The small intestine is primarily responsible for digestion and nutrient absorption. It spans from the pyloric sphincter to the ileocecal valve and connects to the large intestine.

The small intestine is divided into three main sections - the duodenum, jejunum, and ileum. The duodenum, approximately 25 cm long, is nearest the stomach. It acts as a 'mixing bowl,' where chyme (partially digested food) blends with digestive enzymes from the pancreas and liver. The duodenum's unique C-shape wraps around the pancreas.

The jejunum follows the duodenum. It is roughly 2.5 m long and leads to the ileum, which measures about 3.6 m. The ileum joins the large intestine at the ileocecal valve, marking the end of the small intestine.

The jejunum and ileum are found in the central and lower regions of the abdominal cavity. A fan-shaped mesentery extends from the posterior abdominal wall and supports and gives them mobility. The small intestine's complex design and structure facilitate effective digestion and absorption.