chapter 23 digestion study guide spring 09 - You Should Not Be Here

Chapter 23 • Digestive System • Study Guide Page 1 of 7BIOL2112-Chapter23-RespiratorySystem-StudyGuide01.pdf Friday April 10, 2009Structures of the digestive systemMouth and teethSalivary glandsAlimentary canal or GI tract (gastrointestinal)Liver and gall bladderPancreasMechanical digestion in mouth and stomachChemical digestion mostly in duodenumAbsorption occurs mainly in small intestinesPropulsionSegmentation – massages food, moves it backward and forward (Segmentationis mainly for mixing, but there is some propulsion similar to that of peristalsis)Peristalsis – circular muscles contract and push chyme forwardLongitudinal muscles contract and increase the lumen to receive chyme andthen pull chyme forwardTrue peristalsis occurs after segmentation is completeInnate rhythm of pacemaker cellsPacemaker cells set the pace of peristaltic contractionsPhysical cues for pacemakers are mainly stretch. Chemical cues forpacemakers are hormonal and changes in pHNeural control – vagus nerve- and local nerve plexuses (chicken wire)Most of segmentation and peristalsis is controlled by these local plexusesHistology of the alimentary canal Figure 23.6Mucosa has three layersEpithelium –secretion and absorption occur hereconnective tissueand a thin inner muscle layerSubmucosa is connective tissue surrounding the mucosaMuscularis externaSegmentation and peristalsis are performed by muscles of thesubmucosaCircular decreases diameter behind chymeLongitudinal increases diameter in front of chymeC:\Documents and Settings\adele.cunningham\My Documents\APII spring 09\lectures and study guidesAPII spring 09\study guides APII spring 09\chapter 23 digestion study guide spring 09.docSave date: Friday, April 10, 2009 5:27:00 PM

Chapter 23 • Digestive System • Study Guide Page 2 of 7BIOL2112-Chapter23-RespiratorySystem-StudyGuide01.pdf Friday April 10, 2009SerosaIs connective tissue surrounding the GI.Palate Figure 23.7bHard palate – The tongue pushes against the hard palate to form a bolusUvula – dangles from soft palate andRises when you swallow to close off the nasopharynxTongueFiliform papillae give the tongue its textureMost taste buds are fungiform.Foliate taste buds are at the posterior and lateral tongue and function mainly in children.Salivary glands Figure 23.9Function - To form bolusTo begin digestionLocationsScattered in mucosa of oral cavityParotid – anterior to the ear. These are the largest salivary glands.Sublingual under tongue (opens into lower mouth)Submandibular under mandible (opens into lower mouth)Composition of salivaWaterAmylase - digests glucose polymers – starch (plants) glycogen (animals)LysozymeIg A antibodiesSaliva helps inhibit dental caries (cavities)Plaque – biofilm of bacteria on the teethIncludes sugars that bacteria digestAcids from bacterial metabolism can dissolve enamelSwallowingVoluntary at the mouthInvoluntary begins at the oropharynxThe tongue presses against the hard palateForcing the bolus into the oropharynxThe soft palate and uvula rise and block the nasal cavityThe larynx rises and the epiglottis blocks the tracheaEsophagus Figure 23.7aBegins below laryngopharynxWhen it is empty hangs in longitudinal foldsAs food passes, mucus is squeezed from glands in the wallC:\Documents and Settings\adele.cunningham\My Documents\APII spring 09\lectures and study guidesAPII spring 09\study guides APII spring 09\chapter 23 digestion study guide spring 09.docSave date: Friday, April 10, 2009 5:27:00 PM

Chapter 23 • Digestive System • Study Guide Page 3 of 7BIOL2112-Chapter23-RespiratorySystem-StudyGuide01.pdf Friday April 10, 2009Gastroesophageal or cardiac sphincter is a thickening of muscle at the juncture withthe stomach that acts as a valve. A sphincter is a thickening of circular muscle.Heartburn is a condition where acids reflux into the esophagusSymptoms resemble heart attack – pressure behind sternumChronic reflux is gastroesophageal reflux disease GERDCauses of heartburn– Overeating– Overweight– Pregnancy– Hiatal hernia– A hiatal hernia is a weak cardiac sphincter that allows a bitof stomach tissue to protrude into the esophagusGERD is a risk factor forEsophageal cancerStomachWhen empty is only slightly larger than the small intestineand collapses into folds called rugae.Sections of stomach beginning from the juncture with the esophagusCardiacFundus - gas accumulates hereBodyPyloric - the pyloric sphincter controls food entering the duodenum. Only tinyamounts of chyme enter the duodenum at a time.MusculatureIncludes an inner layer of oblique muscleThis extra layer of muscle adds to the churning, mixing action of thestomachMucusAlkaline mucus protects the stomach from digesting itselfStem cells in the pits replace mucus cells in 3 to 6 daysGastric glands in tiny pitsSecrete the hormone gastrinSecrete HCLSecrete the enzyme pepsinogenC:\Documents and Settings\adele.cunningham\My Documents\APII spring 09\lectures and study guidesAPII spring 09\study guides APII spring 09\chapter 23 digestion study guide spring 09.docSave date: Friday, April 10, 2009 5:27:00 PM

Chapter 23 • Digestive System • Study Guide Page 4 of 7BIOL2112-Chapter23-RespiratorySystem-StudyGuide01.pdf Friday April 10, 2009Digestion in the stomachThe presence of food stretches the stomach and raises pHThese two cues stimulate release of gastrinGastrin stimulates muscle contractionsAnd release of HCLHCL lowers pH which changes pepsinogen in the stomach to pepsinPepsin begins protein digestionIn infants another enzyme, rennin, digests milk proteinsThe stomach also secretes intrinsic factor which is essential for absorption of B 12B 12 is necessary for production of erythrocytesA deficiency of B 12 is called pernicious anemiaSmall intestineMovement through the small intestine is mainly by segmentation duringdigestionMost digestion and absorption happen hereAfter digestion peristalsis occursSections:Duodenumfirst after pyloric valvecurls around the pancreasvery short about 10 inchesJejunumMiddle section about 8 feet longIleumlast section ending at ileocecal valve with the large intestineabout 12 feet longDuodenal hormonesGlands secrete mucus rich in bicarbonatesSecretin is secreted in response to stretching from chyme leaving the stomachand lower pHSecretin inhibits gastric motility and secretionSecretin signals the pancreas to secrete pancreatic juice rich inbicarbonate (that raises pH) and rich in enzymes including – amylases,lipases, nucleases, and proteasesTrypsinogen from the pancreas is activated to trypsin in the duodenum.Trypsin activates other proteasesCholecystokinin is secreted by the duodenum. It responds to fatty chyme andstimulates release of bile from the gall bladderCholecystokinin emulsifies fatsC:\Documents and Settings\adele.cunningham\My Documents\APII spring 09\lectures and study guidesAPII spring 09\study guides APII spring 09\chapter 23 digestion study guide spring 09.docSave date: Friday, April 10, 2009 5:27:00 PM

Chapter 23 • Digestive System • Study Guide Page 5 of 7BIOL2112-Chapter23-RespiratorySystem-StudyGuide01.pdf Friday April 10, 2009Most absorption of nutrients happens in the small intestineSmall villi and microvilli increase surface area for better absorptionMicrovilli line the villiA lacteal of the lymphatic system is in the center of each villusFats enter lymph here and give it a milky lookThe villus contracts and pumps lymphEnzymes in the brush border, made of villi and microvilli, completecarbohydrate and protein digestionBetween the villi are crypts. In the cryptsStem cells in the crypts migrate up the villus as they age.Other cells release a watery secretion in which nutrients dissolve.Some cells release hormones such as secretin and CCK.GI cells last only about three to six daysThis rapid division makes them vulnerable to chemotherapeutic drugsand causes nausea and diarrheaMALT – Peyer’s patches lymph follicles increase in number toward the distalend of the intestine, the ileumLiverLocated under the diaphragm, mostly within the rib cageStructure of the liverThe liver has four lobes, but anteriorly only two lobes are visibleRight lobe is largerLeft lobeGall bladderStores, but does not make bileBile is released into the duodenumLiver lobules Figure 23.24Sheets of liver cells are arranged in plates around a central vein in a six-sidedfigure called a lobuleAt each corner are an artery, a vein, and a bile ductBetween the plates of liver cells are leaky capillaries – sinusoidal capillariesC:\Documents and Settings\adele.cunningham\My Documents\APII spring 09\lectures and study guidesAPII spring 09\study guides APII spring 09\chapter 23 digestion study guide spring 09.docSave date: Friday, April 10, 2009 5:27:00 PM

Chapter 23 • Digestive System • Study Guide Page 6 of 7BIOL2112-Chapter23-RespiratorySystem-StudyGuide01.pdf Friday April 10, 2009The digestive function of the liver is to secrete bileBile containsBile saltsBile saltsEmulsify fatsBile salts are recycled at the ileumBilirubin – is a pigment in bile that is the pigment in hemoglobin. OldRBC’s are recycled in the liver.In infants RBC’s have a shorter lifespan and sometimes the livercan’t process old RBCs fast enough, causing jaundice in infantsCCK from the duodenum regulates release of bile from the gall bladder, signaling thegall bladder to contract (bile is made in the liver, not in the gall bladder)Gall stones are crystallized cholesterol resulting from too much cholesterol (or toolittle bile salts) When the duct contracts, the crystals cause pain.Cirrhosis of the liverLiver has tremendous regenerative powersScarring from chronic damage from alcohol outpaces regenerationScarring interferes with filtering of the bloodBlood is diverted to alternate veins that drain into the vena cavaeSome of these alternate veins are at the base of the esophagus, and around thenavelSigns of liver failureVomiting bloodSwollen veins around the navelAscites – fluid accumulation in the abdominopelvic cavityThere are about 18 million alcoholics in the U.S.Signs of alcoholismStrong cravingTolerance – you need to drink more to get highLoss of control – being unable to stop drinking once you startWithdrawal when you stop drinking – nausea, sweating, and shakingPancreasEndocrine function – insulin and glucagonDigestive function – pancreatic juice is high in bicarbonatesAnd inactive forms of protein-digesting enzymes (proteases)Trypsinogen is converted to trypsin in the duodenumTrypsin activates other proteasesPancreatic juice also contains lipases, amylases, nucleasesC:\Documents and Settings\adele.cunningham\My Documents\APII spring 09\lectures and study guidesAPII spring 09\study guides APII spring 09\chapter 23 digestion study guide spring 09.docSave date: Friday, April 10, 2009 5:27:00 PM

Chapter 23 • Digestive System • Study Guide Page 7 of 7BIOL2112-Chapter23-RespiratorySystem-StudyGuide01.pdf Friday April 10, 2009Large intestineMain functions of the large intestine are to absorb water and form fecesHigh in mucus-secreting goblet cellsThe colon has no villiIleocecal valve – this is a true valve that is very resistant to backflow and protects thesmall intestine from bacteria in forming fecesCecum and appendix (the appendix is part of MALT)Ascending – the first section after the ileocecal valveTransverse – crosses the abdominopelvic cavityDescending – on the left side before the sigmoidSigmoid – the last section of colon before the rectumRectum – the straight portion of the colon above the anusHas valve-like flaps that separate gas from fecesAnal canalInvoluntary and voluntary anal sphinctersInvoluntary sphincter is deep to the voluntaryand stimulates the urge to defecateThe anal canal begins where the rectum penetrates pelvic floorDendritic cells sample bacteria in the large intestine and present them to T cellsNormal flora make vitamins B and KNormal flora are part of the innate defense because they inhibit growth of pathogensDiverticulosis is small pockets or herniations of the mucosa caused by lack of bulk inthe diet that would soften stoolDiverticulitis is inflammation of diverticula that is dangerous because of the risk ofcontaminating the peritoneal cavity with fecesC:\Documents and Settings\adele.cunningham\My Documents\APII spring 09\lectures and study guidesAPII spring 09\study guides APII spring 09\chapter 23 digestion study guide spring 09.docSave date: Friday, April 10, 2009 5:27:00 PM