The glandular stomach or proventriculus is an organ of the digestive system of birds that presents a spindle-shaped form craniocaudally, somewhat ventral and to the left.
Caudally unites with the muscular stomach in a constriction which is name isthmus.
The inner surface is covered by simple columnar epithelium; it contains mucin granules. Within the light, an important number of papillae visible macroscopically can be observed. The excretory duct of the multilobular glands of the lamina propria is opened in each papilla. The function of the glands is the production of hydrochloric acid and gastric proteolytic juice of the pepsin type.
At this point the bolus of food mixed with gastric juice will be formed to favor the digestion of the nutrients contained in the diet.
Then it will continue its way towards the muscular stomach or gizzard.