Anatomical and histological aspects of the bovine lingual tonsil

The localization of the bovine lingual tonsil is described as a prerequisite for the removal of specified risk material from the tongue meat in order to restrict the risk arising from bovine spongiform encephalopathy (BSE) to public health. The major part of this tonsil can be located macroscopically by the openings of its follicular crypts at the root of tongue. This part consists of organized aggregations of lymph nodules. Additional solitary primary lymph nodules and diffuse accumulations of lymphocytes are macroscopically invisible but are bilaterally present in the area extending 2 cm caudal to 3 cm rostral to the last vallate papillae. By sectioning the tongue 3 cm rostral to the last vallate papillae, undermining the lingual mucosa to the level of these papillae and making a transverse cut towards the lingual process of the basihyoid bone, the greater part of the lingual tonsil can efficiently be removed. Finally, immunohistochemical staining demonstrated the presence of T and B lymphocytes, suggesting that the bovine lingual tonsil can be considered as a site where an immune response can be induced.     

Pathogenesis of experimental bovine spongiform encephalopathy: preclinical infectivity in tonsil and observations on the distribution of lingual tonsil in slaughtered cattle

The infectivity in tissues from cattle exposed orally to the agent of BSE was assayed by the intracerebral inoculation of cattle. In addition to the infectivity in the central nervous system and distal ileum at stages of pathogenesis previously indicated by mouse bioassay, traces of infectivity were found in the palatine tonsil of cattle killed 10 months after exposure. Because the infectivity may therefore be present throughout the tonsils in cattle infected with BSE, observations were made of the anatomical and histological distribution of lingual tonsil in the root of the tongue of cattle. Examinations of tongues derived from abattoirs in Britain and intended for human consumption showed that macroscopically identifiable tonsillar tissue was present in more than 75 per cent of them, and even in the tongues in which no visible tonsillar tissue remained, histological examination revealed lymphoid tissue in more than 90 per cent. Variations in the distribution of the lingual tonsil suggested that even after the most rigorous trimming of the root of the tongue, traces of tonsillar tissue may remain.     

Bovine lingual tonsil: histomorphological characteristics with special reference to the follicular dendritic cells

In the bovine, the lingual tonsil is localized at the lingual radix. However, as the expansion of the tonsillar tissue was presumed to be much larger than the macroscopically visible part, selected specimens from the bovine tongue were examined to clarify if lymphatic tissue of the lingual tonsil was present rostral of a defined macroscopical landmark, i.e. rostral of the most caudal of the papillae vallatae. The identification of the lymphoreticular system was validated by means of the detection of reticulum cells, especially follicular dendritic cells (FDC). They characterize the tonsillar lymph nodules and distinguish them structurally from unspecific accumulations of lymphocytes. In our study, two monoclonal antibodies, i.e. CNA.42 and D46, detected bovine FDC cells in situ. 'Organized' lymphoid tissue--i.e. solitary lymph nodules and aggregations of lymph nodules, both either with or without surrounding connective tissue, and with or without crypts, but with immunopositive reactions for FDC--could be observed up to 30 mm rostral of the most caudal of the papillae vallatae. As these formations were not identified macroscopically, they shall be referred to as the disseminate part of the lingual tonsil.     

Vallate papillae in the domestic rabbit (Oryctolagus cuniculus f. domestica)

On the root of the tongue in the rabbit there are two symmetrically located vallate papillae, covered by nonkeratinized stratified squamous epithelium. The epithelium is characterized by variable thicknesses, forming epithelial streaks of different length and irregular shape. Taste buds are found both in the epithelium covering the papillae and in the epithelium of the outer walls of the papillae from the side of the furrows. The outer wall of the vallate papillae is gradually transformed with no visible boundary into the surface of the root of the tongue devoid of papillae. The surface of the vallate papillae is uneven. The connective tissue core of the papillae is formed by numerous, irregularly shaped connective tissue papillae, between which epithelial streaks are arranged. Around the connective tissue core of the papillae there is a circular connective tissue fold, with a furrow located on its circumference and the core of the outer wall of the vallate papillae. Numerous excretory ducts of the posterior serous lingual glands (Ebner's glands) open on the fundus of the circular furrow of each vallate papilla. Sometimes excretory ducts of these glands open directly onto the surface of a vallate papilla and then in their vicinity taste buds are found. The results of this study show the structure of vallate papillae on the tongue of adult rabbits, at the same time indicating differences in their structure in comparison to the vallate papillae of other animal species.     

Distribution of the lingual tonsils of cattle designated as specified risk materials

The tonsils of cattle, including palatine tonsils, pharyngeal tonsils, tubal tonsils and lingual tonsils, are designated as specified risk materials (SRM). However, the detailed distribution of lingual tonsils in cattle is unknown. We therefore histologically examined their distribution in 198 tongue specimens from cattle. The examinations confirmed that the presence of lingual tonsils was limited to the tissue of the lamina propria on the dorsal and lateral aspects of the tongue, not reaching the muscular layer below. More than 90% of the lingual tonsils were located between the distribution center of the vallate papillae and the radix linguae (root of the tongue). However, they were also found in the area extending from the lingual torus to the rostral-most vallate papilla in an individual, suggesting that the complete removal of the lingual tonsils requires elimination of the lamina propria extending from the lingual torus to the radix linguae.     

Shortening of the bovine tongue according to regulation (EC) 999/2001 is not complying with the current legal definition of specified risk material - a macroscopical and histological preliminary study

The full elimination of all specified risk material (SRM) in food of animal origin is crucial for consumer protection and is of high priority in inner EU trade. Among other tissues, the tonsils of cattle are considered as SRM. The aim of this study was to evaluate whether the 'cut at the back of the tongue just before the tongue bones' required by EC regulation is sufficient to remove tonsils and lymphatic tissue completely. Eight skulls from cattle were collected for the simulation of a vertical cut according to the EC regulation and the detection of the target at the back of the tongue. Further, specimens of the lingual mucosa were cut out from two tongues and examined microscopically. The most caudal of these specimens was from the macroscopically visible part of the lingual tonsil. The most rostral specimen contained the most caudal Papilla vallata. Simulation of the obligatory ventro-dorsal cut yielded hits at varying locations on the dorsal surface of the tongue, sometimes including tissue of the lingual tonsil. Histological examination of the lingual mucosa gave clear evidence that lymphatic tissue resembling the tissue of a tonsil in terms of its histological organization and infiltration of the mucosal epithelium could even be found in areas with no macroscopically visible lingual tonsils.     

Anatomical and surface ultrastructural investigation of the tongue in the straw-coloured fruit bat (Eidolon helvum,Kerr 1972)

The morphology of tongue in straw-coloured fruit bat from tropical forests was evaluated in relation to frugivorous diets and in comparison with other species that consumes other food types. Gross, stereomicroscopy, scanning electron microscope and histological methods were used. The tongue was relatively long with round tip, which closely fitted into oral cavity. Five types of mechanical papillae included crown-like and trifid filiform papillae. Also bulky, cone-shaped papillae and long conical papillae were identified. These mechanical types also showed variations in shape, size and number of processes of papillae. Transitional forms of these mechanical papillae were present. Fungiform papillae with taste pores were interposed amongst filiform types in apex and body; three ovoid-shaped vallate papillae were in triangular arrangement on root and displayed taste pores. Some bulky, cone-shaped papillae surrounded the vallate papillae. Histologically, mechanical filiform types showed highly keratinized stratified squamous epithelium and dense connective tissue core with secondary papillae. Taste buds appeared in fungiform and vallate papillae. Neutral and acidic secretions were identified in lingual glands of root. The presence of prominent filamentous processes of filiform papillae and conical papillae of the tongue in conjunction with gustatory papillae ensures adaptation to copious fruit diets. The gross morphometric and histometric parameters of the tongue did not differ remarkably from previous values obtained for some fruit bats with comparable weight. This investigation showed similarities with fruit bats such as large flying fox and Egyptian fruit bat and reflect common diet and feeding habits but varied from insectivorous and nectivorous bats.     

Histology, immunohistochemistry and ultrastructure of the equine palatine tonsil

The palatine tonsils of five young horses formed 10-12 cm elongated follicular structures extending from the root of the tongue on either side to the base of the epiglottis and lateral to the glossoepiglottic fold. The stratified squamous non-keratinized epithelium of the outer surface was modified into crypts as reticular epithelium by heavy infiltration of lymphoid cells from underlying lymphoid follicles. In places, lymphoid tissue reaching almost to the surface and with only one to two cell layers intact was identified as the lymphoepithelium. Langerhans cells with Birbeck granules were interspersed between epithelial cells. Lymphoid tissue organized in lymphoid follicles constituted the parenchyma of the palatine tonsil. CD4-positive cells were more numerous and CD8-positive lymphocytes less numerous compared with their distribution in the lingual tonsil. B cells and macrophages were also more numerous than in the lingual tonsil and lectins showed a different pattern of attachment. M cells were not observed. High endothelial venules with well-developed vesiculo-vacuolar organelle had structural evidence of transendothelial and interendothelial migration of lymphocytes. Striated muscles as seen in the deeper lamina propria mucosae of the lingual tonsil were absent. The immunohistological and ultrastructural characteristics of the equine palatine tonsil are similar to those of humans but differ from those of the lingual tonsil and are consistent with a role as an effector and inductor immunological organ.     

Shortening of the Bovine Tongue According to Regulation (EC) 999/2001 is not Complying with the Current Legal Definition of Specified Risk Material – a Macroscopical and Histological Preliminary Study

The full elimination of all specified risk material (SRM) in food of animal origin is crucial for consumer protection and is of high priority in inner EU trade. Among other tissues, the tonsils of cattle are considered as SRM. The aim of this study was to evaluate whether the ‘cut at the back of the tongue just before the tongue bones’ required by EC regulation is sufficient to remove tonsils and lymphatic tissue completely. Eight skulls from cattle were collected for the simulation of a vertical cut according to the EC regulation and the detection of the target at the back of the tongue. Further, specimens of the lingual mucosa were cut out from two tongues and examined microscopically. The most caudal of these specimens was from the macroscopically visible part of the lingual tonsil. The most rostral specimen contained the most caudal Papilla vallata. Simulation of the obligatory ventro‐dorsal cut yielded hits at varying locations on the dorsal surface of the tongue, sometimes including tissue of the lingual tonsil. Histological examination of the lingual mucosa gave clear evidence that lymphatic tissue resembling the tissue of a tonsil in terms of its histological organization and infiltration of the mucosal epithelium could even be found in areas with no macroscopically visible lingual tonsils.     

Histological characteristics and stereological volume assessment of the ovine tonsils

Tonsils form a first line of defence against foreign antigens and therefore play a key role in immunity. Since documented information about ovine tonsils is limited, a study was performed in which the morphological characteristics and the volume of lymphoid tissue present in each ovine tonsil were determined. The tonsils of five adult healthy sheep were examined histologically and the volumes were estimated using the Cavalieri method. The pharyngeal tonsil had a mean volume of 1296.1 ± 205.9 mm³ and was by far the largest ovine tonsil, followed by the paired palatine tonsil with a mean volume of 715.0 ± 110.5 mm³. The tonsil of the soft palate, the paired tubal and paraepiglottic tonsils and the lingual tonsil were much smaller with a mean volume of, respectively, 90.3 ± 24.9 mm³, 80.1 ± 24.3 mm³, 29.7 ± 11.8 mm³ and 10.1 ± 2.8 mm³. The folds and crypts of the pharyngeal and palatine tonsils were covered by a reticular and a non-reticular epithelium. Both tonsils were mainly composed of primary and secondary lymph follicles. The palatine tonsils contained 1–3 crypts with a few secondary infoldings. Lymphoid tissue in the tonsil of the soft palate was located at the nasopharyngeal (dorsal) side of the soft palate. The tubal tonsil was lined with a pseudostratified columnar ciliated epithelium and consisted of scattered lymphoid cells and lymph follicles. The paraepiglottic tonsil consisted of lymph follicles and aggregated lymphoid cells. Its overlying keratinized stratified squamous epithelium was folded and often heavily infiltrated by lymphocytes. The ovine lingual tonsil was not macroscopically visible and did not contain clearly distinguishable lymph follicles. It consisted of aggregations of lymphoid cells that were mainly located within the vallate lingual papillae.     

Ultrastructure of Lingual Papillae in Common Chimpanzee (Pan troglodytes) Foetus,Newborn and Adult Specimens

Among primates, the two recognized species of chimpanzees (common chimpanzee, Pan troglodytes; pygmy chimpanzee, Pan paniscus) are considered to be the most similar to humans. Importantly, in mammals, the food intake behaviour largely determines the tongue morphology, including the type, proportion and distribution of gustatory and non‐gustatory tongue papillae. The lingual papillae form during its development and mature in post‐natal life depending on the different feeding. In this study, we have used scanning electron microscopy to analyse the age‐related changes in the lingual papillae of foetal, newborn and adult P. troglodytes. Four main types of lingual papillae, denominated filiform, fungiform, foliate and vallate, and one subtype of filiform papillae called conical papillae, were found. The main age‐related changes observed in all kinds of papillae were a progressive keratinization and morphological complexity along the lifespan. During the foetal period, there was scarce keratinization, which progressively increases in young animals to adulthood. The number of filiform increased with ageing, and both filiform and fungiform papillae in adult tongues are divided into pseudopapillae. On the other hand, the vallate papillae vary from smooth simple surfaces in foetal tongues to irregular surfaces with grooves and pseudopapillae (microscopic papilla‐shaped formations within the papilla itself) in adults. These results describe for the first time the age‐related variations in the three‐dimensional aspect of lingual papillae of the chimpanzee tongue and provide new data to characterize more precisely these structures in the human closest specie.     

Characteristics of Filiform, Fungiform and Vallate Papillae and Surface of Interface Epithelium-Connective Tissue of the Maned Sloth Tongue Mucosa (Bradypus torquatus, Iliger, 1811): Light and Scanning Electron Microscopy Study

The study of lingual surfaces and the surface of interface epithelium-connective tissue of the tongue of Bradypus torquatus was performed by employing the light and scanning electron microscopy (SEM) techniques. The results revealed that the rostral part of the tongue presents a round apex and covered by filiform and fungiform lingual papillae and a ventral smooth surface. It was observed that the epithelial layer of the dorsal surface possesses the basal, spinosum, granular and cornified epithelial cells. The lamina propria is characterized by a dense connective tissue forming the long, short and round papillae. Numerous typical filiform papillae are located especially in the rostral part intermingled for few fungiform papillae, which were revealed in three-dimensional SEM images. Usually, the fungiform papillae are located in the border of rostral apex of the tongue exhibiting the rounded form. They are covered by keratinized epithelial cells. In the fungiform papillae, several taste pores were observed on the surface. The vallate papillae presented numerous taste buds in the wall of epithelial cells, being that the major number of taste buds is located on the superior half of vallate papilla. The taste pores are surrounded by several laminae of keratinized epithelial cells. The samples treated with NaOH solution and examined by SEM revealed, after removal of the epithelial layer, the dense connective core in original disposition, presenting different sizes and shapes. The specimens stained with Picrosirius and examined by polarized light microscopy revealed the connective tissue, indicating the collagen fibres type I and type III.     

Anatomical localisation and histology of the ovine tonsils

The topography and histologic structure of the various tonsils were studied anatomically and microscopically in 15 sheep aged between 9 and 15 months. The palatine, pharyngeal and paraepiglottic tonsils were readily visible macroscopically. They consisted mainly of secondary lymph nodules and were encapsulated in dense connective tissues. The epithelium covering the tonsils and their crypts was frequently infiltrated heavily by lymphocytes. The tubal tonsil and the tonsil of the soft palate were macroscopically visible after fixation in 2% acetic acid. These tonsils consisted of scattered lymph nodules, aggregations of lymphocytes and diffuse lymphoid tissue. They were not encapsulated, and therefore the borders of these tonsils could not be clearly delineated. The lingual tonsil was not macroscopically visible in sheep and consisted of scattered small aggregations of lymphocytes.     

Characteristics of Dorsal Lingual Papillae of the Bactrian Camel (Camelus bactrianus)

The morphology of dorsal lingual papillae of the Bactrian camel (Camelus bactrianus) was studied by using light and scanning electron microscopy. Filiform and lenticular papillae were considered as mechanical papillae but fungiform and vallate papillae were considered as gustatory papillae. Filiform papillae were distributed mostly in the anterior two-thirds region of the tongue. Each filiform papilla consisted of one primary papilla and a few smaller secondary papillae. Lenticular papillae were distributed on the torus linguae. The larger papillae were arranged in two parallel lines medially whereas the smaller papillae were laterally located. Most of the fungiform papillae were found on the lateral margins of the anterior two-thirds of the tongue. These papillae were small and round. Intra-epithelial taste buds were located on the dorsal surface of each papilla. The vallate papillae were arranged in two rows on each rim of the torus linguae. Each round- and flat-shaped vallate papilla was surrounded by a prominent gustatory groove and an annular pad. A few taste buds were observed in the lateral epithelium of the papillae. The keratinization of the covering stratified squamous epithelium of the mechanical lingual papillae was relatively thicker than those of the gustatory papillae. The lingual papillae of the Bactrian camel exhibited some different characteristics from other domestic ruminants. These morphological characteristics of the tongue of the Bactrian camel might have evolved to assist the camel in prehension and manipulating of the inorganic stiff plants that grow in its environment and therefore might relate to the feed and feeding habits of the animal.     

Papillary architecture of the Leopardus pardalis tongue

The ocelot (Leopardus pardalis) is a Felidae of wide geographical distribution and food flexibility; therefore, it is essential to understand the morphology of the species. Thus, we aimed to describe its lingual morphology in order to gain information regarding the anatomy of this carnivore's digestive system. The tongues ??were removed for ex situ macroscopic and morphometric analyses, as well as for light microscopy and scanning electron microscopy, of fragments of the different lingual regions. The tongue of L. pardalis had an elongated form that was subdivided into the apex, body and root, in which four papillary types were observed: filiform, fungiform, circumvallate and conical. It presented with a stratified, keratinized squamous epithelium, followed by loose and dense connective tissues, as well as a skeletal striated musculature that comprised most of the organ. In addition, in scanning electron microscopy the filiform papillae showed a complex with multiple layers of keratin with triangular shape projected caudally in oral cavity. The fungiform papillae were distributed among the filiform and showed a rounded shape with some gustatory pores, and are keratinized but in a lower intensity if compared with filiform. The vallate papillae, located in lingual root, showed an oval format, had a deep groove surrounded the papillae and some gustatory pores. The conical papillae are located in lingual root and are similar to the filiform. The tongue of L. pardalis resembles other carnivorous species, mainly among felids. However, it differed in relation to the quantity of vallate papillae and the absence of foliate papillae.     

Morphological study of the lingual papillae in the barking deer, Muntiacus muntjak

The morphology of the tongue of the adult barking deer, Muntiacus muntjak, was examined by light and scanning electron microscopy. The result showed that the tongue of the barking deer was elongated with a rounded apex. Four types of lingual papillae were observed: filiform, fungiform, vallate and large conical papillae. The filiform papillae represented the most numerous types of lingual papillae. The fungiform papillae were distributed among the filiform papillae on the rostral and the body portions of the tongue. Ten to thirteen vallate papillae were distributed on both sides of the lingual prominence among the large conical papillae. Histologically, both the fungiform and vallate papillae contain taste buds in the epithelial layer. The distribution and types of lingual papillae found in the barking deer are similar to those in the other species that belong to the family Cervidae.     

Morphology of the dorsal lingual papillae in the black rhinoceros (Diceros bicornis)

The dorsal lingual surface of a black rhinoceros (Diceros bicornis) was examined by scanning electron microscopy. The tongue was about 30 cm in length. There were about 60 vallate papillae on both sides. Filiform, fungiform and vallate papillae were found. The filiform papillae were distributed over the entire dorsal surface of the tongue. The papillae had a hair-like shape. The fungiform papillae were round in shape, and more densely distributed on the lingual apex. No foliate papillae were seen on the dorsal surface. The vallate papillae were located on both sides of the posterior end of the lingual body. Each papilla was surrounded by a groove.     

scanning electron microscopy of lingual papillae in the common shrew, Sorex araneus, L

The dorsal surface of the tongue of the adult common shrew (Sorex araneus L.) was examined by scanning electron microscopy. As in the other insectivores, three types of lingual papillae were observed: filiform, fungiform and vallate papillae. The filiform papillae represented the most numerous type of lingual papillae. The characteristic feature of the filiform papillae, covering the apex and corpus of the tongue, is the two processes tilted to the root of the tongue. The filiform papillae on the lingual apex are reduced in size and structure. Five to six fungiform papillae are placed symmetrically along the left and right border of the corpus of the tongue. Two large oval vallate papillae are located on the radix of the tongue. The posterior surface of the tongue in common shrew is covered with a smooth mucosa with the openings of the serous glands.     

Scanning Electron Microscopic Study of the Lingual Papillae in the Arctic Fox (Alopex lagopus L., 1758)

This study aims to show the distribution and the three-dimensional structure of the lingual papillae in the arctic fox. The macro- and microscopic structure of the tongue and its lingual papillae was studied in 11 adult arctic foxes. Two types of mechanical papillae were distinguished on the dorsal surface of the tongue – filiform papillae and conical papillae. The gustatory papillae in the arctic fox are represented by fungiform, vallate and foliate papillae. The keratinized filiform papillae on the anterior part of tongue are composed of one big posterior process accompanied by 10–12 secondary anterior processes. The number of anterior processes of filiform papillae undergo a complete reduction within the area between the posterior part of the body of the tongue and area of the vallate papillae. The conical papillae cover the whole dorsal surface of the root of the tongue, including the lateral parts surrounding the area of the vallate papillae and the posterior part of the root. The size of the conical papillae increases towards the root of the tongue but their density decreases. In the arctic fox, there are three pairs of vallate papillae distributed on the plan of a triangle. The diameter of vallate papillae in each successive pair is bigger. The wall surrounding the body of the vallate papilla and its gustatory trench is composed of six to eight conical papillae joined at various degree. The foliate papillae on both margins of the tongue consist of seven to nine laminae.