Gut Development - Anatomy & Physiology
The endoderm will form the lining of the gut and the organs that develop from it. Splanchnic mesoderm surrounds the endoderm and orginates from the lateral plate mesoderm. It will form the smooth muscle of the gut that are used in peristalsis.
During endodermal development, the anterior end of the embryo invaginates. This invagination is called the anterior intestinal portal or (AIP). The opposing anterior ends of the endoderm are brought together by this invagination, allowing both ends to fuse together to close the endoderm. A similar process occurs at the posterior of the embryo where an invagination occurs called the caudal intestinal portal or (CIP). This invagination closes the posterior of the endoderm. The invagination and closure spread to the middle of the anterior - posterior axis where they meet at the yolk stalk. After the yolk has been metabolised, the yolk stalk can be closed.
Regionalisation of the Gut
The gut tube will develop into the oesophagus, stomach, small intestine, large intestine and anus. Regionalisation of these tissues occurs through co-ordinated endoderm and splanchnic mesoderm development. The endoderm governs splanchnic mesoderm development by releasing a signalling factor (sonic hedgehog) which induces differential mesoderm development. Sonic hedgehog controls HOX - A gene expression. The gut tube is closed at both ends during early development by the anterior buccopharyngeal membrane and the posterior cloacal membrane. As the head folds ventrally, it comes into contact with the buccopharyngeal membrane causing it to break down and opening the buccal cavity which is lined by ectoderm. At the posterior, the ectoderm invaginates to contact the cloacal membrane inducing the cloacal membrane to break down. Once this has occurred, this opens the anal passage.
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