Chewing breaks up food into smaller pieces that can be swallowed without choking. The salivary glands secrete a mucous solution into the mouth that moistens and lubricates food particles. Saliva contains an enzyme that begins to digest carbohydrates. As food particles begin to dissolve, they react with the chemoreceptors in the mouth, giving rise to the sensation of taste. The pharynx and esophagus provide the pathway by which ingested food and drink reach the stomach.
Primary peristalsis occurs with swallowing, and usually travels the full length of the esophagus.
Secondary peristalsis occurs in response to esophageal distention or irritation caused by gastric reflux, spreading from the point of irritation in the esophagus to the stomach. Once food reaches the stomach, it is stored, dissolved, and partially digested into a solution of hydrochloric acid, enzymes, and food particles that is called chyme . The gastric acid kills most of the bacteria that enter along with the food. Then the stomach pushes the fluid and partially digested food into the duodenum and small intestine to be further digested and absorbed. The large intestine stores the material undigested by the small intestine, and concentrates it by absorbing water.