Small and large intestine condition

• Small intestine


  6 m in length, includes upper fixed (duodenum, 25 cm) and lower mobile part (proximal 2/5th is jejunum and distal 3/5th is ileum)
• Colon


  135 cm long, divided into caecum, ascending colon, transverse colon, descending colon and sigmoid colon
• Rectum


  About 12-15cm in length at the rectosigmoid junction opposite S3, to end at the anorectal junction at the level of pelvic floor
• Ileocecal valve


  Serves as a sphincter to prevent the back reflux to terminal ileum
• Arterial supply


  1. Superior mesenteric artery (SMA) supplies the jejunum and ileum

  2. SMA supplies the colon from caecum to splenic flexure by ileocolic, right colic and middle colic arteries

  3. Inferior mesenteric artery (IMA) supply the descending and sigmoid colon by left colic, sigmoid and superior rectal arteries

  4. Rectum is supplied by: superior rectal artery (from IMA), middle rectal artery (from internal iliac arteries) and inferior rectal artery (from pudendal arteries)
• Venous drainage


  1. Small intestine venous blood drainage is to the superior mesenteric vein (SMV) and from it to the portal vein

  2. Venous drainage of large intestine occurs into superior mesenteric vein (SMV) (which joins the splenic vein to form the portal vein) and inferior mesenteric vein (IMV) (drains into the splenic vein)

  3. Venous drainage of rectum is through: superior rectal vein becomes IMV and finally drain into portal vein, middle and inferior rectal veins are drained via systemic circulation
• Lymphatic drainage


  1. Small intestine contains lymphoid aggregates (peyers patches) which becomes more prominent in the ileum

  2. Colon is drained via lymph node groups in sequence: Epicolic nodes on the wall, Paracolic nodes between the marginal artery and the bowel, Intermediate nodes on the main vessels, Principal nodes alongside the SM and IM vessels

  3. Upper part of rectum is drained along the superior rectal vessels to lymph nodes and finally to pre-aortic nodes, lower part may drain to internal iliac lymph nodes

  
• Wall layers


  1. The mucosa

  2. Submucosa

  3. The muscularis propria

  4. The serosa is part of the visceral peritoneum
• Functions of duodenum


  Responsible mainly for the absorption of carbohydrates, protein, minerals (e.g. calcium, magnesium, iron, chloride, sodium and zinc)
• Functions of small intestine


  Important secretory and digestive functions through the succus entericus
• Functions of right colon

  Absorption of water and sodium to concentrate waste product
• Functions of left colon


  Acts as a reservoir for solid faeces until the time of defecation
• Functions of jejunum


  Responsible for the absorption of glucose, protein, folic acid and vitamins C,B1(thiamine), B2 and B6
• Functions of terminal ileum


  Main site of absorption of amino acids, lipids, cholesterol, and the fat-soluble vitamins (e.g. A,D,E and K)

  Responsible for 90% of bile salt resorption from the gut, resection of the terminal ileum is likely to result in a significant interruption of the enterohepatic circulation, stimulating an increase in bile salt synthesis by cholesterol transmetabolism in the liver, thereby increasing the risk of gallstone formation

  Contains intrinsic factor-dependent receptors that are important in vitamin B12 uptake, the resultant vitamin B12 deficiency may lead to macrocytic anaemia and subacute degeneration of the cord

  Increase in intraluminal osmotic content may result in loosening of the stool after terminal ileal resection