Systems Overall anatomy Fig.
Stomach is muscular with a folded inner surface that can expand when full.
It secretes mucus, acid, and pepsin , a digestive enzyme for breaking meat down to small particles. The secretions come from pits in the wall. The mucus cells secrete mucus, parietal cells secrete acid, and the chief cells secrete pepsinogen. This is converted to pepsin by acid in stomach juice, called chyme . The chyme enters the small intestine when the stomach is full.