Adult gastrointestinal stem cells The gastrointestinal tract is lined with a single sheet of epithelium that is replaced every 4-5 days. The base of a flask-shaped structured called the crypt is where the gastrointestinal stem cells are found. These divide to form daughter cells that travel up the crypt to replace these cells. Dr Simon Leedham's current research focuses on the cell-signaling pathways that control intestinal stem cells and the dysregulation of these pathways in cancer.