PART 3 The Digestive System

Digested residue contains few nutrients The Large Intestine Digested residue contains few nutrients Small amount of digestion by bacteria Main functions Absorb water and electrolytes Mass peristaltic movements force feces toward the rectum Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Gross Anatomy of Large Intestine Subdivided into Cecum, vermiform appendix, colon, rectum, anal canal Special features of large intestine Teniae coli Thickening of longitudinal muscularis Haustra Puckering created by teniae coli Epiploic appendages Fat-filled pouches of visceral peritoneum Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Gross Anatomy of Large Intestine Cecum Blind pouch Beginning of large intestine Vermiform appendix Contains lymphoid tissue Neutralizes pathogens Colon Divided into distinct segments Ascending, transverse, descending, and sigmoid colon Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Gross Anatomy of Large Intestine Rectum Descends along the inferior half of the sacrum Anal Canal The last subdivision of the large intestine Lined with stratified squamous epithelium Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Gross Anatomy of Large Intestine Figure 22.22a Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Gross Anatomy of Large Intestine Figure 22.22b Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Vessels and Nerves of the Large Intestine First half of large intestine Arterial supply - superior mesenteric artery Innervation Sympathetic innervation – superior mesenteric and celiac ganglia Parasympathetic innervation – vagus nerve Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Vessels and Nerves of the Large Intestine Distal half of large intestine Arterial supply - inferior mesenteric artery Innervation Sympathetic innervation – inferior mesenteric and hypogastric plexuses Parasympathetic innervation – pelvic splanchnic nerves Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Defecation Reflex Figure 22.23 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Microscopic Anatomy of Large Intestine Villi are absent Contains numerous goblet cells Intestinal crypts – simple tubular glands Lined with simple columnar epithelial tissue Epithelium changes at anal canal Becomes stratified squamous epithelium Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Mucosa of the Large Intestine Figure 22.24 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings