Question

What is Mesenteries

Answer 1

With the completion of folding in the transverse plane and closure of the abdominal wall, the two apposing lay­ers of the splanchnic mesoderm fuse to form a double layered membrane called primitive mesentery. Each layer of the combined membrane different­iates into a peritoneal layer which consists of a layer of connective tissue overlaid by simple squamous epithe­lium called mesothelium. For a very brief period the primitive mesentery extends all the way from the roof of the intra embryonic coelom to the midventral body wall. It divides the coelom into two halves and contains the gut between its component layers. The primitive straight gut divides the mesentery into two parts: (1) The part above the gut is known as dorsal mes-entery, and (2) the portion below the gut is called as ventral mesentery.
The ventral mesentery is a transitory structure that obliterates very soon. Representative of the ventral mesentery in the adult is a secondary development limited to region of the stomach and proximal part of the duo-denum (for details regarding formation of the ventral mesentery see chapter 6).
The dorsal mesentery is an important structure. At first the gut is broadly attached dorsally, but very soon this region becomes relatively narrower and then the gut is sus­pended throughout most of its length by a distinctive dorsal mesentery. This mesentery extends like a curtain in the midplane and serves as a pathway for the passage for the blood vessels, lymphatics and nerves of the gut. Only the pharynx and the upper esophagus lack a dorsal mesentery because they lie cranially in regions where intraem-bryonic coelom does not extend. The dorsal mesentery of the gut is given distinctive names at its successive, re­gional levels. In a cranial to caudal di­rection, various parts of the dorsal mesentery are named as: mesoe-sophagus, dorsal mesogastrium, mesodudenum, mesentery proper of jejunum and ileum, mesocolon, and mesorectum.
As the embryonic development progresses, some parts of the primitive dorsal mesentery become specialized, other portions, following displacement of the gut, lose their original midline
position and gain secondary attach­ments, while still other portions are lost by obliteration. However, in the adult, the mesenterial system persists in some form or other.