The small intestine, i m sorry is 670 to 760 cm (22 to 25 feet) in length and also 3 to 4 centimeter (about 2 inches) in diameter, is the longest part of the cradle tract. It begins at the pylorus, the juncture with the stomach, and also ends at the ileocecal valve, the point with the colon. The main functional segment of the tiny intestine space the duodenum, the jejunum, and the ileum.

You are watching: The longest part of the alimentary canal is the

The duodenum is 23 to 28 centimeter (9 come 11 inches) long and also forms a C-shaped curve the encircles the head the the pancreas. Uneven the remainder of the little intestine, that is retroperitoneal (that is, that is behind the peritoneum, the membrane lining the abdominal wall). Its very first segment, recognized as the duodenal bulb, is the widest component of the tiny intestine. That is horizontal, passing backward and also to the appropriate from the pylorus, and lies somewhat behind the wide end of the gallbladder. The second part of the duodenum operation vertically downward in prior of the hilum the the best kidney (the point of entrance or leave for blood vessels, nerves, and also the ureters); the is right into this part through the duodenal papilla (papilla of Vater) that the pancreatic juice and bile flow. The third part of the duodenum runs horizontally to the left in former of the aorta and also the inferior vena cava (the major channel for return to the love of venous blood indigenous the lower part of the body and the legs), when the fourth part ascends come the left next of the 2nd lumbar vertebra (at the level of the small of the back), climate bends high solution downward and also forward to sign up with the second component of the little intestine, the jejunum. One acute angle, called the duodenojejunal flexure, is created by the suspension that this component of the small intestine by the ligament the Treitz.

The jejunum creates the upper two-fifths that the remainder of the tiny intestine; it, choose the ileum, has plenty of convolutions and also is attached come the posterior abdominal wall surface by the mesentery, considerable fold of serous-secreting membrane. The ileum is the remaining three-fifths the the tiny intestine, though over there is no absolute point at i beg your pardon the jejunum ends and the ileum begins. In broad terms, the jejunum rectal the upper and also left component of the abdomen listed below the subcostal aircraft (that is, in ~ the level that the 10th rib), while the ileum is situated in the lower and right part. At its termination the ileum opens into the big intestine.

The plan of the muscular coats of the small intestine is uniform throughout the size of the organ. The inner, circular class is thicker than the outer, longitudinal layer. The outermost layer of the tiny intestine is lined by the peritoneum.

Blood and nerve supply


Consider even if it is the continuous band of membranous tissue roughly humans" intestines should be reputed an organ
Learn much more about the mesentery, a consistent folded tape of membranous organization that holds the intestines and other offal in place and also which part researchers think about to be a unique organ.

The superior mesenteric artery (a branch of the abdominal aorta) and also the premium pancreaticduodenal artery (a branch that the hepatic artery) supply the small intestine v blood. These vessels run in between layers the the mesentery, the membrane the connects the intestines with the wall of the abdominal cavity, and also give off big branches that kind a heat of connecting arches from i m sorry branches happen to get in the wall surface of the little bowel. The blood from the intestine is changed by way of the superior mesenteric vein, which, through the splenic vein, forms the portal vein, i beg your pardon drains into the liver.

See more: How Long Can A Rat Go Without Water ? How Long Can Rats Live Without Water

The tiny intestine has actually both sympathetic and parasympathetic innervation. The vagus nerve provides parasympathetic innervation. Forgiveness innervation is noted by branches native the exceptional mesenteric plexus, a nerve network under the solar plexus that complies with the blood vessels right into the tiny intestine and also finally terminates in the Auerbach plexus, which is located in between the circular and longitudinal muscle coats, and the Meissner plexus, i m sorry is located in the submucosa. Plenty of fibrils, both adrenergic (sympathetic) and also cholinergic (parasympathetic), connect these two plexuses.