Answer:
Mechanical Digestion
Step-by-step explanation:
Mechanical digestion in the oral cavity consists of grinding of food into smaller pieces by the teeth, a process called mastication. Chemical digestion in the mouth is minor but consists of salivary amylase (ptyalin, or alpha-amylase) and lingual lipase, both contained in the saliva. Salivary amylase is chemically identical to pancreatic amylase and digests starch into maltose and maltotriose, working at a pH optimum of 6.7 to 7.0. Lingual lipase, also contained in the saliva, hydrolyzes the ester bonds in triglycerides to form diacylglycerols and monoacylglycerols. After sufficient digestion in the oral cavity, the partially digested foodstuff, or bolus, is swallowed into the esophagus. No digestion occurs in the esophagus.
After passage through the esophagus, the bolus will enter the stomach and undergo mechanical and chemical digestion. Mechanical digestion in the stomach occurs via peristaltic contractions of the smooth muscle from the fundus towards the contracted pylorus, termed propulsion. Once the bolus is near the pylorus, the antrum functions to grind the material by forceful peristaltic contractions that force the bolus against a tightly constricted pylorus. The churning by the antrum serves to reduce the size of the food particles and is called grinding. Only particles smaller than 2mm in diameter can pass through the contracted pylorus into the duodenum. The rest of the bolus is pushed back towards the body of the stomach for further mechanical and chemical digestion. This backward movement of the bolus from the pylorus to the body is termed retropulsion and also serves to aid in mechanical digestion. This sequence of propulsion, grinding, and retropulsion repeats until the food particles are small enough to pass through the pylorus into the duodenum. All chyme not pushed through the pylorus during the active digestion process is eventually swept into the duodenum through a relaxed pylorus by a series of strong peristaltic contractions in the stomach. This activity occurs during the inter-digestive phase called migrating motor complexes (MMCs) that function to move the bolus in an aboral fashion to prevent stagnation and bacterial accumulation.