Pharynx

The pharynx (Latin: pharynx), also known as the throat, is a funnel-shaped muscular organ located in the head and neck that connects the oral and nasal cavities with the esophagus and larynx. It is located posterior to the mentioned cavities and above the esophagus and larynx. Within the pharynx intersect the respiratory and digestive paths. Therefore, it functions as a passageway for the air, liquids and digested food that moves further from the upper to the lower respiratory and digestive system organs.

Pharynx anatomy

The pharynx is approximately 12 - 15 centimeters long, with its superior part extending to the external cranial base but the inferior aspect ending at the sixth cervical vertebra level (C6). The upper part is broader, but the lower portion appears narrower.

The pharynx consists of three parts, and it mainly contains muscles. Therefore, it is also called the muscular pharynx.

Pharynx parts

The pharynx is composed of three anatomical parts. Superior to inferior, they are the nasopharynx, oropharynx and laryngopharynx.

Nasopharynx

The nasopharynx is the nasal part of the pharynx. It is the most superior portion of the pharynx that is located at the first and second cervical vertebrae (C1 - C2) level, posterior and inferior to the nasal cavity. The nasopharynx extends from the external cranial base to the uvula of the soft palate.

The upper aspect (roof) of the nasopharynx is firmly connected with the body of the sphenoid bone, and this connection is called the vault of the pharynx (pharyngeal fornix). The nasopharynx is mainly involved in respiratory processes, and therefore it is considered a part of the respiratory system.

Superior attachment line

The superior attachment line of the pharynx to the external cranial base of the skull goes in the posterior and lateral directions from the pharyngeal tubercle of the occipital bone to the petrous part of the temporal bone. The line crosses the basilar part of the occipital bone and reaches the inferior surface of the petrosal part. It continues to go along the inferior surface forward. It has a sharp turn at the junction site of the sphenoid and temporal bones. The superior attachment line continues to go forward and medially to reach the base of the medial plate of the pterygoid process. It firmly fuses with the medial plate and reaches the pterygoid hamulus.

Walls and anatomical landmarks

The anterior wall connects the nasopharynx to the nasal cavity through two openings called the choanae. In the middle of the lateral wall on either side is located one more opening - the pharyngeal orifice of the auditory tube that connects the nasopharynx with the tympanic cavity of the middle ear.

The tympanic cavity receives the air through the auditory tube. This connection between the middle ear and the nasopharynx helps to equalize the pressure on both sides of the tympanic membrane as it is positioned between the external and middle ear. Also, the pharyngeal opening provides drainage of the middle ear if needed. Along the superior aspect and sides of the pharyngeal opening is positioned the torus tubarius - mucosal elevation that marks the pharyngeal end of the cartilaginous part of the auditory tube.

In the posterior wall, behind the torus tubarius, is a deep fossa called the pharyngeal recess. It is also known as the fossa of Rosenmüller or lateral pharyngeal recess, and it is the most common site for nasopharyngeal carcinoma. More below the pharyngeal opening is another mucosal elevation called the torus levatorius. It is a mucosal fold overlying the levator veli palatini muscle.

Inferior to the torus levatorius can be found one more fold called the salpingopharyngeal fold. It covers the salpingopharyngeal muscle. The junction between the superior and posterior wall is marked by the pharyngeal tonsil. It is unpaired lymphoid tissue aggregation situated above the torus tubarius. The pharyngeal tonsil is also called the adenoid tonsil. Paired tubal tonsil, or the Gerlach's tonsil, is located close to the pharyngeal orifice.

Oropharynx

The oropharynx is the middle part of the pharynx that is located posterior to the oral cavity and is its continuation. The oropharynx is situated approximately at the level of the third and fourth cervical vertebrae (C3 - C4). It extends from the uvula of the soft palate to the superior border of the epiglottis.

This part has only one opening called the oropharyngeal isthmus (oropharyngeal opening). Sometimes it is also referred to as the isthmus of fauces. It is situated anteriorly, connecting the oropharynx with the oral cavity. Overall, it is formed by the uvula, palatine and lingual tonsils, root of the tongue and palatopharyngeal arch.

The palatine and lingual tonsils, the root of the tongue and the superior constrictor muscle are located within the oropharynx. The oropharynx is involved in respiratory and digestion processes, and it is considered a part of the respiratory and digestive systems.

Waldeyer's tonsillar ring

The Waldeyer's tonsillar ring is a lymphoid tissue aggregation composed of several unpaired and paired tonsils. Tonsils are located at the borders of the oral and nasal cavities and pharynx, and their layout resembles a ring. The Waldeyer's tonsilar ring is responsible for immune functions such as protection and defense against various antigens, which enter the human body via nasal and oral cavities. Therefore, the Waldeyer's ring protects both organ systems - respiratory and gastrointestinal. It is composed of six tonsils, of which two are unpaired and two paired:

  • Pharyngeal tonsil - unpaired;
  • Lingual tonsil - unpaired;
  • Palatine tonsils - paired;
  • Tubal tonsils - paired.

The upper part of the ring is formed by the single pharyngeal tonsil, but the inferior part is marked by the lingual tonsil. The lateral aspects of the ring include the tubal tonsils being more superior and palatine tonsils inferior.

Laryngopharynx

The laryngopharynx, also known as the hypopharynx, is the most distal and final part of the pharynx. The laryngopharynx is situated at the level of the fifth and sixth cervical vertebrae (C5 - C6). It extends from the superior edge of the epiglottis to the beginning of the esophagus. It ends at the inferior border of the cricoid cartilage of the larynx. Anteriorly to the laryngopharynx is the larynx, but in the inferior direction, it continues as the esophagus. The laryngopharynx is involved in respiratory and digestion processes. Therefore, it is considered a part of the respiratory and digestive systems.

The laryngopharynx has two openings - the laryngeal inlet (also known as the laryngeal aditus) and the esophageal opening. The first one connects the pharynx with the lower airways, but the second leads into the esophagus. On the sides of the laryngeal inlet is located the piriform fossa or sinus - a slight depression in the lateral walls of the pharynx that extends from the pharyngoepiglottic fold to the esophageal opening.

Within the submucosa of the piriform sinus pass the internal and recurrent laryngeal nerves. The piriform fossa is a common site for entrapment of foreign bodies, and mentioned nerves can get injured during removal procedures. The piriform fossa medially borders with the aryepiglottic fold and posterolateral surfaces of the arytenoid and cricoid cartilages of the larynx. Laterally, it ends with the thyroid membrane and thyroid cartilage.

Muscular pharynx

The pharynx contains two groups of very well-developed skeletal muscles. All muscles have pairs, and the following groups are:

  • Constrictor muscles - circular muscles that constrict the pharynx;
  • Levator muscles - longitudinal muscles that lift the pharynx.

Together with the tongue, soft palate and larynx, the muscles of the pharynx are involved in digestion and provide swallowing.

Constrictor muscles

The constrictor muscles are circular pharyngeal muscles, and they extend from the anterior aspect of the pharynx to its sides and end within the midline of the neck posteriorly. Therefore, constrictor muscle fibers form an incomplete circle. All constrictors share the same function - they constrict and narrow the pharynx.

All muscles produce wave-like consecutive contractions that help to move food bolus and swallow it. Muscle fibers from both sides connect in the middle of the posterior wall forming the median pharyngeal raphe that extends downward from the external cranial base. The pharyngeal constrictors include the following muscles:

  • The superior pharyngeal constrictor is the most superior muscle, and it is located in the oropharynx part. It originates from the medial plate and pterygoid hamulus of the pterygoid process of the sphenoid bone, pterygomandibular raphe of buccopharyngeal fascia, posterior end of the mylohyoid line and lingula of the mandible. Fibers insert into the pharyngeal tubercle of the occipital bone and median pharyngeal raphe.
  • The middle pharyngeal constrictor originates from both horns of the hyoid bone and the stylohyoid ligament. Muscle fibers insert at the median pharyngeal raphe and blend with the fibers of inferior and superior constrictors. The upper aspect of the middle constrictor partially covers the lower part of the superior pharyngeal constrictor. The middle pharyngeal constrictor is primarily located in the laryngopharynx.
  • The inferior pharyngeal constrictor extends from the thyroid and cricoid cartilages to the median pharyngeal raphe. The upper aspect of the muscle partially covers the lower portion of the middle pharyngeal constrictor. It is primarily located in the laryngopharynx.

Levator muscles

The levator muscles are longitudinal pharyngeal muscles. All muscles elevate the pharynx during swallowing by shortening and widening it, and they include the following:

  • The stylopharyngeaus muscle extends from the styloid process of the temporal bone to the posterior border of the thyroid cartilage and lateral glossoepiglottic fold. Also, it blends with pharyngeal constrictors.
  • The palatopharyngeus muscle is not only a muscle of the pharynx, but it is also classified as one the muscles of the soft palate. The palatopharyngeal muscle elevates the pharynx and pulls it superiorly, anteriorly and medially. It shortens the pharynx during swallowing and helps to separate the nasopharynx from the oropharynx. The muscle draws the larynx and esophagus towards the root of the tongue. Also, it tenses the soft palate and brings the palatopharyngeal arches closer together. The palatopharyngeus muscle fibers originate from the palatine aponeurosis and posterior border of the hard palate. They form the palatopharyngeal arch and insert in the superior and posterior border of the thyroid cartilage of the larynx and lateral wall of the pharynx.
  • The salpingopharyngeus muscle helps in pressure-equalizing between the pharynx and middle ear as it elevates the pharynx and helps to open the auditory tube during swallowing. It originates from the inferior cartilaginous part of the auditory tube and ends blending with the palatopharyngeus muscle fibers.

Pharynx histology

The wall of the pharynx consists of four layers:

  • Mucosa
  • Submucosa with pharyngobasilar fascia
  • Muscular layer containing pharyngeal muscles
  • Adventitia

The mucosa covers all parts of the pharynx and, in some areas, it also forms mucosal folds. The pharynx is lined with two different types of epithelium. The nasopharynx contains ciliated respiratory epithelium, and it is a continuation of the mucosa of the nasal cavity. The respiratory epithelium is the ciliated pseudostratified columnar epithelium that contains mucus-producing goblet cells. Other parts of the pharynx are lined by the squamous stratified non-keratinized epithelium.

The connective tissue of the submucosa has many blood vessels and is very vascular. The pharynx contains many mucus-producing pharyngeal glands and mucosa-associated lymphoid tissue (MALT) aggregates that include B and T lymphocytes and macrophages, protecting the pharynx against various antigens.

The upper two-thirds of the pharynx has a very well-developed and thick connective tissue layer that becomes thinner towards the esophagus. The muscular layer is composed of two distinct layers - the inner layer contains longitudinal fibers, but the outer has circular skeletal muscle fibers.

Pharynx functions

The primary function of the pharynx is to provide the passage for the air and food from the oral and nasal cavities to other digestive and respiratory system parts. Primary, the pharynx is involved in digestion and breathing processes.

  • The pharynx is a part of the vocal system, and its form and shape allow to make various speech sounds and help in voice production and resonance.
  • As the pharynx can contain a small number of taste buds, it also participates in taste sensation creation.
  • Pharynx takes part in air conditioning.
  • Pharynx mucosa with lymphoid tissue aggregates helps to provide local immunity and defense against various harmful antigenes.
  • The pharynx provides drainage for secretion for nasal and oral cavities and the middle ear.
  • Help in the pressure equalization on both tympanic membrane sides.

Neurovascular supply of pharynx

Arterial blood supply

  • The arterial blood supply for the pharynx provides ascending pharyngeal artery, a branch of the external carotid artery.
  • Arterial blood perfusion also provides dorsal lingual branch from the lingual artery and ascending palatine artery and tonsillar branches from the facial artery. Both are branches of the external carotid artery.
  • Small pharyngeal branches from the inferior thyroid artery also perfuse the pharynx. The inferior thyroid artery is a branch from the thyrocervical trunk.
  • External carotid artery's terminal branch- a maxillary artery and its branches (greater palatine, pharyngeal and pterygoid arteries) also perfuse pharynx.

Venous drainage

Venous drainage for the pharynx provides the pharyngeal plexus carrying blood next to facial and pharyngeal veins and then to the internal jugular vein.

Lymphatic drainage

Pharyngeal lymphatic vessels drain mostly directly into deep cervical nodes or indirectly via the retropharyngeal located behind the pharynx, paratracheal (along the sides of the trachea), and via infrahyoid lymph nodes.

Innervation

Sensory and motor innervation mainly provides the pharyngeal plexus. It makes the pharyngeal branches of the glossopharyngeal nerve (CN IX), vagus nerve (CN X), and sympathetic trunk's cervical part's superior cervical ganglion fibers.

Motor innervation

All pharyngeal muscles, except the stylopharyngeus muscle, innervates fibers from the vagus nerve (CN X). Stylopharyngeus muscle innervates same-named branches from the glossopharyngeal nerve (CN IX).

Sensory innervation

Mainly pharynx receives the innervation from the glossopharyngeal nerve (CN IX). However, the nasopharynx and hypopharynx innervation involve two more nerves. The upper nasopharynx part innervates branches from the maxillary nerve (CN V2).

The sensory innervation oropharynx primarily receives from the glossopharyngeal nerve (CN IX) branches. The vagus nerve (CN X) innervates only the hypopharynx's inferior part. Innervation supplies the internal laryngeal branch from the superior laryngeal nerve.

Pharynx disorders

Disorders affecting the pharynx are common as, for example, almost always a common cold presents with it. The most common part involved is the oropharynx. Most of the cases are self-limiting and don't need specific treatment. Conditions can affect only the pharynx, or pharynx involvement with presenting symptoms can sign a systemic disease.

Pharyngitis

Pharyngitis, also know as the sore throat, is the inflammation of the pharynx. The most common cause is viral etiology. Pharyngitis can present in cases of the common cold, flu, chickenpox, croup, COVID-19, HIV, and many more to follow. The most common bacterial agent causing pharyngitis is Streptococcus, and the condition is called strep throat. Pharyngitis can also cause:

  • Gastroesophageal reflux disease (GERD) or acid reflux in which the acid from the stomach regularly or periodically flows back in the esophagus and throat because of the weak lower oesophageal sphincter
  • Allergic agents
  • Dryness caused by systemic disorders such as Sjogren's disease or by environmental factors
  • Immunosuppression
  • Pollution
  • Various irritants such as tobacco or a large amount of alcohol consumption
  • Pharynx muscle overwork by speaking too long or too loud
  • Cancers

The risk factors include children and young adults, existing allergies, frequent nose or nose sinus infections, and other existing disorders.

Symptoms

It characterizes by a red and painful throat, discomfort, scratchiness sensation, and irritation, usually in the oropharynx area, issues with swallowing or dysphagia, as well as runny nose, a dry cough can be present. Symptoms typically worsen during swallowing or talking. Pharyngitis can present with enlarged regional lymph nodes and swollen tonsils. Sometimes voice changes, usually hoarse voice, can be present. General symptoms such as weakness, malaise, muscle aches, fever, and headaches can be present depending on the causing factor.

Treatment and prevention

The treatment depends on the causing agent, but usually, the condition is self-limiting without any specific treatment. Nonsteroidal anti-inflammatory drugs can reduce pain and inflammation. In case of bacterial infection, the particular treatment includes antibiotics. Usually, there are no complications, but untreated strep throat can lead to more severe glomerulonephritis or rheumatic fever.

Prevention includes regular hand washing, avoidance of sick people and shared food or dishes, usage of hand sanitizers, especially when in public. Prevention includes practicing good coughing and sneezing hygiene.

Enlarged adenoids

Enlarged adenoids present as swollen and enlarged pharyngeal tonsils. Usually, the inflammation is secondary to an infection. Enlarged adenoids affect breathing as they make it hard to breathe through the nose, resulting in breathing through the mouth. Adenoids start to decrease in size around the age of 4 to 5 years, and around teenage years, they are tiny. It is the reason why enlarged adenoids usually have only children.

Adenoids present with mouth dryness and cracked lips, full feeling in the nasal cavity, runny nose. Sleep apnoea, sleep issues, snoring, and loud breathing can be present. Enlarged adenoids can result in ear infections. Treatment depends on the etiology of the factors. Sometimes adenectomy or adenoid removal surgery can be performed.

Obstructive sleep apnoea

Obstructive sleep apnea is a potentially life-threatening condition characterized as repeatedly stopped breathing during sleep. Sleep apnoea presents with several types, but the most common is the obstructive type.

Causes

Obstructive sleep apnoea happens when pharynx muscles lose their tone and become hypotonic and relaxed during sleep resulting in airway narrowing and blockage during the inhalation. It can happen a few to even 40 times per hour, resulting in an inability to reach the deep sleep phase. It can result in a feeling of lack of sleep, although individuals have slept more than necessary.

Symptoms

Symptoms usually include snoring, choking and gasping air during sleep, drowsiness during the day, and fatigue, insomnia during the night. Another person can report episodes of stopped breathing during sleep. Headaches, dry mouth can be present. During the day, it can be hard to concentrate, and there can be mood swings.

Risk factors and complications

The most common risk factors are:

  • Obesity
  • Large tongue or issues causing its enlargement
  • Large, thick and short neck
  • Narrow airways
  • Smoking
  • Older age
  • Gender (man are more likely to have it)
  • Family history
  • Muscle relaxant substances and medications such as sedatives or alcohol
  • Disorders affecting the nose
  • Other diseases such as diabetes, hypertension, or asthma

Some of the complications and issues caused by obstructive sleep apnoea include constant fatigue, hypertension or heart disorders, a higher chance of stroke, depression, problems with performing surgeries, and complications after them.