During embryonic development, the foregut rotates 90°c lockwise around its longitudinal axis, causing the left side of the stomach to face anteriorly and its right side posteriorly ( Fig. 98.1). The foregut blood supply is the celiac artery.The development of the midgut is characterized by rapid elongation of the gut and its mesentery, resulting in the formation of the primary intestinal loop. Over its entire length, the midgut is supplied by the superior mesenteric artery. As a result of this rapid elongation and the simultaneous expansion of the liver, the abdominal cavity of the fetus becomes too small to contain all the intestinal loops. These loops enter the extraembryonic coelomic cavity in the umbilical cord, forming a physiological umbilical herniation during the sixth week of development ( Fig. 98.2). Coincident with this rapid growth, the midgut rotates 270°counterclockwise around the axis of the superior mesenteric artery. At about the third month, the herniated intestinal loops return to the abdominal cavity. The proximal portion of the jejunum is the first part to reenter, and it comes to lie on the left side, whereas the primitive cecum is the last to reenter and descends into the right iliac fossa.The hindgut gives rise to colon and rectum past the distal third of the transverse colon as well as the upper part of the anal canal. The junction of the endodermal and ectodermal parts of the anal canal is formed by the pectinate line, which is found just below the anal columns. The endoderm of the hindgut also gives rise to the internal lining of the bladder and urethra. The hindgut blood supply is the inferior mesenteric artery.
Mesenteries of the abdominal cavityDuring the development of the peritoneal cavity, the splanchnic mesoderm covers the developing gut. Eventually, most of this ventral mesentery is resorbed, except for a small portion between the liver and the stomach that persists as the
Embryology of the abdominal cavity
Abdominal cavityKnowledge of the embryology of the abdominal contents is imperative to understanding the pathophysiology of the various congenital and structural anomalies of the abdominal cavity. The abdominal or peritoneal cavity is formed from a large intraembryonic coelomic cavity during the fourth week of embryonic development. The cells of the somatic mesoderm lining the intraembryonic coelomic cavity become mesothelial and form the parietal layer of the serous membranes lining the outside of the peritoneal, pleural, and pericardial cavities. In a similar manner, the cells of the splanchnic mesoderm layer form the visceral layer of the serous membranes covering the abdominal organs, lungs, and heart [1]. During the fifth to seventh weeks of development, the pleuroperitoneal folds fuse with the septum transversum, and the mesentery of the esophagus thus separates the thoracic cavity from the abdominal cavity. In the cephalic and caudal parts of the embryo, the primitive gut (an endodermal-lined cavity) forms a blind-ending tube, the foregut and the hindgut, respectively....