Tonsils - Anatomy & Physiology

Introduction

Sometimes the term tonsil is used to refer to all mucosal associated lymphoid tissue (MALT). In this article it will specifically deal with tonsils located in the nasopharynx & oropharynx.

The tonsils are part of the MALT and more specifically the GALT. They are located in the nasopharynx and oropharynx and form a ring of lymphoid tissue around the pharynx to protect the openings into the alimentary and respiratory systems.

Structure

The tonsils are non-encapsulated lymphoid tissue. They have crypts lined with stratified squamous epithelium which are infiltrated with lymphocytes.

Species being covered here are dog, cat, horse, cattle and pig.

Pharyngeal

Also called adenoids

Present in all the species they are located on the pharyngeal septum in the nasopharynx. In cattle it is located on the caudal end of the septum.

Palatine

In common speech these are “the tonsil"

Present all species except the pig and are located dorsally in the lateral walls of oropharynx. In cattle and dogs and cats they are compact and in cattle they project away from oropharynx lumen and in cats and dogs they project towards the lumen. In horses they are diffuse.

Soft palate

Present in all the species but are the principal tonsils in the pig. Found on the ventral aspect of the soft palate (roof of oropharynx).

Tubal

Absent in the cat and dog. They are located in the lateral wall of the nasopharynx and provide protection to the entrance of the auditory tubes. Compact in cattle and pigs and diffuse in horses.

Lingual

Found in varying degrees in all species on floor of oropharynx.

Paraepiglottic

Present in the pig and are found rostrolateral to epiglottis base.

Histology

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  Germinal centers (Pharyngeal - cat)

  ^{©RVC 2008}
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  Tonsil crypt (Pharyngeal - cat)

  ^{©RVC 2008}
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  Stratified epithelium (Pharyngeal - cat)

  ^{©RVC 2008}

Functions

The tonsils are a secondary lymphoid tissue and B cells in the tonsils become committed to synthesise IgA.

Links

• Actinobacillus pleuropneumoniae in pigs may remain undetected by serological tests and swabbing in on the palatine tonsil

Originally funded by the RVC Jim Bee Award 2007

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