Functional morphology of the tongue in the domestic turkey (Meleagris gallopavo gallopavo var. domesticus)

Abstract

Nowadays, microstructural and ultrastructural analysis of organs of the avian beak cavity points to new aspects of adaptation to food intake through the various feeding groups. These data should undoubtedly be considered in the time of mass production of compound feed in poultry, when many studies analyze the optimal size of food particles and their doses. Galliformes possess complex mechanisms of food collection and transport in the beak cavity. They collect food by pecking and transport food by using catch-and-throw and slide-and-glue mechanisms. The aim of current research is to conduct functional analysis of the tongue in poultry such as domestic turkey in context of type of food, method of food intake, and transport to the esophagus. The study involves observations of macroscopic and microscopic structures of the tongue mucosa by light microscopy and scanning electron microscopy techniques with histochemical analysis of lingual glands. The obtained results showed that the tongue in domestic turkey fills two-thirds of the beak cavity. The lingual structure responsible for pecking is a rigid plate called lingual nail that works similar to a shovel to collect food. The median groove presented on surface of the tongue indicated path of food transport. The conical papillae on border between the lingual body and root are responsible for the last stage of food transport, while the papillae on the sides of root stabilize the path of food transport. For the first time, the presence of 2 types of cornified mucosal epithelia, orthokeratinized and parakeratinized epithelium, was presented. The analysis of occurrence of complex tubular lingual glands indicates production of mucous secretions composed of neutral mucopolysaccharides, with addition of sialomucins and sulfomucins. Mucous secretions moisturize surface of the tongue, thus facilitating the transport of dry food. The presence of sulfur mucopolysaccharides responds to protective function. To sum up, the tongue in domestic turkey is adapted to collect fine or coarse ground feed in form of mash or pellets through pecking and its transport to the esophagus using the slide-and-glue and throw-and-catch mechanisms.

Pattern Distribution of Connexins in the Ortho- and Parakeratinized Epithelium of the Lingual Mucosa in Birds

“…This is important for a constantly desquamating parakeratinized epithelium. During the cytodifferentiation of the keratinocytes in the ortho- and parakeratinized epithelium of the avian tongue, cells in the intermediate layer change their shape [ 34 , 35 , 36 , 37 , 38 , 39 ]. Firstly, they become polygonal and then flatten.…”

“…The cornified layer, which is the final product of the cornification process of the multilayered epithelia, in the orthokeratinized epithelium is built up by strongly flattened keratinocytes devoid of cell nuclei and organelles [ 34 , 35 , 36 , 37 , 38 , 39 ]. The superficial cells of the orthokeratinized epithelium exfoliate as scales.…”

“…There is a lack of reports about the occurrence of connexins in the species-specific multilayered epithelia of the mucosa of the beak cavity of birds, including the tongue. On the avian tongue, there are two types of cornified epithelia, i.e., ortho- and parakeratinized epithelium, composed only of three layers: basal, intermediate, and superficial [ 33 , 34 , 35 , 36 , 37 , 38 , 39 ]. These epithelia are found in functionally different areas of the avian lingual mucosa.…”

“…The orthokeratinized epithelium is present in areas subject to mechanical stress during food intake, i.e., the lingual nail on the ventral surface of the lingual apex and on the conical papillae of the tongue. In contrast, the parakeratinized epithelium covers areas involved in food transport on the dorsal surface of the tongue [ 36 , 37 , 39 ].…”

Oropharyngeal cavity floor morphology in Eretmochelys imbricata (Testudines: Cheloniidae) hatchlings and evolutionary implications

“…Morphological and functional tongue characteristics differ significantly among tetrapods. Several studies have reported high lingual papillae densities on the surface of reptilian tongues (Beisser et al, 1998; Cizek et al, 2019; Iwasaki, 1990; Iwasaki et al, 1992; Lintner et al, 2012), similarly to amphibians (Jasiflski, 1979; Żuwała & Jakubowski, 2001), birds (Abumandour & El‐Bakary, 2017; Jackowiak et al, 2011; Skieresz‐Szewczyk et al, 2021) and mammals (Barbosa et al, 2020; Barboza & Larkin, 2020; Ciena et al, 2013; Masuko et al, 2007; Okada & Schraufnagel, 2005; Reginato et al, 2020). Only snakes are currently known to lack lingual papillae on the entire tongue surface (El‐Mansi et al, 2020; Iwasaki & Kumakura, 1994; Iwasaki & Yoshihara, 2003).…”