The glottis is the part of the larynx that includes the vocal cords (vocal folds) and the space between them, known as the rima glottidis. It serves as a crucial structure involved in sound production and airflow regulation. The glottis is highly dynamic, capable of opening and closing to control the passage of air into and out of the respiratory tract. It consists of membranous and cartilaginous parts, supported by the arytenoid cartilages, which help in its movement. The glottis is lined with a mucous membrane to maintain moisture and protect against friction during vibration.
Location
The glottis is located within the larynx (voice box), situated between the pharynx above and the trachea below. It lies at the level of the C3 to C6 vertebrae in the neck and is positioned directly above the subglottic region and below the supraglottic structures of the larynx.
Anatomy
Structure of the Glottis
The glottis is a complex structure within the larynx, consisting of the vocal cords (vocal folds) and the rima glottidis, which is the opening between the vocal cords. It plays a structural and mechanical role in controlling airflow and sound production. The glottis is divided into two parts:
- Membranous Glottis – The anterior two-thirds formed by the vibrating portion of the vocal cords, composed primarily of soft tissue.
- Cartilaginous Glottis – The posterior one-third supported by the arytenoid cartilages, which allow movement and tension adjustments.
The combined structure provides flexibility and strength to perform precise movements necessary for vocalization and airway protection.
Rima Glottidis
The rima glottidis is the space between the vocal cords that varies in size depending on the activity:
- Wide Open – During breathing, especially deep inhalation, the rima glottidis is fully open.
- Partially Closed – During phonation, it narrows to allow vibration.
- Completely Closed – During swallowing or activities like straining, it closes tightly to prevent air escape.
Layers of the Vocal Folds within the Glottis
The vocal folds within the glottis have a layered structure that supports vibration and movement:
- Epithelium – The outermost layer made of stratified squamous epithelium, providing protection against mechanical stress.
- Superficial Lamina Propria – A soft, gelatinous layer that allows flexibility and vibration.
- Intermediate Lamina Propria – Contains elastic fibers, adding strength and elasticity.
- Deep Lamina Propria – Composed of collagen fibers that provide structural support.
- Vocalis Muscle – The deepest layer formed by the thyroarytenoid muscle, responsible for tension adjustments and movement of the vocal cords.
Cartilaginous Support
The glottis is supported by cartilaginous structures that assist in movement and stability:
- Arytenoid Cartilages – Paired cartilages located posteriorly that control the opening and closing of the rima glottidis.
- Thyroid Cartilage – Provides anterior attachment for the vocal cords and structural protection.
- Cricoid Cartilage – Located below the glottis, offering additional support for movements.
Ligaments and Membranes
Several ligaments and membranes secure the glottis within the larynx:
- Vocal Ligament – Provides structural support within the vocal cords.
- Conus Elasticus – Connects the vocal cords to the cricoid cartilage, maintaining tension and elasticity.
- Cricothyroid Ligament – Allows movement and adjustments in vocal cord length.
Muscles Associated with the Glottis
Intrinsic laryngeal muscles control the movements of the glottis:
- Adductor Muscles – Close the glottis by bringing the vocal cords together (e.g., lateral cricoarytenoid and arytenoid muscles).
- Abductor Muscles – Open the glottis by separating the vocal cords (e.g., posterior cricoarytenoid muscle).
- Tensor Muscles – Increase tension on the vocal cords for pitch modulation (e.g., cricothyroid muscle).
- Relaxer Muscles – Reduce tension to lower pitch (e.g., thyroarytenoid muscle).
Blood Supply
The glottis is richly vascularized to support its high metabolic activity:
- Arterial Supply – Provided by the superior laryngeal artery and inferior laryngeal artery, branches of the thyroid arteries.
- Venous Drainage – Blood drains through the laryngeal veins into the internal jugular vein.
Nerve Supply
The glottis is innervated by branches of the vagus nerve (Cranial Nerve X):
- Superior Laryngeal Nerve – Provides sensory innervation above the glottis and motor supply to the cricothyroid muscle.
- Recurrent Laryngeal Nerve – Provides motor innervation to all intrinsic laryngeal muscles except the cricothyroid and sensory innervation below the vocal cords.
Lymphatic Drainage
The lymphatic drainage of the glottis is distinct due to minimal lymphatic channels in the vocal cords, limiting early spread of infections and cancers. Lymph drains primarily into the deep cervical lymph nodes located along the internal jugular vein.
Microscopic Anatomy
Under the microscope, the glottis exhibits:
- Epithelium – Stratified squamous epithelium on the vocal cords for durability.
- Mucosal Glands – Secrete mucus for lubrication and protection.
- Elastic Fibers – Provide flexibility for vibration and movement.
Function
Airflow Regulation
The glottis acts as a valve to regulate the flow of air into and out of the lungs.
- Open Position (Abduction) – During breathing, the glottis opens widely to allow unobstructed airflow through the trachea.
- Closed Position (Adduction) – During swallowing or activities like straining, the glottis closes completely to prevent airflow and protect the airway.
- Partial Closure – Adjustments in the size of the glottis control airflow during activities such as whispering or speaking softly.
Voice Production (Phonation)
The glottis is essential for phonation, the production of sound.
- Vibration of Vocal Cords – When air from the lungs passes through the partially closed glottis, it causes the vocal cords to vibrate, generating sound waves.
- Pitch Control – Muscles around the glottis adjust the tension and length of the vocal cords to produce sounds of varying pitches. Tightened cords create higher-pitched sounds, while relaxed cords produce lower-pitched tones.
- Volume Control – The amount of air pressure passing through the glottis determines the loudness of the sound.
Airway Protection
The glottis plays a protective role by preventing foreign substances from entering the trachea and lungs.
- Closure During Swallowing – The glottis closes tightly during swallowing to stop food or liquids from entering the respiratory tract.
- Cough Reflex Activation – If any foreign particle irritates the vocal cords, the glottis triggers a cough reflex to expel the object and clear the airway.
Pressure Regulation and Stabilization
The glottis contributes to intra-abdominal and intrathoracic pressure regulation through a mechanism called the Valsalva maneuver.
- Valsalva Maneuver – The glottis closes while the abdominal and chest muscles contract, generating increased pressure.
- Applications – This pressure is essential during activities such as:
- Lifting heavy objects.
- Childbirth.
- Defecation and urination.
Respiratory Resistance and Filtration
The glottis helps to modulate respiratory resistance by adjusting its size, especially during activities like singing or playing wind instruments.
- It filters air by trapping dust, particles, and pathogens in the mucus lining the vocal cords.
- The mucus also maintains moisture and prevents the drying of airway tissues.
Control of Breathing During Speech
The glottis coordinates breathing with speech and vocalization.
- It alternates between opening for inhalation and partial closure for phonation, ensuring a smooth balance between airflow and sound production.
- The movement of the glottis contributes to pausing and emphasizing words during speech.
Reflexive and Sensory Functions
The glottis contains sensory receptors that detect mechanical and chemical irritants.
- These receptors help trigger reflex actions such as coughing, throat clearing, and gag reflexes, protecting the airway from harmful substances.
- Sensory feedback also assists in maintaining precise control over vocal cord movement and positioning.
Clinical significance
The glottis is crucial for breathing, voice production, and airway protection, making it vulnerable to various disorders. Glottic stenosis, a narrowing of the glottis, can obstruct airflow, leading to breathing difficulties and requiring surgical intervention. Laryngitis, often caused by infections, vocal strain, or allergies, can lead to swelling of the glottis, resulting in hoarseness or voice loss.
Vocal cord paralysis, caused by nerve damage, trauma, or neurological conditions, may affect glottic function, leading to speech and breathing problems. In severe cases, acute airway obstruction may occur, necessitating emergency procedures such as tracheostomy. Glottic tumors, including laryngeal cancer, may cause persistent hoarseness and require early diagnosis for effective treatment.
Evaluation of glottic disorders often involves laryngoscopy and imaging studies, while treatments range from speech therapy and medications to surgery and voice rehabilitation techniques.
