Kaplan Nursing Entrance Practice Exam 2026 – The All-in-One Guide to Exam Success!

The small intestine is the primary site for digestion in the human digestive system. It is where the majority of the breakdown of food occurs, aided by digestive enzymes and bile. The small intestine is divided into three parts: the duodenum, jejunum, and ileum.

During digestion, food that has been partially digested in the stomach enters the duodenum, where it is mixed with bile from the liver and pancreatic juices. These secretions contain enzymes that break down carbohydrates, proteins, and fats into their smallest components: sugars, amino acids, and fatty acids, respectively. The lining of the small intestine is equipped with villi and microvilli, which increase the surface area for absorption, allowing the nutrients to be efficiently absorbed into the bloodstream.

The other regions of the digestive system play distinct roles but are not the primary sites of digestion. For example, the stomach is primarily responsible for the mechanical and chemical breakdown of food, but much of the nutrient absorption still occurs in the small intestine. The large intestine's main function is to absorb water and electrolytes and to prepare waste for excretion, while the esophagus is primarily a conduit for food to travel from the mouth to the stomach.