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In anatomy, the pharyngeal tonsil, also known as the nasopharyngeal tonsil or adenoid, is the superior-most of the tonsils. It is a mass of lymphoid tissue located behind the nasal cavity , in the roof and the posterior wall of the nasopharynx , [ 1 ] where the nose blends into the throat .
The tonsils are a set of lymphoid organs facing into the aerodigestive tract, which is known as Waldeyer's tonsillar ring and consists of the adenoid tonsil (or pharyngeal tonsil), two tubal tonsils, two palatine tonsils, and the lingual tonsils. These organs play an important role in the immune system.
Each tubal tonsil is located posterior to the opening of the Eustachian tube on the lateral wall of the nasopharynx. [1] It is one of the four main tonsil groups forming Waldeyer's tonsillar ring. [2] This ring also includes the palatine tonsils, the lingual tonsils, and the adenoid. [2]
The adenoids, also known as the pharyngeal tonsils, are lymphoid tissue structures located in the posterior wall of the nasopharynx. Waldeyer's tonsillar ring is an annular arrangement of lymphoid tissue in both the nasopharynx and oropharynx. The nasopharynx is lined by respiratory epithelium that is pseudostratified, columnar, and ciliated.
The palatine tonsils are located in the isthmus of the fauces, between the palatoglossal arch and the palatopharyngeal arch of the soft palate.. The palatine tonsil is one of the mucosa-associated lymphoid tissues (MALT), located at the entrance to the upper respiratory and gastrointestinal tracts to protect the body from the entry of exogenous material through mucosal sites.
The tonsils also are lymphatic tissue and help mediate the ingestion of pathogens. Tonsils in humans include, from superior to inferior: nasopharyngeal tonsils (also known as adenoids), palatine tonsils, and lingual tonsils. Together this set of lymphatic tissue is called the tonsillar ring or Waldeyer's ring.
In healthy tonsils the openings of the crypts are fissure-like, and the walls of the lumina are in apposition. A computerized three-dimensional reconstruction of the palatine tonsil crypt system showed that in the centre of the palatine tonsil are tightly packed ramified crypts that join with each other, while on the periphery there is a rather ...
Lingual tonsils are covered externally by stratified squamous epithelium (nonkeratinized) that invaginates inward forming tonsillar crypts. Beneath the epithelium is a layer of lymphoid nodules containing lymphocytes. Mucous glands located at the root of the tongue are drained through several ducts into the crypts of the lingual tonsils.