Özet:

The esophagus in mammalians and avian species is a muscular organ shaped-like a tube. According to its direction, it is composed of sections as pars cervicalis, pars thoracica and pars abdominalis in mammalians, but such long pars cervicalis and short pars thoracica in avian species. Histologically, the wall of esophagus is made up of layers as tunica mucosae, tunica muscularis and tunica adventitia/serosa in mammalians and avian species. In mammalians and avian species, the tunica mucasae consists of four sublayers, characteristic of cutanous mucosae. In the lamina epithelialis, lined by stratified squamous epithelium, the extent of keratinization differs from species. The lamina propria constitues a fine connective tissue, including both collogen fibers and elastic fibers. In humans, there exist glands in the lamina propria superior to esophagus and proximal to the stomach. The glands exist also in lamina propria of birds. The lamina muscularis is made up of longitudinally arranged smooth muscle fibers, whereas the submucasa is composed of loose connnective tissue. The seromucous glands, also called esophageal glands, exist in the submucasa of mammalians. In both species, the tunica muscularis is composed of the layers of circularly and longitudinally arranged, respectively inside and outside. In mammalians, the cervical portion of esophagus is covered with the tunica adventitia, whilst its thoracal section is surrounded by mediastinal pleura. In birds, however, the esophagus, is covered all along with tunica adventitia composed of loose connective tissue. The crop, dilatation of the cervical esophagus toward ventrale in the opening of cavity of the thorax, is a special organ for birds and used for the storage of bolus. Although the crop is smilar to esophagus, its lamina epithelialis is thicker than that of esohagus and it predominantly lacks mucous glands greater of organ. The properties of other layers bear resemblance to that of esophagus

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