Development of the digestive system Development of the digestive system The development of the digestive system concerns the epithelium of the digestive system and the parenchyma of its derivatives, which originate from the endoderm. Connective tissue, muscular components, and peritoneal components originate in the mesoderm. Different regions of the gut tube such as the esophagus, stomach, duodenum, etc. are specified by a retinoic acid gradient that causes transcription factors unique to each region to be expressed. Differentiation of the gut and its derivatives depends upon reciprocal interactions between the gut endoderm and its surrounding mesoderm. Hox genes in the mesoderm are induced by a Hedgehog
Digestive biscuit packs sold annually. Digestives are also popular in food preparation for making into bases for cheesecakes and similar desserts. Chocolate digestive biscuits are also available, coated on the underside with milk, dark or white chocolate. Originally produced by McVitie's in 1925 in the UK as the Chocolate Homewheat Digestive, other varieties include the basic biscuit with chocolate shavings throughout (chocolate "chips" in the biscuit mix), or a layer of caramel, mint chocolate, orange-flavoured chocolate, or plain chocolate. American travel writer Bill Bryson described the chocolate digestive as "a British masterpiece". The McVitie's chocolate digestive is the most popular biscuit in