The Pharynx Flashcards
Describe the pharynx including its widest and narrowest points and its boundaries?
The pharynx is a muscular tube arising from the base of the skull extending down to the level of C6 posterior to the nasal and oral cavities. It is widest at its upper end (opposite the hyoid bone) and narrowest at its inferior end where it becomes continuous with the oesophagus. The posterior wall of the pharynx lies against the prevertebral layer of the deep cervical fascia.
Describe the boundaries and contents of the first part of the pharynx
The nasopharynx.
Boundaries: base of the skull to upper border of soft palate. It is the posterior extension of the nasal cavities, which opens into it through two choanae. The C1 vertebrae lies posteriorly. Within the nasopharynx, the orifice of the pharyngotympanic (or Eustachian) tube and a collection of lymphoid tissue, the pharyngeal tonsil (or adenoids when enlarged) are found.
Discuss the clinical relevance of the tonsils relating to breathing and the ET.
The pharyngeal tonsil, the palatine tonsils and the lymphoid nodules on the dorsum of the tongue form a continuous lymphoid ring (Waldeyer’s ring) around the naso- and oropharynx. The pharyngeal tonsil (or adenoids) are prominent in children but undergo atrophy after puberty.
When chronically inflamed (adenoiditis) they may obstruct the passage of air from the nasal cavities through the choanae into the nasopharynx causing mouth breathing and a “nasal tone” to speech. In addition, by blocking the pharyngotympanic tube, they may cause middle ear infections (otitis media) as drainage and ventilation of the middle ear cavity are impeded.
The pharyngotympanic tube also provides a potential route for infection in the pharynx to spread to the middle ear. This is why it is not uncommon for upper respiratory tract infections to be complicated by middle ear infections.
Why does blocking the ET lead to glue ear and an increased risk of infection?
Cells in middle ear are constantly reabsorbing air. If the ET is blocked a negative pressure then builds up in the middle ear and a transudate forms from the mucosal fluid. This provides a perfect environment for bacteria to proliferate and cause otitis media.
Describe the boundaries and contents of the second part of the pharynx
The second of the pharynx’s three parts, extends from the level of the soft palate to the superior border of the epiglottis. The vertebral bodies of C2 and C3 lie posteriorly. The palatine tonsils lie on either side of the oropharynx in the interval between the palatoglossal and palatopharyngeal arches (the anterior and posterior pillars).
Describe the boundaries and contents of the third part of the pharynx and their clinical relevance
The third and final part of the pharynx, extends from the epiglottis to the oesophagus at the level of the inferior border of the cricoid cartilage, and extends behind the laryngeal inlet. The vertebral bodies of C3- 6 lie posteriorly. On each side of the laryngeal inlet, the laryngopharyngeal cavity has a small depression called the piriform fossa.
The piriform fossa is a common site for foreign bodies (e.g. fishbone, chicken bone, etc.) entering the pharynx to become lodged. Sharp objects may pierce the mucous membrane and injure important structures such as nerves. Many swallowed foreign objects reach the stomach but in some cases, may lodge at the inferior end of the laryngopharynx, which is the narrowest part of the pharynx.
Whats the difference between the cricoid and thyroid cartilages
Cricoid cartilage is a complete ring whilst thyroid cartilage is missing at the posterior aspect.
How does the epiglottis prevent aspiration of liquid?
Epiglottis acts like a pillar when swallowing liquid into two streams around the larynx as well as covering the epiglottis and stopping food from entering the airways. The liquid is directed down the piriform recesses.
What are the longiduinal three muscles that elevate the pharynx and larynx during swallowing and which nerves supply them
Internally, the wall of the pharynx consists of three intrinsic, longitudinal muscles that shorten and widen the pharynx and elevate the larynx during swallowing and speaking.
Stylopharyngeus
Styloid process – posterior border of thyroid cartilage
Glossopharyngeal nerve (CN IX)
Palatopharyngeus
Hard palate – posterior border of thyroid cartilage
Pharyngeal branch of vagus (CN X)
Salpingopharyngeus
Cartilaginous part of ET – merges with palatopharyngeus
Pharyngeal branch of vagus (CN X)
Describe the external and internal muscles of the pharynx
Externally, the walls of the pharynx consist of the circular: superior, middle and inferior constrictors, innervated by the vagus nerve. These relax and contract sequentially from above to below to propel food into the oesophagus. The inferior constrictor has two parts one form the thyroid the other from the cricoid cartilage. These are all innervated by the vagus nerve.
What is killian’s dehiscence?
Between the two muscle belly components of the inferior constrictor there is a small area of weakness known as Killian’s dehiscence. If there is incoordination of the pharynx during swallowing, increased pressure within the pharynx can occur as these muscles attempt to constrict against a closed oesophageal sphincter. This can cause part of the pharyngeal mucosa to herniate through Killian’s dehiscence, forming a pharyngeal pouch. As food is conveyed through the pharynx, some of it may become trapped in the pouch. While small pouches can be asymptomatic, others can cause dysphagia, regurgitation of food and halitosis (bad breath).
Describe the motor and sensory innervation of the pharynx
The vagus nerve (and cranial root of accessory nerve) supply all muscles of the pharynx and soft palate except two: stylopharyngeus (CN IX) and tensor veli palatini (CN V3). The sensory supply, however, differs according to the part of the pharynx. The nasopharynx is innervated by the maxillary nerve (CN V2); the oropharynx by the glossopharyngeal nerve (CN IX) which, as you will recall, also supplies sensory and taste to the posterior third of the tongue; and finally, the laryngopharynx receives sensory innervation from the vagus nerve (CN X)
What is the first stage of swallowing and what happens?
Swallowing Phase 1 (Oral)
A masticated food bolus is transferred to the back of the oral cavity, towards the oropharynx, mainly by movements of the tongue and soft palate this is the voluntary phase of the swallowing (deglutition) process. Hypoglossal nerve is the main one involved.
What is the second stage of swallowing and what happens?
Swallowing Phase 2 (Pharyngeal)
This is followed by a reflex-driven process (involuntary phase), which involves
• Elevation of the soft palate closing off the nasopharynx from the oropharynx – Tensor palatine CN V3 and levator palatine CNX which also open ET tube.
• Tongue is positioned against the hard palate preventing food re-entering the mouth - CN XII
• Contraction of the suprahyoid muscles and the longitudinal pharyngeal muscles causes elevating of the larynx – Suprahyoid = CN V3, CN VII and CN XII and longitudinal muscles = CN IX and CN X.
• This means the pharynx is widened and shortened to receive the bolus and the elevation of the hyoid bone allowed the epiglottis to close over the larynx
• This is followed by an automatic, sequential contraction of the three pharyngeal constrictor muscles forcing food/fluid into the oesophagus.
• Upper oesophageal sphincter then relaxes
What is the third stage of swallowing and what happens?
Swallowing Phase 3 (Oesophageal)
Involuntary, upper striated muscles of the oesophagus (vagus nerve) contract and below this is smooth muscle contracts moving food through the lower oesophageal sphincter
