Dr. T. Balasubramanian M.S. D.L.O.
A ring of lympnoid tissue surround
the naso pharynx and oro pharynx. These lymphoid tissue are
collectively known as the waldayer's ring. Waldayer's ring has two
components, namely the inner and outer rings. The cervical lymph nodes
constitute the outer ring, while the inner ring is constituted by 1.
adenoid at the roof of nasopharynx, 2. tubal tonsils or tonsil of
Gerlac which surround the pharyngeal ends of eustachean tube. These
lymphoid tissue surround the naso pharynx.
The lymphoid tissue surrounding the
oropharynx also constituting the components of the inner Waldayer's
ring are 1. Lingual tonsil in the posterior 1/3 of the tongue, 2.
Palatine tonsils on either side of oro pharynx, and 3. sub epithelial
lymphoid tissue found in the posterior pharyngeal wall. All these
structures of the inner Waldayer's ring are inter linked.
Functions of Waldayer rings: These
Waldayer's rings consitute an antigen sampling center where the
extraneous antigens are caught and sampled stimulating the immune
mechanism. Antigens from inspired air are trapped by the adenoid and
the tubral tonsils. These antigens in turn stimulate release of
immunoglobins by the B lymphocytes. To facilitate eposure and trapping
of antigens the mucosa covering the adenoid is thrown in to grooves
called as furrows. These furrows serve to increase the surface area of
the adenoid tissue, similarly antigens from ingested food are captured
and sampled by the lingual and palatine tonsils. The mucosa covering
the palatine tonsils are thrown in to numerous crypts about 18 - 20 in
each tonsil. These crypts serve to increase the surface area of mucosa
covering the tonsil.
Fig showing the waldayer's ring
Anatomy of palatine tonsils: Palatine tonsils
are the largest member of the inner waldayer's ring. It is almond
shaped and lie on either side of the oropharynx. Develomentally
tonsils arise from the ventral portion of the second pharyngeal pouch,
i.e. ideally named as sinus tonsillaris. The trace of this sinus
is present in tonsil as supra tonsillar cleft.
Fig showing embryology of tonsil
Tonsil is lodged in the tonsillar fossa on either side
of orophayrnx. The tonsillar fossa lies between two pillars,
anterior and the posterior pillars. The anterior pillar is formed
by palato glossus muscle, the posterior pillar is formed by palato
pharyngeus muscle. The outer aspect of tonsil is lined by
condensed capsule formed by the pharyngobasilar fascia a specialised
portion (it is also known to course the surface of the tonsil and
extend into it to form septa that conduct nerves and vessels), deep to
which lie the superior constrictor muscle, lateral to which is the
bucco pharyngeal fascia. The glossopharyngeal nerve and the
stylohoid ligament pass downwards and forwards beneath the lower edge
of the superior constrictor in the lower part of the tonsillar
fossa. These structures collectively constitute the tonsillar
bed. The tonsil is virtually inseparable from its capsule, but the
capsule is united by loose connective tissue to pharyngeal muscles,
hence the tonsillar dissection is carried out in this plane.
The medial surface of the tonsil is free and
faces the oropharynx. It is covered by non-keratinizing
stratified squamous epithelium which is continuous with that of the
lining of the oropharynx. A triangluar fold of mucous
membrane extends back from the paltoglossal fold to cover the
anteroinferior part of the tonsil. This fold of mucous membrane
is known as plica triangularis. In childhood, this fold is
usually invaded by lymphoid tissue and becomes incorporated into the
tonsil.A semilunar fold of mucous membrane passes from the upper aspect
of the palatopharyngeal arch towards the upper pole of tonsil, thus
separating it from the base of the uvula.
Fig showing plica semilunaris
The main artery of the
tonsil is the tonsillar branch of the facial artery which enters the
tonsil near its lower pole by piercing the superior constrictor just
above the styloglossus muscle. Other arteries supplying the
tonsil are lingual artery through its dorsal lingual branches,
ascending palatine branch of facial artery, and ascending pharyngeal
occurs through the para tonsillar vein, and the vessels also pass
through to the pharyngeal plexus or facial vein after piercing the
from the tonsil pierce through the buccopharyngeal fascia and pass to
the upper deep cervial group of nodes, particularly to the
Nerve supply to
the tonsil is from the glossopharyngeal nerve.
Fig showing coronal section of tonsil
Web site contents © Copyright drtbalu 2006, All rights reserved