cells. The mucus allows the acid at pH above 4 to penetrate lining, but below pH 4 (i.e. when acid is more concentrated) the acid cannot penetrate the mucus. This is called viscous fingering. Thus the foveolar cells can pump out a lot of acid, but acid once in the lumen of the stomach is prevented from returning. See also List of human cell types derived from the germ layers Notes References External links - "Digestive System: Alimentary Canal: fundic stomach, gastric glands, base" - see slide #41 Mucus secreting cells Human cells Stomach