In which organ do most chemical reactions and mechanical processes of digestion occur?

The small intestine is the primary site for most chemical reactions and mechanical processes of digestion. This organ is crucial because it is where the majority of nutrient absorption occurs after the breakdown of food.

As food passes through the small intestine, it is mixed with digestive enzymes and bile, which are essential for breaking down carbohydrates, proteins, and fats into their smaller, absorbable components. The walls of the small intestine are lined with tiny, finger-like projections called villi, which increase the surface area for absorption. This structural adaptation further enhances the efficiency of nutrient uptake into the bloodstream.

In contrast, while the stomach does initiate the digestion process through mechanical churning and the action of gastric acids, it primarily prepares food for the small intestine rather than being the site of nutrient absorption. The liver and pancreas have important roles in digestion—like producing bile and digestive enzymes, respectively—but they are not the primary sites where digestion occurs. Instead, they support the digestive process facilitated in the small intestine.