 This is an example of symbiosis.These bacteria also account for the production of gases at host-pathogen interface, inside our intestine(this gas is released as "flatulence" when eliminated through the anus).However the large intestine is mainly concerned with the absorption of water from digested material (which is regulated by the hypothalamus) and the re absorption of sodium, as well as any nutrients that may have escaped primary digestion in the ileum.