Pharynx and Larynx: Parts of the Pharynx, Associated Conditions, Parts of the Larynx and Differences

Our body needs to absorb oxygen, which is captured by the lungs through inspiration, and free of carbon dioxide, which comes out through expiration.

The faringes is a fibromuscular tube that is semicircular in cross section and is located directly before the spine.

It extends from the base of the skull to the lower edge of the cricoid cartilage.

Six muscles are predominantly responsible for the voluntary actions of the pharynx: three pharyngeal constrictor muscles that overlap one above the other and three vertically oriented muscles (stylopharyngeus, salpingopharyngeal and palatopharyngeal).

These muscles help in the act of swallowing. The pharynx is a continuation of the digestive cavity, which provides a route from the oral cavity of the esophagus.

In addition, the pharynx communicates with the nasal cavity, the middle ear cavity and the larynx.

The pharynx is often described from an exterior view and an interior perspective. Depending on the location, the inside of the pharynx is often divided into three sections: the nasopharynx, the oropharynx, and the laryngopharynx.

Parts of the pharynx

Nasopharynx:

The nasopharynx is between the base of the skull and the soft palate, a continuation of the nasal cavity.

Performs a respiratory function by conditioning the inspired air and propagating it to the larynx.

This part of the pharynx is lined with the respiratory epithelium: columnar pseudostratified ciliated epithelium with goblet cells.

The postero-superior nasopharynx contains the adenoid tonsils, which are large between the ages of 3-8 and then recede.

Oropharynx:

The oropharynx is the middle part of the pharynx, located between the soft palate and the upper edge of the epiglottis. It contains the following structures:

  • One third of the back part of the tongue.
  • The lingual tonsils: located in the lower part of the tongue.
  • The palatine tonsils: are found in the tonsilar fossa between the palatoglossal and palatopharyngeal arches of the oral cavity.
  • Upper constrictor muscle.

The oropharynx is involved in the voluntary and involuntary phases of swallowing.

laryngopharynx:

The most distant part of the pharynx is between the upper edge of the epiglottis and the lower edge of the cricoid cartilage, at which point it becomes continuous with the esophagus.

It is located behind the larynx and communicates with it through the laryngeal entrance, lateral to which the pyriform pits can be found.

The laryngopharynx contains the middle and lower pharyngeal constrictors.

Muscles:

The pharynx consists of four layers of muscles, from the inside out:

  • A mucous membrane continues with that of the auditory tubes and the nasal, oral and laryngeal cavities.
  • A fibrous fur:  that is thicker in its superior extension (pharyngobasilar fascia) and that it forms a middle raphe in the posterior part.
  • A muscular fur.
  • A fascial covering (oropharyngeal fascia): covering the outer surface of the muscles.

The wall of the pharynx is composed mainly of two layers of skeletal muscles. The outer circular layer comprises three constrictors.

The inner layer, mainly longitudinal, consists of two elevators: the stylopharyngeus and the pharyngeal palafito.

The constrictors of the pharynx have their fixed points in the anterior larynx, where they are attached to the bones or cartilages, while they expand later, overlap each other from lower to upper and end in a middle tendon raphe in the posterior midline.

The cricopharyngeal fibers have a horizontal orientation and are continuous with the circular fibers of the esophagus. These fibers act like a sphincter and prevent air from entering the esophagus.

A pharyngeal diverticulum can later form to the larynx through the fibers of the lower constrictor.

The middle constrictor arises from the hyoid bone, while the superior constrictor arises from the jaw and sphenoid bone.

The palatopharyngeal muscle arises from the palate, forms the palatopharyngeal fold and inserts into the thyroid cartilage and the side of the pharynx.

The stylopharyngeus muscle arises from the styloid, which passes between the upper and middle constrictors, and is inserted with the pharyngeal palafito.

The stylopharyngeus is supplied by the glossopharyngeal nerve, while the palatopharyngeal and constrictor muscles are innervated by the pharyngeal branch of the vagus nerve through the pharyngeal plexus that is located in the middle constrictor.

The main action for which the muscles of the pharynx combine is swallowing, a complicated neuromuscular act by which food is transferred from the mouth through the pharynx and esophagus to the stomach.

The pharyngeal stage is the swiftest and most complex swallowing phase.

During swallowing, the nasopharynx and vestibule of the larynx are sealed, but the epiglottis adopts a varying position.

The food is usually deviated laterally by the epiglottis and the aryl-epiglottic folds to the piriform recesses of the laryngopharynx.

The pharyngeal ridge is an elevation or bar in the posterior wall of the lower pharynx at the level of the soft palate; It occurs during swallowing by transverse muscle fibers.

Innervation and blood supply:

The motor and most of the sensory supply to the pharynx is carried out through the pharyngeal plexus, which, located mainly in the middle constrictor, is formed by the pharyngeal branches of the vagus and glossopharyngeal nerves and also by the sympathetic nerve fibers.

The motor fibers in the plexus are transported by the vagus nerve and supply all the muscles of the pharynx and the soft palate, except the stylopharyngeus and the tensor of the palatal veil.

The sensory fibers in the plexus come from the glossopharyngeal nerve and provide most of the three parts of the pharynx.

The pharynx is supplied by branches of the external carotid (ascending pharyngeal) and subclavian (lower thyroid) arteries.

Conditions associated with the pharynx

Inflammation:

The most common inflammatory processes of the nasopharynx are pharyngitis and tonsillitis .

Although infectious bacteria can be the cause of pharyngitis and tonsillitis, the most common etiology remains viral infections of the upper respiratory tract .

The most implicated viral pathogens are echoviruses, rhinoviruses, adenoviruses and respiratory syncytial viruses.

A typical visual presentation of the viral etiology would imply erythema, mucosal edema of the nasopharynx and enlarged lymphatic tissue.

A typical presentation of the bacterial etiology would imply erythema of the nasopharynx mucosa together with an exudative membrane.

Because bacterial pharyngitis and tonsillitis can be easily treated with antibiotics, the only serious complications are the sequelae of infections without proper treatment: rheumatic fever and glomerulonephritis derived mainly from strep throat.

Angiofibroma nasofaríngeo:

Nasopharyngeal angiofibroma is an extremely vascularized tumor that usually occurs in adolescent males.

It has a tendency to bleed during surgery. It can be seen as a smooth mass mainly in the posterior nasopharynx.

It is a benign tumor that is locally very aggressive. The majority of patients present with nasal obstruction and epistaxis.

The biopsy is particularly dangerous since the tumor is very vascular.

Angiofibromas tend to bleed during surgery, so it is imperative to keep the patient hypotensive to reduce the risk of bleeding.

Nasopharyngeal carcinoma:

Nasopharyngeal carcinoma is a tumor that has different epidemiological associations and can take three different patterns: keratinizing squamous cell carcinoma (25%), non-keratinizing squamous cell carcinoma (15%) and undifferentiated carcinomas (60%).

The nasopharynx is the most common anatomical location for this carcinoma.

The factors that affect the geographical distribution are heredity, age and infection with the Epstein-Barr virus.

In Africa, it is a childhood cancer; in southern China, it is common in adults but rare in children; and in the United States, it is rare in both adults and children.

Infection with the human papillomavirus may also be associated with the development of nasopharyngeal carcinoma.

Squamous cell carcinoma:

The most common tumor of the laryngopharynx is a squamous cell carcinoma (95%). It usually occurs in men around the sixth and seventh decades of life.

Although it can occur in the postcricoid region or the posterior wall, most occur within the piriform recess. The biggest predisposing factors are the consumption of alcohol and tobacco.

Parkinson’s disease:

The pharynx has a very important role in swallowing, and the interruption of muscle innervation can cause dysphagia or even aspiration.

Aspiration pneumonia is the most common cause of death in Parkinson’s disease , and some data suggest that the pharyngeal plexus can be affected by parkinsonian pathology, causing an alteration of nervous sensitivity and an altered swallowing reflex, leading to the aspiration.

Obstructive sleep apnea :

Sleep apnea can be attributed to enlarged lymphoid tissue or soft palate, but it can also be attributed to oropharyngeal collapse for reasons such as smoking and obesity.

Smoking increases the edematous nature of the mucosa, especially the uvular mucosa, causing a decrease in the diameter of the airway.

Obesity and fat deposition near the pharynx, as well as edema from smoking, causes a decrease in longitudinal traction and wall tension, which facilitates collapse.

There is also a function of relaxation of the pharyngeal musculature during sleep, during which even a minimally collapsed airway does not respond to the appropriate mechanical load.

Larynx

The larynx is a resistant and flexible segment of the respiratory tract that connects the pharynx with the trachea in the neck.

It plays a vital role in the respiratory tract by allowing air to pass through it while preventing food and drinks from blocking the airways.

The larynx is also the “voice box” of the body, since it contains the vocal cords that produce the sounds of speech and singing.

It is a short tube lined with epithelium formed by nine pieces of cartilage and several ligaments that join them.

It is located along the midline of the body in the neck region, deep in the skin and muscles of the neck and anterior to the esophagus and cervical vertebrae.

At its upper end, it borders the hyoid bone and the laryngopharynx.

Physiology:

In the process of swallowing, the larynx plays an important role in the direction of food into the esophagus.

The epiglottis usually resides in a vertical position just anterior to the laryngeal lumen.

This position allows air to pass freely through the larynx during inhalation and exhalation.

When food or liquid is swallowed in the mouth, the food pushes the epiglottis back, turning its free edge to cover the glottis and block the entry of substances ingested to the larynx.

Then, the food passes safely to the esophagus, at which point the epiglottis returns to its resting position.

Occasionally, a person may choke when food passes the epiglottis or adheres to a structure inside the pharynx and blocks the airway.

The vocal cords contract to trap the blockage before it passes into the trachea. The cough pushes the air out of the lungs to avoid blocking the airways.

The sounds are produced in the larynx by the movement of air through it and by the vocal cords, a pair of mobile folds in the mucous membrane.

The vocal cords are connected to the thyroid cartilage at its anterior ends and the arytenoid cartilages at its posterior end.

The air exhaled by the lungs passes through the larynx and vibrates the vocal cords.

Several sets of muscles move the arytenoid cartilages and the cricothyroid joint to adjust the position and tension of the vocal cords and thus control the tone of the sound produced by the larynx.

Entry:

The entrance of the larynx is the passage from the laryngopharynx to the cavity of the larynx. It is set obliquely, looking largely backwards.

It is delimited previously by the upper edge of the epiglottis, on each side by the ariepiglottic folds, and in the lower and posterior part by an interaritenoid fold.

The entrance is laterally related to the pyriform spaces of the laryngopharynx.

The ariepiglottic folds provide lateral feeding channels that lead along the sides of the epiglottis, through the piriform gaps to the esophagus.

The closing of the entrance protects the respiratory tract against the invasion of food and foreign bodies.

This closure is produced by the contraction of the arytenoepiglottic and transverse arytenoid muscles and by the posterior movement of the epiglottis that is produced by the elevation of the larynx.

This elevation increases the base of the epiglottis more than the upper portions, resulting in a posterior inclination thereof.

Cartilages:

The larynx has three unique cartilages (thyroid, cricoid and epiglottic) and three paired cartilages (arytenoid, corniculate and cuneiform).

The thyroid cartilages, cricoids and arytenoids are composed of hyaline cartilage and can undergo calcification, endochondral ossification or both, so they become visible radiographically. The other cartilages are elastic.

The thyroid cartilage comprises two plates in the form of a spring called laminae, which fuse anteriorly but diverge in the posterior part of the larynx.

The laminae produce a median elevation called laryngeal prominence also called ” Adam’s apple “, which is palpable and frequently visible.

The trailing edge of each sheet extends superiorly and inferiorly as horns.

The upper horn is anchored to the tip of the greater horn of the hyoid bone. The inferior horn is articulated medially with the cricoid cartilage.

The lateral surface of each sheet is crossed by an oblique line for the union of the muscles.

The cricoid cartilage is shaped like a signet ring. It comprises a back plate, called lamina, and a narrow and anterior part, the arch.

The lamina is articulated superolaterally with the arytenoid cartilages. The cricoid cartilage is at the level of the C6 vertebra, and its arch is palpable.

The lower edge of the cricoid cartilage marks the end of the pharynx and larynx and, therefore, the beginning of the esophagus and trachea.

The arytenoid cartilages articulate with the superior edge of the lamina of the cricoid cartilage.

Each one has a vertex superiorly positioned (which supports the corniculated cartilage) and a base that comprises its lower part.

The corniculated and inconstant cuneiform cartilages are nodules in the ariepiglottic folds.

The epiglottic cartilage is covered by a mucous membrane to form the epiglottis.

The epiglottis is located behind the root of the tongue and the body of the hyoid bone and anterior to the entrance of the larynx.

The lower end, or stem, of the leaf-shaped cartilage is anchored to the posterior aspect of the thyroid cartilage. Taste buds are present on the posterior surface of the epiglottis.

Joints:

Two synovial joints are present on each side.

The cricothyroid joint, between the lateral face of the cricoid cartilage and the lower horn of the thyroid cartilage, allows mainly the rotation of the thyroid cartilage around a horizontal axis through the joints of the two sides.

This produces a tilting movement where the anterior part of the thyroid cartilage moves forward and downward.

The cricoarytenoid joint, between the superior edge of the cricoid cartilage sheet and the base of the arytenoid cartilages, allows the sliding and rotation of the arytenoid cartilages.

Ligaments:

The thyrohyoid membrane connects the thyroid cartilage with the superior border of the hyoid bone. The median part is thickened to form a ligament.

The membrane is perforated on each side by the internal laryngeal nerve and the superior laryngeal vessels.

The cricothyroid ligament connects the cricoid cartilage arch with the thyroid cartilage.

The term conus elastic is used for elastic fibers that extend upward from the cricoid cartilage to the vocal ligaments.

In acute respiratory obstruction , cricothyrotomy, that is, entry into the larynx between the arch of the cricoid cartilage and thyroid cartilage by penetration of the cricothyroid membrane, is preferable to tracheotomy for the non-surgeon.

The vocal ligament on each side extends posteriorly from its anterior insertion in the thyroid cartilage to a posterior insertion in the vocal process of the arytenoid cartilage.

This “vocal cord” is the upper edge of the elastic cone. The vocal cords are composed of elastic fibers covered with force by a vocal fold of the mucous membrane.

The epiglottis is joined by ligaments to the hyoid bone, to the back of the tongue, to the sides of the pharynx and to the thyroid cartilage.

Cavity:

The cavity of the larynx is divided into three parts: the vestibule, the ventricles and the area between them and the infraglottic cavity.

These regions are defined by the location of the vestibular and vocal folds.

The vestibule extends from the entrance to the vestibular folds.

The ventricle extends laterally in the interval between the vestibular and vocal folds.

Each ventricle resembles a canoe placed on its side, and the two ventricles communicate with each other through the middle portion of the laryngeal cavity.

A small diverticulum, the saccule, which extends upwards from the anterior aspect of each ventricle, has mixed glands and has been called the “oil can” of the vocal cords.

The vestibular folds or “false vocal cords” contain the vestibular ligaments and are more protective than vocal in their function.

The vocal cords from the angle of the thyroid cartilage in the anterior larynx to its later union in the vocal processes of the arytenoid cartilages.

Most of each vocal fold is formed by the muscle vocalis, which is part of the thyroarytenoid muscle.

The vocal cords and processes, together with the interval (rima glottidis) between them, are collectively referred to as the glottis.

The glottic rima is the narrowest part of the laryngeal cavity and can be seen between the more separated vestibular folds during laryngoscopy .

The vocal cords control the flow of air that passes through the rhyme and, therefore, are essential in the production of the voice.

The anterior and intermembranous part of the rhyme lies between the vocal cords, while the posterior and intercartilageous part is located between the arytenoid cartilages.

The rhyme is wider during inspiration and the quieter and narrower breathing during expiration and expiration.

The infraglottic cavity extends from the glottic rima to the trachea.

Closing:

Three levels in the larynx can be closed by the sphincteric muscles:

  • The entrance:  which closes during swallowing and protects the respiratory tract against the invasion of food
  • The vestibular folds:  whose closure traps air in the trachea and makes possible an increase in intrathoracic pressure (such as when coughing) or intra-abdominal pressure (as in urination and defecation).
  • The vocal cords:  approaching during phonation.

The presence of a foreign body is the most common cause of laryngeal spasm, which generally involves not only the glottis but also the entire sphincter musculature of the larynx.

Sensory innervation and blood supply:

The mucosa of the larynx is supplied on each side mainly by the internal laryngeal branch of the superior laryngeal nerve.

The lower part of the larynx receives sensory fibers from the recurrent laryngeal nerve.

The larynx has arterial supply through the superior laryngeal artery (of the superior thyroid), which accompanies the internal laryngeal nerve, and the inferior laryngeal artery (of the inferior thyroid), which accompanies the recurrent laryngeal nerve.

Muscles:

The larynx as a whole can be elevated and depressed by the extrinsic muscles (for example, the stylopharyngeus and the palatoplasm and the infrahyoid muscles).

The intrinsic laryngeal muscles are complicated, but can be classified as follows:

  • The sphincters of the entrance: transverse arytenoids, oblique arytenoids and ariepiglotis.
  • The muscles that close and open the glottic rima: lateral cricoarytenoid (adductor) and posterior cricoarytenoid (abductor).
  • The muscles that regulate the vocal ligaments: tiroartenoides and vocalis; cricothyroid.

Three muscles arise from the cricoid cartilage:

  • The cricothyroid: that arises from the lateral side of the cricoid cartilage and that passes forward to be inserted in the lamina and the lower horn of the thyroid cartilage.
  • The lateral cricoarytenoid: which extends back to the muscular process of the arytenoid cartilage.
  • The posterior cricoaritenoideo: that extends laterally to the muscular process of the aritenoideo cartilage.

Two muscles, closely related to each other, connect the thyroid and arytenoid cartilages: the thyroarytenoid and the vocalis.

Two muscles join the arytenoid cartilages: the transverse and oblique arytenoids.

Abduction of the vocal cords is carried out only by the posterior cricoarytenoid muscles, which, extending laterally from the posterior face of the cricoid cartilage to the muscular processes, rotate the arytenoid cartilages laterally.

Abduction widens the gap in the glottis (between the vocal cords), which is necessary for breathing.

The adduction of the vocal cords is carried out by the lateral cricoarytenoid muscles, which, extending backwards from the arch of the cricoid cartilage to the muscular processes, rotate the arytenoid cartilages medially.

This closes the glottis, as in phonation.

The oblique and transverse arytenoid muscles are necessary to maintain the approximation of the posterior portions of the vocal cords.

After closing the glottis, the vocal cords can be tensed and lengthened by the cricothyroid muscles to change the tone and volume of the voice.

The cricothyroid muscle, by tilting the anterior thyroid cartilage over the cricoid cartilage, will increase the anteroposterior dimension of the larynx and tighten the vocal cord.

Differences between larynx and pharynx

The pharynx is a wide muscular tube, which has a longer length and can reach up to 4-5 inches in most cases.

It is present in the area near the nasal and oral cavities and is used to allow food and other elements to pass through the human body; It is known as throat in simple words.

It is a long area that starts from the mouth and nose and then extends into the esophagus and larynx.

The larynx, on the other hand, is a hollow organ that is also muscular but is what forms the passage of air from the nose to the lungs and also keeps the voice box safe in living organisms.

Both are present close to each other, therefore, confusion arises between them.

There are different regions in a pharynx that help to understand the structure, while the larynx consists of different layers that help produce and understand the sounds.

The larynx is considered as the main part of the respiratory system only while the pharynx is considered part of the respiratory and digestive system.

Another difference between them is that the pharynx is a set of different regions, while the larynx is considered as a particular part of the human body.