Colon (anatomy)
Front of abdomen, showing surface markings for liver, stomach, and large intestine.
Gray's	subject #249 1177
Dorlands/Elsevier	c_47/12249855

The colon is a storage tube for solid wastes. Gray's Anatomy the Respiratory apparatus ( Apparatus Respiratorius Respiratory system Respiratory apparatus Elsevier, the world's largest Publisher of Medical and Scientific literature, forms part of the Reed Elsevier group The main function of the colon appears to be extraction of water and salts from feces. Water is a common Chemical substance that is essential for the survival of all known forms of Life. Feces, faeces, or fæces (see spelling differences) is a waste product from an animal's digestive tract expelled through the Anus In mammals, it consists of the ascending colon, transverse colon, the descending colon, and the sigmoid colon. Mammals ( class Mammalia) are a class of Vertebrate Animals characterized by the presence of Sweat glands, including sweat glands The sigmoid colon ( pelvic colon; sigmoid flexure) forms a loop which averages about 40 cm The colon from cecum to the splenic flexure (the junction between the transverse and descending colon) is also known as the right colon. The cecum or caecum (from the Latin caecus meaning Blind) is a pouch connected to the Ascending colon of the Large The remainder is known as the left colon.

Anatomy

The location of the parts of the colon are either in the abdominal cavity or behind it in the retroperitoneum. The colon in those areas is fixed in location.

Arterial supply to the colon comes from branches of the superior and inferior mesenteric arteries. Flow between these two systems communicates via a "marginal artery" that runs parallel to the colon for its entire length. Historically, it has been believed that the arc of Riolan, or the meandering mesenteric artery (of Moskowitz), is a variable vessel connecting the proximal SMA to the proximal IMA that can be extremely important if either vessel is occluded. However, recent studies conducted with improved imaging technology have questioned the actual existence of this vessel, with some experts calling for the abolition of the terms from future medical literature.

Venous drainage usually mirrors colonic arterial supply, with the inferior mesenteric vein draining into the splenic vein, and the superior mesenteric vein joining the splenic vein to form the portal vein that then enters the liver. In Human anatomy, the inferior mesenteric vein (IMV is a Blood vessel that drains Blood from the Large intestine. In Anatomy, the splenic vein (in the past called the lienal vein) is the Blood vessel that drains Blood from the Spleen. In Anatomy, the superior mesenteric vein (SMV is a Blood vessel that drains Blood from the Small intestine ( Jejunum and Ileum

Lymphatic drainage from the entire colon and proximal two-thirds of the rectum is to the paraortic nodes that then drain into the cisterna chyli. The cisterna chyli (or receptaculum chyli) is a dilated sac at the lower end of the Thoracic duct into which lymph from the Intestinal trunk and two The lymph from the remaining rectum and anus can either follow the same route, or drain to the internal illiac and superficial inguinal nodes. The dentate line only roughly marks this transition.

Ascending colon

The ascending colon, on the right side of the abdomen, is about 12. 5 cm long. It is the part of the colon from the cecum to the hepatic flexure (the turn of the colon by the liver). It is retroperitoneal in most humans. The retroperitoneum (adj retroperitoneal) is the anatomical space in the Abdominal cavity behind ( retro) the Peritoneum. In ruminant grazing animals the cecum empties into the spiral colon. Anteriorly it is related to the coils of small intestine, the right edge of the greater omentum, and the anterior abdominal wall. Posteriorly, it is related to the iliacus, the iliolumbar ligament, the quadratus lumborum, the transverse abdominis, the diaphragm at the tip of the last rib; the lateral cutaneous, ilioinguinal, and iliohypogastric nerves; the iliac branches of the iliolumbar vessels, the fourth lumbar artery, and the right kidney.

The ascending colon is supplied by parasympathetic fibers of the vagus nerve (CN X).

Arterial supply of the ascending colon comes from the ileocolic artery and right colic artery, both branches of the SMA. The Ileocolic Artery is the lowest branch arising from the concavity of the Superior mesenteric artery. 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. While the ileocolic artery is almost always present, the right colic can be absent in 5-15% of individuals.

Transverse colon

The transverse colon is the part of the colon from the hepatic flexure (the turn of the colon by the liver) to the splenic flexure (the turn of the colon by the spleen). Hepatic (or the right colic flexure is the sharp bend between the ascending and the transverse colon. The liver is a vital organ in the human body and is present in Vertebrates and some other animals The splenic (or left colic flexure is a sharp bend between the transverse and the descending colon in the Left upper quadrant of humans The spleen is an organ found in all Vertebrate animals In humans the spleen is located in the abdomen of the body where it functions in the destruction of redundant Red The transverse colon hangs off the stomach, attached to it by a wide band of tissue called the greater omentum. In Human anatomy, the stomach is a J-shaped hollow muscular organ of the Gastrointestinal tract involved in the second phase of Digestion, following Tissue is a cellular organizational level intermediate between cells and a complete organism The greater omentum (also the great omentum, omentum majus, gastrocolic omentum, or epiploön) is a large fold of Peritoneum that On the posterior side, the transverse colon is connected to the posterior abdominal wall by a mesentery known as the transverse mesocolon. In fields of Anatomy, anatomical terms of location are descriptive terms to help identify relative positions or directions within a species The abdominal wall represents the boundaries of the Abdominal cavity. In Anatomy, the mesentery is the double layer of Peritoneum that suspends the Jejunum and Ileum from the posterior wall of the Abdomen The transverse mesocolon is a broad meso-fold of Peritoneum, which connects the Transverse colon to the posterior wall of the Abdomen.

The transverse colon is encased in peritoneum, and is therefore mobile (unlike the parts of the colon immediately before and after it). In higher Vertebrates the peritoneum is the Serous membrane that forms the lining of the abdominal cavity &mdash it covers most of the intra-abdominal More cancers form as the large intestine goes along and the contents become more solid (water is removed) in order to form feces. The large intestine is the last part of the Digestive system: the final stage of the Alimentary canal in Vertebrate Animals Its function is to Feces, faeces, or fæces (see spelling differences) is a waste product from an animal's digestive tract expelled through the Anus

The proximal two-thirds of the transverse colon is perfused by the middle colic artery, a branch of superior mesenteric artery, while the latter third is supplied by branches of the inferior mesenteric artery. The middle colic artery is a branch of the Superior mesenteric artery that mostly supplies the Transverse colon. See also Superior Mesenteric Artery Syndrome In Human anatomy, the superior mesenteric artery (SMA arises from the anterior surface of the Abdominal aorta In Human anatomy, the inferior mesenteric artery, often abbreviated as IMA, supplies the Large intestine from the left colic (or splenic flexure The "watershed" area between these two blood supplies, which represents the embryologic division between the midgut and hindgut, is an area sensitive to ischemia. The midgut is the portion of the Embryo from which most of the Intestines are derived The Hindgut (or epigaster) is the Posterior ( Caudal) part of the Alimentary canal.

Descending colon

The descending colon is the part of the colon from the splenic flexure to the beginning of the sigmoid colon. It is retroperitoneal in two-thirds of humans. The retroperitoneum (adj retroperitoneal) is the anatomical space in the Abdominal cavity behind ( retro) the Peritoneum. In the other third, it has a (usually short) mesentery. Arterial supply comes via the left colic artery. The left colic artery runs to the left behind the Peritoneum and in front of the Psoas major muscle and after a short but variable course divides into an ascending

Sigmoid colon

Diagram of the Human Intestine.

The sigmoid colon is the part of the large intestine after the descending colon and before the rectum. The large intestine is the last part of the Digestive system: the final stage of the Alimentary canal in Vertebrate Animals Its function is to The rectum (from the Latin rectum intestinum, meaning straight intestine) is the final straight portion of the Large intestine in some Mammals The name sigmoid means S-shaped (see sigmoid). The walls of the sigmoid colon are muscular, and contract to increase the pressure inside the colon, causing the stool to move into the rectum. Feces, faeces, or fæces (see spelling differences) is a waste product from an animal's digestive tract expelled through the Anus

The sigmoid colon is supplied with blood from several branches (usually between 2 and 6) of the sigmoid arteries, a branch of the IMA. 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 The IMA terminates as the superior rectal artery. The superior rectal artery ( superior hemorrhoidal artery) is an artery that descends into the Pelvis to supply blood to the Rectum.

Sigmoidoscopy is a common diagnostic technique used to examine the sigmoid colon. Sigmoidoscopy is the Minimally invasive medical examination of the large Intestine from the Rectum through the last part of the colon

Redundant colon

One variation on the normal anatomy of the colon occurs when extra loops form, resulting in a longer than normal organ. This condition, referred to as redundant colon, typically has no direct major health consequences, though rarely volvulus occurs resulting in obstruction and requiring immediate medical attention. A volvulus is a life-threatening bowel obstruction in which a loop of Bowel has abnormally twisted on itself ^[1] A significant indirect health consequence is that use of a standard adult colonoscope is difficult and in some cases impossible when a redundant colon is present, though specialized variants on the instrument (including the pediatric variant) are useful in overcoming this problem. Colonoscopy is the endoscopic examination of the large colon and the distal part of the small bowel with a CCD camera or a Fiber optic ^[2]

Function

The large intestine comes after the small intestine in the digestive tract and measures approximately 1. The large intestine is the last part of the Digestive system: the final stage of the Alimentary canal in Vertebrate Animals Its function is to In Biology the small Intestine is the part of the Gastrointestinal tract (gut between the Stomach and the Large intestine, and comprises 5 meters in length. The metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International Length is the long Dimension of any object The length of a thing is the distance between its ends its linear extent as measured from end to end Although there are differences in the large intestine between different organisms, the large intestine is mainly responsible for storing waste, reclaiming water, maintaining the water balance, and absorbing some vitamins, such as vitamin K. Note The Water Balance method is also a winding mechanism used in mining In Hydrology, a water balance Equation can be used to describes A vitamin is an Organic compound required as a Nutrient in tiny amounts by an Organism. Vitamin K (K from "Koagulations-Vitamin" in German Danish Swedish and Norwegian denotes a group of Lipophilic, Hydrophobic Vitamins that

By the time the chyme has reached this tube, almost all nutrients and 90% of the water have been absorbed by the body. Chyme is the semifluid mass of partly digested food expelled by the stomach into the duodenum A nutrient is food or chemicals that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment At this point some electrolytes like sodium, magnesium, and chloride are left as well as indigestible carbohydrates known as dietary fiber. An electrolyte is any substance containing free Ions that behaves as an electrically conductive medium Sodium (ˈsoʊdiəm is an element which has the symbol Na( Latin natrium, from Arabic natrun) atomic number 11 atomic mass 22 Magnesium (mægˈniːziəm is a Chemical element with the symbol Mg, Atomic number 12 Atomic weight 24 The chloride Ion is formed when the element Chlorine picks up one Electron to form an Anion (negatively-charged ion Cl&minus Carbohydrates (from ' Hydrates of Carbon ' or saccharides ( Greek σάκχαρον meaning " Sugar " are the most Dietary fibers are the indigestible portion of plant foods that move food through the Digestive system, absorbing water and easing Defecation. As the chyme moves through the large intestine, most of the remaining water is removed, while the chyme is mixed with mucus and bacteria known as gut flora, and becomes feces. The large intestine is the last part of the Digestive system: the final stage of the Alimentary canal in Vertebrate Animals Its function is to Water is a common Chemical substance that is essential for the survival of all known forms of Life. In vertebrates mucus is a slippery secretion produced by and covering Mucous membranes It is a viscous Colloid containing Antiseptic enzymes (such as The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have The gut flora are the Microorganisms that normally live in the Digestive tract and can perform a number of useful functions for their hosts The bacteria break down some of the fiber for their own nourishment and create acetate, propionate, and butyrate as waste products, which in turn are used by the cell lining of the colon for nourishment. Fiber or fibre is a class of Materials that are continuous filaments or are in discrete elongated pieces similar to lengths of thread. An acetate, or ethanoate, is either a salt or Ester of Acetic acid. The propionate ( IUPAC name propanoate) Ion is C 2 H 5C OO sup>&minus ( Propionic acid This is an example of a symbiotic relationship and provides about one hundred calories a day to the body. This article is about the biological phenomenon for other uses see Symbiosis (disambiguation The term symbiosis (from the Greek This article is about the unit of energy For its use in Nutrition and Food labelling regulations, see the article on Food energy. The large intestine produces no digestive enzymes — chemical digestion is completed in the small intestine before the chyme reaches the large intestine. Enzymes are Biomolecules that catalyze ( ie increase the rates of Chemical reactions Almost all enzymes are Proteins Digestion is the breaking down of chemicals in the body into a form that can be absorbed In Biology the small Intestine is the part of the Gastrointestinal tract (gut between the Stomach and the Large intestine, and comprises The pH in the colon varies between 5. pH is the measure of the acidity or alkalinity of a Solution. 5 and 7 (slightly acidic to neutral). In Computer science, ACID ( Atomicity Consistency Isolation Durability) is a set of properties that guarantee that Database transactions are

Pathology

There are a number of diseases or disorders of the colon:

• Angiodysplasia of the colon
• Chronic functional abdominal pain
• Colitis
• Colon cancer
• Constipation
• Crohn's disease
• Diarrhea
• Diverticulitis
• Diverticulosis
• Hirschsprung's disease (aganglionosis)
• Intussusception
• Irritable bowel syndrome
• Polyposis (see also Colorectal polyp)
• Pseudomembranous colitis
• Ulcerative colitis and toxic megacolon

References

Additional images

Intestines

Scheme

External links

• Overview and diagrams at seer.cancer.gov
• 09-118h. at Merck Manual of Diagnosis and Therapy Home Edition
• MeSH Large+Intestine
• Virtual Slidebox at Univ. Iowa Slide 393
• SUNY Labs 37:13-0100 - "Abdominal Cavity: The Colon and its Divisions"
• Video: What is Colorectal Cancer?