Anatomy and Physiology of Pharynx

The pharynx is a broad, conical fibromuscular tube forming the upper segment of the air and food passages. Situated posterior to the nasal cavity, oral cavity, and larynx, it spans a length of 12–14 cm, extending from the pharyngeal tubercle at the skull base (basiocciput and basisphenoid) to the lower border of the cricoid cartilage (C6), it becomes continuous to the oesophagus. The width of the pharynx measures approximately 3.5 cm at its base, narrowing to 1.5 cm at the pharyngo-esophageal junction, which is the narrowest segment of the digestive tract apart from the appendix. The pharynx serves as a continuation of the common pathway for both respiration and digestion that begins in the oral cavity.

The pharynx directs air into the laryngeal inlet and food into the digestive tract. It facilitates the equalization of pressure within the middle ear through the eustachian tube and contributes to vocalization, aiding in speech.

Boundaries of the Pharynx

• Superiorly: Basisphenoid and basiocciput
• Inferiorly: Esophagus
• Posteriorly: Retropharyngeal space and vertebral column
• Anteriorly: Nasal cavity, oral cavity, and larynx

Structure of the Pharyngeal Wall

The pharyngeal wall comprises five primary layers, listed from innermost to outermost:

• Mucous Membrane
• Submucosa
• Pharyngeal Aponeurosis (Pharyngobasilar Fascia)
• Muscular Coat
• Buccopharyngeal Fascia (Loose Areolar Sheath)

1. Mucous Membrane. The mucous membrane lines the pharyngeal cavity and is continuous with the mucous membranes of the eustachian tubes, nasal cavities, mouth, larynx, and oesophagus. The nasopharynx is lined with ciliated pseudostratified columnar epithelium, while the rest of the pharynx has non-keratinized stratified squamous epithelium. Numerous mucous glands are scattered throughout this layer.
2. Submucosal Layer. The submucosal layer, or lamina propria, is situated beneath the mucosa and comprises connective tissue with elastic fibres. This layer also contains aggregates of gut-associated lymphoid tissue that form Waldeyer’s ring. The submucosa is thick and integrates with the fibrous pharyngobasilar layer, which also forms the tonsillar capsule.
3. Pharyngeal Aponeurosis (Pharyngobasilar Fascia). This fibrous layer lines the muscular coat, particularly thick near the skull base but thin and indistinctly. It fills the gap left in the muscular coat near the skull base.
4. Muscular Coat. The muscular coat consists of two layers of muscles, each with three muscles. The constrictor muscles have fibres oriented in a circular direction relative to the pharyngeal wall, while the longitudinal muscle fibres are oriented vertically.
   • External Layer (Constrictor Muscles): This layer includes the superior, middle, and inferior constrictor muscles, which constrict the pharynx during swallowing. All constrictor muscles are innervated by the pharyngeal branch of the vagus nerve [X].
   • Internal Layer (Longitudinal Muscles): This layer includes the stylopharyngeus, salpingopharyngeus, and palatopharyngeus muscles, which elevate the pharyngeal wall during swallowing. The stylopharyngeus is innervated by the pharyngeal branch of the glossopharyngeal nerve [IX], while the other two are supplied by the pharyngeal branch of the vagus nerve [X]. (All the muscles of the pharynx are supplied by the vagus nerve except the stylopharyngeus which is supplied by the glossopharyngeal nerve).
5. Buccopharyngeal Fascia. A thin layer that coats the outside of the muscular part of the wall and is a component of the pretracheal layer of cervical fascia.

 

Divisions of the Pharynx. 

Based on these anterior relationships the pharynx is arbitrarily subdivided into three parts:

• Nasopharynx (Epipharynx)
• Oropharynx
• Hypopharynx (Laryngopharynx)

Nasopharynx (Epipharynx)

It is the uppermost part of the pharynx, located behind the posterior choanae of the nasal cavities. It extends from the pharyngeal tubercle at the skull base to the soft palate or the level of the horizontal plane passing through the hard palate. The nasopharyngeal space comprises a roof, posterior wall, anterior wall, two lateral walls and a floor that communicates with the oropharynx below via the pharyngeal isthmus.

• Roof: Formed by the sloping base of the skull, comprising the posterior part of the body of the sphenoid bone and the basilar part of the occipital bone. The roof and posterior wall are contiguous due to the sloping nature of these bones. A large collection of lymphoid tissue, known as adenoids are located at the junction of the roof and posterior wall. Adenoids are subepithelial lymphoid tissue collections and they increase in size until about six years of age, then gradually disappear.
• Posterior Wall: Formed by the arch of the atlas vertebra covered by prevertebral muscles and fascia.
• Floor: Formed by the soft palate anteriorly, deficient posteriorly, allowing communication with the oropharynx.
• Anterior Wall: Formed by the posterior nasal apertures or choanae, separated by the posterior border of the nasal septum.
• Lateral Wall: The lateral wall of the nasopharynx consists mainly of the superior constrictor muscle and its overlying mucosa. Each lateral wall features the pharyngeal opening of the eustachian tube, located approximately 1.25 cm behind the posterior end of the inferior turbinate. Opening is at the level of the superior border of the palate or the floor of the nose. This opening is surrounded by an elevation known as the torus tubarius, created by the cartilage of the eustachian tube. Above and behind this elevation lies a recess called the fossa of Rosenmüller, which is the most common site for nasopharyngeal carcinoma and is crucial for targeted biopsies when investigating carcinoma of an unknown primary origin. Additionally, a ridge known as the salpingopharyngeal fold extends from the lower end of the torus tubarius to the lateral pharyngeal wall, raised by the underlying muscle.

Lymphatic Drainage. The lymphatics of the nasopharynx, including those of the adenoids and the pharyngeal end of the eustachian tube, drain into the upper deep cervical jugular nodes. This drainage occurs either directly or indirectly through the retropharyngeal and parapharyngeal lymph nodes. Additionally, these lymphatics drain into the spinal accessory chain of nodes located in the posterior triangle of the neck. Lymphatic drainage can also cross the midline to the contralateral lymph nodes.

Functions of the Nasopharynx

1. Air Conduction: The nasopharynx serves as a passageway for air, warmed and humidified in the nose, as it moves towards the larynx and trachea.
2. Middle Ear Ventilation: Through the eustachian tube, the nasopharynx ventilates the middle ear and equalizes air pressure on both sides of the tympanic membrane, which is essential for proper hearing.
3. Isolation During Swallowing and Speech: The elevation of the soft palate against the posterior pharyngeal wall and Passavant’s ridge isolates the nasopharynx from the oropharynx during activities such as swallowing, vomiting, gagging, and speaking.
4. Voice Resonance: The nasopharynx acts as a resonating chamber during voice production. Disorders such as nasopharyngeal obstruction and velopharyngeal incompetence can impact this function.
5. Mucus Drainage: The nasopharynx functions as a drainage channel for mucus secreted by the nasal and nasopharyngeal glands.
6. Pressure Equalization and Vocalization: The nasopharynx helps equalize pressure within the middle ear and assists in vocalization, contributing to speech.

Oropharynx

Boundaries of the Oropharynx

• Anterior Wall: Deficient superiorly and bounded by the anterior boundary of the palatoglossus muscles (anterior pillars), facilitating communication with the oral cavity. Inferiorly, it is formed by the posterior third of the tongue, containing lingual tonsils and valleculae. Valleculae are cup-shaped depressions between the base of the tongue and the anterior surface of the epiglottis, bounded medially by the median glossoepiglottic fold and laterally by the pharyngoepiglottic fold, and are prone to retention cysts.
• Posterior Wall: Related to the retropharyngeal space and lies opposite the second and upper part of the third cervical vertebrae.
• Lateral Wall: Formed by the anterior and posterior pillars and the palatine tonsils located between these pillars.
• Superior Wall: Composed of the soft palate.

Lymphatic Drainage. Lymphatics from the oropharynx drain into the upper jugular chain, particularly the jugulodigastric (tonsillar) node. The soft palate, lateral and posterior pharyngeal walls, and the base of the tongue also drain into the retropharyngeal and parapharyngeal nodes, and subsequently into the jugulodigastric and posterior cervical group. The base of the tongue may drain bilaterally.

Functions of the Oropharynx

1. Conduit for Air and Food: The oropharynx serves as a passageway for both air and food.
2. Facilitation of Deglutition: It plays a crucial role in the pharyngeal phase of swallowing (deglutition).
3. Speech Contribution: The oropharynx contributes to the vocal tract, particularly for the production of certain speech sounds.
4. Taste Appreciation: It aids in taste perception, with taste buds located in the base of the tongue, soft palate, anterior pillars, and posterior pharyngeal wall.
5. Local Defense and Immunity: The oropharynx provides local defense and immunity against harmful intruders in the air and food passages. This function is mediated by subepithelial masses of lymphoid tissues forming Waldeyer’s ring, strategically placed at the entry portals of air and food. B-lymphocytes in the germinal centres of these follicles produce secretory antibodies of the IgA class, while T-lymphocytes in the parafollicular region produce cell-mediated immunity against various pathogens. IgM and IgG antibodies secreted by plasma cells address pathogens entering these lymphoid masses.

 

Hypopharynx (Laryngopharynx)

The hypopharynx, the lowest part of the pharynx, lies behind and partially on the sides of the larynx. It extends from the level of the hyoid bone superiorly (C3) to the lower border of the cricoid cartilage (C6), where it becomes continuous with the oesophagus.

Diagram of Hypopharynx

Clinically, it is subdivided into three regions: the pyriform sinus, the post-cricoid region, and the posterior pharyngeal wall.

1. Bilateral Pyriform Sinus (Fossa): Located on either side of the larynx, extending from the pharyngoepiglottic fold to the upper end of the esophagus, forming a lateral channel for food. Foreign bodies may lodge in the pyriform fossa, and tumors can silently expand within this space until metastatic lymphadenopathy manifests. The internal laryngeal nerve runs submucosally in the lateral wall of the sinus, making it accessible for local anesthesia. Pain is referred to the ear in carcinoma of the pyriform sinus. It is bounded laterally by the thyrohyoid membrane superiorly and the thyroid cartilage inferiorly, and medially by the aryepiglottic fold and posterolateral surfaces of the arytenoid and cricoid cartilages.
2. Post-Cricoid Region (Pharyngo-Esophageal Junction): It forms the anterior wall of the laryngopharynx, extending from the level of the arytenoid cartilages and connecting folds to the inferior border of the cricoid cartilage. It is a common site for carcinoma in females with Plummer–Vinson syndrome.
3. Posterior Pharyngeal Wall: Extends from the level of the hyoid bone superiorly to the lower border of the cricoid cartilage, where the hypopharynx transitions to the esophagus.

Lymphatic Drainage. The pyriform sinus is richly supplied with lymphatics that exit through the thyrohyoid membrane and drain into the upper jugular chain. The posterior wall’s lymphatics terminate in the lateral pharyngeal or parapharyngeal nodes and then drain into the deep cervical lymph nodes. The postcricoid region’s lymphatics also drain into the parapharyngeal nodes, with additional drainage into the nodes of the supraclavicular and paratracheal chains. The rich lymphatic network in the pyriform fossae explains the high frequency of nodal metastases in carcinoma of this region.

Functions of the Hypopharynx.

• The hypopharynx, analogous to the oropharynx, serves an essential role in physiological functions, acting as a critical conduit for both air and food.
• It significantly contributes to the vocal tract, enhancing the resonance of specific speech sounds.
• It helps in the process of deglutition.
• Proper coordination between the contraction of the pharyngeal muscles and the relaxation of the cricopharyngeal sphincter at the upper end of the oesophagus is imperative.
• A lack of this coordination, as observed in instances where the cricopharyngeal sphincter fails to relax during the contraction of the pharyngeal muscles, can result in serious consequences, such as the formation of a hypopharyngeal diverticulum.

Other important structures:

Killian’s Dehiscence

Killian’s dehiscence is a potential gap between the thyropharyngeus (with oblique fibres) and cricopharyngeus (with transverse fibres) parts of the inferior constrictor muscle. This gap is known as the “gateway of tears” because perforation can occur here during esophagoscopy. It is also the site for the herniation of pharyngeal mucosa in cases of pharyngeal pouches.

Waldeyer’s Ring. Waldeyer’s ring consists of lymphoid tissue aggregates in the subepithelial layer of the nasopharynx and oropharynx. This ring includes:

1. Nasopharyngeal tonsil (adenoids)
2. Palatine tonsils
3. Lingual tonsil
4. Tubal tonsils (in the fossa of Rosenmüller)
5. Lateral pharyngeal bands
6. Nodules (in the posterior pharyngeal wall)

Pharyngeal Spaces. Two potential spaces related to the pharynx where abscesses can form are:

1. Retropharyngeal Space: Located behind the pharynx and extending from the skull base to the bifurcation of the trachea.
2. Parapharyngeal Space: Situated laterally to the pharynx, containing the carotid vessels, jugular vein, last four cranial nerves, and the cervical sympathetic chain.

Nasopharyngeal Bursa. An epithelial-lined median recess within the adenoid mass, the nasopharyngeal bursa extends from the pharyngeal mucosa to the periosteum of the basiocciput. It represents the notochord’s attachment to the pharyngeal endoderm during embryonic life and can be the site of persistent postnasal discharge, crusting, or abscess formation (Thornwaldt’s disease).

Rathke’s Pouch. Represented by a dimple above the adenoids, Rathke’s pouch is a remnant of the buccal mucosal invagination that forms the anterior lobe of the pituitary. A craniopharyngioma may arise from this structure.

Tubal Tonsil. Situated at the tubal elevation, the tubal tonsil is a subepithelial lymphoid tissue collection, continuous with adenoid tissue, forming part of Waldeyer’s ring. When infected, it can cause eustachian tube occlusion.

Sinus of Morgagni. The sinus of Morgagni is an anatomical space located between the base of the skull and the upper free border of the superior constrictor muscle. It serves as a conduit for several structures: (i) the eustachian tube, (ii) the levator veli palatini muscle, (iii) the tensor veli palatini muscle, and (iv) the ascending palatine artery, a branch of the facial artery.

Passavant’s Ridge. Passavant’s ridge is a mucosal ridge formed by the fibres of the palatopharyngeus muscle. It encircles the posterior and lateral walls of the nasopharyngeal isthmus. During contraction, the soft palate makes firm contact with this ridge, effectively isolating the nasopharynx from the oropharynx during swallowing and speech.

Epithelial Lining of the Nasopharynx. The nasopharynx, functionally an extension of the nasal cavity, is lined by pseudostratified ciliated columnar epithelium.

———— End of the chapter ————

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Anatomy and Physiology of Pharynx Best Lecture Notes Dr Rahul Bagla ENT Textbook

Reference Textbooks.

• Scott-Brown, Textbook of Otorhinolaryngology-Head and Neck Surgery.
• Cummings, Otolaryngology-Head and Neck Surgery.
• Stell and Maran’s, Textbook of Head and Neck Surgery and Oncology.
• Ballenger’s, Otorhinolaryngology Head And Neck Surgery
• Susan Standring, Gray’s Anatomy.
• Frank H. Netter, Atlas of Human Anatomy.
• B.D. Chaurasiya, Human Anatomy.
• P L Dhingra, Textbook of Diseases of Ear, Nose and Throat.
• Hazarika P, Textbook of Ear Nose Throat And Head Neck Surgery Clinical Practical.
• Mohan Bansal, Textbook of Diseases of Ear, Nose and Throat Head and Neck Surgery.
• Hans Behrbohm, Textbook of Ear, Nose, and Throat Diseases With Head and Neck Surgery.
• Logan Turner, Textbook of Diseases of The Nose, Throat and Ear Head And Neck Surgery.
• Arnold, U. Ganzer, Textbook of  Otorhinolaryngology, Head and Neck Surgery.
• Ganong’s Review of Medical Physiology.
• Guyton & Hall Textbook of Medical Physiology.

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Dr. Rahul Bagla
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Keywords: Bilateral Pyriform Sinus (Fossa), Post-Cricoid Region, Posterior Pharyngeal Wall, Waldeyer’s ring, Adenoids, Anatomy and Physiology of Pharynx, Pharyngeal muscle anatomy, Nasopharynx structure and function, Oropharynx physiological role, laryngopharynx anatomy details, Pharyngeal constrictor muscles function, Soft palate and pharynx interaction, Pharyngeal reflex mechanism, Epiglottis role in swallowing, Pharynx involvement in speech, Pharyngeal anatomy in Respiratory System