False-colour scanning electron micrograph (SEM) of the surface of the gastric epithelium lining the human stomach. The lining of an empty mammalian stomach is arranged in folds or rugae to maximise the surface area available for digestion. These folds produce the cobbled effect visible here, disappearing when the stomach is full. The inner stomach layer, the gastric mucosa, consists of simple, mucus-secreting columnar cells; invaginations of the mucosa into the underlying layer form gastric pits & glands. The stomach functions to produce hydrochloric acid, mucus, digestive enzymes & hormones. Magnification: x100 at 6x7cm size.