Introduction - The University of Alabama at Birmingham | UAB
IntroductionThe digestive system consists of:The digestive tractAccessory organs of digestionDigestive tractMouthPharynxEsophagusStomachSmall intestineLarge intestineIntroductionAccessory Organs of the Digestive TractTeethTongueSalivary glandsPancreasLiverGallbladderIntroductionFunctions of the Digestive SystemIngestionMechanical processingDigestionSecretionAbsorptionExcretionCompaction IntroductionFunctions of the Digestive System (details)IngestionBringing food and liquids into the mouthMechanical processingChewing and swallowing foodDigestionChemical breakdown of food into nutrient formSecretionSecretion of products by the lining of the digestive tractSecretion of products by the accessory organs of digestionIntroductionFunctions of the Digestive System (continued)Absorption The movement of nutrients from the small intestine to the bloodstreamExcretion The removal of waste products from the digestive tractCompaction Progressive dehydration of organic wastesAn Overview of the Digestive SystemHistological Organization of the Digestive TractThere are four major layers of the digestive tractThe mucosaThe submucosaThe muscularis externaThe serosaAn Overview of the Digestive SystemThe MucosaThe inner lining of the digestive tractThis is a mucous membraneCells of the mucosa are either stratified or simpleOral cavity and esophagus are lined with nonkeratinized stratified squamous cells (resist stress and abrasion)Stomach, small intestine, and large intestine are lined with simple columnar cells (for secretion and absorption)An Overview of the Digestive SystemThe MucosaThe mucosa of the small intestine makes up folds called plicaePlicae increase the surface area for increased absorptionLamina propriaContains blood vessels / nerves / smooth muscle / lymphatic vesselsAn Overview of the Digestive SystemThe SubmucosaSurrounds the muscularis mucosaeLarge blood vessels and lymphatics are in this layerSubmucosal plexus innervates the mucosaConsists of sensory neuronsConsists of parasympathetic gangliaConsists of sympathetic postganglionic fibersAn Overview of the Digestive SystemThe Muscularis ExternaSurrounds the submucosaDominated by smooth muscle fibersForms sphincters or valvesInnervated by myenteric plexusThis is a network of parasympathetic ganglia and sympathetic postganglionic fibersAn Overview of the Digestive SystemThe SerosaCovers the muscularis externaOutermost layer of the digestive systemAn Overview of the Digestive SystemMuscularis Layers and the Movement of Digestive MaterialsThe digestive tract consists of smooth muscleMuscularis mucosa and muscularis externa have pacemaker cellsProduce two types of muscle contractionsPeristalsisSegmentationAn Overview of the Digestive SystemMuscularis Layers and the Movement of Digestive MaterialsPeristalsisThe muscularis externa propels material through the digestive tract SegmentationMaterial is churned and fragmented and at the same time is propelled through the digestive tract by peristaltic contractionsAn Overview of the Digestive SystemThe PeritoneumThe serosa (visceral peritoneum) is continuous with the parietal peritoneumThe abdominal organs lie within the peritoneal cavity or the abdominal cavityIntraperitoneal organsRetroperitoneal organsSecondarily retroperitoneal organsAn Overview of the Digestive SystemIntraperitoneal OrgansOrgans that lie within the peritoneal cavityOrgans are surrounded completely by the visceral peritoneumExamples:Stomach LiverIleum An Overview of the Digestive SystemRetroperitoneal OrgansOrgans are covered by the visceral peritoneum on their anterior surfaceThese organs lie outside the visceral peritoneumExamples:KidneysUretersAbdominal aortaAn Overview of the Digestive SystemSecondarily Retroperitoneal OrgansThese organs form as intraperitoneal but soon become retroperitonealThe change occurs during embryonic development as the associated visceral peritoneum fuses with the opposing parietal peritoneumExamples are:Pancreas Duodenum An Overview of the Digestive SystemMesenteriesThese are fused double sheets of peritonealmembraneFunction:Stabilize the position of organsStabilize the position of blood vesselsProvide the attachment of blood vessels going to and from the small intestineAn Overview of the Digestive SystemMesenteries (continued)All but the duodenum is suspended in a sheet of mesentery called the mesentery properMesocolon Mesentery attached to the large intestineTransverse mesocolon Mesentery attached to the transverse colonSigmoid mesocolon Mesentery attached to the sigmoid colonAn Overview of the Digestive SystemMesenteries (continued)Fusion FasciaThe ascending colon, descending colon, and rectum are attached to the posterior abdominal wall via this fused mesenteryLesser OmentumThis mesentery lies between the stomach and the liver Greater OmentumThis mesentery extends from the stomach and covers the rest of the abdominal organs on the anterior surfaceThe Oral CavityStructures within the Oral CavityTongueUvulaPalatoglossal archesSalivary glandsTeethThe Oral CavityAnatomy of the Oral CavityLined by oral mucosaConsists of nonkeratinized stratified squamous cellsThe oral mucosa is continuous with:Lining of the cheeksLining of the lipsLining of the gumsThe Oral CavityAnatomy of the Oral CavityThe roof of the oral cavity consists of:Hard palateThis is the palatine process of the maxilla and the palatine boneSeparates the oral cavity from the nasal cavitySoft palateSeparates the oral cavity from the nasopharynxThe soft palate makes up the palatoglossal arch / palatopharyngeal arch / uvulaThe floor of the oral cavity consists of:The tongueThe Oral CavityAnatomy of the Oral CavityThe oral cavity also houses the palatine tonsilsThese lie between the palatoglossal and palatopharyngeal archesThey are lateral to the uvulaThe Oral CavityThe TongueHas numerous functionsManipulation of foodSensory analysisSecretion of enzymes to aid in fat digestionMovement for the formulation of wordsThe Oral CavityTongue (continued)Can be divided into different areasBodyAnterior portion of the tongueRootPosterior portion of the tongueDorsumSuperior portion of the tongueContains the papillaePapillae contain the taste budsThe Oral CavityTongue (continued)Embedded glandsRelease lingual lipaseBegins digestion of fatLingual frenulumThin fold of mucous membrane that attaches the tongue to the floor of the mouth AnkyloglossiaTerm referring to a short lingual frenulumThe Oral CavityTongue (continued)Consists of two muscle groupsIntrinsic tongue musclesAlter the shape of the tongueExtrinsic tongue musclesGross movements of the tongueExamples:Hyoglossus / Styloglossus / Genioglossus / Palatoglossus Both sets of muscles are controlled by N XIIFigure 10.7 Muscles of the TongueThe Oral CavitySalivary GlandsThere are three pairs of salivary glandsParotidSublingualSubmandibularAll three glands produce salivary amylasePartially digests carbohydratesThe Oral CavitySalivary GlandsParotid salivary glandsThe largest of the three salivary glandsLocated on the lateral side of the face in the area of the ramus of the mandibleEnzyme drains to the mouth cavity via the parotid ductParotid duct lies on the masseter muscleThe Oral CavitySalivary GlandsSublingual salivary glandsCovered by the mucous membrane of the floor of the mouthConsists of numerous sublingual ducts that open along either side of the lingual frenulumSubmandibular salivary glandsLocated on the floor of the mouth, deep into the mandible, inferior to the mylohyoid lineSubmandibular ducts open posterior to the mandibular teethThe Oral CavityRegulation of the Salivary GlandsSecretions are controlled by the autonomic nervous systemParasympatheticAccelerates salivary secretionsSympatheticReduces salivary secretionsThe Oral CavityThe TeethDesigned for masticationAnatomy of teethCrownNeckRoot DentinePulp cavityRoot canalApical foramenPeriodontal ligamentThe Oral CavityTeeth AnatomyCrownCovered by enamelConsists of dentineConsists of pulp (highly vascularized)NeckArea of gingivaRoot Consists of root canalConsists of artery, vein, and nerveThe Oral CavityTeeth AnatomyDentineMineralized matrixDifferent than bone; it does not contain cellsPulp cavitySpongy area and highly vascularizedRoot canalArteries and veins and nerves pass through the root canal to the pulp cavity areaThe Oral CavityTeeth AnatomyApical foramenAn opening at the distal end of the root canalPeriodontal ligamentAnchors the root of the tooth to the alveolar socketsThe articulation at this point is called gomphosisThe Oral CavityTypes of TeethDesigned for masticationFour incisors per jawTwo cuspids per jawFour bicuspids per jawFour to six molars per jawThe Oral CavityDental SuccessionDuring development, two sets of teeth formDeciduous teethUsually 20 deciduous teethPermanent teethUsually 32 permanent teethThe Oral CavityA Dental Frame of ReferenceLabial surfaceOuter surface of teeth nearest the lining of the cheeks or lipsPalatal surfaceInner surface of the teethMesial surfaceOpposing surface between the teethOcclusal surfaceThe surface of the teeth of the mandible that face the surface of the teeth of the maxilla (the “grinding” surface)The PharynxThe PharynxServes as a common passageway for food, liquid, and airPharyngeal muscles involved in swallowing:Pharyngeal constrictorsPalatopharyngeusStylopharyngeusPalatal The PharynxThe PharynxPharyngeal constrictorsPush the bolus toward the esophagusPalatopharyngeusElevates the larynxStylopharyngeusElevates the larynxPalatal musclesRaise the soft palateThe PharynxThe Swallowing Process Process of swallowing is called deglutitionThere are three phasesBuccal phaseThe tongue pushes the food to the oropharynx areaPharyngeal phaseThe epiglottis closes over the glottis and swallowing beginsEsophageal phaseUpper esophageal sphincter opens and the bolus begins moving down the esophagusThe EsophagusThis is a hollow muscular tube that extends from the pharynx region to the stomachIt is 25 cm long and 2 cm in diameterLocated posterior to the tracheaEnters the peritoneal cavity by passing through the esophageal hiatus of the diaphragmInnervated by the vagus nerve from the esophageal plexusContains upper and lower esophageal sphinctersThe EsophagusHistology of the Esophageal WallThe esophageal wall is made of:Mucosa liningSubmucosaSmooth muscle layer (muscularis mucosae)Muscularis externaThe esophagus does not have a serosa layerThe StomachThe stomach performs three major functions:Bulk storage of ingested foodMechanical breakdown of ingested foodChemical digestion of ingested foodThe end result is the production of chymeThe StomachAnatomy of the StomachThe stomach is intraperitoneal and is located:In the left hypochondriac, epigastric, and a portion of the umbilical and left lumbar regionsThe stomach consists of:Lesser curvatureGreater curvatureCardiaFundusBodyPylorus The StomachAnatomy of the Stomach (continued)Gastric rugaeRelaxed stomach: mucosa forms numerous muscular ridgesRugae permits expansion of the stomachA stretched stomach exhibits less prominent rugaeSmooth muscle layersCircular musclesLongitudinal musclesOblique musclesThe StomachMesenteries of the StomachThe mesenteries associated with the stomach are called the greater and lesser omentumGreater omentumExtends from the greater curvature of the stomach and drapes across the surface of the small intestineLesser omentumExtending from the lesser curvature of the stomach to the liver is the hepatogastric ligamentExtending from the pylorus/duodenum region to the liver is the hepatoduodenal ligamentThe StomachBlood Supply to the StomachThere are three branches from the celiac trunk that supply the stomachLeft gastric arterySupplies blood to the lesser curvature and cardiaSplenic arterySupplies blood to the fundusBranches to form the left gastroepiploic artery, which supplies the greater curvatureCommon hepatic arteryBranches to form the right gastric, right gastroepiploic, and gastroduodenal artery to supply the greater and lesser curvaturesThe StomachHistology of the StomachLined with simple columnar epitheliumStructures within the lining of the stomachGastric pitsGastric secretory cellsMucous neck cellsParietal cellsChief cellsEnteroendocrine cellsThe StomachHistology of the StomachGastric pitsProduce cells to continuously replace lost stomach cellsMucous surface cellsProduce copious amounts of mucus to protect the lining of the stomachMucous neck cellsProduce mucus to lubricate the food entering the stomachThe StomachHistology of the StomachParietal cellsSecrete intrinsic factor and hydrochloric acidIntrinsic factor Facilitates the absorption of vitamin B12 from the small intestine into the bloodstream, which is used during erythropoiesisHydrochloric acid Kills microorganisms and activates pepsinogenThe StomachHistology of the StomachChief cellsSecrete pepsinogen, which is converted to pepsin via the action of hydrochloric acidEnteroendocrine cellsThese are cells of the stomach that produce hormones. The G cells produce the hormone gastrin. Gastrin causes the parietal and chief cells to release their productsThe StomachRegulation of the StomachThe production of stomach acid and enzymes is controlled by the CNSCNS regulation involves:Vagus nerve (parasympathetic innervation)Triggered by the sight and thought of foodCeliac plexus (sympathetic innervation)The StomachRegulation of the StomachFood enters the stomach and the stomach stretchesStretching causes the G cells to release gastrinGastrin causes the parietal and chief cells to release their productsThe Small IntestineFeatures of the Small IntestineApproximately 20 feet in length / 1.5–2.5 inches in diameterConsists of:Duodenum10 inches long; receives digestive enzymes from the pancreas, bile from the liver and gallbladderJejunum8 feet long; most of the digestion and absorption occurs in the jejunumIleum12 feet longThe Small IntestineSupport of the Small IntestineJejunum and ileum are supported by the mesentery properDuodenum is not associated with any mesenteryBlood supplyBranches of the superior mesenteric artery and intestinal arteriesNerve supplyParasympathetic innervation via the vagus nerveSympathetic innervation via the superior mesenteric ganglion The Small IntestineHistology of the Small IntestineThe lining contains:PlicaeEach plica consists of numerous microvilli (villi)Within each villus are capillariesVilli will absorb the digested nutrients from the lumen of the small intestine into the capillariesThe Small IntestineHistology of the Small IntestineIntestinal cryptsAppear at the base of the villi New epithelial cells are formed in this areaContain enteroendocrine cellsThese cells produce intestinal hormones, including cholecystokinin and secretinThese cells produce enzymes with antibacterial activityThe Small IntestineHistology of the Small IntestineEach villus also contains a lactealLacteals absorb material that cannot be absorbed by the capillariesExamples would be large lipid-protein complexesThe Small IntestineRegional SpecializationThe DuodenumContains duodenal submucosal glandsProduces large amounts of mucusThis mucus consists of buffers to provide some protection against the acidic chymeEntering into the small intestine at the hepatopancreatic sphincter regionBile from the liver and gallbladderBuffers from the pancreasDigestive enzymes from the pancreas The Small IntestineRegional SpecializationThe Jejunum and IleumJejunumHas prominent plicae and villiMost nutrient absorption occurs hereIleumContains prominent lymphoid centers called aggregated lymphoid nodules (Peyer’s patches)The Small IntestineRegulation of the Small IntestineUpon vagal stimulation, the enteroendocrine cells of the small intestine release:SecretinCauses the liver to begin making bileCauses the pancreas to release buffers into the duodenumCholecystokininCauses the pancreas to release digestive enzymes into the duodenumCauses the gallbladder to contract thus releasing stored bile into the duodenumCauses the hepatopancreatic sphincter to openThe Large IntestineFeatures of the Large IntestineApproximately 5 feet in lengthApproximately 3 inches in diameterConsists of the following regionsCecumAscending colonTransverse colonDescending colonSigmoid colonRectum The Large IntestineFunctions of the Large IntestineReabsorption of waterResults in compaction of waste (forms feces)Absorption of vitamins produced by the housed bacteriaStorage of fecal material prior to defecationThe Large IntestineBlood Supply to the Large IntestineReceives blood from branches of the superior mesenteric arteryReceives blood from branches of the inferior mesenteric arteryThe Large IntestineThe CecumThe cecum is intraperitonealThe ileum connects to the medial surface of the cecumAn ileocecal valve regulates the movement of material from the ileum to the cecumThe vermiform appendix attaches to the cecumAppendix is about 9 cm in lengthThe mesoappendix (mesentery) helps anchor the appendix to the ileum and the cecumThe Large IntestineThe ColonThe regions of the colon are:Ascending colonTransverse colonDescending colonSigmoid colonThe Large IntestineThe ColonWaste material leaves the ileum and enters the cecumWaste material goes “up” the ascending colonAround the hepatic flexure“Across” the transverse colonAround the splenic flexure“Down” the descending colonAround the sigmoid flexureTo the sigmoid colonInto the rectumThe Large IntestineThe ColonThe wall of the colon has pouches that allow for expansion called haustraLongitudinal muscles called taeniae coli aid in the process of peristalsisThe serosa of the large intestine has numerous “flaps” of sacs of fat attached to but yet extending from the intestine called omental appendicesThe Large IntestineThe RectumTemporarily stores waste matterThe last portion of the rectum is the anal canalThe anal canal consists of anal columnsThe anal canal ends at the anusThe Large IntestineHistology of the Large IntestineWalls are thinner than the walls of the small intestineThe walls lack villiHas numerous goblet cellsHas very distinctive intestinal cryptsProduces lots of mucus to lubricate undigested materialContains large lymphoid nodulesThe Large IntestineRegulation of the Large IntestineMovement of waste material to the transverse colon is slowThis allows for appropriate reabsorption of waterMovement through the rest of the large intestine is rapid (mass movement)This forces material into the rectum for later defecationDistension of the rectal wall stimulates the urge to defecate / internal sphincter opensFecal material moves into the anal canal / external sphincter opensAccessory Glandular Digestive OrgansThe accessory organs of digestion are:Salivary glandsLiverGallbladderPancreasAccessory Glandular Digestive OrgansThe LiverThe largest visceral organ of the bodyThe liver is involved in:Metabolic regulationHematological regulationBile productionAccessory Glandular Digestive OrgansMetabolic RegulationAll blood leaving the digestive tract enters the liver through the hepatic portal systemHepatocytes adjust the circulating metabolites before the blood enters into systemic circulationAccessory Glandular Digestive OrgansHematological Regulation The liver is the largest blood reservoir of the bodyAs blood passes through the liver:Phagocytic cells remove old or damaged erythrocytesLiver cells synthesize plasma proteins for blood clotting (for example)Accessory Glandular Digestive OrgansBile ProductionBile is made by liver cells (hepatocytes)Bile is stored in the gallbladderBile is secreted into the duodenum when it is neededBile emulsifies fat (from the diet) in the small intestineThis emulsification process makes it easier for lipase to do the actual digestion of fatAccessory Glandular Digestive OrgansAnatomy of the LiverFalciform ligament Marks the boundary between the left and right lobesThe inferior portion of the falciform ligament becomes thick and round and is called the round ligamentThe round ligament used to be the fetal umbilical veinThe falciform ligament spreads on the surface of the liver attaching to the inferior side of the diaphragmThis spreading ligament is called the coronary ligamentAccessory Glandular Digestive OrgansBlood Supply to the LiverTwo blood vessels supply the liverHepatic artery properHepatic portal veinAccessory Glandular Digestive OrgansHistological Organization of the LiverThe liver is divided into approximately 100,000 liver lobulesEach lobule is separated by the interlobular septumThe center of each lobule consists of a vein from the hepatic portal systemThe hepatocytes are arranged in such a manner forming cellular lines extending from the central vein outwardAccessory Glandular Digestive OrgansHistological Organization of the LiverSpaces are created between the lines of hepatocytes; these spaces are called sinusoidsSinusoids consist of:Capillaries: leading to the central veinKupffer cells: phagocytic cells of the liverAccessory Glandular Digestive OrgansHistological Organization of the LiverEach lobule of the liver has a hexagonal shapeAt each of the six corners is:Branch of the hepatic portal veinBranch of the bile ductBranch of the hepatic artery properThe above three branches form the hepatic triad Accessory Glandular Digestive OrgansBile Secretion and TransportHepatocytes produce bileBile enters:Bile canaliculiBile travels to the bile ductsBile then collects in the left and right hepatic ductsBile travels through the common hepatic ductBile can travel through the common bile duct to the duodenum (through the hepatopancreatic sphincter) or travel through the cystic duct into the gallbladder for storageAccessory Glandular Digestive OrgansThe GallbladderThe gallbladder is divided into three regionsFundusBodyNeckThe cystic duct leads from the neck of the gallbladder to the common bile ductAccessory Glandular Digestive OrgansGallbladder FunctionStorage of bileBile modificationAccessory Glandular Digestive OrgansBile Storage and ModificationWhen the hepatopancreatic sphincter is closed:Bile enters the cystic duct and into the gallbladderThe gallbladder can store 40–70 ml of bileWater is continuously removed from the stored bile thereby concentrating the bile more and moreIf food entering the small intestine is high in fat content, the small intestine cells will release cholecystokininCholecystokinin will cause the gallbladder to release bileAccessory Glandular Digestive OrgansGallbladder (bile release)CCK will cause the gallbladder to contract to release bileCCK also causes the hepatopancreatic sphincter to openBile enters the cystic ductBile enters the common bile ductThe hepatopancreatic sphincter opensBile enters the duodenum of the small intestineBile will then emulsify fatAccessory Glandular Digestive OrgansThe PancreasThe pancreas is posterior to the stomachThe pancreas consists of:Head: nearest the curvature of the duodenumBody: extends toward the spleenTail: rounded end of the pancreas nearest the spleenPancreatic duct: delivers secretions from the pancreas to the duodenum (through the hepatopancreatic sphincter)Accessory Glandular Digestive OrgansHistological Organization of the PancreasConsists of lobulesWithin each lobule are:Acinar cellsProduce digestive enzymesEnzymes travel through the pancreatic duct to the small intestinePancreatic isletsProduce hormonesHormones enter into the bloodstream to travel to target organsAccessory Glandular Digestive OrgansPancreatic Enzymes (from Acinar Cells)LipasesDigest lipidsCarbohydrasesDigest carbohydratesNucleasesDigest nucleic acidsProteinasesDigest proteinAccessory Glandular Digestive OrgansPancreatic Hormones (from Pancreatic Islets)InsulinGlucagonSomatostatinAccessory Glandular Digestive OrgansThe Regulation of Pancreatic SecretionCholecystokininFrom the small intestine will cause the pancreas to release its digestive enzymesSecretinFrom the small intestine will cause the pancreas to release buffersWhen food leaves the stomach and enters the duodenum, the chyme is mixed with acid in the stomach. Therefore, acidic chyme is entering the duodenum. Buffers are used to maintain a normal small intestine pH of about 7 or 8Aging and the Digestive SystemStem cell reproduction declinesTissue repair decreases – the tissues become more fragileSmooth muscle tone decreasesMotility decreases – constipation increasesCumulative damage becomes apparentGradual loss of teethAccumulation of toxins over timeCancer rate increasesColon cancerPharyngeal cancer ................
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