The intestines are a long, coiled series of organs that perform the final stages of digestion and absorption in the body. They extend from the end of the stomach down to the anus, occupying a substantial portion of the abdominal cavity. These organs process food, extracting nutrients and water before eliminating waste. The intestines are divided into the smaller-diameter small intestine and the wider large intestine, each following a specific anatomical path within the abdomen.
The Small Intestine: Anatomical Placement and Segments
The small intestine is situated centrally within the abdominal cavity, tightly coiled to fit its immense length into a relatively small area. Despite its narrower diameter of about one inch, this organ is the longest section of the gastrointestinal tract, measuring approximately 10 to 22 feet in a living person. This extensive coiling maximizes the surface area for nutrient absorption. The small intestine is anatomically divided into three distinct segments, beginning with the duodenum.
The duodenum is the first, shortest segment, a C-shaped tube roughly 10 inches long. It curves around the head of the pancreas and receives partially digested food from the stomach. It is primarily located in the upper abdomen, with a large portion fixed behind the peritoneum. Following the duodenum is the jejunum, the middle section, which is generally about 8 feet long. The jejunum and the final segment, the ileum, are highly mobile and occupy the central and lower abdominal space. The ileum is the longest portion, measuring around 12 feet, and connects to the large intestine at the lower right side of the abdomen.
The Large Intestine: Defining Its Frame and Path
The large intestine is shorter, about 5 feet long, but is named for its wider diameter of roughly three inches. Its location is distinct, creating a border or frame around the centrally located mass of the small intestine. It begins in the lower right abdomen and follows a defined path that outlines the abdominal cavity’s perimeter.
The path starts with the cecum, a pouch-like structure in the lower right quadrant where the small intestine empties its contents. It then ascends vertically as the ascending colon, moving upward along the right side of the abdomen toward the liver. At the liver, it makes a sharp turn, known as the right colic flexure, to become the transverse colon. The transverse colon travels horizontally across the upper abdomen, positioned below the stomach and liver. It continues until it reaches the spleen on the left side, making another sharp turn called the left colic flexure. From there, the tube moves downward as the descending colon, traveling along the left side toward the pelvis. The path concludes with the S-shaped sigmoid colon, which coils in the lower left abdomen before connecting to the rectum, the final storage area before waste elimination.
The Support System: How the Intestines are Secured
The intestines are held securely in place by a complex set of membranes, rather than floating loosely inside the abdomen. The peritoneum is a thin, smooth membrane that lines the walls of the abdominal cavity and wraps around the organs. This membrane consists of two layers: the parietal peritoneum lining the cavity wall and the visceral peritoneum covering the organs.
The mesentery is a specific, double-layered fold of the peritoneum that plays a structural role in intestinal placement. This structure anchors the jejunum and ileum of the small intestine to the posterior abdominal wall. The mesentery provides secure attachment while allowing the necessary movement for peristalsis, the muscular contractions that push food along the tract. Blood vessels, nerves, and lymphatic vessels all travel through this supporting membrane to reach the intestinal segments. This system ensures the intestines remain in their correct anatomical position and prevents them from tangling.