Question

Briefly discuss the early development, that is, from gastrulation to the early formation of alimentary canal, of the vertebrate digestive system.

Answer 1

Early development from gastrulation to the alimentary canal:

In the vertebrates, the digestive system (gastrointestinal tract GIT) arises initially during the process of gastrulation from the endoderm of the trilaminar embryo (week 3) which extends from the buccopharyngeal membrane to the cloacal membrane. The GI tract and the other digestive organs later have contributions from all the germ layers.

During the 4th week three distinct regions (fore-, mid- and hind-gut) extend the length of the embryo and will contribute different components of the GIT. The large mid-gut is generated by lateral embryonic folding which "pinches off" a pocket of the yolk sac, the two compartments continue to communicate through the vitelline duct.

The oral cavity (mouth) is formed following breakdown of the buccopharyngeal membrane (oropharyngeal or oral membrane) and contributed to mainly by the pharynx lying within the pharyngeal arches. Loss of buccopharyngeal membrane opens the tract to amniotic fluid through the remainder of development, and during the fetal period is actively swallowed.

From the oral cavity the next portion of the foregut is initially the pharynx, a single gastrointestinal (oesophagus) and respiratory (trachea) common tube, that lies behind the heart.

The stomach and colon (derived from the gut proper), develop as swellings of the primitive gut. In contrast, gut-related derivatives (e.g. those structures that derive from the primitive gut, but are not part of the gut proper), generally develop as out-pouchings of the primitive gut.

Formation of parts of the alimentary canal in short:

1)midgut: The portion of the embryo from which most of the intestines develop.
2)foregut: The anterior part of the alimentary canal of an embryo, from the mouth to the duodenum.
3)hindgut: The posterior (caudal) part of the alimentary canal. In mammals, it includes the distal third of the transverse colon and the splenic flexure, descending colon, sigmoid colon, and rectum.

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