24 Luxor 10 is the large intestine large intestine or the colon extends from the ileocecal sphincter to the anus the subdivisions are the cecum the colon the rectum and the anal canal the colon has an ascending section a transverse section and a descending section as well as a sigmoid section inferior to the cecum is the appendix and when that becomes inflamed you can develop appendicitis if the appendix is ruptured you can have gangrene or peritonitis and that can be life-threatening the large intestine is only about five feet long but it's about two and a half inches in diameter the ascending and descending parts are retroperitoneal mean they're found in the back of the abdominal cavity rather than in the front the initial part is called the cecum and dangling from the cecum is the veriform appendix the last eight inches the GI tract is the rectum and that is a chamber it's a storage chamber until it's time to defecate the anal Canal has two sphincters in it it has an internal sphincter that's smooth muscle and then the external sphincter is skeletal muscle which is under voluntary control this is just showing the large intestine the ascending the transverse descending the over here is the cecum the sigmoid colon and then the rectum and then the anus there are two flexors there's a hepatic flexure and a colic flexor splenic flexure excuse me this is where it makes the turn so we have the ascending colon it makes a turn excuse me to become the transverse colon and it does so at liver so that's called the hepatic flexure then it's going to turn again around the area of the spleen and travel downward these little pockets are called hostra as I said inflammation in the appendix um can cause a lot of problems things that can cause inflammation include blockage of the Lumen by chyme foreign bodies carcinoma stenosis or stiffening or kinking the symptoms of appendicitis include a high fever elevated white blood cell count it's particularly neutrophils so the neutrophil count is above 75 percent and you have a fever and the referred pain as well as anorexia and nausea and vomiting you probably have appendicitis the pain localizes in the right lower quadrant this can progress very quickly to gangrene and perforation which can cause peritonitis generally within 24 to 36 hours the mucosa large intestine has no Villi or permanent circular folds it does have these depressions the crypts um it has in which there are simple columnar epithelium and lots and lots and lots of goblet cells there's not a lot of absorption that happens here so the need for having as many columnar epithelial cells as we have in the small intestine isn't there however as the last bit of water is removed and the feces solidifies you're going to need a lot of goblet cells to produce mucus to lubricate the feces as it's moving through the intestine muscularis has specialized portions of longitudinal muscle called teniere coli and these contract and gather the colon into pouches that are called hostra the uh if someone develops polyps in the colon they generally grow pretty slow they're usually benign but anytime a polyp is present and it's seen through endoscopy it's it's removed because they can develop into cancer this shows the histology of the large intestine so we have these little holes where it goes down and forms Crips these have mainly mucous cells also some absorptive cells to absorb water and some intestinal glands another view of the large intestine you can see the surface is going to look very smooth except for these tiny pores that lay down into the Crips we have a muscular layer the internal circular layer is normal but the outer one it has these 108 coli which are shorter bands and it causes a pleating effect needs formation of Hosta are these pouches the serosa is visceral peritoneum and the appendix has lymphatic tissue mechanical movements are large intestine fluid hostile churning peristalsis and mass peristalsis the peristaltic waves come in about 3 to 12 contractions per minute the Hostile churning as the the kind moves from the ilium into the cecum and and starts moving it these pouches are relaxed and they fill up from below by muscular contractions so there's contraction behind again like we saw before that's going to move the chyme up sort of like an elevator move it up into the next pouch and then that pouch is going to contract and move it up to the next pouch and so forth and that's called hostile churning the gastro ileal reflex happens when the stomach is full the gastrin hormone causes the ileocecal sphincter to relax so that the small intestine will empty out and make room for the contents of the stomach to move into it The gastropolic Reflex happens again when the stomach fills there's a strong peristaltic wave that's going to move the contents of the transverse colon into the rectum again to make room in the large intestine for the the contents of the small intestine to move into it this is why um in the morning when you feed your dog they have to go to the bathroom right away because is their stomach full fills um the food that's already there and the small intestine moves to large intestine the food and large intestine feces and large intestine then moves into the rectum there are no enzymes secreted only mucus and large intestine most of the chemical digestion is occurring from bacterial fermentation any undigested carbohydrates are fermented into carbon dioxide methane gas that gives the contributes to the smell of feces any undigested proteins are broken down into simpler substances called indols that too provides odor and the bilirubin that enters into the large intestine is converted into is broken down and that produces color bacteria produce vitamin K as well as vitamin B the some electrolytes are absorbed in large intestine after about three to ten hours 90 percent of the water has been removed feces are semi-solid by the time it reaches the transverse colon and feces consist of dead epithelial cells undigested foods and lots of bacteria so the large intestine absorbs mainly water electrolytes and some vitamins although most water absorption happens in the small intestine large intestine is going to absorb that last bit to solidify the feces and that makes an important organ of maintaining the body's water balance the elimination of feces from the rectum it's called defecation and this is reflexive it's aided by voluntary contractions the diaphragm and abdominal muscles when someone Bears down the external anal sphincter can be voluntarily controlled except for in infants and that allows us to either defecate or postpone the defecation again that gastrocolic reflex is going to move feces here into the rectum once it does there's stretch receptors similar to stretch receptors we have an earth stomach that are going to Signal the sacral spinal cord and then the parasympathetic nerves contract muscles to the rectum and relax the internal anal sphincter diarrhea happens when chyme passes to quickly through the intestine and not enough water is reabsorbed constipation can happen if the person has decreased intestinal motility and too much water is reabsorbed so the remedy for constipation is fiber increased exercise and also drinking more water dietary fiber can be classified as insoluble and soluble and both types are going to affect what goes on in the GI tract insoluble fiber is made from the Woody parts of plants and it can come from things like wheat bran vegetable skins things like that and it helps to protect against colon cancer it provides some bulk and helps move things through your GI tract bacteria also feed on the insoluble fiber which makes makes uncomfortable gas in a lot of people soluble fiber forms a gel-like consistency it comes from Beans oats the pith of citrus fruit and apples and this helps to lower our blood cholesterol as we saw in the last lecture by preventing reabsorption of bile salts so liver has to use cholesterol to make more colonoscopy uses elongated flex flexible fiber optic endoscope to visually examine the lining of the colon look for polyps or other problems and an occult blood test is used to screen for colorectal cancer that the occult blood test means blood in the feces