الفهرس 
Esophagus and cropOnly 14 pages are availabe for public view
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Abstract
The normal structure of the digestive tract of the turkey, and its development at various stages, was studied using LM, SEM and TEM. The period covered included post-fertilization to post-hatching.
The histological structure of the turkey gut is very similar to that of the chicken digestive tract, except that 1) the muscularis mucosae always consists of only one layer of smooth muscle; and 2) the esophageal glands open into a crypt-like structure close to the esophageal-proventricular junction, especially near lymph nodules.
During early post fertilization development, the esophageal lumen appears star-shaped in cross section, with a lining epithelium of two layers of cuboidal cells. No epithelial buds of mucous glands were observed at early stages. The development of the crop was similar to that of the esophagus except that the lumen was rounded and not stellate in shape. With later development the esophageal lumen became wider and the thickness of the lining epithelium layer increased. Its superficial layer became stratified. Mucous glands appeared as epithelial buds within the lamina propria, and later formed a lining of a single layer of low columnar to high cuboidal cells. The muscularis mucosae was an incomplete ring of elongate mesenchymal cells which developed between the lamina propria and tunica submucosa. The surface epithelium showed pits with well-defined grooves with the glands opening into these. The basal layer of the lining epithelium projected down to form the papillae of the lamina propria. The esophageal glands opened to the lumen by short ducts through the lining epithelium.
The structure of the crop was the same as that of the esophagus except there were no glands and the thickness of the stratified squamous epithelium was greater. The
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papillae of the lamina propria projecting into the epithelium were! mote=lounded-rtliaii in the esophagus. The mucus glands were continuously present in the lamina propria; above the level of first lobule of the proventricular glands, at the esophageal-proventricular junction.
After hatching, the mucosa of the esophagus was thrown into numerous longitudinal folds of variable length. The outer epithelial layer had a tendency to desquamate. The epithelial basement membrane was well developed. The basal germinal layer of the epithelium showed mitotic figures and reacted strongly with PAS/Alcian Blue technique. The esophageal glands were mucus in nature. The tunica submucosa was thin and it was hardly visible in some places, while in others it widened out to include substantial amounts of fibrous connective tissue. The thickness of the crop’s lining epithelium increased and was thicker than that of the esophagus. With progressive post-hatch development, the surface epithelium became more convoluted and thicker, the mucosal pits deeper. The stratified squamous epithelium became thicker, with a clearly-defined basal layer. At the esophageal-proventricular junction there were strands of longitudinal muscle passing over the glandular lobule surface to contact the inner surface of the muscularis mucosae. Before the point of junction, the stratified squamous epithelium lost a great number of its cell layers and was substantially narrowed. The stratified squamous epithelium was invaginated to form crypts whose lining epithelium was a simple columnar, mucus secreting type of cell.
The lamina propria later became more cellular and more infiltrated with lymphocytes, with the papillary bodies being well developed. The lumina of the mucus glands increased in size, as did their activity, shown by a strong reaction to both PAS and
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:Aidattiakte technique. The: secretory materials of the glands showed as homogenous darklyistiained peripheral portions of rER cisternae.
The lining epithelium was much more developed at 16 days post hatching. The layers of cells became more numerous than in previous ages, the upper layers changed to be more squamous and had a great tendency to desquamate. The lamina propria was more cellular than at earlier ages. The mucus glands were more active, indicated by a stronger reaction to PAS & Alcian Blue technique.
The crop was similar in its development to the esophagus, but lacked mucus glands and had a thicker epithelial lining. The papillae of the lamina propria were more invaginated and rounded, and the lumen was wider than that of the esophagus.
The proventriculus, at early post fertilization stages, was lined by a simple columnar type epithelium without folds. Simple branched tubular glands were observed within the lamina propria; these contained epithelial buds. These glands were inactive in early stages, indicated by a lack of reaction with PAS/Alcian Blue. The SEM showed only minimal development of these glands in early stages. An isolated thin sheath of longitudinally oriented smooth muscle fibers was the only component of the muscularis mucosae. Irregular mucosal folds appeared later, and epithelial buds were transformed into a complex glandular structure. A duct system was formed from primary, secondary, and tertiary ducts. Oxyntico-peptic cells appeared: these were pyramidal to round with a distinctly vesicular central nucleus. These cells had numerous mitochondria, and prominent Golgi complexes. Argyrophil cells (CS+) were observed throughout the post fertilization stages, with their numbers increasing with progressive development. Before the end of post fertilization stage, the proventricular mucosa became convoluted, forming
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clear plicae and sulci of varying lengths. The glandular and’thie Cti’18t `systeiii were
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well developed. Lymphoid infiltration was increased within the latiiina cproPria.„( the
muscularis externa showed more extensive development of the muscle fibers.
After hatching, the proventriculus showed continued development of its plicae and sulci, and the lining epithelium became even more strongly reactive to PAS/Alcian Blue. The surface of these cells showed a hexagonal shape. Glands with a compound tubulo-alveolar architecture formed from tubules resting on the basement membrane; these were the proventricular glands that grew progressively more complex in their structure. Oxyntico-peptic cells were flask-like in shape with many ribosomes covering the outer surface of their nuclei, and abundant mitochondria. These cells were negatively stained with the PAS/Alcian Blue technique. With continued development, the plicae developed independently within the organ lumen, becoming arranged concentrically about the elevated openings of the compound glands. Mucosecretory cells were characteristic of the columnar epithelium. The collagen and reticular fibers, which made up the connective tissue core of the glandular sinus, increased in number. Endocrine cells were more common in the deep region of the glands than the upper parts. These cells showed variable numbers of secretory granules in their cytoplasm and a well-developed Golgi complex. The lamina propria became more cellular and contained large numbers of blood vessels and some elastic tissue. The peculiar appearance of the cells on the laminae of the proventricular glands is due to a lack of junctional complexes at the apical ends. The cells lining the alveoli, especially in the deep portion, were wider and larger than the cells nearer the neck. These cells had oval mitochondria in the supranuclear cytoplasm. Variably large numbers of secretory granules were found in the apical cytoplasm of these
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cells and they had microvilli. The endocrine cells were numerous. These had a large pvI.Mentrals located nuclei and sometimes were characterized by cytoplasmic processes.
The lining epithelium of the gizzard in the early post-fertilization stages was stratified columnar. In some places the lining epithelium invaginated to form crypt-like structure. No clear structural arrangement was observed in the lamina propria. With further development the lining epithelium invaginated to form gastric pits, and the epithelium changed to a tall columnar type. Tubular branched glands characteristic of the gizzard were found within the lamina propria. Three types of cells lining the gizzard glands were detected: chief cells, basal cells and endocrine cells. The secretion of the gastric glands produced a distinct cornified layer. These secretions reacted strongly with PAS/Alcian Blue and the Verhoeff-Masson stains. The depth of the glands increased and showed more penetration down into the lamina propria as development continued.
The thickness of the cornified layer increased and appeared laminated after hatching. Glandular pits became clearer, distinct and deeper in the lamina propria, which became more cellular. The principal secretory cells lining the glands were cuboidal to low columnar, with well-developed rough endoplasmic reticulum. Basal cells were observed only in the depth of the glands, and they were few in numbers. Endocrine cells were less numerous than the other two types. These were rounded and located basally between the glandular cells. The muscle cells were given direction by thin, slightly wavy,
connective tissue.
The tendinous layer developed considerably post hatching. It was formed from bundles of parallel collagenous fibers with few fibrocytes. The muscular layer formed the bulk of the wall of the gizzard. No argentaffin cells were observed in turkey stomach at
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any stage, nor was a muscularis mucosae present. At the,junttion betweeil thoginarei t(nd duodenum, mucus glands replaced the cornified layer and the gizzard rglandii.,rVilli appeared, and there were lymphatic aggregations at this junction. The lengths of the tubular glands increased and their lumina were wider and filled the lamina propria. They were arranged in-groups, separated by collagen fibers and reticular fibers.
The development of the intestine was a feature of both pre- and post-hatching
stages, with a histological structure very similar among the three parts of the small
intestine. Through most of the post fertilization period, the villi were shorting knob-like
in their shape. The formed over a compact mesenchymal layer, and goblet cells were
difficult to identify. The tunica submucosa was an undifferentiated mesenchymal layer in
early stages. The lining epithelium developed into the columnar absorptive type with a
strong reaction to the PAS/Alcian Blue technique. The length of villi continually increased, their shape changed, and with progressive development showed some degree of branching. The muscularis mucosae was formed from one layer of smooth muscle fibers and in some places, it extended into the lamina propria. The simple tubular glands (crypts of Lieberkuhn) were observed. These glands were located at the base of the villi. They decreased toward the end of small intestine, as did the length of villi. The argyrophil ”CS+” and argentaffin ”MF+” cells were observed in both pre- and post-hatching development. Throughout the post-hatching period the length of villi and their shaped were variable, especially in the large intestine. The lining epithelium of post-hatching intestine reacted strongly with PAS/Alcian Blue, and was also positive to Best’s carmine. The lamina propria was highly cellular and filled the core of the villi. The diameter of intestine was variable from one part to another, the diameter of the jejunum
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I rlWascamalleit• than the diameter of the duodenum, and the diameter of the ileum was smallor thAn that of jejunum.
The large intestine development in post fertilization was similar to the development of small intestine except the villi were shorter. The goblet cells were numerous.
Caecum formed from three regions, proximal parts wall was thicker than middle and distal ones.
Argentaffin cells were found in the lining epithelium of the rectum, few crypt of Lieberkiihn were observed.