九乡新闻网郑州地铁8号线规划站点:The Histology of Chicken's Digestive System
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The Histology of Chicken's Digestive System
Cantello JL
In the chicken the salivary glands are of the mucous variety. They are located in the roof and floor of the oral cavity, tongue, and pharynx. Taste buds are present but sparse. They are associated with the ducts of salivary glands at the base of the tongue and the pharynx.
The esophagus has the usual seven layers. It is lined by a thick, nonkeratinized, stratified squamous epithelium. The muscularis externa is composed of smooth muscle along the entire length of the esophagus. Mucous glands occur in the lamina propria, but are lacking throughout most of the crop, which is a caudal diverticulum located approximately two-thirds of the way down the esophagus. The crop has a structure identical to the rest of the esophagus, but it lacks mucous glands.
The stomach of the chicken consists of a glandular proventriculus and a muscular ventriculus. The mucosa of the proventriculus is thrown into folds. Depressions between the folds are called sulci. The epithelium is simple columnar except at the base of the sulci, where it is cuboidal. The wall of the proventriculus consists of large, compound, tubular glands. The secretory cells, which are cuboidal to low columnar, produce both pepsinogen and hydrochloric acid, thus combining the function of mammalian chief and parietal cells. Each gland opens to the lumen of the stomach through a conical papilla.
The ventriculus is a highly muscular grinding organ. It is lined by an epithelium that invaginates into the lamina propria, forming elongated pits, each of which bears terminal tubular gastric glands. Cells of the latter secrete a thick, horny material. Although keratinlike, this substance, usually called keratinoid, is not chemically equivalent to keratin. It forms the tough inner lining, about
The intestine of the chicken is similar in structure throughout its length. It consists of a duodenum, jejunum, ileum, and large intestine. A pair of blind, elongated ceca join the intestine at the junction of the ileum and large intestine. The terminal end of the large intestine joins the coprodeum of the cloaca. Villi are present throughout the small and large intestines. They are longest in the duodenum, but gradually shorten and thicken caudally. In the coprodeum they are stumpy and rounded. Villi are present in the ceca also, becoming flattened toward the blind end. Crypts of Lieberkuhm are short and open between the villi, as in mammals. Although the wall of the intestine of the chicken is similar to that of the mammal, the absence of duodenal glands and an extremely thin submucosa in the chicken are notable differences.
As in mammals, the liver is covered by a mesothelium beneath which is a layer of connective tissue, Glisson’s capsule. Lobes of the liver are subdivided into numerous lobules indistinctly separated from one another. The radiating plates of hepatocytes in each lobule are two cells wide in the chicken. In contrast, those of mammals are one cell wide.
The gallbladder of the chicken is similar to that of the mammal. The mucosa is lined by a simple columnar epithelium and is strongly folded into villuslike projections when contracted.
The pancreas of the chicken resembles that of the mammal. The exocrine portion is tubuloacinar. Lobulation is indistinct because of the lack of interlobular connective tissue. Islets of Langerhans are abundant. Two types of islets, alpha and beta, can be easily recognized. Columnar alpha cells characterize the alpha islet. Polygonal beta cells are the principal cells of the beta islets. Alpha islets produce glucagons, whereas beta islets form insulin.