Vìsnik Dnìpropetrovsʹkogo Unìversitetu: Serìâ Bìologìâ, Ekologìâ (Sep 2014)
Histological structure of the digestive tract of waders (Aves, Сharadrii)
Abstract
Histological structure of digestive tracts of 12 species of waders (Aves, Сharadrii) has been studied: Pluvialis squatarola (Linnaeus, 1758), Charadrius hiaticula (Linnaeus, 1758), Recurvirostra avosetta (Linnaeus, 1758), Tringa ochropus (Linnaeus, 1758), T. glareola (Linnaeus, 1758), T. nebularia (Gunnerus, 1767), T. erythropus (Pallas, 1764), Philomachus pugnax (Linnaeus, 1758), Calidris minuta (Leisler, 1812), C. ferruginea (Pontoppidan, 1763), C. alpina (Linnaeus, 1758) and Gallinago gallinago (Linnaeus, 1758). The features of histological structure of all parts of the digestive tract of the waders species under analysis were defined and adaptations in the structure of the digestive system to distant migrations were detected. It is determined that the histological structure of the wall of the esophagus of the studied species of waders is universal, and the relief of mucosa is folded; stratified squamous epithelium of the mucous membrane has an insignificant degree of hornification. A large number of esophagus glands is observed in the lamina propria of the mucosa; these glands secrete mucus which facilitates the movement of food along the esophagus. The muscular coat is well-developed and formed by longitudinal and circular layers of smooth muscle tissue. It is found that characteristics of histological structure of the stomach wall of the waders species under analysis are presupposed by the following functions: 1) glandular stomach wall provides secretion of digestive enzymes through active secretory activity of glands of deep complex; 2) secretion (mucus) of simple tubular glands is excreted to the surface of glandular stomach performing the protective function; 3) the wall of the muscular stomach provides mechanical treatment of food through well-developed muscle layer and solid layer of the cuticle. It is established that the waders’ intestine is shortened, that is compensated by the complication of the relief of intestinal mucosa by plates that form complex mazes and anastomoses, several times increasing the absorbing surface of the intestine. The plates are covered with a single layer of prismatic bordered epithelium which includes Goblet cells, the number of which increases in the caudal direction of intestines. It is found out that the particular feature of the histological structure of the examined wall of the waders’ small intestine is multi-layer location of crypts in the mucosa. A large number of cambial cells with figures of mitosis were noticed in the crypt, which indicated the intensive processes of proliferation of intestinal enterocytes. These features in the structure of the wall of the small intestine are considered as adaptations to distant migrations and are connected with waders’ intense nutrition on migration stops. For the first time Meckel diverticulum has been found in waders and its histological structure has been described. It is established that waders’ Meckel diverticulum is a lymphoid-epithelial organ and it serves as the immune system of waders’ digestive tract. It is stated that the wall of waders’ rectum has wrinkles that contribute to its stretching; mucous membrane has the plate relief, it is lined with a single layer of epithelium bordered with many Goblet cells. It is revealed that different parts of the investigated waders’ cecum have uneven development of histological structures and the presence of lymphoid tissue clusters in the lamina propria mucosa indicates the functional belonging of the cecum to the immune defense system of waders’ digestive tract; the presence of mainly bordered enterocytes in the surface epithelium indicates its osmo-regulatory function
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