proventriculus [FBbt_00005752]

proventriculus

ID: FBbt_00005752

Bulb-shaped organ at the junction of the foregut and midgut that regulates the passage of food into the midgut. The proventriculus folds back on itself to produce three epithelial layers: internally the posterior region of the esophagus, an intermediate (recurrent) layer, derived from the ectodermal foregut and the midgut, and an external anterior projection of the endodermal midgut, which grows over the esophageal region. The inner two layers form the gastric valve (cardial valve) while the outer layer is defined as the wall of the proventriculus. The cuticle that lines the inner wall is thicker than other regions in the cardia, and it forms several longitudinal folds, causing the esophageal lumen to appear irregular in cross section. Between the intermediate and outer wall is the cardia lumen, which opens posteriorly into the lumen of the midgut. The anterior region secretes the peritrophic membrane into the cardia lumen. The epithelium is surrounded by a thin tunic of striated muscle fibers.

This structure is more correctly referred to as the 'cardia'. Strictly, proventriculus refers to a modification of the foregut, just anterior to the stomodeal valve, found in many insects. Drosophila has no such foregut modification (Miller, 1950). However, the term 'proventriculus' is the one most commonly used for this structure.