Physical digestion is the process by which food is mechanically broken down into smaller pieces through the actions of chewing, grinding, and mixing. In the mouth, physical digestion begins when food is chewed by the teeth. This process breaks the food into smaller pieces, mixes it with saliva, and forms it into a ball called a bolus. The bolus is then swallowed and passes down the esophagus into the stomach.
Once the food enters the stomach, it is mixed with gastric juices and further broken down through a process called churning. Churning mixes the food with gastric juices and mechanical forces generated by the muscles of the stomach wall. This helps to break the food down into even smaller pieces and begins the process of breaking down the complex molecules in the food into simpler molecules that can be absorbed by the body.
Overall, physical digestion in the mouth and stomach involves mechanical processes that break food down into smaller pieces and mix it with digestive enzymes, allowing for more efficient chemical digestion and absorption of nutrients.