The pancreas lies between the stomach and small intestine and secretes additional digestive enzymes and buffers to neutralize conditions. The liver secretes bile which breaks up fats for digestion. The large intestine is where water and minerals are absorbed. The large intestine contains large populations of bacterial cells that break down nutrients and synthesize a number of vitamins. Most of the material eliminated from the body is a combination of bacterial cells and cellulose.
Some materials pass through the gastro-intestinal tract without being digested.
Also, variations on this theme allow some animals to obtain nutrients from plant material. Diabetics lack the capacity to produce sufficient insulin for glucose absorption. Insulin must be injected daily. Hindgut fermenters include horses, elephants, humans, among others. In humans, this structure is largely nonfunctional and called the appendix .