal cords) and the laryngeal inlet. This prevents food and liquids from entering the trachea and directs them into the esophagus.
• Movement Coordination: The movement of the epiglottis is tightly coordinated with the actions of the tongue, hyoid bone, and larynx during swallowing. As the tongue pushes food toward the back of the throat, the larynx elevates, and the epiglottis folds backward. This seals the airway and ensures that ingested material is safely routed into the digestive system.
• Prevention of Aspiration: By covering the glottis, the epiglottis plays a crucial role in preventing aspiration, a condition where food or liquids accidentally enter the airway, potentially leading to choking, infections such as aspiration pneumonia, or even life-threatening airway obstruction.

Regulation of Airflow During Breathing

Although its primary role is in protecting the airway during swallowing, the epiglottis also aids in regulating airflow during respiration.

• Resting Position: In its resting position, the epiglottis stands upright, allowing air to pass freely through the larynx and into the trachea. This unobstructed airflow ensures that oxygen reaches the lungs and carbon dioxide is expelled.
• Breathing Modulation: During speech or certain breathing maneuvers, the position of the epiglottis can influence airflow and pressure. The precise regulation of the epiglottis, along with the vocal cords, helps in the modulation of airflow and contributes to various respiratory reflexes.

Role in Speech and Sound Production

The epiglottis plays a secondary, yet important, role in speech by contributing to the shaping of sounds produced in the larynx, particularly in specific languages that use epiglottal sounds.

• Vocal Modulation: The epiglottis, along with the vocal cords, can influence the resonance and quality of sound produced during phonation (voice production). Although it is not directly involved in producing sound, its position and movement can affect airflow and sound vibration within the larynx, influencing the tone of the voice.
• Epiglottal Sounds: In some languages, the epiglottis contributes to the formation of specific epiglottal consonants, where airflow is restricted by the epiglottis. These sounds are rare but are seen in languages such as Arabic and certain Caucasian languages. In these cases, the epiglottis works in conjunction with the vocal cords to produce the characteristic sounds.

Initiating the Cough Reflex

The epiglottis plays an important role in the cough reflex, a protective mechanism that helps clear the airway when foreign particles or irritants enter the larynx.

• Sensory Stimulation: When irritants such as dust, food particles, or fluids come into contact with the laryngeal mucosa or the epiglottis itself, sensory receptors are triggered. These receptors send signals to the brain, which activates the cough reflex.
• Forceful Expulsion: The epiglottis works with the vocal cords to close the airway temporarily during the cough reflex. This closure allows pressure to build up in the lungs. When the vocal cords and epiglottis suddenly open, the trapped air is forcefully expelled, clearing the airway of irritants and protecting the lungs from potential harm.

Facilitation of Swallowing

The epiglottis aids in guiding food and liquids toward the esophagus during swallowing by serving as a physical barrier and directing mechanism.

• Channeling Bolus: As the epiglottis folds down, it helps guide the food bolus (the mass of chewed food) toward the esophageal opening while preventing it from entering the larynx and trachea. This coordination ensures that the bolus passes into the digestive tract without interfering with the respiratory pathway.
• Formation of Valleculae: The epiglottis also forms two small depressions called the valleculae between its base and the tongue. These valleculae serve as temporary holding areas for food or liquid during swallowing, helping to facilitate the smooth movement of the bolus toward the esophagus.

Reflexive Functions and Sensory Role

The epiglottis is also involved in several reflexive functions, thanks to its sensory innervation from the superior laryngeal nerve (a branch of the vagus nerve).

• Gag Reflex: The gag reflex can be triggered if the epiglottis or the surrounding tissues are stimulated by a foreign object, such as during medical procedures or accidental contact with food. This reflex helps protect the airway from objects that could cause choking or airway blockage.
• Swallowing Reflex: The sensory innervation of the epiglottis also contributes to the swallowing reflex, which ensures that the epiglottis folds down during the act of swallowing to properly protect the airway and direct food into the esophagus.

Clinical Significance

The epiglottis is crucial for protecting the airway during swallowing, and any dysfunction can lead to serious medical conditions. Epiglottitis, an inflammation of the epiglottis, can cause swelling and potentially life-threatening airway obstruction, particularly in children. It often requires emergency treatment, including airway management. Aspiration can occur if the epiglottis fails to properly close over the airway during swallowing, leading to food or liquids entering the trachea, which can result in aspiration pneumonia or choking.

In certain medical procedures, such as intubation or endoscopy, the epiglottis is carefully navigated to avoid damaging it or blocking the airway. Its role in the cough and gag reflexes is also significant for protecting the lungs from foreign objects. Therefore, the epiglottis is a critical component of both the respiratory and digestive systems, and its proper functioning is essential for overall health and safety during swallowing and breathing.