Large Intestine

aka the colon greater diameter than small intestine and is about 1.5 meters long goes up on the right, across abdomen, down on the left, and turns in toward pelvis wall lacks villi absorbs water and stores feces (NO digestion) mucus is the only significant secretion –protects the wall from abrasive action of material passing through, binds particles of fecal matter, and its alkalinity helps control pH 100 trillion bacteria call your colon home –breakdown certain molecules that our bodies can’t digest (ex. oligosaccharides in cellulose) –bacteria produce gas as a byproduct of their metabolism

Parts of Large Intestine cecum, colon, rectum, and anus cecum – start of lg. intestine –dilated pouch-like structure –vermiform appendix – narrow closed tube that hangs from cecum; no known function colon – ascending, transverse, descending, sigmoid (curve) rectum – follow the curvature of the sacrum and ends about 5 cm below the coccyx anal canal – last 2.5 – 4 cm –opening to outside called the anus –guarded by 2 sphincters: internal and external

Review Questions 1.What are the general functions of the large intestine? 2.Describe the parts of the large intestine. 3.How does the structure of the large intestine differ from that of the small intestine? 4.What substances does the large intestine absorb?

Movements mixing and peristalsis are similar to small intestine but slower occurs 2 or 3 times a day (following meals) and results in mass movements defecation reflex (similar to respiration) –hold breath (diaphragm contracts) and contract abs –internal pressure rises and forces feces into rectum –triggers sphincters to relax and feces forced out control of external anal sphincter allows us to control defecation

Feces materials not digested or absorbed plus water, electrolytes, mucus, shed intestinal cells, and bacteria about 75% water and bacteria color is derived from bile pigments (breakdown of hemoglobin) odor comes from a variety of compounds that bacteria produce

Review Questions 1.How does peristalsis in the large intestine differ from peristalsis in the small intestine? 2.List the major events that occur during defecation. 3.Describe the composition of feces.