The large intestine, also known as the large bowel, is the last part of the gastrointestinal tract and of the digestive system in vertebrates. Water is absorbed here and the remaining waste material is stored as feces before being removed by defecation.
The duodenum is the first section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear, and the terms anterior intestine or proximal intestine may be used instead of duodenum. In mammals the duodenum may be the principal site for iron absorption. The duodenum precedes the jejunum and ileum and is the shortest part of the small intestine.
The ileum is the final section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms posterior intestine or distal intestine may be used instead of ileum. Its main function is to absorb vitamin B12, bile salts, and whatever products of digestion that were not absorbed by the jejunum.
The mesentery is an organ that attaches the intestines to the posterior abdominal wall in humans and is formed by the double fold of peritoneum. It helps in storing fat and allowing blood vessels, lymphatics, and nerves to supply the intestines, among other functions.
In human anatomy, the inferior mesenteric artery, often abbreviated as IMA, is the third main branch of the abdominal aorta and arises at the level of L3, supplying the large intestine from the distal transverse colon to the upper part of the anal canal. The regions supplied by the IMA are the descending colon, the sigmoid colon, and part of the rectum.
The superior mesenteric vein is a blood vessel that drains blood from the small intestine. Behind the neck of the pancreas, the superior mesenteric vein combines with the splenic vein to form the hepatic portal vein. The superior mesenteric vein lies to the right of the similarly named artery, the superior mesenteric artery, which originates from the abdominal aorta.
In the anatomy of humans and homologous primates, the ascending colon is the part of the colon located between the cecum and the transverse colon.
The right colic artery arises from about the middle of the concavity of the superior mesenteric artery, or from a stem common to it and the ileocolic.
The middle colic artery is a branch of the superior mesenteric artery that mostly supplies the transverse colon. It arises just below the pancreas. It passes inferiorly and anteriorly between the layers of the transverse mesocolon, and divides into left and right branches. The right branch anastomoses with the right colic artery, and the left anastomoses with the left colic artery, a branch of the inferior mesenteric artery. This sequence of anastomses are frequently referred to as the marginal artery of the colon.
The left colic artery is a branch of the inferior mesenteric artery.
The ileocolic artery is the lowest branch arising from the concavity of the superior mesenteric artery.
The intestinal arteries arise from the convex side of the superior mesenteric artery. They are usually from twelve to fifteen in number, and are distributed to the jejunum and ileum.
There are two colic flexures, or curvatures in the transverse colon. The one on the right, the right colic flexure is known as the hepatic flexure.
The midgut is the portion of the embryo from which most of the intestines develop. After it bends around the superior mesenteric artery, it is called the "midgut loop". It comprises the portion of the alimentary canal from the end of the foregut at the opening of the bile duct to the hindgut, about two-thirds of the way through the transverse colon.
The appendicular artery, also known as appendiceal artery, commonly arises from the terminal branch of the ileocolic artery, or less commonly from the posterior cecal artery or an ileal artery. It descends behind the termination of the ileum and enters the mesoappendix of the vermiform appendix. It runs near the free margin of the mesoappendix and ends in branches which supply the appendix.
The preaortic lymph nodes lie in front of the aorta, and may be divided into celiac lymph nodes, superior mesenteric lymph nodes, and inferior mesenteric lymph nodes groups, arranged around the origins of the corresponding arteries.
The inferior mesenteric lymph nodes consist of:
The colic branch of ileocolic artery is a small artery in the abdomen. The ileocolic artery of the superior mesenteric artery branches off into the ascending colic artery, the anterior and posterior cecal arteries, the appendicular artery, and the ileal branches.
The following outline is provided as an overview of and topical guide to human anatomy:
