Epithelial cells located inside the stomach are specialized for secretory activity. The four major kinds of the cells include mucus cells, chief cells, parietal cells, and G cells. Mucus cells, which secrete alkaline mucus that protects the stomach from self-digestion, are the most abundant gastric epithelial cells. They line the entire lumenal surface, even reaching into the necks of gastric glands, where they are referred to as mucus neck cells. Chief cells are found along the lower portions of gastric glands. The primary function of chief cells is to secrete pepsin, an enzyme that catalyzes the breakdown of protein to peptides. Parietal cells are larger than chief cells and exhibit invaginated apical plasma membranes that form intracellular secretory canaliculi. The secretory product of parietal cells is hydrochloric acid. G cells serve as the source of gastrin and are located in the mucosa of the pylorus.

The cytoskeletal filamentous actin network was targeted in a rat stomach tissue sample (presented above) with phalloidin conjugated to Alexa Fluor 568. Phalloidin is a member of the phallotoxin group of bicyclic peptides isolated from the deadly Amanita phalloides mushroom. The tissue section was also labeled for nuclear DNA with Hoechst 33342 and the Golgi complex with Oregon Green 488 conjugated to wheat germ agglutinin (WGA). Images were recorded in grayscale with a 12-bit digital camera coupled to a Nikon Eclipse 80i microscope equipped with bandpass emission fluorescence filter optical blocks. During the processing stage, individual image channels were pseudocolored with RGB values corresponding to each of the fluorophore emission spectral profiles.