The dissertation presents new findings from a comprehensive morphological study of the digestive tract of the Yemen chameleon during the first year of postnatal ontogeny. The study aimed to determine the features of its morphofunctional organization and age-related dynamics. Anatomical dissection, histological, histochemical, morphometric, and mathematical methods were used.
The oesophagus of the Yemen chameleon is a short, thin tube that begins at the oropharynx, passes through the cervical visceral space, and continues into the cylindrical stomach. The boundaries between the oesophagus and the empty stomach, as well as between the stomach and the duodenum, are poorly defined. The small intestine consists of the duodenum, jejunum, and ileum. The jejunum forms a U-shaped loop and continues into the short ileum, which opens into the colon. The large intestine includes the colon and rectum. The colon has a diverticulum corresponding to the caecum, while the rectum continues into the cloaca. A characteristic feature is the partial or complete black pigmentation of the intestinal serosa.
The relief of the mucous membrane differs depending on the anatomical region. The oesophagus contains longitudinal folds, while the stomach has thick folds running in different directions. Longitudinal folds are formed in the duodenum, jejunum, and ileum, with their number and height gradually decreasing. The ileum and colon are separated by the ileocolic valve. The mucous membrane of the colon and rectum forms longitudinal folds, the colonic diverticulum has a smooth surface, and the cloaca contains pronounced longitudinal folds.
During the first year of life, the body weight of the chameleons increases 185.9-fold, with the most intensive growth occurring during the second and third months. The snout-to-vent length increases 6.7-fold, while the length of the digestive tract increases 3.8-fold. The absolute weights of the stomach and intestine increase 170.5-fold and 226.3-fold, respectively, whereas their linear dimensions increase 5.1-fold.
The walls of the oesophagus, stomach, and intestine consist of mucous, muscular, and outer membranes. The mucous membrane includes the epithelial layer, lamina propria, muscularis mucosae, and submucosa, while the muscular membrane consists of an inner circular and an outer longitudinal layer. In the cranial part of the oesophagus, the epithelium is simple columnar and consists of ciliated and goblet cells. The middle and caudal parts are dominated by epithelial cells with microvilli and secretory granules, indicating their involvement in the synthesis and accumulation of enzymes. The epithelial cells form interglandular protrusions that perform a mechanical supporting function. The lamina propria contains tubular glands with secretory portions and short excretory ducts.
By the age of one year, the height and width of the interglandular protrusions increase 5.1-fold and 3.2-fold, respectively, while gland depth increases 6.5-fold. The thickness of the oesophageal wall increases 5.9-fold, that of the mucous membrane 4.6-fold, and that of the muscular membrane 8.4-fold. The most pronounced changes in the lamina propria are associated with an increase in gland depth.
The gastric mucosa is lined with simple columnar epithelium containing surface mucous cells and oxynticopeptic cells. The glands are densely arranged within the lamina propria, and villus-like protrusions are formed between their openings. The PAS-positive reaction of mucocytes and deep glandular cells indicates the presence of neutral mucins and a combination of enzymatic and mucus-producing functions. The most intensive thickening of the gastric wall and mucous membrane occurs during the first month of life, whereas the muscular membrane develops most intensively up to two months of age.
Crypts and intercryptal protrusions were identified in the duodenum, with the crypt depth being almost three times greater than the height of the protrusions. The mucous membrane of the jejunum forms high folds containing centrally located slit-like lymphatic sinuses. The ileum has a similar structure, although its folds are smaller and fewer in number. The presence of large lymphatic sinuses suggests that the jejunum and ileum are the main sites of intensive lipid absorption.
The colonic mucosa contains crypts and the highest intercryptal protrusions, while its muscular membrane and muscularis mucosae have the greatest thickness. The wall of the colonic diverticulum is thinner and does not form folds. The rectum is characterized by a thick mucous membrane, wide crypts, intercryptal protrusions, numerous goblet cells, and a considerable amount of loose fibrous connective tissue.
The obtained results demonstrate substantial age-related changes in the structures of the digestive tract of the Yemen chameleon.
