The fundus of the stomach is the second part of the stomach. The rugae contain several specialized cells to help aid in digestion including parietal cells (HCl- Hydrochloric acid production by releasing H+ and Cl-), Chief cells (pepsin production by releasing pepsinogin which reacts with HCl to make pepsin), and Mucus cells (to release mucus and coat the stomach, protecting it from the low pH, high acid environment).


In this picture, the stomach has been cut open and the rugae are visible (the left probe is touching them; the right probe is pointing out a parasite worm in the stomach):