Morphological Observation on the Prenatal Development of the Human Gastrointestinal Tract

Suh, Yeon Lim; Chi, Je G

Abstract

A total of 322 fetuses and 29 embryos were examined light microscopically to evaluate the morphological development of the human gastrointestinal tract with increasing gestational age. The human embryos were analysed by reconstruction of serial section slides. One hundred and forty fetuses ranging from 15 to 41 weeks of gestation were used for correlating the gestational age and the body weight with the measurement of the small and large intestines. 1) The esophagus develps from the distal part of the foregut through a partition of the tracheoesophageal septum. Initially the esophagus is short, but it elongates rapidly and reaches its final relative length and position by the seventh week. The epithelium of the esophagus proliferates and completely obliterates the lumen by the seventh week, but recanalization occurs by the ninth week. The esophageal epithelia consist of three different groups of cells; stratified squamoid cells, ciliated columnar cells and tall columnar cells by the 21th week. 2) The stomach appears as a fusiform enlargement of the caudal part of the esophagus at the fourth week. During next two weeks the stomach acquires its adult shape and final position. The primordial gastric pits and the parietal cells appear at the eighth and eleventh weeks, respectively. 3) As the midgut elongates, it forms a ventral U-shaped loop, called primitive intestinal loop by the fifth week. At this stage the cecum appears as a swelling from the caudal limb of the intestinal loop. By the seventh week the bulks of the caudal limb of the intestine herniate into the umbilical cord, in which the loop rotates 90 degrees counterclockwise around the axis of the superior mesenteric artery. During the tenth week, the intestine returns to the abdomen and undergoes a further 180 degrees counterclockwise rotatation. 4) The cloaca is divided into two parts by a urorectal septum at the fifth week. By the seventh week the urorectal septum has fused with the cloacal membrane, dividing it into a dorsal anal membrane and ventral urogenital membrane. The anal membrane ruptures at the eighth week. 5) During the sixth week the duodenal lumen becomes completely filled with proliferating epithelium. The villi project from the mucosa of the small and large intestines at the eighth and eleventh weeks, respectively. The villi of large intestine become resorbed again after the 21th week. At the fifth week Paneth cells appear through the entire length of the intestine including the rectum, but disappear in the colon and the rectum after the 36th week. 6) The developing Auerbach's plexuses are well recognized along the outside of muscle coat throughout the gastrointestinal tract, but demonstrate no immunoreactivity for the anti-neuron specific enolase antibody. The neuroblasts in the myenteric plexus reveal strong positivity for the anti-neuron specific enolase antibody at the eleventh week, but the ganglion cells differentiate by the fourteenth week. 7) Differentiation of the gastrointestinal wall and development of the myenteric plexus begin form the esophagus and progress caudally down to the colon. But the anorectal wall is differentiated from the cloaca more earlier than the esophagus, stomach and colon are. 8) The small and the large intestines elongate progressively with the increasing gestational age and body weight and increase approximately 5.6 and 5.4 folds, respectively during the 25 weeks from the 15th to 41th week of gestation. At the 40th gestational week the small intestine is 5.68 times the length of the colon. 9) The correlation between the body weight (BW), crown-rump length (CR) and intestianl length (small intestine (SI), large itestine (LI) is presented as: SI (cm)= -33.67 + 4.14CR + 11.62 (BW)(1/3), LI (cm)= 5.56 + 0.76CR + 0.007BW (gm), CR (cm)= 7.82 + 0.015 SI + 0.41 (BW)(1/2).