Y khoa, dược - The digestive system

29The Digestive System29-2Learning Outcomes29.1 List the functions of the digestive system.29.2 Trace the pathway of food through the alimentary canal.29.3 Describe the structure and functions of the mouth, teeth, tongue, and salivary glands.29.4 Describe the structure and function of the pharynx.29-3Learning Outcomes (cont.)29.5 Describe the swallowing process.29.6 Describe the structure of the esophagus and tell how it propels food into the stomach.29.7 Describe the structure and functions of the stomach.29.8 List the substances secreted by the stomach and give their functions.29-4Learning Outcomes (cont.)29.9 Describe the structure and functions of the small intestine.29.10 List the substances secreted by the small intestine and describe the importance of each.29.11 Describe the structure and functions of the large intestine, including the anal canal and rectum.29.12 Explain the structures and functions of the liver, gallbladder, and pancreas.29-5Learning Outcomes (cont.)29.13 List the substances released by the liver, gallbladder, and pancreas into the small intestine and give the function of each secretion.29.14 Tell what types of nutrients are absorbed by the digestive system and where they are absorbed.29.15 Describe the causes, signs and symptoms, and treatments of various diseases and disorders of the digestive system.29-6IntroductionDigestion Mechanical and chemical breakdown of foods into forms that body cells can absorb The organs of the digestive system carry out digestionTwo categoriesAlimentary canal organs Accessory organs29-7Alimentary Canal Wall of alimentary canal Mucosa Innermost layer; epithelial tissueSecretes enzymes and mucus into lumenAbsorbs nutrientsSubmucosa Inferior to mucosa; loose connective tissue, blood vessels, glands, and nervesBlood vessels carry away absorbed nutrientsMuscular layer Just outside submucosa; layers of smooth muscleContracts to move materials through the canal29-8Alimentary Canal (cont.)Serosa Double-walled outermost layer: peritoneumVisceral peritoneum Innermost wall of serosaSecretes serous fluid to keep outside of canal moistParietal peritoneumAbdominal liningMovementsChurning – mixes substances in the canalPeristalsis – propels substances through the tract29-9Apply Your KnowledgeWhat are the layers of the wall of the alimentary canal and what do they do?ANSWER: The layers are:Mucosa: innermost layer; secretes enzymes and mucus into the canal and absorbs nutrientsSubmucosa: inferior to the mucosa; carries away absorbed nutrientsMuscular layer: just outside the submucosa; contracts to move materials through the canalSerosa: double-walled outer layer; secretes serous fluid to keep outside of canal moistBravo!29-10The MouthBuccal cavity Mechanical digestionTakes in food and reduces its size by chewingStarts chemical digestionSaliva contains the enzyme amylase, which breaks down carbohydrates29-11The Mouth (cont.)Cheeks hold food in mouthLips – sensory nerve fibers that judge temperature of foodTongue Skeletal muscles covered by mucous membraneLingual frenulum – holds tongue to floor of mouthMixes food, holds food between teeth, contains taste budsLingual tonsils – lymphatic tissue destroys bacteria and viruses on back of tongue29-12The Mouth (cont.)Palate Roof of mouthSeparates oral cavity from nasal cavityUvula – portion of soft palate that hangs down in throatLymph tissuePalatine tonsils (oropharynx)Pharyngeal tonsils – adenoids (nasopharynx)29-13The Mouth (cont.)Teeth – decrease size of food particlesIncisors – bite off food piecesCuspids – tear tough foodBicuspids and molars – grind foodSalivary glandsCellsSerousMucousGlands ParotidSubmandibularSublingual 29-14Apply Your KnowledgeMatching: ___ Buccal cavity A. Saliva___ Roof of mouth B. Mouth___ Grind food C. Bolus___ Adenoids D. Palate___ Water, enzymes, and mucus E. Bicuspids___ Mass of food mixed with saliva and mucus F. Pharyngeal glandDEFABBANSWER:Very Good!29-15PharynxThroatFunctions Connects nasal cavity with oral cavity for breathingPushes food into esophagusDivisions NasopharynxBehind nasal cavityOropharynxBehind oral cavityLaryngopharynxBehind larynxContinues as esophagus29-16Pharynx (cont.)Swallowing – automatic processSoft palate rises, uvula covers opening between nasal and oral cavityEpiglottis covers larynx, keeping food out of itTongue presses against roof of mouth, forcing food into oropharynx29-17Pharynx (cont.)Muscles in pharynx contract, moving food toward esophagusEsophagus opensFood is pushed into esophagus by muscles of pharynx29-18The EsophagusMuscular tube connecting pharynx to stomachEsophageal hiatus – hole in diaphragm through which esophagus passesCardiac sphincter Circular band of muscle at the opening of the stomachcontrols movement of food into stomach29-19Apply Your KnowledgeMatching:___ Connects nasal cavity with oral cavity A. Cardiac sphincter___ Covers the opening of larynx B. Esophageal hiatus___ Hole in diaphragm C. Sphincter___ Controls movement of food into stomach D. Epiglottis___ Circular bands of muscle E. PharynxCABDEANSWER:CORRECT!29-20The StomachBelow the diaphragm in the upper left quadrant of the abdominal cavityFunctionsReceive food from esophagusMix bolus with gastric juiceStart protein digestionMove food into small intestineSectionsCardiac region Fundus Body PylorusPyloric sphincter Controls movement of substances into small intestineStomach29-21The Stomach (cont.)Lining of stomachRugae – folds of the inner liningGastric glandsMucous cells – secrete mucus to protect the liningChief cells – secrete pepsinogen  pepsin, which digests proteinParietal cells Hydrochloric acid needed to convert pepsinogen to pepsinIntrinsic factor needed for vitamin B12 absorptionStomach29-22Back29-23The Stomach (cont.)Gastric glands stimulated byParasympathetic nervous system Gastrin (hormone)Cholesystokinin (hormone) secreted by the small intestine inhibits gastric glandsStomach absorbs alcohol, water, and some fat-soluble drugsChyme – mixture of food and gastric juices29-24Apply Your KnowledgeWhat are the functions of the stomach?ANSWER: The stomach’s functions are to receive the bolus of food, mix it with gastric juice, start protein digestion, and move food into the small intestine. It also absorbs alcohol, water, and some drugs.Right Answer!29-25The Small IntestineTubular organ extending from the stomach to the large intestineFunctionsDigestionAbsorption of nutrientsDuodenum C-shaped ShortJejunum Coiled Majority of small intestineSmall Intestine29-26The Small Intestine (cont.)Ileum – attached to large intestineMesentery Fan-like tissue that holds jejunum and ileum in the abdominal cavityAttaches to the posterior wall of the abdomenIleocecal sphincterControls movement of chyme from the ileum to the cecum of the large intestineSmall Intestine29-27The Small Intestine (cont.)Lining of small intestineMicrovilli – increase surface areaIntestinal glandsMucus and waterEnzymes Peptidases – digest proteinsSucrase, maltase, and lactase – digest sugarsIntestinal lipase – digests fatsPrimary controlsParasympathetic nervous system Stretching of intestinal wall29-28Back29-29Apply Your KnowledgeANSWER: She cannot produce lactase and cannot digest lactose, which is the sugar in dairy products.Your patient states that she is lactose intolerant. What does that mean? Nice Job!29-30The Large Intestine Extends from the ileum to the anusCecumBeginning of large intestineVeriform appendix Ascending colon Portion that goes up the right side of the abdominal cavityLarge Intestine29-31The Large Intestine (cont.)Transverse colon – crosses abdominal cavity from right to left Descending colon – down left side of abdominal cavitySigmoid colon – S-shaped portion in pelvic cavityAbsorbs water and electrolytesLarge Intestine29-32The Rectum and Anal CanalRectum – off sigmoid colonAnal canalLast few centimeters of rectumOpening to outside of body is the anusLarge Intestine29-33The Rectum and Anal Canal (cont.)FecesLeftover chymeConsists of undigested solid materials, little water, ions, mucus, cells of intestinal lining, and bacteriaDefecation reflexTriggered by periodic contractions of large intestineAllows anal sphincters to relax29-34Back29-35Apply Your KnowledgeMatching:___ Vermiform appendix A. Feces___ Crosses the abdomen B. Ascending colon___ Up right side of abdomen C. Anal canal___ S-shaped tube D. Defecation reflex___ Down left side of abdomen E. Sigmoid___ Leftover chyme F. Transverse colon___ Last section of rectum G. Cecum___ Allows anal sphincters to relax H. Descending colonHGFEDCBAANSWER:Super!29-36The LiverLobular organ in right upper quadrantLarge right lobe and smaller left lobeHepatic lobules – contain macrophagesHepatocytes – process nutrients in blood and make bilePart of liver’s functionStore vitamins and iron29-37The Liver (cont.)Hepatic portal vein – carries blood from digestive organs to hepatic lobulesHepatic duct – bile from liverHepatic duct merges with cystic duct from gallbladder and forms common bile duct Common bile duct – delivers bile to duodenum29-38The GallbladderSmall sac-like structure located beneath the liverOnly function is to store bileCholecystokinin causes the gallbladder to release bileGallbladder29-39Apply Your KnowledgeWhat is the route of bile through the liver and gallbladder?ANSWER: Bile is made in the hepatocytes and leaves the liver through the hepatic duct. The hepatic duct merges with the cystic duct from the gallbladder to form the common bile duct, which delivers bile to the duodenum.Excellent!29-40The Pancreas Pancreatic amylase –  digests carbohydrates Pancreatic lipase –  digests lipids Nucleases – digest nucleic acidsTrypsin, chymotrypsin, and carboxypeptidase – digest proteins Located behind the stomach Acinar cells produce pancreatic juice, which contains  these enzymes:29-41The Pancreas (cont.)Also secretes bicarbonate ions into duodenumNeutralize acidic chyme Enzyme release stimulated byParasympathetic nervous systemHormones secretin and cholecystokinin (from small intestine) 29-42Apply Your KnowledgeWhat are the pancreatic enzymes and what do they do?ANSWER: They are:Pancreatic amylase – digests carbohydratesPancreatic lipase – digests lipidsNucleases – digest nucleic acidsTrypsin, chymotrypsin, and carboxypeptidase – digest proteinsGood Job!29-43The Absorption of NutrientsNutrients are necessary food substancesCarbohydratesProteinsLipidsVitamins MineralsWater29-44The Absorption of Nutrients (cont.)Carbohydrates – provide energyPolysaccharides – starchesMonosaccharides and disaccharides – simple sugarsCellulose – provides fiber or bulkLipids – used for energy when glucose levels are lowTriglycerides Cholesterol – essential for cell growth and function29-45The Absorption of Nutrients (cont.)Protein – used for growth and repair of tissueEssential amino acids body cannot makeVitamins Fat-solubleWater-solubleMinerals – used to make enzymes, cell membranes, and proteins29-46Apply Your KnowledgeTrue or False: ___ Carbohydrates are starches, simple sugars, and cellulose.___ Excess glucose is stored in the gallbladder as glycogen.___ Triglycerides are the least abundant lipids___ Linoleic acid is an essential fatty acid.___ A, D, E and K are water-soluble vitamins.___ Minerals are used by cells to make enzymes.FFFTTANSWER:Tlivermostfat-solubleImpressive!29-47Aging and the Digestive SystemDecreased motility – GERDDecreased absorptionMore likely to develop ulcers and cancersDecreased ability to detoxify bloodSense of taste alteredDietary changes due toIsolationDepression 29-48Common Diseases and DisordersDisease/DisorderDescription AppendicitisInflammation of the appendix; can be life-threatening if not treated promptlyCirrhosisChronic liver disease; normal tissue is replaced with nonfunctional scar tissueColitisInflammation of the large intestine; can be acute or chronicColorectal cancerArises from lining of rectum or colon; curable if treated early29-49Common Diseases and Disorders (cont.)Disease/DisorderDescription ConstipationDifficult defecationCrohn’s diseaseInflammatory bowel disease; typically effects small intestineDiarrheaWatery and frequent feces; usually self-limitingDiverticulosisAbnormal pouches in the intestinal wall; no inflammation present29-50Common Diseases and Disorders (cont.)Disease/DisorderDescription DiverticulitisInflammation of diverticuli (abnormal pouches in intestinal wall) of the intestineGastritisInflammation of the stomach lining; “upset stomach”HeartburnGastroesophageal reflux disease (GERD); stomach acids push into esophagusHemorrhoidsVaricose veins of rectum or anusHepatitis Inflammation of the liver; various types29-51Common Diseases and Disorders (cont.)Disease/DisorderDescription Hiatal herniaPortion of stomach protrudes into the chest through an opening (usually the esophageal hiatus) in the diaphragmInguinal herniaPortion of large intestine protrudes in the inguinal canal (where thigh and trunk meet) or, in males, into the scrotumOral cancerUsually involves the lips or tongue but can occur anywhere in the mouth; tends to spread rapidly29-52Common Diseases and Disorders (cont.)Disease/DisorderDescription Pancreatic cancerFourth leading cause of cancer deaths in the U.S.Stomach cancer Commonly in cardiac portion of the stomach; occurs more frequently in Japan, Chili, and IcelandStomach ulcersBreakdown in lining of the stomach; can be caused by bacteria (H. pylori) or smoking, alcohol, excessive aspirin use, and hypersecretion of stomach acid29-53Apply Your KnowledgeMatching:___ Inflammation of the large intestine A. Heartburn___ Inflammatory bowel disease B. Hemorrhoids___ Watery and frequent feces C. Constipation___ Difficult defecation D. Crohn’s disease___ Inflammation of the stomach lining E. Colitis___ Inflammation of pouches in the intestinal wall F. Diarrhea___ GERD G. Gastritis___ Varicose veins of rectum H. DiverticulitisHGFDCBAEANSWER:Nice Job!29-54In Summary29.1 The digestive system uses mechanical and chemical mechanisms to break down food into forms that the body’s cells can use.29.2 The pathway of food through the alimentary canal starts with the mouth through the pharynx, esophagus, stomach, small intestines, large intestines, and anal canal.29.3 The mouth takes in food and the teeth assist in reducing its size through chewing. The tongue mixes food and holds it between the teeth. The salivary glands produce saliva to assist in moistening and breaking down food.29-55In Summary (cont.)29.4 The pharynx is a long muscular tube extending from behind the nose to the esophagus, connecting the oral and nasal cavities. It also acts to push food into the esophagus.29.5 The soft palate rises, closing the opening between the nasal and oral cavities. The epiglottis covers the laryngeal opening. Food is forced into the oropharynx by the tongue, and the pharynx contracts, pushing food to the esophagus.29.6 The esophagus is a muscular tube that pushes food toward the stomach through muscular contractions. At the end of the esophagus is the cardiac sphincter, the entrance to the stomach.29-56In Summary (cont.)29.7 The stomach is in the LUQ. It receives food, mixes it with gastric juices, starting protein digestion, and moves food into the small intestine. The stomach has four regions: cardiac region, fundus, body, and pylorus.29.8 The stomach’s gastric glands include mucous cells that secret mucus, chief cells that secret pepsinogen, and parietal cells that secrete hydrochloric acid and intrinsic factor.29.9 The small intestine carries out most of the nutrient absorption. The sections of the small intestine are, in order, duodenum, jejunum, and ileum.29-57In Summary (cont.)29.10 The small intestine secretes peptidases to digest protein; sucrase, maltase and lactase, which digest sugars; and intestinal lipase, which digests fats.29.11 The components of the large intestine are the cecum with its vermiform appendix, ascending colon, transverse colon, descending colon, sigmoid colon, rectum, and anal canal ending in the anus. The large intestine’s primary job is to rid the body of solid waste by defecation.29-58In Summary (cont.)29.12 The liver is in the RUQ. It stores vitamins and iron and produces macrophages to fight infection. The gallbladder stores the bile produced by the liver. The pancreas produces pancreatic juices that assist in carbohydrate, lipid, and protein digestion. 29.13 The liver secretes bile for fat digestion. Bile is released by the gallbladder for fat digestion. Pancreatic juices contain pancreatic amylase for carbohydrate digestion; lipase for lipid digestion; nucleases to digest nucleic acids; and trypsin, chymotrypsin, and carboxypeptidase to digest proteins. 29-59In Summary (cont.)29.14 Nutrients absorbed by the body include carbohydrates, proteins, lipids, vitamins, minerals, and water. Most of the absorption takes place in the small intestine.29.15 Common diseases and disorders of the digestive system include inflammatory disorders such as appendicitis and colitis; cancers including colorectal, oral, and pancreatic cancers; as well as common symptoms such as diarrhea, constipation, and GERD. For more detailed information regarding these and other common disorders, please see the Pathophysiology section at the end of this chapter.29-60Take all that is given whether wealth, love or language; nothing comes by mistake and with good digestion all can be turned to health. ~ George HerbertEnd of Chapter 29