<Li> Egestion (Excretion): Removal of undigested materials from the digestive tract through defecation . </Li> <P> Underlying the process is muscle movement throughout the system through swallowing and peristalsis . Each step in digestion requires energy, and thus imposes an "overhead charge" on the energy made available from absorbed substances . Differences in that overhead cost are important influences on lifestyle, behavior, and even physical structures . Examples may be seen in humans, who differ considerably from other hominids (lack of hair, smaller jaws and musculature, different dentition, length of intestines, cooking, etc .). </P> <P> The major part of digestion takes place in the small intestine . The large intestine primarily serves as a site for fermentation of indigestible matter by gut bacteria and for resorption of water from digests before excretion . </P> <P> In mammals, preparation for digestion begins with the cephalic phase in which saliva is produced in the mouth and digestive enzymes are produced in the stomach . Mechanical and chemical digestion begin in the mouth where food is chewed, and mixed with saliva to begin enzymatic processing of starches . The stomach continues to break food down mechanically and chemically through churning and mixing with both acids and enzymes . Absorption occurs in the stomach and gastrointestinal tract, and the process finishes with defecation . </P>

Where is water absorbed in the digestive tract