Researchers studying neural crest cell migration in a human fetus observe normal activity beginning at the 8th week of embryogenesis with interruption during the 12th week, when migration is typically completed. Which of the following structures is most likely to lack innervation as a result of this disruption?

Question

Researchers studying neural crest cell migration in a human fetus observe normal activity beginning at the 8th week of embryogenesis with interruption during the 12th week, when migration is typically completed.  Which of the following structures is most likely to lack innervation as a result of this disruption?

Quizplus · Accepted Answer

11ec160b_3741_c0d3_9249_4726bbb0ac21_MD0001_00 Normally, neural crest cells start migrating to the intestinal wall in early embryogenesis and give rise to ganglion cells of the submucosal (Meissner) and myenteric (Auerbach) plexus of the bowel wall. These parasympathetic ganglia are responsible for intestinal peristalsis. Neural crest cells enter the developing foregut mesenchyme and then migrate caudally along the entire length of the bowel; they are present in the wall of proximal colon by the 8th week of gestation and in the rectum by the 12th week. The arrest of migration of neural crest cells causes Hirschsprung disease, in which a distal segment of colon lacks ganglion cells. Because neural crest cells migrate caudally, the rectum is always involved. The absence of parasympathetic ganglia in the colonic wall causes the affected segment to be narrowed because it cannot relax. The passage of intestinal contents through this area is difficult, and compensatory dilation of the proximal colon occurs. Newborns with Hirschsprung disease often fail to pass meconium within 48 hours of birth. They may also develop signs of intestinal obstruction, such as bilious vomiting and abdominal distension. The bowel is filled with stool, but the rectum is empty; anal sphincter tone is usually increased. (Choice A) Degeneration of neural crest cells forming the myenteric plexus in the esophagus causes achalasia (ie, esophageal dilation with absent peristalsis). However, the condition is most often due to autoimmune destruction of mature neurons; failed neural crest migration is a very rare etiology. (Choices B, C, D, E, and F) Although total colonic aganglionosis can occur, the cecum and transverse colon are not commonly involved in Hirschsprung disease. Total intestinal aganglionosis (eg, duodenum, jejunum, ileum) has also been described but is extremely rare. The rectum is most likely to be affected by a problem with neural crest cell migration, as it is at the very end of the migration path. Educational objective: Hirschsprung disease is caused by abnormal migration of neural crest cells (ganglion cell precursors) during embryogenesis. Because neural crest cells migrate caudally down the bowel from the foregut, the rectum is always affected. __________ References: The developmental etiology and pathogenesis of Hirschsprung disease. (http://www.ncbi.nlm.nih.gov/pubmed/23528997)

Researchers Studying Neural Crest Cell Migration in a Human Fetus