is last 35 of length empties into large intestine Small Intestine SI 18 38

Is last 35 of length empties into large intestine

This preview shows page 8 - 12 out of 16 pages.

is last 3/5 of length; empties into large intestine Small Intestine (SI) 18-38 ± Surface area increased by foldings and projections ± Large folds are plicae circulares ± Microscopic finger- like projections are villi ± Apical hair-like projections are microvilli Small Intestine (SI) continued 18-40 ± Attached to microvilli are brush border enzymes that are not secreted into lumen ± Enzyme active sites are exposed to chyme Intestinal Enzymes 18-43
Image of page 8
11/4/2013 9 Intestinal Contractions and Motility ± 2 major types of contractions occur in SI: ± Peristalsis is weak and slow and occurs mostly because pressure at pyloric end is greater than at distal end ± Segmentation is major contractile activity of SI ± Is contraction of circular smooth muscle to mix chyme (shown in diagram) 18-44 ± Has no digestive function but absorbs H 2 O, electrolytes, B and K vitamins, and folic acid ± Internal surface has no villi or crypts and is not very elaborate ± Contains large population of microflora ± = 10 13 to 10 14 commensal bacteria of 400 species ± which produce folic acid and vitamin K and ferment indigestible food to produce fatty acids ± And reduce ability of pathogenic bacteria to infect LI ± antibiotics can negatively affect commensals Large Intestine (LI) or Colon 18-49 ± Extends from ileocecal valve at end of SI to anus ± Outer surface bulges to form pouches (haustra) ± Chyme from SI enters cecum , then passes to ascending colon , transverse colon , descending colon , sigmoid colon , rectum , and anal canal Large Intestine (LI) or Colon continued 18-50
Image of page 9
11/4/2013 10 ± SI absorbs most water but LI absorbs 90% of water it receives ± Begins with osmotic gradient set up by Na + /K + pumps ± Water follows by osmosis ± Salt and water reabsorption stimulated by aldosterone ± LI can also secrete H 2 O via active transport of NaCl into intestinal lumen Fluid and Electrolyte Absorption in LI 18-51 Defecation ± After electrolytes and water have been absorbed, waste material passes to rectum, creating urge to defecate ± Defecation reflex begins with relaxation of the external anal sphincter allowing feces to enter anal canal ± Longitudinal rectal muscles contract to increase rectal pressure; internal anal sphincter relaxes ± Excretion is aided by contractions of abdominal and pelvic muscles which push feces from rectum 18-52 Structure of Liver ± Liver is the largest internal organ ± Hepatocytes form hepatic plates that are 1 2 cells thick ± Plates are separated by sinusoids which are fenestrated and permeable even to proteins ± Contain phagocytic Kupffer cells 18-54
Image of page 10
11/4/2013 11 ± Food absorbed in SI is delivered 1st to liver ± Capillaries in digestive tract drain into the hepatic portal vein which carries blood to liver ± Hepatic vein drains liver ± Liver also receives blood from the hepatic artery Hepatic Portal System 18-56 Enterohepatic Circulation -- Is recirculation of compounds between liver and intestine -- Many compounds are released in bile, reabsorbed in SI, and returned to liver to be recycled
Image of page 11
Image of page 12

You've reached the end of your free preview.

Want to read all 16 pages?

  • Fall '08
  • BRINN
  • GI Tract

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture