The immunological defense of the body is a function of the lymphatic system, which also drains the excess fluids between cells. This system is composed of:

• Lymphoid organs

• Lymph nodes

• Lymphoid nodules

• Lymphatic vessels

Lymphoid nodules have a simpler architecture than the lymphoid organs or lymph nodes. They consist of a dense cluster of lymphocytes without a surrounding fibrous capsule. These nodules are located in the respiratory and digestive tracts, areas routinely exposed to environmental pathogens.

Tonsils are the lymphoid nodules located along the inner surface of the pharynx. They form Waldeyer's tonsillar ring (pharyngeal lymphoid ring) which is the first line of immunological defense of the digestive tract. It surrounds the naso- and oropharynx, with some tonsils located above and some below the soft palate. The ring consists of (from top to bottom):

• 1 pharyngeal tonsil (adenoid) on the roof of the nasopharynx.

• 2 tubal tonsils posterior to the opening each auditory tube on each side.

• 2 palatine tonsils (tonsils) on the lateral walls of the oropharynx.

• 1 lingual tonsil on the posterior 1/3 of the tongue.

Some books list two pharyngeal tonsils for considering the left and right halves of the pharyngeal tonsil as separate structures. Similarly the lingual tonsil is frequently considered as a group because it consists of a number of little prominences (rounded masses). This can be confusing, but it reflects differences in wording, rather than differences in biological structure.

Like other lymphoid nodules, tonsils are not enclosed in a complete fibrous capsule. The epithelium of the pharynx invaginates deeply into the tonsil to form tonsillar crypts. These structures, which accumulate all sorts of materials taken into the body through eating and breathing, actually “encourage” pathogens to penetrate deep into the tonsillar tissues where they are acted upon by numerous white blood cells and eliminated.

Tonsils have specialized antigen capture lymphocytes called M cells that allow for the uptake of antigens produced by pathogens. These M cells then alert the underlying B and T lymphocytes in the tonsil that a pathogen is present and an immune response is stimulated. B cells are activated and proliferate in areas called germinal centers in the tonsil. These germinal centers are places where B memory cells are created and antibodies are produced.

This seems to be the major function of tonsils—to help children’s bodies recognize, destroy, and develop immunity to common environmental pathogens so that they will be protected in their later lives. Tonsils tend to reach their largest size near puberty, and they gradually undergo atrophy thereafter. However, they are largest relative to the diameter of the throat in young children.

Clinical significance

Tonsils can become enlarged or inflamed (tonsillitis). The most common treatment is with anti-inflammatory drugs such as ibuprofen or with antibiotics if bacterial in origin. Tonsilitis involving palatine tonsils is dangerous because the swelling may interfere with breathing and/or swallowing. Tonsillectomy, the surgical removal of the palatine tonsils was common in the past. The development of modern drugs has greatly reduced the need for such removal, but it is still conducted in children who frequently develop throat infections with swelling of the tonsils.

The adenoid (pharyngeal tonsil) can enlarge nearly to the size of a ping pong ball and completely block airflow through the nasal passages. The patient switches to inhalation through an open mouth. The enlarged adenoid can also obstruct the nasal airway enough to affect the voice even without actually stopping nasal airflow altogether.

Another type of clinical occurrence involving tonsils is the development of tonsilloliths. These tonsil stones are calcified aggregates of bacterial and cellular debris that form in the tonsillar crypts, the crevices of the tonsils. While they occur most commonly found in the palatine tonsils, they may also occur in the lingual tonsils. Tonsilloliths can grow to a few millimeters in diameter before they are noticed. They may produce no symptoms, they may cause bad breath, or produce some pain during swallowing. Larger stones may be associated with an infection of the tonsil.

Summary

Tonsils are lymphatic nodules that form the first immunological defense of the digestive tube, at the pharynx. There are pharyngeal, tubal, lingual and palatine tonsils. They have tonsillar crypts that facilitate the entrance of antigens and pathogens deep into the tonsil, where they are processed and destroyed. During respiratory infections, tonsils can become swollen or inflamed. When the palatine tonsils become severely swollen they can hinder swallowing or even breathing. The situation can usually be controlled with medication but when infections are frequent, the palatine tonsils may be surgically removed.

Key terms

Lymphoid tissues, lymphoid nodules, immunological defenses, pharyngeal tonsil, adenoid, tubal tonsil, palatine tonsil, lingual tonsil, tonsil, tonsillectomy, tonsillar crypt, lymphocyte, tonsillitis, tonsillolith.

Figure credits

Figure 1 by OpenStax College - Anatomy & Physiology, Connexions Web site. http://cnx.org/content/col11496/1.6/, Jun 19, 2013., CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=30148305

Figure 2 by OpenStax College - Anatomy & Physiology, Connexions Web site. http://cnx.org/content/col11496/1.6/, Jun 19, 2013., CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=30148317

Figure 3 by Henry Vandyke Carter - Henry Gray (1918) Anatomy of the Human Body (See "Book" section below)Bartleby.com: Gray's Anatomy, Plate 1027, Public Domain, https://commons.wikimedia.org/w/index.php?curid=566973

Figure 4 by Michael Katotomichelakis, Dimitrios G Balatsouras, Konstantinos Bassioukas, Nikolaos Kontogiannis, Konstantinos Simopoulos, Vassilios Danielides. - Recurrent prurigo nodularis related to infected tonsils: a case report. Journal of Medical Case Reports. 2008; 2:243. doi:10.1186/1752-1947-2-243, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=4979803

Figure 5 by Glacko2021 at the English language Wikipedia, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=21331822