Final answer:
In embryonic development, migration during the formation of the primitive gut follows a directional process dictated by whether the organism is a Protostome or a Deuterostome, with the blastopore forming the mouth or anus, respectively. Postnatal gastrointestinal motility involves peristaltic movement initiated in the duodenum that migrates through the small intestine.
Step-by-step explanation:
The process of gastrulation in embryonic development is crucial as it leads to the formation of the primitive gut and the eventual development of the gastrointestinal tract. During gastrulation, a third cell layer (mesoderm) is formed, which differentiates into various structures between the ectoderm and endoderm. This process results in the formation of a digestive cavity, known as the archenteron. In some organisms, identified as Protostomes ('mouth first'), the mouth forms from the blastopore, while in others, identified as Deuterostomes ('mouth second'), the anus forms from the blastopore and the mouth forms on the opposite end. The formation of the primitive gut is a directional process that begins with the development of the blastopore and continues with the establishment of the mouth and anus at opposite ends of the developing gut.
In the context of postnatal gastrointestinal function, the mucosa of the small intestine secretes motilin, which triggers peristalsis and migration of a motility complex. These complexes begin in the duodenum and move slowly down the intestine, pushing contents through the digestive system over 90 to 120 minutes until reaching the ileum where the process restarts.