Tonsils are collections of lymphoid tissue facing into the aerodigestive tract. The set of lymphatic tissue known as Waldeyer's tonsillar ring includes the adenoid tonsil, two tubal tonsils, two palatine tonsils, and the lingual tonsil.
sagittal view of tonsils and throat anatomy.
|Latin||Tonsilla, Tonsillae (pl.)|
When used unqualified, the term most commonly refers specifically to the palatine tonsils, which are masses of lymphatic material situated at either side of the back of the human throat. The palatine tonsils and the nasopharyngeal tonsil are lymphoepithelial tissues located near the oropharynx and nasopharynx (parts of the throat).
Tonsils in humans include, from anterior (front), superior (top), posterior (back), and inferior (bottom):
|Adenoids (also termed "pharyngeal tonsils")||Ciliated pseudostratified columnar (respiratory epithelium)||Incompletely encapsulated||No crypts, but small folds||Roof of pharynx|
|Tubal tonsils||Ciliated pseudostratified columnar (respiratory epithelium)||Roof of pharynx|
|Palatine tonsils||Non-keratinized stratified squamous||Incompletely encapsulated||Long, branched||Sides of oropharynx between palatoglossal|
and palatopharyngeal arches
|Lingual tonsils||Non-keratinized stratified squamous||Incompletely encapsulated||Long, branched||Behind terminal sulcus (tongue)|
Normally, each tonsil measures up to 2.5 cm in length, 2.0 cm in width and 1.2 cm in thickness.
Humans have four tonsils: the pharyngeal tonsil, tubal tonsil, palatine tonsil, and the lingual tonsil. 
These immunocompetent tissues are the immune system's first line of defense against ingested or inhaled foreign pathogens, and as such frequently engorge with blood to assist in immune responses to common illnesses such as the common cold. Tonsils have on their surface specialized antigen capture cells called M cells that allow for the uptake of antigens produced by pathogens. These M cells then alert the underlying B cells and T cells in the tonsil that a pathogen is present and an immune response is stimulated. B cells are activated and proliferate in areas called germinal centres in the tonsil. These germinal centres are places where B memory cells are created and secretory antibody (IgA) is produced.
The many but small side effects of having tonsils are bleeding of the tonsils, chronic tonsillitis, and other rare diseases of the tonsils. Many of these symptoms are the common ailment to why many doctors recommend a tonsillectomy on their patients.
Tonsils can become enlarged (adenotonsillar hyperplasia) or inflamed (tonsillitis) and may require surgical removal (tonsillectomy). This may be indicated if they obstruct the airway or interfere with swallowing, or in patients with frequent recurrent tonsillitis. However, different mechanisms of pathogenesis for these two subtypes of tonsillar hypertrophy have been described, and may have different responses to identical therapeutic efforts. In older patients, asymmetric tonsils (also known as asymmetric tonsil hypertrophy) may be an indicator of virally infected tonsils, or tumors such as lymphoma or squamous cell carcinoma.
Tonsillitis is a disorder in which the tonsils are inflamed (sore and swollen). The most common way to treat it is with anti-inflammatory drugs such as ibuprofen, or if bacterial in origin, antibiotics, e.g. amoxicillin and azithromycin. Often severe and/or recurrent tonsillitis is treated by tonsillectomy.
A tonsillolith is material that accumulates on the tonsil. They can range up to the size of a peppercorn and are white/cream in color. The main substance is mostly calcium, but they have a strong unpleasant odor because of hydrogen sulfide and methyl mercaptan and other chemicals.
Tonsil enlargement can affect speech, making it hypernasal and giving it the sound of velopharyngeal incompetence (when space in the mouth is not fully separated from the nose's air space). Tonsil size may have a more significant impact on upper airway obstruction for obese children than for those of average weight.
As mucosal lymphatic tissue of the aerodigestive tract, the tonsils are viewed in some classifications as belonging to both the gut-associated lymphoid tissue (GALT) and the mucosa-associated lymphoid tissue (MALT). Other viewpoints treat them (and the spleen and thymus) as large lymphatic organs contradistinguished from the smaller tissue loci of GALT and MALT.
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