Mechanical digestion is the process of physically breaking down food that begins in the mouth. This step in the digestion process prepares food for further processing via chemical digestion.
The tongue, saliva and teeth are crucial structures that allow mechanical digestion to take place. These structures work together to break down solid food so it can be swallowed and travel further through the digestive tract. When food is present in the mouth, a signal is sent to the brain instructing it to secrete more saliva to soften the food. The saliva contains an enzyme that aids in this softening process.
Whereas the physical softening of the food via the liquid saliva is considered mechanical digestion, the enzymatic process of chemically breaking down the food is chemical digestion. While the teeth chew the food and break it down into smaller pieces, the tongue moves it around to push it further into the digestive tract.
Several structures ensure the food follows the appropriate pathway in digestion. The soft palate located on the roof of the mouth ensures food does not pass through the nasal cavity. The epiglottis exists on the tongue and prevents food from entering the windpipe. This structure also restricts the entry of air into the esophagus. Once food has traveled down the windpipe, digestion can continue in the stomach.