The sigmoid colon is the part of the large intestine that is closest to the rectum and anus. It forms a loop that averages about 35–40 centimetres (14–16 in) in length. The loop is typically shaped like a Greek letter sigma (ς) or Latin letter S. This part of the colon normally lies within the pelvis, but due to its freedom of movement it is liable to be displaced into the abdominal cavity.
The abdominal aorta is the largest artery in the abdominal cavity. As part of the aorta, it is a direct continuation of the descending aorta.
In human anatomy, the superior mesenteric artery (SMA) arises from the anterior surface of the abdominal aorta, just inferior to the origin of the celiac trunk, and supplies blood to the intestine from the lower part of the duodenum through two-thirds of the transverse colon, as well as the pancreas.
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 human anatomy, the marginal artery of the colon, also known as the marginal artery of Drummond, the artery of Drummond, and simply as the marginal artery, is an artery that connects the inferior mesenteric artery with the superior mesenteric artery. It is sometimes absent, as an anatomical variant.
A nerve plexus is a plexus of intersecting nerves. A nerve plexus is composed of afferent and efferent fibers that arise from the merging of the anterior rami of spinal nerves and blood vessels. There are five spinal nerve plexuses, except in the thoracic region, as well as other forms of autonomic plexuses, many of which are a part of the enteric nervous system. The nerves that arise from the plexuses have both sensory and motor functions. These functions include muscle contraction, the maintenance of body coordination and control, and the reaction to sensations such as heat, cold, pain, and pressure. There are several plexuses in the body, including:
The sigmoid arteries, two or three in number, run obliquely downward and to the left behind the peritoneum and in front of the psoas major, ureter, and internal spermatic vessels. They originate from the inferior mesenteric artery branch of the abdominal aorta.
The right colic artery is an artery of the abdomen. It is a branch of the superior mesenteric artery. It supplies the ascending colon. It may be removed in a right hemicolectomy.
The middle colic artery is an artery of the abdomen. It is a branch of the superior mesenteric artery that mostly supplies the transverse colon. Parts of it may be removed in different types of hemicolectomy.
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.
The inferior mesenteric plexus is derived chiefly from the aortic plexus.
There are two colic flexures, or curvatures in the transverse colon. The one on the right, the right colic flexure is also known as the hepatic flexure.
The abdominal aortic plexus is formed by branches derived, on either side, from the celiac plexus and ganglia, and receives filaments from some of the lumbar ganglia.
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 superior hypogastric plexus is a plexus of nerves situated on the vertebral bodies anterior to the bifurcation of the abdominal aorta.
The superior mesenteric ganglion is a ganglion in the upper part of the superior mesenteric plexus. It lies close to the origin of the superior mesenteric artery.
The inferior mesenteric lymph nodes consist of:
The superior mesenteric lymph nodes may be divided into three principal groups:
