The pancreas lies between the stomach and small intestine and secretes additional digestive enzymes and buffers to neutrallize 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 a 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. In humans, this structure is largely nonfunctional and called the appendix . Foregut fermenters include cows, sheep, buffalo, etc. The fermentation vat is located before the small intestine in a large and elaborate stomach called the rumen . This system is much more efficient, but is slower and requires higher quality forage.