The genetic code within DNA determines what proteins are made by the cell. Molecules combine in specific ways to form microscopic cells. The CELL is the basic living structural and functional unit of the organism. The simplest living organisms, such as bacteria and protozoa, consist of only one cell. Together, cells form tissues.
Parietal cells produce acid used in digestion.
Mucous cells secrete a thick mucus that protects the stomach lining from stomach acid. Chief cells produce digestive enzymes that break down food. Together, these cells of the epithelium contribute to the function of digestion. The 4 basic tissue types in the human body are epithelial tissue, muscle tissue, connective tissue, and nervous tissue. The heart, liver, stomach, intestines, lungs, pancreas, and brain are examples of organs.