Histology of the lingual vallate papillae of the dromedary camel (Camelus dromedarius)

Abstract

The present study aimed at investigating the histological structures of the
vallate papillae of the tongue of the dromedary camel. Samples were taken
from the tongues of 5 healthy adult dromedary camels, then processed by
standard routine histological technique. The vallate papillae were broad,
encircled by a distinctive sulcus, and exhibited concave dorsal surfaces. The
papillae were covered with stratified squamous epithelium which was made
up of several layers of cells arranged from the basement membrane to the outer
surface as follows: basal layer; spinosum layer; squamous layer; corneum
layer. The lamina propria sub mucosa showed two well-defined layers. The
first one was located beneath the epithelium and characterized by loose
connective tissue. The second layer was much thicker and composed mainly
of dense irregular collagenous fibres. Deep to the circumvallate papilla was a
group of prominent tubulo-acinar glands (von Ebner’s glands). The main ducts
of the glands opened directly into the surrounding sulcus at different levels. In
general, the histological structures of the vallate papillae of the dromedary
camel were similar to those of other domestic mammals. The well-developed
von Ebner’s glands suggested their abundant serous secretion that reflected on
the high capability of gustation.

Full text

RESEARCH ARTICLE
University of Bahri Journal of Veterinary Sciences 2022; 1(2):72-79
http://journal.bahri.edu.sd/index.php/ubjvs
*Corresponding Author
Email Address: mortadamahgoub@bahri.edu.sd
72
Histology of the lingual vallate papillae of the dromedary
camel (Camelus dromedarius)
M.M.O. Elhassan*, Lemiaa Eissa, Rasha B. Yaseen
Department of Anatomy, College of Veterinary Medicine, University of Bahri, Khartoum, Sudan
KEY W O R D S
A B S T R A C T
Camel
Histology
Tongue
von Ebner’s glands
The present study aimed at investigating the histological structures of the
vallate papillae of the tongue of the dromedary camel. Samples were taken
from the tongues of 5 healthy adult dromedary camels, then processed by
standard routine histological technique. The vallate papillae were broad,
encircled by a distinctive sulcus, and exhibited concave dorsal surfaces. The
papillae were covered with stratified squamous epithelium which was made
up of several layers of cells arranged from the basement membrane to the outer
surface as follows: basal layer; spinosum layer; squamous layer; corneum
layer. The lamina propria sub mucosa showed two well-defined layers. The
first one was located beneath the epithelium and characterized by loose
connective tissue. The second layer was much thicker and composed mainly
of dense irregular collagenous fibres. Deep to the circumvallate papilla was a
group of prominent tubulo-acinar glands (von Ebner’s glands). The main ducts
of the glands opened directly into the surrounding sulcus at different levels. In
general, the histological structures of the vallate papillae of the dromedary
camel were similar to those of other domestic mammals. The well-developed
von Ebner’s glands suggested their abundant serous secretion that reflected on
the high capability of gustation.

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INTRODUCTION
Dromedary camel (Camelus dromedarius) is considered as an
important livestock species which adapted to live in regions
with high temperature and dry climate (Al-Dahash and Sassi,
2009). Large population of this unique animal is existed in the
arid lands of Eastern Africa including Sudan, Somalia,
Ethiopia, Kenya and Djibouti (Gebreyohanes and Assen,
2017).
Camel has developed several morphological adaptations to live
in harsh conditions. One of these adaptations is that the
dromedary camel has very sturdy mouth to maintain the
efficient feeding of thorny and rough-stem plants which
naturally grow in the arid regions (El Sharaby et al., 2012). In
addition, several studies on the mouth of camel have described
the anatomical features of camel tongue (Qayyum et al., 1988;
Takehana et al., 2001; Peng et al., 2008; Salehi et al., 2010; El
Sharaby et al., 2012; Thanvi et al., 2020). With regards to its
dorsal surface, similar to ruminants, the tongue of camel is
characterized by the presence of fungiform and vallate papillae,
and the lack of foliate papillae as well (Thanvi et al., 2020).
Generally, the vallate papillae are classified as gustatory
papillae with taste buds (Abou-Elhamd et al., 2018). Each
papilla is encircled by a papillary groove and an annular pad of
the surrounding lingual mucosa (Qayyum et al., 1988).
Although several studies have displayed the microstructure of
the vallate papillae of camel, it is believed that detailed
histological structures are much less documented. Therefore,
the present study was conducted to provide histological
information on the vallate papillae of the tongue of the
dromedary camel.
Figure 1: Photomicrograph of vallate papilla showing the concave dorsal surface with non-keratinized stratified squamous
epithelium (arrowheads), sulcus (stars), taste buds (arrow), lamina propria submucosa (LM), and von Ebner’s glands (G). Masson’s
trichrome stain.
MATERIALS AND METHODS
Five apparently healthy adult dromedary camels (aged 5 to 7
years) were used in this study. The animals were slaughtered at
a local abattoir in Omdurman city, Sudan. Histological samples
were taken from the dorsal surface of the animal tongues within
20 min after slaughter. Samples were fixed in 10 % neutral
buffered formalin (pH 7.4) for 5 days and then processed for
routine histological technique (Bancroft and Gamble, 2008).
Briefly, specimens were dehydrated in a series of alcohol
dilutions, cleared in xylene, and embedded in paraffin wax.

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Sections of 4-5 µm were cut, deparaffinized in xylene, and
rehydrated in decreasing concentrations of alcohol. In the next
steps, sections were stained with heamatoxylin and Eosin
(H&E), or Masson’s trichrome stains.
The stained sections were examined using a light microscope
(Olympus BX63-Japan) connected to a digital camera
(Olympus DP72). Photomicrographs were captured using
video image software (Cell Sens 510- Olympus).
Fig. 2: Photomicrograph of vallate papilla (V) showing thick epithelium (E) at the dorsal surface and thin epithelium at the
lateral surface (e). H&E stain.
RESULTS
The vallate papilla was broad, encircled by a distinctive sulcus,
and exhibited a concave dorsal surface. It was covered by
stratified squamous epithelium. Immediately beneath the
epithelium was a well-defined lamina propria submucosa (Fig.
1).
The stratified squamous epithelium covered the papilla was
either non-keratinized or parakeratinized. The non-keratinized
epithelium was seen at the concave part of the dorsal papillary
surface (Fig. 1). The parakeratinized epithelium was observed
in the other regions of the papilla. The thickness of the
epithelium varied distinctively according to the region. The
greater thickness was seen on the upper surface of the papilla
whereas the lesser one was located at the lateral surface of the
sulcus (Fig. 2).

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Fig. 3: Photomicrograph of the vallate papilla showing the layers of the stratified squamous epithelium. The basal layer of columnar
cells (arrow), spinosum layer (S) of stratified cells with prominent spinous processes, squamous layer (arrowhead), and corneum
layer (C). Taste bud within the epithelium (TB). Masson’s trichrome stain.
The epithelium was composed of several layers of cells
arranged from the basement membrane to the outer surface as
follows: basal layer; spinosum layer; squamous layer; corneum
layer. The basal layer consisted of a single layer of columnar
cells. Some of these cells showed tiny spinous processes in their
lateral and upper surfaces. The spinosum was composed of
multiple layers of cells which were predominantly polyhedral
in shape. They exhibited numerous well-developed spinous
processes, as compared to the cells of the basal layer, radiated
from their outer surfaces (Fig. 3). The squamous layer
comprised different layers of flattened cells which had small
spinous processes. The latter reduced gradually in the layers
towards the outer surface (Fig. 3).
Taste buds were located in the lateral side of the vallate papilla.
They were spherical in shape and connected to the groove by
taste pores (Fig. 4A). The taste buds presented two types of
cells, large spindle-shaped neuroepithelial cells with prominent
nuclei, and small sustentacular cells, some of which showed
mitotic activity (Fig. 4B, C). Nonmyelinated nerve was
observed emerging from the basal area of the taste buds (Fig.
4A).
The lamina propria sub mucosa showed two well-defined
layers. The first layer was located beneath the epithelium, and
characterized by loose connective tissue. The second layer was
much thicker and composed mainly of dense irregular
collagenous fibres (Fig. 5). Deep to the circumvallate papilla,
the lamina propria submucosa exhibited a group of small
tubulo-acinar glands (von Ebner’s glands). Each gland was
covered by a connective tissue capsule predominantly
composed of collagenous fibres. Many thin trabeculae were
observed extending from the capsule, and divided the gland
into lobules. Serous acini separated by collagenous fibres
existed within each lobule. The duct system included
intralobular and interlobular ducts, both of which were lined by
simple cuboidal epithelium, and the main duct was almost lined
with stratified cuboidal epithelium. The main ducts of the
glands opened directly into the surrounding sulcus at different
levels (Fig. 6).

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Fig. 4: Photomicrograph of the lateral surface of a vallate papilla (V). A: gustatory sulcus (star), taste pore (arrowhead),
nonmyelinated nerve (arrow) arising from the base of the taste bud. B: spindle-shaped neuroepithelial cells with prominent nuclei
(arrowheads), sustentacular cells (arrows). C: sustentacular cell showing mitotic activity (arrow). A, H&E stain. B & C, Masson’s
trichrome stain
DISCUSSION
In the present study, the general histological structure of the
vallate papillae of the camel was similar to the findings reported
in camel by Qayyum et al. (1988) and El Sharaby et al. (2012),
as well as in other domestic animals (Kobayashi et al., 2005;
Eurell and Frappier, 2006).
In this study, the first three layers (basal, spinosum, and
squamous layers) of the stratified epithelium displayed cells
with spinous processes. However, such spinous processes were
less developed in the basal and squamous layers as compared
to the spinosum layer. Similar observation was indicated in
previous study carried out on donkey by Abd-Elnaeim et al.
(2002).
Taste buds in the current findings were located at the lateral
side of the vallate papillae but no buds were observed within
the dorsal surface of the papillae. Similar findings have been
reported by Takehana et al. (2001) in bactrian camel and El
Sharaby et al. (2012) in dromedary camel. However, taste buds
were reported in the dorsal surface of the tongue of camel
foetus during the third trimester of gestation (Abou-Elhamd et
al., 2018). The absence of the taste buds in the dorsal surface

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of the tongue of adult camel might have been due to a postnatal
development as a result of cellular involution that may
accompany increasing depths of the papillary circular grooves
(Abou-Elhamd et al., 2018).
Fig. 5: Photomicrograph of a vallate papilla showing the lamina propria submucosa. Loose connective tissue (L) with fine
collagenous fibres located beneath the epithelium (E). Dense connective tissue (D) with irregular connective tissue fibres.
Masson’s trichrome stain
The histological structures of the taste buds in this study were
similar to previous investigations conducted in mammals (Abd-
Elnaeim et al., 2002; Shao et al., 2010; El Sharaby et al., 2012;
Mescher, 2018). Nonetheless, the taste buds of camel need
further electron microscopical investigations to identify their
fine cellular structures.
In this study, prominent von Ebner’s glands were observed in
the lamina propria submucosa deep to the circumvallate papilla.
Each gland emptied into the sulcus through a separate duct. It
is known that the continuous flow of the serous secretion over
the taste buds would wash away food particles and
subsequently the taste buds can receive and process new
gustatory stimuli (Mescher, 2018). Therefore, it is plausible
that the presence of well-developed von Ebner’s glands along
with their numerous ducts may indicate the abundant secretion
of the glands, resulting in effective gustation of the dromedary
camel.
The general histological structures of the vallate papillae of the
dromedary camel were similar to those of other domestic
mammals. The well-developed von Ebner’s glands suggested
their abundant serous secretion that reflected on the high
capability of gustation. Further electron microscopical studies
are suggested in camels to elucidate the fine structures of the
taste buds.

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Fig. 6: Photomicrograph of vallate papilla showing von Ebner’s glands. A and B: main ducts (arrowheads) of the gland (G) open
into the gustatory sulcus (star). B: connective tissue capsule (arrow) surrounding the gland. C: Interlobular duct with simple
cuboidal epithelium (arrowhead), and the main duct with stratified cuboidal epithelium (arrow) of the serous gland (G). D: dense
collagenous fibres of the capsule (C) surrounding the gland; serous acini (A); intralobular duct (arrowhead) opens into the
intralobular duct (arrow). Masson’s trichrome stain.
CONCLUSION
The general histological structures of the vallate papillae of the
dromedary camel were similar to those of other domestic
mammals. The well-developed von Ebner’s glands suggested
their abundant serous secretion that reflected on the high
capability of gustation. Further electron microscopical studies
are suggested in camels to elucidate the fine structures of the
taste buds.
COMPETING OF INTERESTS
The authors declare that they have no competing interests.
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