The colon (large intestine) is the distal part of the gastrointestinal tract, expanding from the cecum to the anal canal. The receives spend food from the small intestine, indigenous which the absorbs water and also electrolytes to form faeces.
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Anatomically, the colon deserve to be split into four parts – ascending, transverse, descending and also sigmoid. This sections form an arch, i m sorry encircles the tiny intestine.
In this article, us shall look at the anatomy of the colon – the anatomical structure and also relations, neurovascular supply, and clinical correlations.
The colon averages 150cm in length, and can be split into four parts (proximal to distal): ascending, transverse, descending and also sigmoid.
The colon begins together the ascending colon, a retroperitoneal framework which ascends superiorly native the cecum.
When the meets the right lobe of the liver, it transforms 90 levels to move horizontally. This revolve is recognized as the right colic flexure (or hepatic flexure), and marks the start of the transverse colon.
The transverse colon extends indigenous the ideal colic flexure come the spleen, whereby it turns another 90 levels to allude inferiorly. This revolve is well-known as the left colic flexure (or splenic flexure). Here, the colon is attached come the diaphragm by the phrenicocolic ligament.
The transverse colon is the the very least fixed component of the colon, and also is change in place (it can dip into the pelvis in tall, thin individuals). Unequal the ascending and descending colon, the transverse colon is intraperitoneal and is attached by the transverse mesocolon.
After the left colic flexure, the colon move inferiorly towards the pelvis – and is referred to as the to decrease colon. That is retroperitoneal in the majority of individuals, but is located anteriorly come the left kidney, passing over its lateral border.
When the colon begins to rotate medially, it i do not care the sigmoid colon.
The 40cm lengthy sigmoid colon is located in the left reduced quadrant of the abdomen, extending from the left iliac fossa to the level the the S3 vertebra. This journey gives the sigmoid colon its characteristics “S” shape.
The sigmoid colon is attached to the posterior pelvic wall by a mesentery – the sigmoid mesocolon. The long size of the mesentery permits this part of the colon to be particularly mobile.
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Fig 1 – outline of the 4 main components of the colon.
The paracolic gutters room two spaces between the ascending/descending colon and the posterolateral abdominal muscle wall.
These structures space clinically important, together they enable material that has been released from inflamed or infected ab organs to accumulate elsewhere in the abdomen.
The huge intestine has a number of characteristic features, which permits it to be distinguished from the small intestine:Attached come the surface of the huge intestine space omental appendices – tiny pouches of peritoneum, filled through fat.Running longitudinally along the surface ar of the big bowel space three strips that muscle, known as the teniae coli. Castle are referred to as the mesocolic, free and omental coli.The teniae coli contract come shorten the wall of the bowel, producing sacculations well-known as haustra.The big intestine has actually a lot wider diameter compared to the little intestine.
These features cease at the rectosigmoid junction, whereby the smooth muscle of the teniae coli expand to type a complete layer in ~ the rectum.
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Fig 2 – The macroscopic attributes of the huge intestine.
The neurovascular it is provided to the colon is closely linked come its embryological origin:Ascending colon and proximal 2/3 of the transverse colon – derived indigenous the midgut.Distal 1/3 that the transverse colon, descending colon and sigmoid colon – derived from the hindgut.
As a general rule, midgut-derived frameworks are supplied by the exceptional mesenteric artery, and also hindgut-derived frameworks by the inferior mesenteric artery.
The ascending colon obtain arterial supply from two branches that the superior mesenteric artery; the ileocolic and right colic arteries. The ileocolic artery offers rise to colic, anterior cecal and also posterior cecal branches – every one of which supply the ascending colon.
The transverse colon is derived from both the midgut and also hindgut, and so that is supplied by branches of the superior mesenteric artery and also inferior mesenteric artery:Right colic artery (from the remarkable mesenteric artery)Middle colic artery (from the remarkable mesenteric artery)Left colic artery (from the worse mesenteric artery)
The descending colon is provided by a solitary branch that the worse mesenteric artery; the left colic artery. The sigmoid colon receives arterial supply via the sigmoid arteries (branches the the inferior mesenteric artery).
Marginal Artery the Drummond
The marginal artery (of Drummond) is a clinically crucial vessel that provides collateral supply come the colon – thereby preserving arterial supply in the situation of occlusion or stenosis of among the major vessels.
As the terminal vessels of the superior mesenteric and also inferior mesenteric artery approach the colon, they separation into plenty of branches, i beg your pardon anastomose with each other. These anastomoses type a consistent arterial channel i beg your pardon extends the length of the colon – the marginal artery. Long, right arterial branches (called vasa recta) arise from the marginal artery to supply the colon.
The venous drainage that the colon is comparable to the arterial supply:Ascending colon – ileocolic and right colic veins, i beg your pardon empty right into the superior mesenteric vein.Transverse colon – center colic vein, i beg your pardon empties into the premium mesenteric vein.Descending colon – left colic vein, i m sorry drains into the inferior mesenteric vein.Sigmoid colon – drained by the sigmoid veins right into the inferior mesenteric vein.
The remarkable mesenteric and also inferior mesenteric veins eventually empty into the hepatic portal vein. This allows toxins absorbed from the colon come be processed by the liver for detoxification.
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Fig 3 – The significant arteries and veins providing the colon.
The innervation to the colon is dependence on embryological origin:Midgut-derived frameworks (ascending colon and proximal 2/3 of the transverse colon) obtain their sympathetic, parasympathetic and also sensory supply via nerves from the superior mesenteric plexus.
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Hindgut-derived structures (distal 1/3 the the transverse colon, to decrease colon and sigmoid colon) receive your sympathetic, parasympathetic and sensory supply via nerves from the worse mesenteric plexus:Parasympathetic innervation via the pelvic splanchnic nervesSympathetic innervation via the lumbar splanchnic nerves.