Which structures contribute to mechanical digestion?

• A. Enzymes, acids, bile
• B. Villi, microvilli, lacteals
• C. Teeth, tongue, peristalsis
• D. Mucus, water, electrolytes

Answer: (C)

Mechanical digestion is the physical breakdown and movement of food to prepare it for chemical digestion. Teeth chew and crush the food, greatly increasing surface area for subsequent processing. The tongue helps by shaping the chewed food into a cohesive bolus, mixing it with saliva, and guiding it for swallowing. Once in the stomach and intestines, rhythmic contractions of the smooth muscles—peristalsis and local mixing—physically churn and propel the contents, breaking them into smaller pieces and mixing them with digestive secretions. These actions are about physical fragmentation and movement rather than chemical change.

Enzymes, acids, and bile effect chemical changes in the food, not the mechanical breakup. Villi, microvilli, and lacteals are involved in absorption, not the mechanical processing of food. Mucus, water, and electrolytes aid lubrication and digestion-related processes, but they don’t drive the mechanical breakdown of food.