Atoms > molecules > cells > tissue > organ > organ system > organism! Structure of the gut wall! inside to outside:! Mucosa - lines the lumen! serves as protective layer! absorption of end products! in direct contact with the food and hard acidic enzymes, therefore cells turn over ever 2-5 days ! Digestive secretions ! mucus - viscous material produced by goblet cells ! mucus moistens, lubricated, and protects the gi tract ! Enzymes - protein molecules that speed up chemical reactions ! are not changed during reactions ! different enzymes needed for different reactions ! Digestive hormones ! can affect both the cells lining the digestive tract and the secretions made by the accessory organs ! Stomach mucosa stimulates secretion of hydrochloric acid (hcl) and pepsinogen by gastric glands in the stomach and increases gastric motility and emptying somatostatin stomach and duodenal mucosa inhibits the following:! Gastric inhibitory peptide duodenal mucosa inhibits gastric secretion and motility.