When we eat, the nutrients and energy we need to function must be extracted from the food and absorbed into the body. The process responsible for this is known as digestion. The human digestive system must be able to process our eating habits and our omnivorous diet, and has adapted them to function at an optimal level and is controlled by our autonomic nervous system from the brain. The digestive system is a set of automated processes and organs, enzymes, secretions, some accessory organs and a pipe (or tube) that starts from the mouth and ends in the anus, called the alimentary system. The processes that occur along the alimentary canal determine how we take in these various nutrients, differentiating what the body can use for survival and functioning and what it does not need or has in excess of its requirements. This excess food is passed through the alimentary canal at the opposite end and expelled as waste. The entire digestive process begins in the mouth. As we eat and ingest food, the chewing action in the mouth uses the jaw, muscles, and teeth to grind, crush, and break solid masses of food into smaller particles. Food is moistened by saliva, a secretion released from small ducts inside the mouth. An enzyme within the composition of saliva called amylase works to dissolve certain food particles and break down starchy foods, turning them into glucose. The advantage of this reduction in the size of food, throughout the digestive tract, is to maximize the surface area and make it easier and faster for our body to absorb nutrients. Mucus in saliva also keeps the mouth and upper digestive tract lubricated. As we swallow food, it passes through the mouth and begins its journey down the pharynx and is moved down the esophagus to...... middle of paper.... ..of proteins, carbohydrates and fats. The villi also contain lymph nodes to help fight antigens ingested with food. When chyme leaves the small intestine, it enters the large intestine from the cecum. The large intestine is wider but considerably shorter in length than the small intestine. It is within the large intestine that bile salts and excess water are removed to give food waste a thicker consistency. Finally, the waste food passes through another sphincter and into the intestine where it must pass through a final sphincter before leaving the body at the anus. The entire digestion process typically takes about three days but can be affected by bacteria, illness, disease. and it is totally automated. The brain controls the autonomic system to influence the involuntary contraction and relaxation of the muscles that make up the walls of the digestive tract.