Pathophysiology
Embryologically the beginnings of the GI tract are formed at the 4th week of gestation. Due to the rapid growth of the intestinal loop, it becomes too large to remain in the abdominal cavity, and therefore expands into the yolk sac (future umbilicus). The loop returns to the abdomen by the 8th week of gestation. As it re-enters the abdomen it rotates, and is fixed into position.4
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If this part of foetal development goes wrong, it can result in malrotation, which will be discussed later.
Once development is complete, 3 distinct lengths of the GI tract can be separated according to their blood supply:
- Foregut: coeliac axis
- Midgut: superior mesenteric artery
- Hindgut: inferior mesenteric artery
Another relevant embryological structure is the vitelline duct, which connects the yolk sac to the mid-end ileum within the foetus. If this structure persists into infancy it is named Meckels diverticulum. Due to its rich arterial supply from the vitelline artery (a branch of the superior mesenteric artery) it can cause bleeding in the GI tract.5