—The small intestine is a convoluted tube, extending from the pyloric end of the stomach to the ileo-caecal valve where it terminates in the large intestines. It fills up the greater part of the abdominal and the pelvic cavity. It is about twenty feet in length and gradually diminishes in size from the commencement to the termination.
The small intestines are surrounded at the top and at the sides by the large intestines. The small intestines are held in place by the mesentery, a part of the peritoneum, which connects or fastens to the spine.
The small intestines are divisible into three portions: Duodenum, Jejunum, and the Ileum.
Arteries.—The main arterial supply to the small intestines is through the superior mesenteric artery.
The superior mesenteric vein withdraws the main part of the blood from the small intestines.
Duodenum.
—The duodenum has received its name from being about equal in length to the breadth of twelve fingers (ten inches).
It is the shortest, widest and the most fixed part of the small intestines, being closely and firmly attached to the posterior abdominal wall. It is not covered by the mesentery. The upper half of the duodenum is in the epigastric region and the lower half is in the umbilical region. It is practically in the median line of the body.
The duodenum is shaped like a horseshoe, the opening being directed toward the left. The arteries supplying the duodenum are the pyloric and the pancreatic duodenal branch of the superior mesenteric. The veins correspond to the arteries.
The pancreatic duct and the bile duct empty into the duodenum at its middle portion.