Nursing 105

Essentials of Nursing Study Guide

Chapter Two: Elimination

©2018 Achieve Page 37 of 160 2.1 The Large Intestine The large intestine extends from the ileocecal valve to the anus. It has seven parts: the cecum, the ascending colon, transverse colon, descending colon, sigmoid colon, rectum and anus (external orifice). The main function of the large intestine is the absorption of water and nutrients (significant amounts of sodium and chloride), mucal protection of the intestinal wall (from trauma of the acids formed in fecal material) and fecal elimination. It starts in the right iliac region of the pelvis, just at or below the right waist, where it is joined to the bottom end of the small intestine. From here it continues up the abdomen, then across the width of the abdominal cavity, and then it turns down, continuing to its endpoint at the anus. The large intestine takes about 16 hours to finish the digestion of the food. The colon absorbs vitamins which are created by the colonic bacteria - such as vitamin K (especially important as the daily ingestion of vitamin K is not normally enough to maintain adequate blood coagulation), vitamin B12, thiamine and riboflavin. The large intestine also compacts feces and stores fecal matter in the rectum until it can be discharged via the anus in defecation. The large intestine differs from the small intestine by being much wider and having a longitudinal layer of the muscularis that has been reduced to 3 strap-like structures known as the taeniae coli . The wall of the large intestine is lined with simple columnar epithelium. Instead of having the evaginations of the small intestine (villi), the large intestine has invaginations (the intestinal glands). While both the small intestine and the large intestine have goblet cells, they are more abundant in the large intestine. Also along the large intestine are haustra , which are bulges caused by the contractions of the taeniae coli and epiploic appendages , which are small fat accumulations along the viscera. Locations along the colon are: • The ascending colon • The right colic flexure (hepatic) • The transverse colon • The transverse mesocolon • The left colic flexure (splenic) • The descending colon • The sigmoid colon Functions of the Large Intestine The large intestine houses over 700 species of bacteria that perform a variety of functions. The large intestine absorbs some of the products formed by the bacteria inhabiting this region. Undigested polysaccharides (fiber) are metabolized to short-chain fatty acids by bacteria in the large intestine and absorbed by passive diffusion. The bicarbonate that the large intestine secretes helps to neutralize the increased acidity resulting from the formation of these fatty acids. These bacteria also produce large amounts of vitamins, especially vitamin K and biotin (a B vitamin),