The human
palatine tonsils (PT) are covered by
stratified squamous epithelium
A stratified squamous epithelium consists of squamous (flattened) epithelial cells arranged in layers upon a basal membrane. Only one layer is in contact with the basement membrane; the other layers adhere to one another to maintain structural i ...
that extends into deep and partly branched tonsillar crypts, of which there are about 10 to 30.
The crypts greatly increase the contact surface between environmental influences and lymphoid tissue. In an average adult palatine tonsil the estimated
epithelial surface area of the crypts is 295 cm
2, in addition to the 45 cm
2 of epithelium covering the
oropharyngeal surface.
The crypts extend through the full thickness of the tonsil reaching almost to its hemicapsule. In healthy tonsils the openings of the crypts are fissure-like, and the walls of the
lumina are in apposition. A computerized three-dimensional reconstruction of the palatine tonsil crypt system showed that in the centre of the palatine tonsil are tightly packed ramified crypts that join with each other, while on the periphery there is a rather simple and sparse arrangement.
The crypt system is not merely a group of
invaginations of the tonsillar epithelium but a highly complicated network of canals with special types of epithelium and with various structures surrounding the canals, such as blood and lymphatic vessels and germinal centers.
Macrophages and other
white blood cells concentrate by the tonsillar crypts as well, in response to the microorganisms attracted to the crypts. Accordingly, the tonsillar crypts serve a forward sentry role for the
immune system, by providing early exposure of immune system cells to infectious organisms which may be introduced into the body via food or other ingested matter.
However, the tonsillar crypts often provide such an inviting environment to
bacteria that bacterial colonies may form solidified "plugs" or "stones" within the crypts. In particular, sufferers of chronic
sinusitis or
post-nasal drip frequently suffer from these overgrowths of bacteria in the tonsillar crypts. These small whitish plugs, termed "
tonsilloliths" and sometimes known as "tonsil stones," have a foul smell and can contribute to
bad breath; furthermore, they can obstruct the normal flow of
pus from the crypts, and may irritate the throat (people with tonsil stones may complain of the feeling that something is stuck in their throat).
References
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Lymphatics of the head and neck
Tonsil