In the context of the stomach, what is its main digestive function?

• A. Absorbing most nutrients, including amino acids and monosaccharides, into the bloodstream
• B. Producing bile to emulsify fats for digestion in the small intestine
• C. Reabsorbing water and compacting feces for elimination
• D. Initiating protein digestion by mixing food with gastric acid and pepsin to form chyme

Answer: (D)

Verified step by step guidance

1. Identify the primary role of the stomach in digestion, which is different from nutrient absorption or bile production.
2. Recall that the stomach's environment is highly acidic due to gastric acid (hydrochloric acid), which helps denature proteins and activate digestive enzymes.
3. Understand that pepsin is the main enzyme secreted in the stomach, responsible for breaking down proteins into smaller peptides.
4. Recognize that the stomach mechanically mixes food with gastric acid and pepsin, turning it into a semi-liquid mixture called chyme.
5. Conclude that the stomach's main digestive function is initiating protein digestion by combining chemical breakdown (acid and enzymes) with mechanical mixing to prepare food for further digestion in the small intestine.