Chapter 18 Digestive System PG 173 Digestive System

Chapter 18 Digestive System

PG. 173 Digestive System

Digestive System • Food must be converted by physical and chemical changes before it can be used by the cells; this process is called digestion • Digestion accomplished by action of various digestive juices containing enzymes (chemical substances that promote chemical reactions in living things) • Composed of: • Alimentary canal: aka digestive tract or gastrointestinal (GI) tract; consists of oral cavity, pharynx, gullet, stomach, small intestines, large intestines, and anus • Accessory organs: tongue, teeth, salivary glands, pancreas, liver, gallbladder

Activities/Functions of Digestion 1. Ingestion • Getting the food into the body • Involves the mouth, including the teeth, lips, and tongue 2. Propulsion • Begins after ingestion and continues all the way along the GI tract • Initiated by swallowing at the pharynx and peristalsis (the symmetrical contraction of muscles that move food along the remainder of the GI tract) 3. Mechanical Breakdown • Reduces food into smaller pieces and increases the surface area of the food • Chewing, churning in the stomach, and further churning by muscular contractions in the small intestines all contribute

Activities/Functions of Digestion 4. Chemical Breakdown • Part of process historically known as digestion • Enzymes in lumen (central opening of alimentary canal into stomach) and on the walls of the GI tract break large food molecules into smaller molecules 5. Absorption • Involves movement of small food molecules from lumen of small intestines into blood • Blood carries food to other parts of body 6. Defecation • Expulsion of food that was not absorbed • Waste matter, or feces, exits body via the anus

Layers of the Digestive System • Mucosa - Innermost lining made of epithelial cells - Secretes slimy mucus lubricates canal and insulates digestive tract • Submucosa - Connective tissue with fibers, blood vessels, and nerve endings • Muscularis Externa - Skeletal muscle that allows the voluntary act of swallowing in mouth, pharynx and esophagus - Rest of the tract consists of smooth muscle helping to break down food and propel food through tract • Serosa - Slippery membrane that helps minimize friction between organs

Lining of the Digestive System • Peritoneum • Two layers – Parietal: outer lining; lines body wall – Visceral: inner lining; wraps around organs – Layers connected by the mesentery (double layer where blood, lymphatic vessels, and nerves travel) which helps to hold organs in proper place *Greater omentum is a specialized part of mesentery located at the anterior portion of abdominal cavity that hangs over the abdominal organs like a protective apron containing large amounts of fat

Organs of Digestion

Organs of Digestion

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Organs of Digestion • Mouth/Oral or Buccal Cavity - Inside covered with mucous membrane; uvula hanging from soft palate prevents food from entering nasal cavity when swallowing • Tongue (Accessory Organ) - Helps with chewing and swallowing; sense of taste coupled with sense of smell; lingual frenum attaches tongue to floor of mouth • Salivary Glands (Accessory Organ) - 99. 5% water, rest is chlorides which activate salivary amylase, mucin and lysozyme to kill bacteria and begin breaking down complex carbohydrates into simple sugars

Organs of Digestion • Teeth (Accessory Organ) - Gingivae support and protect teeth; teeth masticate food increasing the surface area enabling digestive enzymes to work more efficiently - Develop two sets of teeth: deciduous/milk teeth (20) and permanent teeth (32) • Esophagus/Gullet - Muscular tube about 25 cm long between pharynx and stomach; esophageal sphincter allows food to enter stomach but prevents regurgitation into esophagus • Stomach - Three parts: upper fundus, middle greater curvature, and lower pylorus; end of stomach contains pyloric sphincter regulating entrance into duodenum; innermost layer has folds called rugae when not distended with food - Millions of gastric gland that secrete gastric juice necessary for digestion: gastrin, HCl, pepsinogen, and rennin (infants and children)

Organs of Digestion • Small Intestines - Mucosa is in numerous folds called plicae circularis; final preparation of food to be absorbed; coiled portion can be as long as 20 ft; lining has villi which aids absorption - Three sections: duodenum (site where pancreatic duct and common bile duct enter), jejunum, and ileum • Pancreas (Accessory Organ) - Located behind stomach; acting as exocrine and endocrine gland; islets of Langerhans produce insulin and glucagon; acini cells produce digestive juices. - Pancreatic juices include: protease, lipase, bile, maltase, lactase, sucrase, and peptidase • Liver (Accessory Organ) - Largest organ in body; portal vein carries products of digestion from small intestines to liver - Manufactures bile (necessary for digestion of fat); produces and stores glucose; detoxifies alcohol and drugs; stores vitamins A, D, E, and K; manufactures blood proteins; prepares urea; breaks down hormones no longer in use; removes worn-out RBC from circulation

Organs of Digestion • Gallbladder (Accessory Organ) - Small green organ in inferior surface of liver; stores and concentrates bile when not needed • Large Intestines/Colon - Ileum empties intestinal chyme (semiliquid food) into the side wall of large intestines through opening called ileocecal valve; large amounts of mucous are secreted easing the passage of fecal material - 5 feet long and 2 inches in diameter: ascending colon, transverse colon, descending colon, sigmoid colon • Appendix - Finger-like projection protruding into abdominal cavity; massive amounts of lymphoid tissue plays a role in immunity • Anal Canal - Terminal 1 inch of rectum; external opening is anus guarded by two anal sphincter muscles remaining closed until defecation (evacuation of large intestines) occurs

Teeth/Accessory Organ of Digestion

Stomach

Small Intestine

Accessory Organs of Digestion

Accessory Organs of Digestion

Large Intestine

Metabolism • Within the cells, nutrients are changed into energy • Aerobic metabolism: nutrients are combined with oxygen (oxidation) releasing energy • Anaerobic metabolism: reduces fats without the use of oxygen *Anabolism: using released energy to build new substances from simpler ones *Catabolism: using released energy to break down substances into simpler ones

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Effects of Aging • Decrease sensory ability of taste buds • Reduction of saliva • Loss of teeth • Slowing peristalsis

Disorders – Digestive System • Stomatitis: inflammation of soft tissues of oral cavity • Gingivitis: gum disease due to tartar build up • Periodontal disease: chronic bacterial infection of the gums and surrounding tissue that causes oral bacteria byproducts to enter bloodstream leading to heart attacks • Gastroesophageal reflux disease (GERD): weak cardiac sphincter muscle connecting esophagus to stomach allowing stomach’s contents to flow upwards causing heartburn and possible chest pain

Disorders – Digestive System • Hiatal hernia: stomach protrudes above diaphragm through esophagus opening • Heartburn: acid indigestion; many causes other than GERD • Pyloric stenosis: narrowing of pyloric sphincter at lower end of stomach; projectile vomiting may occur • Gastritis: acute or chronic inflammation of stomach lining caused by bacteria or virus; produces discomfort, nausea, and vomiting • Gastroenteritis: inflammation of mucous membrane lining of stomach and intestinal tract; common cause is a virus leading to diarrhea and vomiting for 24 -36 hours

Disorders – Digestive System • Enteritis: inflammation of intestine caused by virus, bacteria, protozoan, or allergic reaction to certain foods • Ulcer: sore or lesion that forms in mucosal lining of stomach or duodenum where acid and pepsin are present; most result from bacterial infection or non-steroidal anti-inflammatory drugs NOT from stress, spicy foods or alcohol; burning pain in abdomen between sternum and navel • Inflammatory bowel diseases (IBD): autoimmune diseases that causes chronic diarrhea, vomiting, abdominal cramping, blood in stool, weight loss, and fatigue; affects 1 million Americans • Crohn’s Disease-can occur anywhere in digestive tract; generally penetrates every layer of tissue in affected area; may have remissions and flare-ups • Ulcerative colitis-typically found in colon and rectum; innermost lining

Disorders – Digestive System • Appendicitis: appendix becomes inflamed; if ruptures can cause bacteria to spread into peritoneal cavity • Pancreatitis: inflammation of pancreas; severe pain in upper abdomen that may reach to the back • Hepatitis: inflammation of liver; symptoms are fever, nausea, anorexia, and jaundice; different strains of virus include A, B, C, D, and E • Hepatitis A-spreads through contaminated water or food; vaccine available • Hepatitis B-transmitted through blood and bodily fluids; vaccine available • Hepatitis C-intravenous drug use • Hepatitis D-requires coinfection with B type • Hepatitis E-transmitted through fecal-oral route

Disorders – Digestive System • Cirrhosis: chronic, progressive, inflammatory disease of liver due to replacement of normal tissue with fibrous connective tissue; ¾ caused by excessive alcohol consumption; symptoms include fatigue, nausea, weight loss, itchy skin, abdominal pain, spider angiomas, edema, bruising and bleeding, jaundice, gallstones, splenomegaly, and toxins in blood and brain • Cholecystitis: inflammation of gallbladder which can block cystic duct, inhibiting the release of stored bile • Gallstones: collections of crystallized cholesterol in gallbladder; can block bile duct causing pain and digestive disorders; some must be removed surgically

Disorders – Digestive System • Diverticulosis: little sacs develop in the wall of the colon; many people will follow a restricted diet • Hemorrhoids: veins around the anus or lower rectum become swollen and inflamed; results from straining due to defecation, aging, chronic constipation, pregnancy, and diarrhea • Diarrhea: loose, watery and frequent bowel movements; may result from irritation of colon’s lining by bacterial, viral, or parasitic infections, poor diet, nervousness, toxic substances, or irritants in food • Constipation: defecation is delayed and becomes difficult due to colon absorbing excessive water from feces; can be caused by lack of fiber, dehydration, or anxiety/fear