Jochen Lennerz, M.D., Ph.D., Department of Pathology and Immunology, Washington University School of Medicine, St. Louis, MO, and Jason Mills, M.D., Ph.D. The University of Washington at St. Louis

This is a section of a mouse stomach. Food will be digested in the black area at the top of the picture. The large green cells in the middle of the image produce stomach acid, while the cells at the bottom (highlighted in magenta) make digestive enzymes. The acid and enzymes are squirted up toward the food. The red cells at the top line the surface of the stomach and secrete mucus. The mucus barrier protects these beautiful stomach cells from self-digestion.