The function of the gastrointestinal tract (GI tract) is to process food. During this process, food is moved from the mouth to the anus. Feeding and drinking are voluntary activities, but are strongly influenced by signals from higher brain centers involved in the sensations of satiety and thirst. Once ingested, water and nutrients are extracted from food without any conscious control. Throughout the entire process, the ingested material is moved along the GI tract. Finally, the undigested and non-absorbed materials are released as feces from the anus (under voluntary control when socially appropriate!).