Clinical meaning
Meckel's diverticulum represents the prototypical vitelline duct anomaly, arising from incomplete involution of the omphalomesenteric (vitelline) duct during the fifth to seventh week of embryonic development. The vitelline duct connects the primitive midgut to the yolk sac and provides nutritional support to the developing embryo before placental circulation is established. Normal embryogenesis requires complete regression of this duct by week 7, mediated by apoptotic signaling through the BMP (bone morphogenetic protein) and Wnt/β-catenin pathways that regulate mesenteric and ductal remodeling. Failure of apoptosis in the intestinal segment of the vitelline duct results in a persistent blind-ending pouch - Meckel's diverticulum.
The spectrum of vitelline duct anomalies includes: (1) Meckel's diverticulum (most common; persistence of the intestinal end), (2) vitelline duct cyst (persistence of the middle segment, forming an isolated cyst), (3) vitelline duct fistula (complete persistent patent duct from ileum to umbilicus, presenting with intestinal content drainage from the umbilicus), (4) fibrous band (a cord-like remnant connecting the diverticulum to the umbilicus, creating a potential axis for volvulus), and (5) umbilical sinus (persistence of the umbilical end only).
The heterotopic tissue within Meckel's diverticulum arises from aberrant differentiation of pluripotent endodermal stem cells during embryonic gut regionalization. The gastric heterotopia contains functionally active parietal cells expressing H+/K+ ATPase proton pumps that secrete hydrochloric acid, and chief cells producing pepsinogen. This ectopic acid production creates a hostile microenvironment at the junction between gastric-type and ileal-type mucosa, where the ileal epithelium lacks the protective mechanisms of native gastric mucosa - specifically, the surface mucus-bicarbonate barrier, prostaglandin-mediated cytoprotection, and the rapid epithelial turnover (every 3-5 days) that characterizes gastric mucosa. The result is peptic ulceration of the adjacent ileal mucosa with erosion into submucosal arterioles, producing hemorrhage.