Tonsils

The tonsils are collections of lymphoid tissue located in the mucosa of the pharynx. They play a critical role in the body's first line of defense by sampling antigens entering through the mouth and nose. Together, the tonsils form a ring of protective tissue known as Waldeyer’s ring.

Types of Tonsils

Structure

• Non-encapsulated or partially encapsulated lymphoid tissue
• Covered by mucous membrane epithelium (stratified squamous for palatine and lingual; ciliated columnar for pharyngeal)
• Contain crypts (invaginations) to increase surface area for antigen exposure (especially in palatine and lingual tonsils)
• Composed of lymphoid follicles with germinal centers for B cell proliferation

Function

• Immune surveillance: Trap and respond to pathogens entering via mouth or nose
• Antibody production: Site of local IgA production by activated B cells
• Antigen presentation: T and B lymphocytes are activated in response to foreign particles

Blood Supply

• Palatine tonsils: Tonsillar branch of facial artery (main), others include dorsal lingual, ascending palatine, ascending pharyngeal arteries
• Pharyngeal tonsil: Ascending pharyngeal and pharyngeal branch of maxillary artery
• Lingual tonsil: Dorsal lingual artery

Innervation

• Palatine tonsils: Glossopharyngeal nerve (CN IX) – sensory; causes referred ear pain in tonsillitis
• Pharyngeal and tubal tonsils: Pharyngeal branch of vagus (CN X)

Lymphatic Drainage

• Drains primarily to the jugulodigastric node (a prominent node of the deep cervical group)

Waldeyer’s Ring

A circular arrangement of lymphoid tissue in the pharynx:

• Pharyngeal tonsil (roof of nasopharynx)
• Palatine tonsils (oropharynx)
• Lingual tonsils (posterior tongue)
• Tubal tonsils (nasopharynx near auditory tube)

Clinical Significance

• Tonsillitis: Inflammation of the palatine tonsils; often bacterial or viral
• Adenoid hypertrophy: Enlarged pharyngeal tonsil; may obstruct nasal breathing and affect speech
• Tonsillectomy: Surgical removal of palatine tonsils, usually for recurrent tonsillitis or sleep apnea
• Referred Otalgia: Tonsillar inflammation can cause ear pain via glossopharyngeal nerve

Comparative Anatomy

Tonsillar tissue is found in many mammals, but the complete Waldeyer’s ring is especially developed in humans due to reliance on oral and respiratory exposure routes. It provides rapid immune response against ingested or inhaled pathogens.