Postnatal development of the upper digestive tract in the Japanese quail

Abstract

The structure and postnatal development of the upper digestive tract of Japanese quails were studied using 72 birds aged from day-old to 60 days for proper understanding of their functional peculiarities. The growth, morphology and histology of the tongue, pharynx, cervical and thoracic parts of oesophagus, crop, proventriculus and gizzard were studied using six birds at each age group. The age groups studied were at three days interval upto 15 days and thereafter at five days interval upto 30 days and then at ten days interval upto 60 days of age. Maximum weight of each part was recorded at 60 days of age. But maximum contribution to body weight by each part occurred within the first week of age.

The tongue, pharynx and oesophagus were lined by stratified squamous epithelium, which showed keratinization on the anterior two-third of the ventral surface of the tongue and on the papillae of the tongue and pharynx. Filiform, conical and fungiform papillae were present on the base of the tongue. The rostral lingual glands contained both serous and mucous end pieces, but posterior glands showed only mucous cells. The taste buds were associated with the glandular ducts. The skeleton of the tongue showed signs of ossification from 30th day of age, with the tip of the entoglossal bone remaining cartilaginous even upto 60 days of age.

In the pharynx, pharyngeal tonsil and palatine, sphenopterygoid and cricoarytenoid salivary glands were noticed. In addition to mucous and pieces the medial palatine glands exhibited serous and pieces also. Within the choanal slit and laryngeal inlet the squamous epithelium changed into respiratory epithelium. Laryngeal cartilages were cricoids, procricoid and paired arytenoids.

The oesophagus was represented by a long cervical and short thoracic parts with a diverticulum, the crop. The epithelium on the top of the longitudinal mucosal folds was higher in the cervical oesophagus. Mucous glands were present throughout the oesophagus and crop but much reduced in the greater curvature of the crop and lymphoid tissue was absent at the region. Muscularis mucosa and submucosa entered into the longitudinal folds. Tunica muscularis consisted of iner circular and outer longitudinal layers of smooth muscles. Tunica adventitia was the outermost layer. A well developed oesophageal tonsil was present at the oesophago- proventricular junction.

THh spindle-shaped proventriculars had a mucosa studied with minute nodules. Surface epithelium consisted of cuboidal to columnar cells. Lamina propria contained simple tubular glands. Muscularis mucosa consisted of scattered bundles of longitudinagl smooth muscle fibres. The compound tubular glands in the submucosa were lined by oxyntico peptic cells which had a dentate appearance. Tunica muscularis consisted of inner and oter longitudinal and middle circular layers of smooth muscle fibres. Outermost was the serosa. At the isthmus, the glands and outer longitudinal muscle layer of proventriculus disappeared and the lamina propria contained glands similar to those of gizzard.

The biconvex dis-shaped gizzard had a greater dorsoventral diameter than cranio – caudal diameter. Internal to the serous lining was the tendon layer which was thickest at the tendinous aponeurosis and absent at the blind sacs. The lateral muscles consisted of a single layer of smooth muscle where as the blind sacs had inner longitudinal and outer circular muscle layers. Submucosa was dense and the muscularis mucosa absent. The tubular gland in the lamina propria were lined mainly by chief cells, and few basal and intermediate cells.Tall columnar cells which showed supranuclear PAS positive reaction, constituted the surface epithelium. The gizzard lining consisted of arrays of vertical columns, secreted by the tubular glands and a matrix produced by surface cells. The junction of gizzard with duodenum was marked by a constriction of muscularis mucosa forming a fold of the muscularis and tunica propria. Posterior to the fold spatula –shaped duodenal villi and coiled tubular glands with goblet cells were observed.