Digestive system diagram. There is a distinction between internal and external digestion. The human digestive system is made up of the gastrointestinal (GI) tract-also called the digestive tract-and the liver, pancreas, and the gallbladder. The digestive system converts food into nutrients for the body. A description of the digestive system’s function and organs. Human digestive system converts food you eat into nutrients, which the body uses for energy, growth and cell repair. The digestive process starts even before the first bite of food. Find out more about the digestive system and how our bodies break down and absorb the food we eat.