Seasonal Variations in the Digestive Tract of the Little Owl, Athene noctua: Anatomical, Histological, and Scanning Electron Microscopical Studies

Avian Gastroenterology: Anatomy and Assessment

Gastrointestinal disease is a common presenting complaint in avian patients as owners can readily identify clinical signs associated with disorders of the gastrointestinal system. In birds, vastly different diets, environments, and feeding strategies have resulted in vast anatomic and physiologic differences between families. Practitioners treating avian patients should be familiar with the normal gastrointestinal anatomy and physiology of the species they are treating as well as how these species differences affect the diet and husbandry of captive and noncaptive avian patients.

Descriptive embryological insights of the colorectum of quail embryos with concern to its functional morphology

BACKGROUND

Quail is an interesting emerging bird species gaining attention in developmental embryology research due to its small size, quick lifespan, and fast growth rate. These characteristics make quail an ideal model for examining the development of the gastrointestinal tract. Consequently, the embryonic development of the colorectum was conducted to provide a comprehensive understanding of its functions in digestion, absorption, and immunity.

METHODOLOGY

The morphological anatomy and microscopical structure of the colorectal wall of 74 embryos were studied using light and scanning electron microscopy (SEM). Histologically, the embryos were collected and dissected to extract the intestine. The samples were then fixed in 10% neutral buffer formalin for a minimum of 24 h, and in 2.5% glutaraldehyde buffer formalin for semithin processing and scanning electron microscopy.

RESULTS

The wall of the embryonic colorectum on the hatching day consisted of three layers; mucosa, muscularis externa, and serosa. Mucosa was a simple layer of columnar enterocytes interspersed with goblet cells that appeared as cub-like shaped cells. Additionally, two ganglionic plexuses were also developed in the colorectal wall; Auerbach plexus (among the colorectal tunica muscularis) and Meissner plexus (submucosal plexus).

CONCLUSION

The morphological characteristics of the quail colorectum at different ages were closely related to its functional features.

Developmental morpho-analysis of the caecum in Japanese quail embryos (Coturnix coturnix japonica)

In the current study, we are focusing on the microanatomical structure of quail caecum during the prehatching time to try to understand the function and the role of each cell-built quail caecum reaching how caecum plays an essential role in immunity and absorption. The morpho-developmental features of the quail caecum were described in detail daily from the third incubation day (ID) till hatching time, investigating the gross morphology, microscopic, and ultrastructure using light and scanning electron microscope. The embryonic caecum appeared grossly as two lateral outpocketings with blinded ends, emerging laterally at the junction between the small and large intestine (the ileocaecal junction). The primordia of two caeca, represented by two lateral swellings from the hindgut on the fourth ID, continued growing till the day of hatching, where the caecal wall consisted of three apparent layers: mucosa, musculosa, and serosa. At the time of hatching, the quail caecum was still not fully mature and will continue growing posthatching. The findings in this study can be applied in further studies intended to understand the physiological mechanisms of the caecum during prehatching and posthatching periods. RESEARCH HIGHLIGHTS: Caecum is one of the hindgut derivatives that started as two lateral swellings. The caecal wall consisted of three layers; mucosa, musculosa, and serosa. The caecum plays an essential role in immunity maintenance. Caecum continues to grow posthatching as it is not fully mature at hatching time.

Anatomical, histochemical, and immunohistochemical observations on the gastrointestinal tract of Gallinula chloropus (Aves: Rallidae)

Background

Gallinula chloropus (Linnaeus, 1758) is a wild aquatic omnivorous bird characterized by a marked resistance to harsh environmental conditions and a worldwide distribution. In this study, anatomical, morphometrical, histochemical, and immunohistochemical techniques were employed to study the structure of the gastrointestinal tract of Gallinula chloropus.

Results

The esophagus appeared tubular with no distinct crop. Both superficial (SPG) and deep (DPG) proventricular glands were present. The DPG filled about two-thirds of the total wall thickness. Histochemically, the mucosubstances revealed mixed alcian blue-PAS positive reactions. They were mainly localized in the acini of the esophageal glands and SPG, gastric surface epithelium, duct system of DPG, and intestinal goblet cells. The highest number of goblet cells per every 1 mm2 of the intestinal mucosa was seen within the ileum and rectum, 2555 ± 468 and 2607 ± 653 respectively. Notably, glucagon immunoreactive (IR) cells were abundant in the mucosa of the small and large intestines and the proventriculus, while somatostatin IR cells were concentrated within the acini of the DPG. IR cells for the mitosis marker phospho-histone H3 (PHH3) were highest within the entire intestinal crypts and mucosa-associated lymphoid tissues (MALT). In contrast, cells IR for the apoptosis marker C.CASP3 were remarkable in epithelial cells at the tips of intestinal villi and in MALT, reflecting the dynamic nature of the latter mentioned structures.

Conclusions

The findings of the present study advance our knowledge of the gross and microscopic anatomy of the gastrointestinal tract in wild birds and could help to enhance the productivity of Aves via improving gut health.