Small Intestine

The small intestine is divided into three parts: the duodenum, jejunum, and ileum. The duodenum is closest to the stomach and wraps around the pancreas in a C-shape. The jejunum follows the duodenum, while the ileum is the longest section, connecting to the large intestine at the ileocecal valve.

The duodenum receives digestive secretions from the pancreas and liver. This section acts as a mixing chamber where chyme, the partially digested food from the stomach, blends with these secretions. The duodenum's unique C-shaped anatomy wraps around the pancreas, facilitating this mixing process.

The small intestine has internal circular folds that dramatically increase its surface area. This enormous surface area makes the small intestine the primary organ for mechanical and chemical digestion in the small intestine, enabling efficient nutrient absorption throughout its length.

The jejunum is where the majority of chemical digestion and nutrient absorption occurs in the small intestine. Located in the central and lower abdomen, this approximately 2.5-meter section follows the duodenum and leads to the ileum, playing a crucial role in extracting nutrients from food.

The jejunum and ileum are located in the central and lower regions of the abdominal cavity, encircled by the large intestine. They are suspended by a fan-shaped mesentery extending from the posterior abdominal wall, which provides support and allows them mobility for proper digestive function.

The ileocecal valve marks the junction where the ileum, the final section of the small intestine, connects to the large intestine. This valve controls the passage of material from the small intestine into the large intestine, serving as an important anatomical and functional boundary in the digestive tract.

The duodenum measures approximately 25 centimeters, the jejunum is roughly 2.5 meters long, and the ileum extends about 3.6 meters. Together, these three sections form the complete small intestine, with the ileum being the longest portion of this critical digestive organ.