Anatomy of the pharynx and esophagus

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Introduction0:00–0:25

The cervical viscera are composed of three layers based on their main functions. The most superficial layer is the endocrine layer which contains the thyroid and parathyroid glands, then there’s the respiratory layer which contains the larynx and the trachea, and finally, the deepest layer is the alimentary layer which contains the pharynx and the esophagus.

Pharynx0:25–1:50

So, let’s start with the pharynx which also has a respiratory function because it conducts air to the larynx, from where it passes through the trachea and into the lungs.
The pharynx extends from the cranial base to the inferior border of the cricoid cartilage anteriorly and the inferior border of the C6 vertebra posteriorly.
It’s located posterior to the nasal and oral cavities and it extends inferiorly past the larynx, where it continues with the esophagus.
Now, the pharyngeal wall consists of three layers: the buccopharyngeal fascia is the most external layer, covering the pharynx and, inferiorly, it’s continuous with the pretracheal fascia.
Then, there is a muscular layer which has an outer circular part and an inner longitudinal part, and the innermost mucous membrane which has a thick submucosa that contributes to the pharyngobasilar fascia.
Moreover, the posterior wall of the pharynx lies against the prevertebral layer of the deep cervical fascia. The interior of the pharynx is divided into three parts: the nasopharynx which is located posterior to the nose and superior to the soft palate, the oropharynx which is located posterior to the mouth, and the laryngopharynx which is located posterior to the larynx.
The nasopharynx is the posterior extension of the nasal cavities and communicates with the nose through two paired openings called choanae, which are separated by the posterior end of the nasal septum.

Nasopharynx1:50–4:00

The roof and the posterior wall of the pharynx form a continuous surface that lies inferior to the body of the sphenoid bone and the occipital bone.
On the lateral wall of the nasopharynx, there’s the opening of the pharyngotympanic tube, also called the auditory tube or the eustachian tube which connects the nasopharynx to the tympanic cavity.
Superior to this opening, there is the cartilage of the pharyngotympanic tube, called torus tubarius, and inferior to this opening, there’s an elevation of mucosa as it overlies the levator veli palatini muscle.
From the medial end of the pharyngotympanic tube, a vertical fold of mucous membrane extends inferiorly, called the salpingopharyngeal fold which covers the salpingopharyngeus muscle.
This muscle raises the pharynx during swallowing, while at the same time opening the pharyngeal orifice of the pharyngotympanic tube.
This last action helps equalize the pressure in the pharynx to that of the auditory canal. Finally, posterior to the torus tubarius and the salpingopharyngeal fold there is the pharyngeal recess, which is a slit-like projection of the pharynx that extends laterally and posteriorly.
Now, the pharynx contains abundant lymphoid tissue. In some regions, the lymphoid tissue is aggregated and forms masses called tonsils.
Pharyngeal tonsils, called adenoids when enlarged, can be found in the mucous membrane of the roof and posterior wall of the nasopharynx just above the pharyngeal recess.
Additionally, there are tonsils located in the submucosa near the orifice of the pharyngotympanic tube called tubal tonsils.

Quiz4:00–4:23

Let’s take a quick break and try to identify the nasopharynx as well as the structures contained by it. The second part, or the oropharynx, lies posterior to the oral cavity which is bounded superiorly by the soft palate, inferiorly by the base of the tongue and laterally by the palatoglossal and palatopharyngeal arches.

Oropharynx4:23–6:50

It extends from its superior border of the soft palate to the superior border of the epiglottis. Between the base of the tongue and the epiglottis there is a midline fold of mucosa called the median glossoepiglottic fold, and between the base of the tongue and the lateral border of the epiglottis there is another fold of mucosa called the lateral glossoepiglottic fold.
Between these two folds there is a depression called the epiglottic vallecula - which serves a role in temporarily storing the saliva so as to not trigger the swallowing reflex.
Now, the oral cavity and the oropharynx are separated by a line formed by the palatoglossal arch. Posterior to the palatoglossal arch, there’s the palatopharyngeal arch which descends along the lateral wall of the oropharynx.
These are the two folds you can see in the back of the mouth when someone is opening up to say “ahhhhhhh”. Between these two arches there is a space called the tonsillar sinus where the palatine tonsils can be found.
The palatine tonsil is supplied by a branch of the facial artery called the tonsillar artery, which passes through the superior pharyngeal constrictor muscle and enters the inferior pole of the tonsil.
The tonsil is drained by the external palatine vein, which descends from the soft palate and passes close to the lateral surface of the tonsil before it enters the pharyngeal venous plexus.
Now, the palatine tonsils along with the pharyngeal and tubal tonsils located in the nasopharynx, in addition to the lingual tonsil located in the posterior part of the tongue, form an incomplete circular band of lymphoid tissue around the superior part of the pharynx called the pharyngeal lymphatic ring or the Waldeyer ring.
The anteroinferior part of the ring is formed by the lingual tonsil, the lateral parts of the ring are formed by the palatine and tubal tonsils, and the posterior and superior parts are formed by the pharyngeal tonsil.
Let’s take a quick break and try to identify the oropharynx as well as the tonsils that form the pharyngeal lymphatic ring.

Quiz6:50–7:12

Finally, the laryngopharynx is posterior to the larynx and extends from the superior border of the epiglottis and the pharyngoepiglottic folds to the inferior border of the cricoid cartilage, where it narrows and eventually becomes the esophagus.

Laryngopharynx7:12–8:36

Now, the posterior and lateral walls of the laryngopharynx are formed by the middle and inferior pharyngeal constrictor muscles, and internally the wall is formed by the palatopharyngeus and stylopharyngeus muscles.
The laryngopharynx communicates with the larynx via the laryngeal inlet on its anterior wall. On each side of the laryngeal inlet there is a small depression called the piriform fossa or recess which is covered by mucosa and is separated from the laryngeal inlet by the aryepiglottic fold.
The piriform fossa is bounded laterally by the medial surfaces of the thyroid cartilage and the thyrohyoid membrane, and medially by the lamina of the cricoid cartilage, both covered in mucous membrane.
Deep to the mucous membrane of the piriform fossa, there are branches of the internal laryngeal and recurrent laryngeal nerves which are exposed to injury if a foreign body lodges in the fossa.
Let’s take another break and see if you can identify the laryngopharynx, as well as the structures contained by it. Now, let’s move on and take a look at the pharyngeal muscles.

Quiz8:36–8:56

Pharyngeal muscles8:56–13:43

The pharynx has two layers of muscles: an external circular layer composed of three muscles - superior, middle and inferior pharyngeal constrictors, and an internal longitudinal layer composed also of three muscles - palatopharyngeus, stylopharyngeus and salpingopharyngeus.
Now let's take a big gulp, and try to digest these muscles that help us speak and swallow! So first, let’s start with the external layer which has three muscles: the superior pharyngeal constrictor, the middle pharyngeal constrictor and the inferior pharyngeal constrictor, all of which come in mirrored pairs.
Although these are skeletal muscles, they contract involuntarily, in sequence from the superior to the inferior constrictor during swallowing to help, well, constrict the wall of the pharynx.
So far so good! The pharyngeal constrictors have a strong internal fascial lining called the pharyngobasilar fascia, and a thin external fascial lining called the buccopharyngeal fascia which, as we mentioned before, blends inferiorly with the pretracheal layer of deep cervical fascia.
The superior pharyngeal constrictor originates on the pterygomandibular raphe, and the adjacent parts of the medial pterygoid plate and mandible.
The middle pharyngeal constrictor arises from the stylohyoid ligament and the greater and lesser horns of hyoid bone and its inferior fibers lie deep to the inferior constrictor muscle.
Finally, the inferior pharyngeal constrictor arises from the oblique line of the thyroid cartilage and from the side of the cricoid cartilage.
The most inferior fiber of the inferior constrictor is called the cricopharyngeal part, which is continuous with the esophagus.
Now, all of the pharyngeal constrictors curve towards the back and insert on a fibrous line called the pharyngeal raphe.
All three constrictors are innervated by the pharyngeal branch of the vagus nerve and the pharyngeal plexus of nerves which has contributions from the vagus and glossopharyngeal nerves, as well as the sympathetic nerves.
Now, let’s switch gears and take a look at the internal layer which is also composed of three muscles: palatopharyngeus, stylopharyngeus, and salpingopharyngeus.
The palatopharyngeus muscle arises from the hard palate and the palatine aponeurosis and inserts on the thyroid cartilage and on the pharyngeal wall.
Or simply, from the palate to the pharynx, hence palatopharyngeus. The salpingopharyngeus muscle arises from the cartilaginous part of the pharyngotympanic tube and blends with the palatopharyngeus muscle to the same insertion.
The stylopharyngeus arises from the styloid process of the temporal bone and attaches to the thyroid cartilage along with palatopharyngeus.
Yet again, from the styloid to the pharynx, hence the name stylopharyngeus! Easy right?
The palatopharyngeus and salpingopharyngeus muscles are innervated by the pharyngeal branch of vagus nerve and by the pharyngeal plexus, while stylopharyngeus is innervated by the glossopharyngeal nerve, or Cranial Nerve IX.
All these muscles elevate the larynx and shorten the pharynx during swallowing and speaking. Now, there are also a few other muscles that can be seen from a posterior view of the pharynx.
First up, the sternocleidomastoid, and here we can see where it inserts onto the mastoid process. Medial to that, there’s the posterior belly of the digastric muscle, which also attaches on the mastoid process of the temporal bone.
Finally, there’s the stylohyoid muscle, which in a similar fashion to the stylopharyngeus muscle, originates on the styloid process.
Before we move on, let’s take a break and see if you can identify the pharyngeal muscles. Now, speaking of the posterior pharynx, there are a number of vessels we can visualize and identify.

Quiz13:43–13:57

First, there are the common carotid arteries, and their branching into the internal and external carotid arteries. Branches of the external carotid artery supply the pharynx.

Vascular supply13:57–14:33

Lateral to the internal carotid artery, there’s the internal jugular vein as it travels through the internal jugular foramen.
Finally, lower down, we can also visualise the inferior thyroid artery after it branches from the thyrocervical trunk to supply the thyroid gland, as well as nearby structures such as the pharynx.
To go along with the vessels of the posterior pharynx, there are also numerous nerves running through and supplying this area that we can identify.
First off, the pharynx is innervated by the pharyngeal plexus, located on the posterolateral aspect of the pharynx, which has motor, sensory, and sympathetic fibers.

Innervation14:33–16:42

The motor fibers are derived from the vagus nerve, or Cranial Nerve X, via its pharyngeal branches and they supply all muscles of the pharynx and soft palate, except for the stylopharyngeus and the tensor veli palatini muscle, which is a muscle that tenses the soft palate, thereby helping to elevate it.
The sensory fibers are derived from the glossopharyngeal nerve, or Cranial Nerve IX, and they are distributed to all three parts of the pharynx.
Now, there are three nerves that exit the jugular foramen medial to the internal jugular vein: namely the vagus nerve, the glossopharyngeal nerve, as well as the spinal accessory nerve.
Remember, the vagus nerve gives rise to a pharyngeal branch, as well as the superior laryngeal nerve and its subsequent terminal branches, called the internal branch and external branch.
Also remember, the vagus nerve branches into the recurrent laryngeal nerves in the inferior part of the neck, and we can see these recurrent laryngeal nerves ascending back up towards the larynx on either side of the esophagus in the tracheo-esophageal groove.
We can also identify the hypoglossal nerve in the submandibular triangle passing laterally to the carotids but medial to the internal jugular vein.
Then, just posterior and medial to the carotid arteries, there is the sympathetic trunk and the superior cervical ganglion.
Alright! Now let’s switch gears and look at the esophagus which is a muscular tube that connects the pharynx to the stomach.
The esophagus is continuous with the laryngopharynx at the pharyngoesophageal junction, which appears externally as a constriction produced by the cricopharyngeal part of the inferior pharyngeal constrictor muscle, and is the narrowest part of the esophagus and is also known as the superior esophageal sphincter.

Esophagus16:42–18:37

The esophagus can be divided into three parts: the upper part, which consists of striated muscle, the lower part, made up of smooth muscle, and the middle part, consisting of a mixture of striated and smooth muscle.
This means that the upper part of the esophagus is under voluntary control when we swallow, and the lower part is under autonomic control and initiates reflexive peristalsis when food is present, with the middle part being under a mix of voluntary and autonomic control.
Now, the only part of the esophagus that is found in the neck is the upper part, called the cervical esophagus which begins immediately posterior to the inferior border of the cricoid cartilage, at the level of the C6 vertebra, where it enters the superior mediastinum via the superior thoracic aperture, becoming the thoracic esophagus.
It lies between the trachea to which it’s attached by loose connective tissue, and the cervical vertebral column. On the right side, there’s the right lobe of the thyroid gland as well as the right carotid sheath with its contents.
And on the left side, there’s the left lobe of the thyroid gland, the left carotid sheath and also the thoracic duct which adheres to the left side of the esophagus.
At the root of the neck, the cervical esophagus comes into contact with the cervical pleura. Now, the arterial supply of the cervical esophagus is provided by branches of the inferior thyroid artery that anastomose with each other across the midline.
Tributaries of the inferior thyroid veins drain the cervical esophagus. The innervation of the upper half of the esophagus is provided by somatic motor and sensory fibers, and the innervation of the lower half is provided by parasympathetic, sympathetic and visceral sensory fibers.

Neurovascular supply18:37–19:06

Alright, as a quick recap: The pharynx extends from the cranial base to the inferior border of the cricoid cartilage anteriorly and the inferior border of the C6 vertebra posteriorly.
It’s located posterior to the nasal and oral cavities and it extends inferiorly past the larynx, where it’s continuous with the esophagus.
The interior of the pharynx is divided into three parts: the nasopharynx, which is located posterior to the nasal cavity and superior to the soft palate, the oropharynx, which is located posterior to the oral cavity and extends from the soft palate to the superior border of the epiglottis, and the laryngopharynx, which is located posterior to the larynx, extending from the superior border of the epiglottis to the inferior border of the cricoid cartilage.

Review19:06–20:30

The pharynx has two layers of muscles: an external circular layer composed of superior, middle and inferior pharyngeal constrictors, and an internal longitudinal layer composed of the palatopharyngeus, stylopharyngeus and salpingopharyngeus.
The esophagus begins in the neck where it’s continuous with the laryngopharynx at the pharyngoesophageal junction. The upper part is composed of striated muscle, the middle part is mixed, and the lower part is composed of smooth muscle.
cartilage. The pharynx has two layers of muscles and external circular layer.
Composed of two, pure middle and inferior for a joke instructors and an internal longitudinal layer composed of the palatopharyngeus, stylopharyngeus.
It's a Pingo fringes. The esophagus begins in the neck.
Where is continuous with the laryngeal? Pharynx at the Flamingo esophageal Junction.
The other part is composed of striated muscle. The middle part is mixed and the lower part is composed of