Wednesday, February 25, 2015
Pharynx Anatomy
Pharynx
The pharynx, a channel for both air and food, has three parts. Read about the nasopharynx, oropharynx and hypopharynx, the three divisions of the pharynx.
The pharynx is a passageway located within the neck and is part of both the respiratory and digestive systems since it serves as a conduit for both air and food. Anatomically, the pharynx is divided into three parts – the nasopharynx, oropharynx and hypopharynx – from above downwards.
The pharynx connects the nasal and oral cavities above with the trachea (or the wind pipe) and the esophagus (or the food pipe) below. Although the main function of the pharynx is to ensure that food and air are directed into their respective pathways, all three subdivisions comprise many structures with varied functions. Let’s take a look at each of them.
Nasopharynx– Uppermost Division of the Pharynx
The Nasopharynx is the upper part of the pharynx, as the prefix of the word suggests, it is the nasal part of the pharynx. The Nasophaynx runs from the base of the skull to the top of the soft palate and is connected via the Eustachian tubes to the middle ear. It is the constriction and expansion of these tubes that regulate pressure in the middle ear in response to atmospheric changes, and can cause problems when air pressure changes dramatically, such as when taking off in a plane. At the back of the nasopharynx the choanae is a space which connects the pharynx to the nasal cavities. The pharyngeal tonsils, more widely referred to as the adenoids, are situated at the back wall of the nasopharynx and are an example of lymphatic tissue that can swell if an infection is present, causing the familiar ‘nasal’ tone of voice associated with colds.
Structures in the nasopharynx include:
- openings of the Eustachian tubes – these are tubes connecting the ear cavities with the pharynx. Their purpose is to ventilate the middle ear and equalize middle ear pressure with atmospheric pressure for optimal hearing.
- fossa of rosenmuller – This is a small but deep cavern, often the starting point for cancer in these parts.
- adenoids – a collection of lymphoid tissue located in the roof of the nasopharynx. It is part of the immune system and helps protect the body from infective organisms. Adenoids are usually only present in children. They regress in size and gradually disappear as the child grows older.
- tubal tonsils – also lymphoid tissue, located around the Eustachian tube openings.
The Nasal Cavity
On the lateral walls of the nasopharynx are the pharyngeal ostia, the opening of the auditory tube. These are supported and tethered by the torus tubarius formed by the stiff end of the cartilage which lifts the mucus membrane. From this opening there are two folds: the salpingopharyngeal fold which contains the salpingopharyngeal muscle amongst its mucus membrane, and the salpingopalatine fold, which is smaller and contains the levator veli palatini muscle. Posterior to the ostium of the auditory tube is the fossa of Rosenmüller (the pharyngeal recess). This is where the pharyngeal tonsil is located, which is particularly prominent during childhood and consists of lymphoid tissue similar to the adenoids. Above the tonsil is a depression in the mucous membrane known as the pharyngeal bursa.
The Oropharynx and HypopharynxOropharynx
The oropharynx lies behind the oral cavity, and forms the portion of the pharynx below the nasopharynx, but above the laryngopharynx. This section extends from the uvula which is the end of the palate, to the level of the hyoid bone. The oropharynx opens into the mouth through the isthmus faucium. On the anterior wall of the oropharynx is the base of the tongue and the epiglottic vallecula. The epiglottis, a flap of cartilaginous tissue, covers the glottis when food is being swallowed; this small flap of connective tissue plays a major role in keeping the respiratory tract free from food being inhaled accidentally. On the sides of the oropharynx are two palatine arches, and between these is the palatine tonsil. The roof of the oropharynx is the soft palate and the uvula.
Structures in the oropharynx include:
soft palate – this structure actually marks the boundary between the nasopharynx and oropharynx. When food swallowed is pushed into the oropharynx by the tongue, the soft palate immediately stretches to touch the pharyngeal wall, completely sealing off the oropharynx from the nasopharynx, preventing food from regurgitating into the nose and instead directing it down towards the esophagus. tonsils – these are lymphoid structures located on either side of the entry to the oropharynx from the oral cavity. These are the structures removed when a person undergoes tonsillectomy. base of the tongue – one-third of the tongue is actually fixed and located in the oropharynx. pharyngeal band – small nodules of lymphoid tissue scattered along the posterior pharyngeal wall.
Structures in the oropharynx include:
Hypopharynx
The hypopharynx, which forms the lower third of the pharynx, is also known as the laryngopharynx as it connects the throat to the oesophagus. It is below this point that bifurcation occurs, forming the larynx and oesophagus, and separating the respiratory and digestive routes. The oesophagus is posterior to the larynx and is accommodated by the ability of the trachea to collapse slightly upon food being swallowed due to its C-shaped cartilaginous rings.
Cervical Spinal NervesThe hypopharynx’s uppermost point is at the hyoid bone, which lies at approximately the same level as the 4th-6th cervical vertebrae. The pharynx is innervated by a number of nerves with their roots in the cervical spine. Damage to these nerve pathways can result in problems with the correct functioning of all three sections with ramifications for proper control of the separation of the larynx and oesophagus. Faults in innervation, both motor and sensory, in this area may prevent the two pathways functioning properly.
Motor innervation occurs through the glossopharyngeal nerve (IX), the vagus nerve (X), the allied spinal accessory nerve (XI), and the recurrent laryngeal nerve. Sensory innervation in the oropharynx section occurs as a result of the glossopharyngeal nerve (IX), with the vagus nerve (X) providing for the nasopharynx and the hypopharynx/laryngopharynx. As the sensory fibers from the glossopharyngeal nerve (IX) and the vagus nerve (X) enter the brainstem they are bundled together and terminate in the trigeminal nucleus. The trigeminal nerve (CN5) is responsible for creating a complete sensory map of the face and mouth with pain, touch, temperature and position signals all processed through this nerve. Accordingly, trigeminal neuralgia as a result of disc herniation, disc bulging, spondylolisthesis and spinal kyphosis or slippage, amongst other conditions, can be responsible for serious problems with the innervation of the face, jaw, and pharynx. Facial pain, jaw pain, neck pain, problems with chewing and swallowing, a sensation of a lump in the throat, and muscular spasms in the face, jaw, and neck can all result from compression of the cervical spinal nerves.
Functions of the Pharynx
The main function of the pharynx is to act as a channel for food and air, directing each to its respective destination. Peristaltic or propulsive waves in the pharynx during deglutition or swallowing help drive food into the esophagus. It is very important that food be prevented from entering the trachea as anything other than air entering this passage into the lungs can result in dangerous aspiration or choking.
The lymphoid structures in the pharynx play a role in immunity. Together with the adenoids, tubal tonsils and the pharyngeal band, the tonsils form what is called the Waldeyer’s ring, a ring of protection around the nose and mouth, common portals of entry for infection. The pharynx also provides resonance to voice.
The pharynx, divided into three parts namely the nasopharynx, oropharynx and hypopharynx, acts as a passage for both air and food and plays an important role in respiration, deglutition and immunity.
Conditions affecting the Pharynx
The location of the thyroid, and parathyroid glands in the neck also impacts the action of the pharynx and larynx, with any swelling in the area due to conditions such as Hashimoto’s Thyroiditis or hypothyroidism, capable of causing constriction of circulation and nerve pathways. In addition, conditions such as cervical arthritis, disc herniation, spinal stenosis, spondylolisthesis, and fibromyalgia may cause inflammation, neuralgia, radiculopathy, and difficulties with swallowing, controlling the airway, and even changes in the voice. Muscle spasms and cramps, found in conditions such as temporomandibular joint syndrome and fibromyalgia, are also possible mechanisms for dysfunction in this area.
The Tonsils
The Tonsils
The pharynx contains specialised lymphatic tissue that is designed to prevent pathogens’ entry into either the digestive, or the respiratory system. This ‘ring’ of lymphatic tissue consists of three groups: the nasopharyngeal tonsils (adenoids), the palatine tonsils (tonsils), and the lingual tonsils on the posterior surface of the tongue. The presence of recurrent infections can lead to inflammation and pain in these structures with many tonsillectomies performed in an attempt to prevent further tonsillitis. Whether this removal of lymphatic tissue has adverse consequences for systemic immunity is open for debate, with orthodox and naturopathic physicians often holding significantly differing opinions. Infection of the tonsils can cause glands to swell in other areas of the neck and may involve a stiff neck andneck pain along with fever and other bodily aches and pains.
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