The path at which food flows through the digestive system begins with the mouth. Food then is transported from the mouth to the pharynx, from the pharynx to the esophagus, from the esophagus to the stomach, from the stomach to the small intestine, from the small intestines to the large intestine, from the large intestines and finally to the anus.

In the beginning, once food enters our mouths, digestion begins. The mouth is the point at which foods enters the digestive tract. Once food has entered into the mouth, it stimulates the flow of saliva from the salivary glands. The saliva moistens the food, and carries dissolved food molecules to the taste buds. Saliva helps digest food because it contains the enzyme salivary amylase, which begins breaking starches into sugars. Chewing food is important for digestion. Chewing breaks food into small pieces and thereby increases the surface area that is in contact with digestive juices. The tongue helps mix food with saliva and aids chewing by constantly repositioning food between the teeth. Chewing also breaks apart fiber that traps nutrients, Axia 2009.

The foods that we have eaten form into a bolus; which is a ball of chewed food mixed with saliva. From the mouth, the bolus moves into the pharynx, the part of the gastrointestinal tract responsible for swallowing. Food passes through the pharynx on its way to the stomach. During swallowing, the air passages are, blocked by a valve-like flap of tissue called the epiglottis, so food goes to the stomach, not the lungs, Axia 2009.

In the esophagus extends from the pharynx to the stomach. The bolus of food is, moved along by rhythmic contractions of the smooth muscles, a process called peristalsis. This contractile movement, which is, controlled automatically by the nervous system, occurs throughout the gastrointestinal tract, pushing the food bolus along from the pharynx through the large intestine. To move from the esophagus into the stomach, food must pass through a sphincter, a muscle that encircles the tube of the digestive tract and acts as a valve. When the sphincter muscle contracts the valve is, closed thus, allowing the foods that we have eaten, not to come back up, Axia 2009.

The stomach is an expanded portion of the gastrointestinal tract that serves as a temporary storage place for food. The bolus is held in the stomach, and is mixed with highly acidic stomach secretions to form a semiliquid food mass called chyme. To move from the stomach to the small intestine, chyme must pass through the pyloric sphincter.

The small intestine is the main site of digestion of food and absorption of nutrients. The pancreas secretes pancreatic juice, which contains bicarbonate and digestive enzymes. Pancreatic amylase continues the job of breaking starches into sugars that was, started in the mouth by salivary amylase. Pancreatic protein digesting enzymes, including trypsin and chymotrypsin, continue to break protein into shorter chains of amino acids. Intestinal digestive enzymes, found attached to or inside the cells lining the small intestine. In addition, the intestinal enzymes aid to the digestion of sugars into single sugar units and the digestion of short amino acid chains into single amino acids. Bile secreted into the small intestine mixes with fat and breaks it into smaller globules, allowing pancreatic enzymes, called lipases, to more efficiently access the fat and digest it.

Materials that have not been absorbed in the small intestine enter the large intestine through a sphincter. This sphincter prevents material from the large intestine from reentering the small intestine.