Histological studies
Gizzard was observed as the spheroid component with four tunics from inside to outside as the tunica mucosa, tunica sub-mucosa, tunica muscularis and tunica serosa. In the luminal surface of mucosal folds, a cuticle layer of koilin was evident. It was a keratinous hard membrane which works as the support system for the grinding of food material in ventriculus. In the region of lamina propria of mucosa, there were long tubular glands that were surrounded by by cuboidal as well as columnal epithelial cells. In between the long mucosal folds, the horizontal koilin was also noticed (Fig 1). Rarely, the tubular glands were replaced by acinar glands. These glands were placed adjoining to koilin membrane at abluminal end (Fig 2).
The substantial horizontal koilin layer was also observed as the surrounding connective tissue in between the acinar glands and lymphoid aggregation. The acinar glands and horizontal koilin were shown their prominancy in absence of lamina propria (Fig 3 and 4).
The tunica submucosa was present in squeezed manner rather than the mucosa, wherein the interwoven collagen fibers were seen. The tunica musculariswas present as a thin inner circular and a thick outer longitudinal layer. It was intermingling with collagen and elastic fibers. The outermost tunica serosa has shown its existence as the limiting membrane which has bordering adipose connective tissue with blood vessels (Fig 5).
Histochemical studies
The PAS reaction was observed for glycogen at koilin layer, also at the mucosal folds and glandular epithelium (Fig 6). The activity for alkaline phosphatase was detected in the koilin layer and connective tissue septae (Fig 7).
The intensity of acid phosphatase activity was very mild in between the koilin layer and mucosal folds (Fig 8).
The succinic dehydrogenase activity was observed at the koilin layer and also at internal and external tunica muscularis (Fig 9).
The present study in respect of ventricle or gizzard has revealed the long mucosal folds along with the tubular glands in lamina propria. It was surrounded by the mixed epithelium after cuboidal and columnar cells that was in accordance to the reportings revealed by
(Rodrigues et al., 2012) in Blue and Yellow macaws. The present studies also showed the mucosal low folds which were covered by simple columnar epithelium continuous with lamina propria located tubular mucous glands which was similar to the findings of (
Mehra and Kumar, 2020) in Gizzard of the Broiler chicken. The horizontal koilin in between long mucosal folds was also detected with some traces of the koilin cuticle in the crypts of gastric glands. A few acinar glands in mucosal layer of ventriculus at the bordering abluminal end of koilin membrane. The observance of tubular glands in present studies is not being supported by available documentation as various accessible evidential records have identified the ventriculus or gizzard as the muscular stomach only. The encountered alteration might be attributed to the output of higher quantum of secretion required while maintaining softer and workable cuticlar layer of koilin for the grinding of ingested food material. Therefore, pertaining to gizzard and its histomorphological findings it is appropriate to be termed as Glandulo muscular stomach.
A thin interior circular and a thick exterior longitudinal muscle fiber layer were observed as reported by
Zhu (2015) in Black-tailed crake (
Porzana bicolor) and
Al-Saffar and Al-Samawy (2015) and in Mallard (
Anas platyrhynchos). The tunica serosa showed the connective tissue wherein blood vessels were embedded as reported by
Al-Saffar and Al-Samawy (2015) in Mallard (
Anas platyrhynchos).
The PAS activity for glycogen observed at koilin layer, mucosal folds and glandular epithelium were in concurrence with as reported by
Hamdi et al., (2013) in black winged kite (
Elanuscaeruleus), black tailed crake (
Porzana bicolor) (
Zhu, 2015) and cattle egret (
Bubulcus ibis) (
Hussein and Rezk, 2016). These observations by different workers were completely in agreement with the present findings. Positive activity showing components were involved into the optimal function for which glycogens acted as the source of energy. The lymphocytic aggregation and the glycogen may show their presencetogether. However, the glycogen beyond limitation may results the infection which can be arrested by natural defense mechanism after lymphoid aggregation. Hence both were seen as the check and balance mechanism in maintaining normal function of tissue.
The present findings have revealed weak alkaline phosphatase activity at the koilin layer, connective tissue septae of submucosa, mucosal layer and tunica muscularis. Moreover, the very mild activity of acidic phosphatase was noticed in between the koilin layer and mucosal folds. The present findings were in complete consensus with
Selvan et al., (2008) in post hatched Guinea fowl and
Das et al., (2017) in Kadaknath fowl as they had negative activity. The lower of alkaline phosphatase and acidic phosphatase activity was there which exhibited the functional superiority of that organ component.
Higher activity of succinic dehydrogenase was observed in the koilin layer and the internal and external tunica muscularis. Contrary,
Selvan et al., (2008) has noticed negative activity of succinic dehydrogenase in post hatched guinea fowl. The enzyme succinic dehydrogenase functions for mitochondrial cell respiration and thereby the energy generation. Even, the presence of this enzyme work to inhibit the cancerous growth by oxygen modulation. As the gizzard has stronger musculature and grinding koilin membrane it necessitate the oxygen modulation. Exhibition of intense activity of this enzyme at koilin layer and also at internal as well as external tunica muscularis might be considered as the natural but defense mechanism of the bird and the supportiveness towards conclusive findings unearthed by present studies.
