Digestive System
Digestive System

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- foregut tube begins as a rostral outpouching (diverticulum) of yolk sac endoderm into rostral embryonic mesoderm, ventral to notochord - prochordal plate (future buccopharyngeal membrane) is created by endoderm of foregut tube abutting against ectoderm (ectoderm against endoderm without intervening mesoderm), rostral to notochord and caudal to cardiogenic area - prochordal plate → buccopharyngeal membrane = future pharyngeal opening - during embryonic folding, heart tube (from cardiogenic area) with first segment of aorta (future ventral aorta, sending paired aortic arches dorsally at sides of foregut) fold into ce rvicothoracic region, ventral to foregut which is ventral to dorsal aorta - during embryonic folding, ectodermal surface of prochordal plate becomes ventral and rostral to heart, bending foregut tube anteriorly at cranial end of n otochord - mouth - stomodeum is the embryonic mouth, lined by ectoderm , and formed by outgrowths of the facial processes around the margins of the buccopharyngeal membrane - facial processes are expanded by ectomesenchyme, produced by neural crest cell migration into the facial processes and branchial arches ( see facial embryology ) - buccopharyngeal membrane breaks down by programmed cell death (apoptosis) at the beginning of the fourth week - facial processes - midline fronto - nasal process - bilateral maxillary processes - bilateral mandibular processes (which fuse at the midlin e to create the chin) - maxillary and mandibular processes → derived from first pair of branchial arches © } which fuse in midline creating the ‘premaxilla’ - foregut