Anatomy of the Intestines

The small and large intestines absorb nutrients and water from digested food.

The small intestine is narrow and stretches about 22 feet long, fitting compactly within the abdominal cavity.

Acidic chyme from the stomach enters the duodenum, the first section of the small intestine, and then moves into the jejunum, the next section.

To increase absorption, the inner lining of the small intestine forms mucosal folds known as plicae circulares. These folds are covered with finger-like projections called villi. The epithelial cells that line the villi have tiny extensions on their apical surfaces called microvilli.

Together, these three structures greatly increase the surface area of the small intestine and help it absorb nutrients efficiently.

The last and longest part of the small intestine is the ileum. It connects to the large intestine, which is about 5 feet long, through the ileocecal valve.

The first section of the large intestine is the cecum, which has a smooth inner surface without folds or villi. Hanging from the bottom of the cecum is the appendix, a small structure that is linked to immune function.

Above the cecum, the ascending colon begins, followed by the transverse colon.

Throughout the large intestine, water and electrolytes are absorbed, and the remaining material gradually turns into feces.

The final sections—the descending colon, sigmoid colon, and rectum—store feces until it leaves the body through the anus.