The tonsils are a collection of lymphoid tissue that are found in the mucosa of the pharynx.
These masses of lymphoid tissue form an important part of our immune system and act as the first line of defense against ingested or inhaled pathogens.
There are four primary groups of tonsils which are arranged into a ring around the pharynx (oropharynx and nasopharynx), known as the pharyngeal lymphoid ring (a.k.a. Waldeyer’s ring).
This article will look at the anatomy, location, function, neurovascular supply and histology of the tonsils. A focal point will also be placed on the clinical relevance of the tonsils.
|Definition||Collection of lymphoid tissue clustered in the mucosa of the pharynx.|
|Function of the tonsils||Provide immunological protection; first line defense against ingested or inhaled pathogens|
|Types of tonsils and locations||
-Pharyngeal tonsils/adenoids: single tonsil located in the roof of the nasopharynx
-Tubal tonsils: bilateral tonsils located inside the mucosa of the lateral walls of the nasopharynx
-Palatine tonsils: bilateral tonsils located on either side of the oropharynx and lie between the palatopharyngeal and palatoglossal arches and posterior to the oropharyngeal isthmus
-Lingual tonsils: single tonsil located at the base of the posterior ⅓ of the tongue
- Palatine tonsils
- Pharyngeal tonsils (Adenoids)
- Lingual tonsils
- Tubal tonsils
- Clinical points
The tonsils are a type of mucosa associated lymphoid tissue (MALT) which surround the opening of the nasal and oral cavities. They contain aggregations of lymphoid nodules that are spread through the mucosal lining of the pharynx. These aggregations contain T cells, B cells and macrophages which are key for immunological protection against any pathogens entering the pharynx. These aggregations of lymphatic nodules are clustered around the posterior opening of the oral and nasal cavities.
There are four main types of pharyngeal tonsils in humans: palatine, pharyngeal, lingual and tubal tonsils.
The palatine tonsils, commonly referred to simply as the tonsils, form the lateral borders of the pharyngeal lymphoid ring. They are located in the isthmus of fauces (hence also known as the faucial tonsils), between the palatoglossal arch anteriorly and the palatopharyngeal arch posteriorly. Laterally, they are enclosed by a thin fibrous capsule and are covered in stratified squamous epithelium on the pharyngeal side. The tonsil is penetrated by 15-20 tonsillar crypts whose lumens contain lymphocytes, bacteria and desquamated epithelial cells. The walls of these crypts possess numerous lymphatic nodules which increases the surface area for antigen sampling by the lymphoid tissue.
The palatine tonsils receive their blood supply via tonsillar branches of five arteries:
- Ascending palatine branch of the facial artery
- Tonsillar branch of the facial artery
- Ascending pharyngeal branch of the external carotid artery
- Dorsal lingual branch of the lingual artery
- Lesser palatine branch of the descending palatine artery.
Venous drainage is to the internal jugular vein via a peritonsillar plexus of lingual and pharyngeal veins.
The nerve supply to the palatine tonsils arises from the maxillary division of the trigeminal nerve (cranial nerve V2) as well as the tonsillar branches of the glossopharyngeal nerve (cranial nerve IX).
Pharyngeal tonsils (Adenoids)
The pharyngeal tonsil, also known as the adenoids, is the most superior component of the pharyngeal lymphoid ring and lies in the superior part (vault) of the nasopharynx. It is attached to the periosteum of the sphenoid bone by connective tissue. The pharyngeal tonsil is covered with ciliated pseudostratified columnar (i.e. respiratory) epithelium.
The covering capsule is thinner compared to the palatine tonsils and has no crypts. The epithelium is thrown into folds, with the lamina propria containing a mass of lymphoid tissue with numerous lymphoid nodules.
Blood supply to the pharyngeal tonsil arises from the:
- Ascending pharyngeal and palatine arteries
- Tonsillar branch of the facial artery
- Pharyngeal branch of the maxillary artery
- Artery of the pterygoid canal
- Basosphenoid artery (branch of the inferior hypophyseal artery).
Venous blood flows via the pharyngeal plexus, which drains indirectly to the internal jugular veins (IJV).
The pharyngeal tonsil is innervated by branches of the pharyngeal plexus, while lymphatic drainage passes via the retropharyngeal and the pharyngomaxillary nodes.
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The lingual tonsils are small round elevations that sit on the most posterior part of the base/pharyngeal part of the tongue. They are considered a collection of lymphoid tissue which vary greatly in size and shape. They are covered by stratified squamous epithelium which invaginates to form a single crypt.
The blood supply to the lingual tonsils arises from the lingual artery, tonsillar branch of the facial artery and ascending pharyngeal branch of the external carotid artery
Venous drainage of the lingual tonsils is achieved via the dorsal lingual branch of the lingual vein.
The nerve supply is from the tonsillar branches of the glossopharyngeal nerve (cranial nerve IX).
Lymphatic drainage from the lingual tonsil drains into the jugulodigastric and deep cervical nodes.
The tubal tonsils are located just posterior to the pharyngeal opening of the auditory tube in the nasopharynx. They form the lateral part of the pharyngeal lymphoid ring and are covered by ciliated pseudostratified (respiratory) epithelium.
The tubal tonsils receive arterial blood supply from the branches of the sphenopalatine and ascending pharyngeal arteries.
The lymphatic drainage of the tubal tonsils is via the retropharyngeal and the deep cervical lymph nodes.
This inflammatory condition of the tonsils is due to viral or bacterial infections. Viral infections account for the majority of the tonsilitis cases.
- Sore infection
- Hoarseness or loss of voice
- Dysphagia- difficulty swallowing
- A visible white or yellow coating on the tonsils upon examination.
Supportive treatment includes use of painkillers, as well as antibiotics in some cases to prevent the occurrence of complications like tonsillar abscess.
This is a surgical procedure where the palatine tonsils are removed from each side of the oropharynx. The surgery is usually needed due to:
- Airway obstruction from enlarged tonsils
- Sleep apnoea
- Recurrent tonsillitis
The tonsils are highly vascularised therefore, hemorrhage is a possible complication of this surgery.
Repeated inflammation of these tonsils may result in accumulation of bacterial and mucus debris that calcifies, resulting in the formation of tonsoliths. Tonsilloliths are also known as tonsil stones and are small white plugs projecting from the crypts.
- Foul smelling breath
- Sore throat
- Cough due to irritation from the tonsil stone
Supportive treatment may include antibiotics, however definitive treatment is surgery. This includes surgical removal of the stones or cryptolysis which is a surgery that reduces frequency of tonsil stones.
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