Digestion and Absorption

Chapter 3: Digestion and Absorption Fig. 3.1 Levels of organization Cells Require energy, ATP Requires nutrients Form tissues Form Organs Form Organ systems Four Types of Tissue in the Human Body Epithelial  lines the body surfaces holds structure together Connective  Muscle  for movement communication Nervous  Fig. 3.2 Organs and Systems Digestive System Alimentary canal- mouth to anus  Functions Movement  Secretion  Digestion  Absorption  Elimination  Nutrient production (by bacteria)  Digestive System Alimentary canalmouth to anus GI Tract Food Bolus Chyme Mouth Esophagus Stomach Duodenum Ileum Jejunum Cecum Ascending colon Transverse colon Descending colon Sigmoid colon “Waste” Functions of the Sphincters Cardiac or lower esophageal sphincter  Prevents reflux of stomach content to cause heartburn and ulcers Controls the amount of stomach content into the small intestine Controls the amount of bile into the small intestine Prevents large intestine content (bacteria) back up into the small intestine Pyloric sphincter  Sphincter of Oddi  Ileocecal sphincter  Fig. 3.8 Digestion and the Mouth Cooking Mastication Saliva    Enzymes to help breakdown simple sugars Mucus to lubricate the food for easier swallowing Lysozyme to kill bacteria Taste receptors (Flavor is enhanced with the olfactory cells) Enzymes to help breakdown fatty acids Tongue    Epiglottis The Swallowing Process http://www.uclan.ac.uk/facs/health/nursing/sonic/scenarios/uclananim/wh olebodyzoom.swf The Stomach Lower esophageal sphincter and pyloric sphincter Capacity of ~4 cups Secretion of hydrochloric acid and enzymes  Destroys ingested proteins Holds food for 2-4 hours Results in the formation of chyme Mucus layer prevents autodigestion Secretion of the intrinsic factor Physiology of the Stomach What stimulates acid production? Stimulated by Animation of acid production Gastrin Stomach distention Histamine Thoughts of food (nerve input) Food itself Prevents autodigestion Stop secretion when pH is ~2 Thick mucus layer Stomach Acid Destroys activity of protein Converts pepsinogen to pepsin Partially digests dietary protein Assists in calcium absorption The Small Intestine The Small Intestine Duodenum  ~10 inches in length  Primary site of digestion Jejunum  ~4 feet in length  Some digestion Ileum  ~5 feet in length  Little digestion Movement Along the Intestine Peristalsis  A ring of contraction propelling material along the GI tract Segmentation  A back-and-forth action that breaks apart food Peristaltic wave that contracts over a large area of the large intestine to help eliminate waste Mass movement  Movement http://www.lionden.com/peristalsis.htm Digestive Enzymes Enzymes speed up chemical reactions Enzymes lower the amount of energy needed for the action to proceed Each enzyme acts on specific substance Enzyme release and activation are controlled by nerves and hormones Enzymes are only released when needed http://www.tvdsb.on.ca/westmin/science/sbi3a1/digest /enzymes.htm Physiology of the Small Intestine The wall is folded Villi projections are located on the folds Absorptive cells (enterocytes) are located on the villi Microvilli is located on the villi Glycocalyx is located on the microvilli Increases intestinal surface area 600 x The Small Intestine Intestinal Mucosa Absorptive cells Produced in crypts Migration and maturation from the crypts to the tips of the villi Degradation of cells at the tips of the villi by digestive enzymes Newly formed cells constantly migrate to replace dying ones (< 6 days) High turnover causes the cells to deteriorate during nutrient deficiency In the Small Intestine Bile acid from the liver via the gallbladder Bicarbonate ions from the pancreas Muscle contractions to mix the food with digestive juices Food remains 3-10 hours in the small intestine ~95% of digestion takes place here Site of Absorption Types of Absorption Passive    Intestinal wall is permeable to the nutrient Going from higher to lower concentration No energy expended A carrier shuttles substances into the absorptive cells Going from higher to lower concentration No energy expended Facilitated    Active  Uses a carrier and ATP Phagocytosis and pinocytosis Endocytosis  http://www.uclan.ac.uk/facs/health/nursing/sonic/scenarios/uclananim/wholebodyzoom.swf Types of Absorption Circulation Intestinal villi drains into Portal circulation   Water-soluble Portal vein Fat-soluble Large particles Thoracic duct Left subclavian vein Lymphatic circulation     Enterohepatic Circulation Bile circulation Liver gallbladdersmall intestine portal vein  liver ~98% of bile is recycled The Large Intestine Little digestion occurs Indigestible food stuff Absorption of 85-90% of the water, some minerals, vitamins Formation of feces for elimination A Summary ORGAN FUNCTIONS Mouth Esophagus Stomach Chewing Digestion of starch Passage way Food Storage Acid kills bacteria Some protein digestion Small Intestine Large Intestine Anus Liver Gallbladder Pancreas Final digestion Absorption Absorption of water, minerals Elimination Production of bile Store and release bile Enzymes and bicarbonate Hormones Gastrin Secretin Cholecystokinin Gastric Inhibitory Peptide Gastrin Originated from the pyloric region of the stomach and upper duodenum Stimulated by food, thoughts of food Stimulates flow of stomach enzymes and HCl Stimulates contraction of cardiac sphincter Slows gastric emptying Secretin Originated from the duodenum, jejunum Stimulated by the presence of acidic chyme and the presence of peptones in the duodenum Stimulates the secretion of bicarbonate Slows gastric emptying Cholecystokinin (CCK) Originated from the duodenum, jejunum Stimulated by food, presence of fat and protein in the duodenum Stimulates contraction of gallbladder and flow of bile Stimulates the release of enzyme rich pancreatic fluids Slows gastric emptying Gastric Inhibitory Peptide (GIP) Originated from the duodenum, jejunum Stimulated by fats and protein Inhibits the secretion of stomach acid and enzymes Slows gastric emptying The Gastrointestinal Tract-Recap Content Review Recite the path of the the gastrointestinal tract. What is the goal of digestion? What is a sphincter and what is its main role in the digestive system? What is cholecystokinin (CCK)? What makes the small intestine so effective in absorbing the nutrients? GI Problems Ulcers Helicobacter pylori Heavy use of aspirin Excessive acid production in the stomach Symptoms  Pain 2 hours after eating Treatment Antibiotics  Antacid  Heartburn Gastroesophageal reflux disease Gnawing pain in the upper chest Acid from the stomach to the esophagus Treatment      Smaller meals Less fatty meals Stop smoking Do not lie down after eating Avoid offending foods Constipation Slows movement of fecal matter Increases fluid reabsorption; hardening of the feces Causes:   Results from ignoring normal urge Antacids, calcium and iron supplements Plenty of dietary fiber and fluids Laxatives Treatment   Hemorrhoids Swollen veins of the rectum and anus Causes:  Added stress and pressure to the vessels Treatment Check with physician  Warm compresses to reduce pain  Adequate fiber and fluid  Irritable Bowl Syndrome Visible abdominal distension Crohn’s disease No cure Eliminate specific foods Content Review What can cause an ulcer? How can you avoid constipation? How can you treat an ulcer?