Anatomical PositionThe colon averages 150cm in length, and can be divided into four parts (proximal to distal): ascending, transverse, descending and sigmoid. Show
Ascending ColonThe colon begins as the ascending colon, a retroperitoneal structure which ascends superiorly from the cecum. When it meets the right lobe of the liver, it turns 90 degrees to move horizontally. This turn is known as the right colic flexure (or hepatic flexure), and marks the start of the transverse colon. Transverse ColonThe transverse colon extends from the right colic flexure to the spleen, where it turns another 90 degrees to point inferiorly. This turn is known as the left colic flexure (or splenic flexure). Here, the colon is attached to the diaphragm by the phrenicocolic ligament. The transverse colon is the least fixed part of the colon, and is variable in position (it can dip into the pelvis in tall, thin individuals). Unlike the ascending and descending colon, the transverse colon is intraperitoneal and is enclosed by the transverse mesocolon. Descending ColonAfter the left colic flexure, the colon moves inferiorly towards the pelvis – and is called the descending colon. It is retroperitoneal in the majority of individuals, but is located anteriorly to the left kidney, passing over its lateral border. When the colon begins to turn medially, it becomes the sigmoid colon. Sigmoid ColonThe 40cm long sigmoid colon is located in the left lower quadrant of the abdomen, extending from the left iliac fossa to the level of the S3 vertebra. This journey gives the sigmoid colon its characteristic “S” shape. The sigmoid colon is attached to the posterior pelvic wall by a mesentery – the sigmoid mesocolon. The long length of the mesentery permits this part of the colon to be particularly mobile. Adobe Stock, Licensed to TeachMeSeries Ltd Fig 1 – The large intestine extends from the cecum to the rectum. It is comprised of the ascending, transverse, descending and sigmoid colon. Paracolic GuttersThe paracolic gutters are two spaces between the ascending/descending colon and the posterolateral abdominal wall. These structures are clinically important, as they allow material that has been released from inflamed or infected abdominal organs to accumulate elsewhere in the abdomen. Anatomical StructureThe large intestine has a number of characteristic features, which allows it to be distinguished from the small intestine:
These features cease at the rectosigmoid junction, where the smooth muscle of the teniae coli broaden to form a complete layer within the rectum. By OpenStax College [CC BY 3.0], via Wikimedia Commons Fig 2 – The macroscopic features of the large intestine. Anatomical RelationsThe colon has numerous important anatomical relations in the abdomen, as shown in Table 1:
Neurovascular SupplyThe neurovascular supply to the colon is closely linked to its embryological origin:
Arterial SupplyAs a general rule, midgut-derived structures are supplied by the superior mesenteric artery, and hindgut-derived structures by the inferior mesenteric artery. The ascending colon receives arterial supply from two branches of the superior mesenteric artery; the ileocolic and right colic arteries. The ileocolic artery gives rise to colic, anterior cecal and posterior cecal branches – all of which supply the ascending colon. The transverse colon is derived from both the midgut and hindgut, and so it is supplied by branches of the superior mesenteric artery and inferior mesenteric artery:
The descending colon is supplied by a single branch of the inferior mesenteric artery; the left colic artery. The sigmoid colon receives arterial supply via the sigmoid arteries (branches of the inferior mesenteric artery). Marginal Artery of DrummondThe marginal artery (of Drummond) is a clinically important vessel that provides collateral supply to the colon – thereby maintaining arterial supply in the case of occlusion or stenosis of one of the major vessels. As the terminal vessels of the superior mesenteric and inferior mesenteric artery approach the colon, they split into many branches, which anastomose with each other. These anastomoses form a continuous arterial channel which extends the length of the colon – the marginal artery. Long, straight arterial branches (called vasa recta) arise from the marginal artery to supply the colon. Venous DrainageThe venous drainage of the colon is similar to the arterial supply:
The superior mesenteric and inferior mesenteric veins ultimately empty into the hepatic portal vein. This allows toxins absorbed from the colon to be processed by the liver for detoxification. Fig 3 – The major arteries and veins supplying the colon. InnervationThe innervation to the colon is dependent on embryological origin:
Lymphatic DrainageThe lymphatic drainage of the ascending and transverse colon is into the superior mesenteric nodes. The descending colon and sigmoid drain into the inferior mesenteric nodes. Most of the lymph from the superior mesenteric and inferior mesenteric nodes passes into the intestinal lymph trunks, and on to the cisterna chyli – where it ultimately empties into the thoracic duct. Which aspect of the large intestine is located highest or most superior in the abdomen quizlet?The right colic flexure is the most superior portion of the large intestine. The average time to scan the large intestine during a computed tomography colonography is: a) 1 hour.
What is the most superior part of the small intestine?Duodenum. The superior part (duodenal bulb/ampulla) is the only intraperitoneal part, as the hepatoduodenal ligament and greater omentum attach to it.. The descending part of the duodenum has an opening called the major duodenal papilla (tubercle of Vater).. Where is large intestine located?Where is the large intestine located? The large intestine is in your lower abdominal cavity from your waist down. It surrounds the small intestine in a sort of a square question mark shape, with the tail of the question mark ending at the anal canal.
Which part of the large intestine is located between the rectum and descending colon?Structure and Function
The sigmoid colon is an “S” shaped portion of the large intestine that begins in front of the pelvic brim as a continuation of the descending colon and becomes the rectum at the level of the third sacral vertebrae.
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