Where does food begin its chemical digestion?

Where does food begin its chemical digestion?

• A. In the small intestine, from enzymes
• B. In the stomach, from stomach acids
• C. In the mouth, from enzymes in saliva
• D. In the cecum or rumen, from microorganisms

Answer: (C)

Chemical digestion begins in the mouth because saliva brings enzymes that start breaking down food molecules right away. The primary enzyme in saliva, salivary amylase, begins digesting starches into smaller sugars as you chew. There’s also some fat digestion from lingual lipase, but most fat digestion happens later in the small intestine with pancreatic lipase. Chewing helps by grinding food and mixing it with saliva, increasing the surface area for enzymes to act. In the stomach, acidic conditions and pepsin start protein digestion, and the small intestine handles the bulk of enzymatic digestion with pancreatic and brush-border enzymes. In some animals, microbial fermentation in the rumen or cecum plays a role, but the first enzymatic chemical breakdown in humans occurs in the mouth.

Chemical digestion begins in the mouth because saliva brings enzymes that start breaking down food molecules right away. The primary enzyme in saliva, salivary amylase, begins digesting starches into smaller sugars as you chew. There’s also some fat digestion from lingual lipase, but most fat digestion happens later in the small intestine with pancreatic lipase. Chewing helps by grinding food and mixing it with saliva, increasing the surface area for enzymes to act. In the stomach, acidic conditions and pepsin start protein digestion, and the small intestine handles the bulk of enzymatic digestion with pancreatic and brush-border enzymes. In some animals, microbial fermentation in the rumen or cecum plays a role, but the first enzymatic chemical breakdown in humans occurs in the mouth.