Tonsils (Waldeyer ring)
Anulus lymphoideus pharyngis
Also known as: Waldeyer ring, Waldeyer's ring, pharyngeal lymphoid ring, tonsillar ring, lingual tonsil, tubal tonsil
A ring of partially encapsulated lymphoid tissue guarding the entrances to the digestive and respiratory tracts: the pharyngeal tonsil (adenoids), paired tubal tonsils, paired palatine tonsils and the lingual tonsil.
Overview
The tonsils are aggregates of mucosa-associated lymphoid tissue (MALT) arranged around the upper pharynx where inhaled and ingested antigens first make contact with the immune system. From above downwards the ring comprises the pharyngeal tonsil (adenoids) on the roof and posterior wall of the nasopharynx, the tubal tonsils around the pharyngeal openings of the auditory tubes, the palatine tonsils in the lateral walls of the oropharynx, and the lingual tonsil on the posterior third (pharyngeal part) of the tongue.
Unlike lymph nodes, tonsils have no afferent lymphatics and are only partially encapsulated (a capsule lies only on the deep surface of the palatine tonsil). Instead, their surface epithelium dips down into crypts (or folds) lined by reticulated epithelium infiltrated by lymphocytes, dendritic cells and M-like cells, which sample antigen directly from the lumen and pass it to underlying lymphoid follicles with germinal centres. They produce IgA and IgG and help prime mucosal immunity in childhood. Tonsillar tissue is largest between about 3 and 10 years of age and regresses after puberty.
- Location
Around the nasopharynx and oropharynx — the "gateway" where the airway and food passages begin.
Parts & subdivisions
- Single, in the roof/posterior wall of the nasopharynx; respiratory epithelium with folds; largest at 3–7 years.
- Paired, around the torus tubarius at the pharyngeal openings of the auditory tubes; hypertrophy can block the tubes and contribute to otitis media.
- Paired, in the tonsillar fossae between the palatoglossal and palatopharyngeal arches; stratified squamous epithelium with deep crypts. "The tonsils" of everyday speech.
- Collection of lymphoid follicles on the posterior third of the tongue, each with a single shallow crypt lined by stratified squamous epithelium; drains to the deep cervical nodes.
Anatomy
- Lymphatic drainage
Retropharyngeal and deep cervical nodes (palatine tonsil → jugulodigastric node).
- Histology
Lymphoid follicles with germinal centres beneath a surface epithelium that is respiratory (pharyngeal and tubal tonsils) or stratified squamous non-keratinised (palatine and lingual tonsils), invaginated into crypts or folds.
- Development
Palatine tonsil epithelium derives from the 2nd pharyngeal pouch; lymphocytes infiltrate during the second half of fetal life; germinal centres form after birth.
Function
- Sample inhaled and ingested antigens and initiate mucosal (IgA) and systemic immune responses.
- Provide early immune protection against upper respiratory and oral pathogens, particularly in childhood.
Clinical significance
Adenotonsillar hypertrophy and sleep apnoea
The commonest cause of obstructive sleep apnoea in children (snoring, witnessed apnoeas, poor sleep, behavioural problems, rarely cor pulmonale); adenotonsillectomy is usually curative.
Tonsillar cancer and lymphoma
Human papillomavirus (HPV-16)-associated squamous-cell carcinoma arises in the crypt epithelium of the palatine and lingual tonsils — a rapidly rising cancer in younger non-smokers, often presenting as a cystic neck node; it has a better prognosis than tobacco-related disease (p16-positive). Waldeyer ring is also a common site of extranodal non-Hodgkin lymphoma (asymmetric tonsillar enlargement in an adult needs biopsy).
Compiled from standard anatomy and physiology references — see the Lymphatic & Immune System sources. For education only; not medical advice.