Which part of the small intestine is responsible for the initial phase of digestion?

The duodenum is the first section of the small intestine and plays a critical role in the initial phase of digestion. This part of the digestive system is where most chemical digestion occurs and is primarily responsible for the breakdown of food. When partially digested food, known as chyme, enters the duodenum from the stomach, it is mixed with bile from the liver and digestive juices from the pancreas. These substances contain enzymes that help further break down carbohydrates, proteins, and fats, making nutrients more available for absorption.

The jejunum and ileum, which are the subsequent parts of the small intestine, are primarily involved in the absorption of nutrients rather than the initial digestion. The colon, or large intestine, is involved in absorbing water and electrolytes from indigestible food matter and is not responsible for digestion in the same sense that the small intestine is. Therefore, the duodenum's role at the beginning of the small intestine is fundamental to initiating digestion.