Gut Development - Anatomy & Physiology

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Introduction

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 for peristalsis.

Endoderm Development

1. At the anterior of the embryo, the endoderm invaginates.
   • This invagination is called the Anterior Intestinal Portal (AIP).
2. The ends of the endoderm are brought together by this invagination, which fuse together to close the endoderm.
3. A similar process occurs at the posterior of the embryo, an invagination occurs called the Caudal Intestinal Portal (CIP).
   • This closes the endoderm at the posterior of the embryo.
4. The invagination and closure spread to the middle of the anterior - posterior axis where they meet at the yolk stalk.
5. 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 develop.
• 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 to begin with.
  • It is closed at the anterior by the buccopharyngeal membrane, and at the posterior by the cloacal membrane.
  • As the head folds ventrally, it comes into contact with the buccopharyngeal membrane causing it to break down.
  • This opens the buccal cavity.
    • The buccal cavity is lined by ectoderm.
  • At the posterior, the ectoderm invaginates to contact the cloacal membrane. This induces the cloacal membrane to break down.
  • This opens the anal passage.