Each structure in your gastrointestinal tract -- which includes your mouth, esophagus, stomach, small intestine, large intestine and accessory organs -- plays a critical and unique role in digestion. Although most digestion occurs in the small intestine, digestion itself begins in the mouth.
Breaking Down Digestion
The digestion process is a combination of chemical and mechanical digestion. Chemical digestion breaks down food via a chemical change, in which the digestive juices and enzymes break down food into components small enough to enter the GI tract, the blood cells or the lymph cells. Mechanical digestion breaks down food via chewing or grinding in the mouth as well as via the muscular activity in the stomach and intestines. Both types of digestion begin in the mouth.
As soon as you think about food, see food or smell food, your salivary glands release saliva, which helps digestion. Each component of saliva -- including water, mucus, electrolytes and enzymes -- serves a unique function. The enzyme in saliva, which is called salivary amylase, begins the chemical breakdown of starches. Mucus lubricates the food, which helps food stick together and mucus also coats and protects the inside of your mouth. Saliva also starts to dissolve small food particles and makes dry food moist enough to swallow comfortably.
Thrashing Teeth and Tongue
Your teeth and tongue play a role in mechanical digestion. When you chew, your teeth cut and grind your food into smaller pieces that are easier for you to swallow and for your digestive system to break down. Your tongue moves the food around your mouth and mixes it with saliva so that the components of saliva can perform their functions.
Moving Things Along
Once the food is broken down and mixed with saliva, it is referred to as a bolus, which is a mass of food soft enough for you to swallow. Your tongue pushes the bolus to the back of your mouth and into your pharynx, which is the cavity that connects the mouth to the esophagus. Once the bolus enters the pharynx, your involuntary swallowing reflex kicks in and the food begins its travel down your esophagus.