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CHAPTER 16 Digestive System Pictures from Essentials of Anatomy & Physiology, Third Edition PowerPoint by Laurie Forsythe Overview • Provides fuel (food) to cells and enzymes and chem. to the body. • Mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, anus. • Accessory organs – salivary glands, gallbladder, liver, pancreas. • Absorption - sub pass through the wall of intestine & enter circulation system. • Reabsorption - water is removed from wastes 7 returned to body. 6 processes of the digestive system 1. Ingestion – food enters dt thru mouth. 2. Mechanical processing – physical handling of solid foods (by tongue, teeth, mixing motions of dt). 3. Digestion – chem. breakdown of food so it can be absorbed by epithelium. 4. Secretion – water, acids, enzymes, buffers by dt & acces organs. 5. Absorption – small organic (C) molecules, electrolytes, vitamins, water that move across the digestive epithelium into the interstitial fluid. 6. Excretion – removal of waste products from body (compacted). Components of digestive system Fig. 16-1 Structure of small intestine Fig. 16-2 Peristalsis Fig. 16-3 Muscle contractions along the digestive tract that move materials along. Oral cavity Fig. 16-4 • 4 Functions 1. Examine material before swallowing. 2. Mechanically chew food via teeth, tongue, surfaces of the palate (mouth). 3. Lubricate food by mixing w mucous and salivary secretions 4. Begins digestion of carbs & lipids w help of salivary enzymes. Tongue - moves food around, sensory info – bitter, sweet, etc. Salivary Glands Fig. 16-5 • Produce saliva …1-1.5 liters of saliva each day; 99.4% water w some ions, buffers, enzymes. Lubricates the mouth, controls bacteria. • Salivary amylase enzyme that breaks down carbs that can by absorbed by digestive tract. Teeth Fig. 16-6 • Dentin - bulk of the tooth, made of mineralized sub similar to bone. • Crown - top of the tooth, coated with enamel. • Enamel - crystalline form of calcium phosphate – hardest biologically manufactured sub. Protects tooth • Root - below gum, root dentin covered by cementum. Pharynx • Passage… for solid food, liquids, air. • Smooth muscles propel food down the esophagus. Esophagus • Begins at pharynx & ends at stomach - ~ 1 ft long & diam of .75 “ • Lies behind trachea in neck. • Secretions of mucous glands keep food from sticking to the sides. • Peristalsis contractions move materials down the esophagus. Esophageal hiatus Fig. 16-7g • Enters peritoneal cavity thru opening in diaphragm before empting into the stomach • Hiatal hernia – abdominal organs slide into thoracic cavity thru esophageal hiatus Stomach Fig. 16-8 • Ingested food …mixes w secretions from glands of stomach. • 4 functions – Temp storage of food. – Mechanical breakdown of food. – Acids & enzymes break down chem. bonds of food. – Production of intrinsic factor – cmpd necessary for absorption of vit B12. Chyme • Viscous, highly acid mixture of partially digested food. • Forms from the action of gastric and salivary secretions mixed w food. Pyloric sphincter • Muscular valve . . . that regulates the flow of chyme from stomach to small intestine. Rugae • Ridges & …folds in the lining of the empty stomach that disappear as the stomach expands to digest food. • Covered with … alkaline mucous to protect the stomach lining from acids & enzymes when empty. • As the stomach stretches …the gastric pits & gastric glands secret gastric juice. • Mucous epithelium – secretes mucous that covers & protects lining from acids, etc • Gastric pits – opening to gastric glands that secrete gastric juice Stomach Anatomy Fig. 16-8c,d Gastric wall • Lined by …mucous epithelium • Intrinsic factor – helps absorption of vit B12 in the intestine. • Hydrochloric acid (HCl) – lowers pH of gastric juice to 1.5-2.0. Kills microorganisms, breaks down cell walls & connective tissues in foods, activates enzymatic secretions of other cells. • Pepsinogen (inactive form of pepsin) - secreted by cells in stomach. HCl converts pepsinogen to pepsin – enzyme that splits proteins. • Gastrin – stimulated by … stretch receptors in stomach (from eating) stimulate gastrin. – Gastrin triggers secretion of …intrinsic factor,HCl & pepsinogen. – Chyme is being formed and …and the “food” is being “digested”. • Gastritis – inflammation of …gastric mucous. • Peptic ulcer – digestive aids & enzymes ... erode the stomach lining or part of the small intestine. – Caused from much acid being produced or inadequate production of mucous lining. 80% caused by bacteria – Little or no nutrient absorption occurs in the stomach although digestion begins here. Most carbs, lipids & proteins are only partially broken down. Small Intestine • 90% of nutrient absorption occurs here – rest in large intestine. • ~ 20 - 25‘ long. Fig. 16-11 • Intestinal mucosa has villi – increase surface area for absorption. Fig. 16-12 • Smooth muscle contractions help move materials along. • Intestinal glands secrete intestinal juice, mucus & hormones. • Intestinal juice – moistens chime, helps buffer acids, dissolves digestive enzymes and the prod of digestion. • Most of the enzymes & buffers are contributed by liver & pancreas. 3 subdivisions of small intestine Fig. 16-10 Duodenum • Pyloric valve (sphincter) opens to allow chyme to enter duodenum. • First foot closest to stomach. • Receives chyme from stomach and secretions from pancreas & liver. Jejunum • Next 8’. • Most of chemical digestion & nutrient absorption. • Weight control – removal of a significant portion of jejunum Ileum • Last 12’. • Ends in a valve that controls flow into the large intestine. • Continues process of nutrient absorption & readsorption of water. Pancreas Fig. 16-3 • Lies behind stomach, ~6" long, pinkishgray, lumpy, tissue is soft & easily torn. • Primarily exocrine organ.. Pancreas function • Exocrine - secrete water, ions, pancreatic juice (mixture of digestive enzymes & buffer into small intestine. • Endocrine - pancreatic islet (~1% of cells) - secrete insulin & glucagon into blood. Pancreatic enzymes secreted • Lipases - attack lipids • Carbohydrases – digest sugars & starches • Proteases - ~70% of the total enzyme production break proteins apart Liver Fig. 16-14 • Largest organ (>200 known functions), reddishbrown, firm texture, 2 lobes, mostly in the right abdominopelvic region. Fig. • Limited ability to regenerate Liver lobule Fig. 16-15 • Basic functional unit of the liver. Blood comes from hepatic artery & hepatic portal vein • Hepatocytes - liver cells. Common hepatic duct Fig. 16-16 • Smaller ducts carry bile thru liver, leaves thru chd flows into the duodenum (thru common bile duct) or gallbladder (thru cystic duct). Table 16-2 Major Functions of the Liver • Refer to Table 16-2 for more of the functions • Converts glucose to glycogen for storage • Regulates composition of the blood • Largest reservoir of blood in the body • Produces bile Bile • Made in liver but stored & excreted by the gallbladder into the lumen (central space) of duodenum • Mostly responsible for “emulsification” of lipids Gallbladder Fig. 16-14, 16-16 Pear shaped just behind the right (larger) liver lobe 2 major functions: bile storage & bile modification/concentration Gallstones – when bile sits too long in gallbladder & becomes too concentrated (bile salts precipitate) Hepatopancreatic sphincter Fig. 16-16c • Valve that releases bile into the duodenum when stimulated by other hormones • More bile is released if the chyme contains large amts of fats Large Intestine Fig. 16-17 •Horseshoe-shaped, begins at end of ileum & ends at anus. • Lies below liver & stomach, "frames" small intestine. • ~5' long, aka large bowel. Divided into 3 parts. Main functions • Reabsorb water (removed from wastes & returned to body) & compact feces. • Absorb important vitamins made by bacterial action. • Store fecal material before defecation. • Divided into 3 parts: cecum, colon, rectum Cecum Fig. 16-17 • First portion; collects & stores material from ileum, begins process of compaction. • Sphincter (valve) guards connection between ileum & cecum • Appendix attaches in back – function with the lymphatic system Colon • Divided into 4 regions: ascending, transverse, descending, sigmoid • Larger diam & thinner wall than small intestine. • Pouches (haustra) that permit enlargement & elongation. • Colon cancer occurs here. • Reabsorption of water, produces feces. Rectum Fig. 16-7b • End of digestive tract. • Feces exit thru anus. • Internal anal sphincter & external anal sphincter (voluntary muscle control) Absorption in the Large Intestine • Efficiency of digestions, avg comp of feces: 75% water, 5 % bacteria, rest if indigestible materials & remains of epithelial cells • Absorbs bile salts, & vitamins, organic waste products (bilirubin from the breakdown of hemoglobin) and toxins generated by bacteria Bacteria in large intestine • Responsible for generating – vit K (needed by liver to produce clotting factor) – biotin (needed to metabolize glucose) – Vit B5 (needed for making steroid hormones & neurotransmitters). • Convert bilirubin (from the breakdown of hemoglobin) into other products which are excreted in the urine (yellow) or give feces it’s distinct color • Break down peptides remaining in feces to generate ammonia, hydrogen sulfide. • Indigestible carbo (beans) used by bacteria & produce intestinal gas Lactose Intolerance • Primary carbo in milk. Lactose - broken down by lactase in the intestinal mucosa. If this stops = intolerant