University of Colorado Boulder



Digestive System Part 2Accessory digestive organsSalivary glandsLiverGallbladderPancreasLiverFunctions: performed by hepatocyteProcess nutrients in bloodEx: glucose (in blood plasma) <-> glycogen (stored in hepatocytes)Makes blood proteinsStores fat-soluble vitaminsMetabolizes poisons and drugsProduces bile = cholesterol, bile salts, bilirubinExcrete bilirubin (from broken down red blood cells)Emulsify fat: keep fats in smaller globs so enzymes can digest them better -> improves fat digestionGross Anatomy:Vessels connect on visceral (posterior) sideHepatic veins: carry blood away, back to heartPorta hepatis: region where other vessels connect to liverVessels at porta hepatis:Common hepatic duct: carries bile (out of liver)Hepatic arteries: blood with oxygen (into liver)Hepatic portal vein: unique! (into liver)Blood and lymph flow focusing on liver:Sugars and amino acids:Absorbed by blood capillariesGo directly to liver via hepatic portal veinLipids:Absorbed by lacteals of lymphatic systemBypass liverEnter blood of veins near heartMicroscopic anatomy:Liver lobules:Functional units = hexagonal unit with plates of liver cells (hepatocytes)Each lobule has:Central vein: delivers blood to hepatic veinsHow blood gets to central vein:Liver sinusoids: leaky capillariesFluid (plasma) flows onto hepatocytes by way of fenestrations (holes)Also contains hepatic macrophages (Kupffer cells)Portal triad: group of 3 vesselsContains:Portal arteriole: branch of hepatic arterySupplies O2 to liver cellsPortal venule: branch of hepatic portal veinBrings nutrients from digestive tract for storage and processingBile duct:Carries bile (from hepatocytes) out of liverHow bile gets to bile duct:Bile canaliculi: between hepatocytesPathology:Jaundice: yellowing of skin and mucosaeDue to excess bilirubin throughout body tissuesDue to liver failureEx: due to hepatitis = inflammation of liverSummary of pathway of blood flow:From intestines, etc.: hepatic portal vein -> portal venule -> sinusoid -> central vein -> hepatic veinFrom heart: hepatic artery -> portal arteriole -> sinusoid -> central vein -> hepatic veinGallbladderGeneral features:On visceral (posterior) surface of liverStores and concentrates bileReleases bile to duodenum when stimulatedNot essentialPathway of bile flow:Accumulation of bile between meals: liver -> bile ducts -> common hepatic duct -> common bile duct (closed sphincter so backs up) -> cystic duct -> gallbladderRelease of stored bile from gallbladder (to emulsify fats – aid digestion): gallbladder -> cystic duct -> common bile duct -> duodenumPathology:Gallstones: mainly cholesterol crystalsIf gallbladder is removed, common bile duct takes over storage functionPancreasFunctions:Exocrine secretions: released into lumen of duodenumAcinar cells: secrete most of body’s digestive enzymesEpithelium of small ducts: secrete bicarbonate to neutralize stomach acidEndocrine secretions: released into bloodPancreatic islet cells: secrete insulin and glucagonHormones controlling storage of glucose and its release into the bloodFor example at the liverGross anatomy:Located posterior to stomachPancreatic duct(s): empties into lumen of duodenumRespiratory SystemFunctionRespiration: exchange of gases (oxygen and carbon dioxide) with the environmentConsists of 4 processes:Ventilation: move air in/out of lungs (active process)External respiration: gas diffuses between lungs and blood (passive process)Two above processes are functions of respiratory systemGas transport via blood (active process)Internal respiration: gas diffuses between blood and cells (passive process)Two above processes are functions of cardiovascular systemZonesConducting zone: passageways for air, no diffusionVentilation: external nose through most tubes in lungsRespiratory zone: the anatomical zone where oxygen diffuses into bloodExternal respirationPulmonary alveoliRespiratory bronchiolesWalls of conducting zoneLayers: mucosa, submucosa (some organs have other too)Mucosa contains:Epithelium:Areas exposed to food: nonkeratinized stratified squamousMost areas: pseudostratified ciliated columnarMajor function: removing debrisCT: lamina propriaGlands secrete mucus to trap debris:Goblet cells (1 celled glands): in mucosal epitheliumSeromucous glands: in lamina propria and submucosaOrgans of respiratory systemExternal nose:External nares: nostrils (entrance/exit)Nasal cavity:Nasal septum separates left and right nasal cavitiesEpithelium: pseudostratified ciliated columnarDebris are swept posteriorly to be swallowedHighly vascularized lamina propria: warms and moistens the inspired airParanasal sinuses: paired air spaces in the bones of the skullConnect to nasal cavities by drainage ductsWarm and moisten the inspired airSinusitis: sinus infectionPharynx: where respiratory/digestive tracts intersectDivisions of pharynx:Nasopharynx: nasal cavity (pseudostratified ciliated columnar)Oropharynx: oral cavity (stratified squamous)Laryngopharynx: larynx and esophagus (stratified squamous)During swallowing soft palate folds upward to seal of nasopharynxLarynx:Functions:Gateway to the lungsSpeech (voicebox)Structures: most are hyaline cartilageThyroid cartilage:Laryngeal prominence: Adam’s apple (larger in males)Cricoid cartilage: inferior to thyroid cartilageArytenoid cartilage: attached to back of cricoid cartilage (A like shape of cartilage)Epiglottis: swallowing elevates the larynx -> epiglottis passively tilts down -> laryngeal inlet (opening) closesElastic cartilageVocal folds: true vocal cordsVibrated by the air to produce soundRima glottides: opening between vocal foldsGlottis: rima glottides + vocal foldsAttached directly to thyroid cartilage (at anterior end) and arytenoid cartilages (at posterior end)Open/close by moving arytenoid cartilages in transverse planeControl of pitch: cricoid cartilage moves in sagittal plane (around joint between cricoid and thyroid)Carries arytenoid cartilages alongIncreases tension in vocal folds -> higher pitchVestibular folds: false vocal cordsSuperior to vocal foldsNo direct role in most sound productionImportant for holding breath against pressure in the thoracic cavityEpithelium:Superior larynx: occasional contact with foodStratified squamousInferior larynx (below vocal folds):Pseudostratified ciliated columnarTrachea:Location: in mediastinumTissues:Epithelium: pseudostratified cilated columnar Rings of hyaline cartilage to prevent collapseSmooth muscleElastic CT: for elastic recoil (more efficient ventilation)NOTE: Same tissues continue through most of the conducting zonePrimary bronchi:First part of the bronchial treeThe only bronchi outside the lungsLocation: in mediastinumLungs:Contains:Most of bronchial tree (except for primary bronchi): part of the conducting zonePulmonary alveoli: most of the respiratory zonePleurae: serous membranes surrounding the lungs (superficial to deep)Parietal pleura (outer pleura)Pleural cavity: spaceContains pleural fluidSlight vacuum is important for breathingVisceral pleura: inner pleuraDivisions of the lungs:Lobes:Left lung: 2 lobesRight lung: 3 lobesBronchopulmonary segments (parts of lobes):About 10 per lungBronchial tree:Connects trachea to alveoliRight and left primary (main) bronchi (outside lung)Second lobar bronchi (1 per lobe)Tertiary (segmental) bronchi (1 per bronchopulmonary segment)Bronchioles (<1mm wide)Terminal bronchioles: end of conducting zoneRespiratory bronchioles: start of respiratory zone (attached to alveoli)Pathologies:Asthma: allergic inflammationSmooth muscle of bronchioles contractsIncreased mucus secretionRespiratory zone:Pulmonary alveoli: where gas exchange occurs by diffusionCovered with pulmonary capillariesVery short diffusion distanceVery large surface areaNo mucus! (would slow down diffusion)Pathologies:Emphysema: walls between alveoli break down -> decreased surface areaAlveolar macrophages: trap dustCells of alveolar wall:Type I cells: main component of alveolar liningSimple squamous epitheliumThinnest for diffusionType II cells:Simple cuboidal epithelial cellsSecrete surfactant: molecule that decreases surface tension of water (allows alveoli to expand)Respiratory Distress Syndrome:Common in premature infantsInsufficient surfactant producedDifficult to expand alveoliVentilationBreathingInspiration: Active processDiaphragm and external intercostals contract -> increase thoracic volume -> decrease pressure in lungs -> air entersExpiration:Passive process: muscles relaxTissues recoil (elastic CT)Pathologies:Pneumothorax: presence of air in the pleural cavityCauses lung collapseCardiovascular SystemFunctionTransport and deliver (via the blood):Nutrients and metabolic wasteO2 and CO2HormonesHeat, etc.Circulatory routesPulmonary circuit:Delivers blood to and from the lungsFor external respirationSystemic circuit:Delivers blood to and from the rest of the bodyFor internal respirationGeneral circulatory principlesCapillary beds: where exchange takes placeArtery: delivers blood from the hear to the capillary bedsMost arteries have oxygenated blood but not allVein: delivers blood from capillary bedsBack to the heart (most veins)Or to another capillary bedPortal veinsMost veins have deoxygenated blood but not allHepatic portal systemThe heartA muscular pump that circulates the bloodFour-chamberedSurrounded by pericardial cavityCoverings of heart (superficial to deep):Enclosed in pericardiumFibrous pericardium (outer): not serosaParietal layer of serous pericardiumPericardial cavity: contains serous fluidVisceral layer of serous pericardium (epicardium)Pathologies:Cardiac tamponade: compression of the heart due to excess fluid in pericardial cavityWall of heart (outer to inner):Epicardium (visceral layer of serous pericardium)Myocardium: cardiac muscleEndocardium:Epithelium: simple squamous (endothelium)Lines inner heart (including valves)Chambers and vessels:Overview of heart, chambers, valves, and vessels (diagram)Atria: receive blood from veinsRight atrium: receives deoxygenated blood from:Inferior and superior vena cavaCoronary sinus: returns blood from heart tissueLeft atrium: receives oxygenated blood from:Pulmonary veinsVentricles: eject blood from heartRight ventricle: pumps deoxygenated blood to:Pulmonary trunk -> pulmonary arteriesLeft ventricle: pumps oxygenated blood to:AortaCoronary arteries (supplying blood to heart tissues) are branches of aorta* A to V: arteries before veins, atria before ventriclesHeart valves: prevent backflow of bloodAtrioventricular valves (AV valves): between atrium and ventricleTricuspid valve (R AV): between R atrium and ventricleBicuspid valve (L AV, mitral): between L atrium and ventricleChordae tendinae:Hold valved in placeAnchored to papillary musclesPrevents eversion (prolapse)Try before you buySemilunar valves (SL valves): between great arteries and ventriclesAortic SL valve: between left ventricle and aortaPulmonary SL valve: between right ventricle and pulmonary trunkHeart sounds in each heart beat:First sound (“lub”): closing of both AV valves when ventricles begin contractingSecond sound (“dup”): closing of both SL valves when ventricles being relaxingConducting system:Heart muscle has intrinsic rhythmConducting system: specialized cardiac muscle cellsInitiates electrical signal (“firing”)Signals heart chambers to contract in proper sequenceSignal spreads from one cardiac muscle cell to another through gap junctionsSequence of conduction:1. Sinoatrial node (SA node): pacemakerNOTE: All cardiac muscle cells can spontaneously fire, but SA node cells have fastest rate2. Atrioventricular node (AV node)3. Bundle of His (AV node)4. Bundle of branches5. Purkinje fibersDisorders of conducting system:Heart block: damage to AV node or Bundle of His (only path from atria to ventricles)Signal doesn’t reach ventricles: ventricles still beat but at slower paceArtificial pacemaker restores normal functionBloodA type of connective tissueComponents of blood:Plasma: fluid with dissolved nutrients, etc.Erythrocytes (red blood cells): carry oxygenLeukocytes (white blood cells): immune cellsPlatelets: cell fragments for clot formationBlood vesselsFunction of blood vessels:Capillary: allows diffusion between blood and other tissuesArtery: carries blood away from heartVein: carries blood away from capillariesEventually back to heartGeneral structure of blood vessel wall:Tunica intima:Has endothelium: simple squamousTunica media:Smooth muscle, collagen, elastin – all circularly arrangedTunica externa:Collagen, elastin – all longitudinally arrangedArteries:Structure (compared to veins and capillaries)Subject to highest pressureThicker wallsMainly due to thicker tunica mediaMore elasticTypes of arteries:Elastic arteries: conducting arteriesLargest arteries: 1 cm – 1 inch wideThick wall, highest elastin contentVery elastic: smoothes out pressure fluctuationsMuscular arteries:Most of the named arteries0.3 mm – 1 cmThickest tunica media relative to vessel diameterRegulate blood pressure and distributionArterioles:Smallest arteries: 0.1 – 0.3 mmRegulate blood pressure and distributionCapillaries:Structure: facilitates diffusionWall only has tunica intima (mostly endothelium)Very thin wallTiny: capillary diameter < 0.01 mm wideAll blood in capillary is close to wallMany branches: large surface areaCapillary beds:Precapillary sphincters open when tissue is active:Lets blood into capillariesPrecapillary sphincters close when tissue inactive:Shuts off exchangeBlood still travels across through metarteriole and thoroughfare channelTypes of capillaries:Continuous capillaries:Many tight junctions between endothelial cellsIn brain:Completely sealed by tight junctionsAll molecules must go across membrane of endothelial cellLeast leaky of allBlood-brain barrierIn most organs (muscles, lungs, skin, etc.):Not completely sealed by tight junctionsSmall molecules can pass through intercellular clefts (where tight junctions are absent)Fenestrated capillaries:Have fenestrations: holes through endothelial cells (in other aspects, similar to continuous capillaries)Allows more rapid exchange of small moleculesKidney, endocrine glands, intestines, synovial membrane (places where filtration most important)Discontinuous capillaries:Have fenestrationsIntercellular clefts are large (very few tight junctions)Allows exchange of proteins and cells, lots of fluidLiver, lymphoid organs (spleen, bone marrow)Veins:Structure:Very low pressure systemThinner wall than arteries:Less smooth muscle and elastin (collapsible)Larger lumen than arteries:Blood reservoir65% of total body bloodHave valves to prevent backflow of bloodTypes of veins:Venules (small veins):Receive blood from capillariesVeins (other than venules):Receive blood from venulesPortal veins: deliver blood from capillary bed to capillary bedEx: hepatic portal veinMechanisms of enhancing venous return:Return of blood to heart is slow because of low pressure -> need way to enhance blood return to heartEx: skeletal muscular pumpPressure changes (and valves) dive blood back to heartLymphatic and Immune SystemsLymphatic systemFunction:A system of vessels and nodes that returns excess tissue fluid to the bloodNeeded because plasma tends to leak out of blood capillariesNOTE: Most cells get oxygen and nutrients directly from interstitial fluid (tissue fluid)Filters pathogens to be targeted by immune systemPathway of flow:Throughout most of body, tissue fluid (interstitial fluid) enters lymphatic capillariesThe fluid is now called lymphMoves through lymph vessels and lymph nodesBlood plasma -> tissue fluid -> lymphReturned to the blood at veins at the base of the neckStructures:Very low pressure system:Uses valves to maintain flow directionLymphatic capillaries:Wall: endothelium (simple squamous epithelium)Minivalves:Formed by loose edges of cellsLarge lymph vessels:Has valves (similar to those of veins)Lymph nodes:Contains reticular CT (with reticular fibers)Lymph flows throughPathogens are filtered out by immune cellsPathology:Lymphedema: accumulation of interstitial fluid due to poor lymphatic drainageEx: elephantiasis (extreme)Caused by parasitic wormImmune systemFunction:A system of cells, tissues, and organs that is dispersed widely throughout the body to defend against pathogensCells:Leukocytes: white “blood” cellsExamples:Macrophages:Engulf foreign material/debrisNOT specific to one type of antigenPresents antigen on cell surfaceLymphocytes:Recognizes and attacks one specific type of antigenMust be activated firstEx: by macrophageTissues and organs:Lymphoid tissue: reticular CT with lots of lymphocytesCommon in places where pathogens may enterEx: MALT (mucosa associated lymphoid tissue)Lymphoid organs: mostly lymphoid tissuePrimary lymphoid organs:Where lymphocytes are madeThymus and red bone marrowSecondary lymphoid organs:Contain mature lymphocytesLymph nodesSpleenTonsilsAppendixPeyer’s patchesNervous SystemFunctionReceive sensory input: monitor changes inside and outside the bodyIntegration (most complex): processes and interprets sensory inputMotor output: causes a response by activating effector organs (muscle or gland)Properties:All cells are naturally chargedNervous tissue: uses electrical charge for rapid communicationOrganizationCentral nervous system (CNS):BrainSpinal cordPeripheral nervous system (PNS): nerves and gangliaRegional divisions:Spinal nerves: nerves that transmit signals to and from spinal cordCrania nerves: nerves that transmit signals to and from brainFunctional divisions: they are all connected!Afferent (sensory): carries impulses to CNSSomatic sensory: monitors external environment, skin, body wall, limbsVisceral sensory: monitors visceral organsEfferent (motor): carries impulses to effector organsSomatic motor (usually voluntary):To skeletal muscleVisceral motor (involuntary): autonomic nervous systemTo cardiac and smooth muscle, glandsSympathetic: “fight or flight”Parasympathetic: “rest and digest”Histology of nervous systemNeurons: nerve cells – but NOT always found in nervesProperties:Function: rapid transmission and integration of signalsSpecialized for conducting electrical impulsesCannot divide after birth: BUT new neurons can be generated from stem cellsAnatomy of a typical (multipolar) neuron:Cell body (soma):Contains nucleusDendrites:Receive signals from other cellsSend signals to cell bodyAxon:Receives signals from axon hillock of cell bodyAxon terminals: transmit signal to other neuronsMyelin sheath:Made of glial cellsInsulates axons from each otherSpeeds up signalNodes of Ranvier: gaps in myelinSynapse: site of neuron-neuron communicationMost are chemical, using neurotransmitter that diffuses across synaptic cleftSome are electrical, using gap junctionsPathology:Multiple sclerosis: an autoimmune disease of the CNSResults in damage to both myelin and axonsTypes of neuronsFunctional classification:Sensory (afferent) neurons:Carry signals to CNSMake up the sensory division of PNSNOTE: axon terminal is (typically) in CNSMotor (efferent) neurons:Carry signal from CNS to effectorMake up the motor division of PNSNOTE: cell body is (typically) in CNSInterneurons: between sensory and motor neuronsFound entirely within CNSStructural classification:Multipolar (many things to cut):Many processesMost neurons (typical)Bipolar (two things to cut):One axon, one fused dendriteFound in some sensory organsUnipolar/pseudounipolar (one thing to cut):Typical sensory neuronsReceptive endings, no dendritesAxon with peripheral and central processesNeuroglia/glia: support cellsProperties:Don’t send nervous signalsOutnumber neuronsContinue dividing through out lifeMost brain cancers are gliomas: tumors of glial cellsTypes:Found in CNS only:Oligodendrocytes: forms myelin sheathAstrocytes: most abundant, controls environment around neuronsMicroglia: immune cellsEpendymal cells: lines fluid-filled cavities, propels fluidFound in PNS only:Schwann cells: forms myelin sheathSatellite cells: controls environment around neuron cell bodiesHistology of gross anatomy:Nerve: group of axons traveling together in the PNSNerve anatomy (deep to superficial):Endoneurium: surrounds axonPerineurium: surrounds each subgroup of axonsEpineurium: wraps around outside of nerveFascicle: subgroup of axonsNerves vs. neurons:Each nerve contains the axons of many neuronsAxons are also called nerve fibersAxons carry signals toward the axon terminalsMost nerves carry signals in both directions because contain neurons oriented in both directionsOnly exceptions are some cranial nervesGanglion: collection of neuron cell bodies in PNSGrey and white matter: general types of nervous tissue in CNSWhite matter: myelinated axonsGray matter: everything else = unmyelinated axons, dendrites, cell bodiesTract: collection of axons traveling together inside the CNSWhite matterNucleus: collection of neuron cell bodies inside the CNSGray matterBrainComplexity:100 billion neuronsMany synapses per neuronDevelopment:Neural tube: fluid filledPrimary brain vesicles:Prosencephalon: forebrainMesencephalon: midbrainRhombencephalon: hindbrainSecondary brain vesicles:Forebrain:TelencephalonDiencephalonMidbrain:MesencephalonHindbrain:MetencephalonMyelencephalonAdult brain structures (rostral to caudal):Telencephalon: cerebrumDiencephalon: diencephalon*Mesencephalon: midbrain*Metencephalon (they “met”):PonsCerebellum*Myelencephalon: medulla oblongata* = brain stemVentricles: fluid-filled cavitiesLateral ventricles in cerebrumThird ventricle in diencephalonCerebral aqueduct in midbrainFourth ventricle between pons, cerebellum, medulla oblonglataCerebrospinal fluid:CSF: fluid that fills ventriclesCushions brainTransports nutrients, wastes, other chemicalsChoroid plexus:Found in all 4 ventriclesProduces the CSFContains:Capillaries: produce CSF by filtrationEpendymal cells: modify CSFCirculation of CSF: propelled by cilia of ependymal cellsProduced in later ventricles3rd ventricle (also makes CSF)Cerebral aqueduct4th ventricle (also makes CSF)Central canal of spinal cord (some CSF)AperturesSubarachnoid spaceArachnoid villiDural sinuses (combines with blood from veins)Internal jugular veinsBack to heartMeninges: 3 layers of CT surrounding the CNSProtect the CNSContains a portion of the CSFDura mater: outer layer (“tough mother”)Periosteal layer (outer): periosteumMeningeal layer (inner)Dural sinus: space between these layers that carries bloodFunctions as a veinArachnoid mater: middle layer (“spidery mother”)Subarachnoid space: contains CSF and large blood vesselsPia mater: inner layer (“gentle mother”)Carries small blood vessels to nervous tissuePathologies:Spina bifida:Neural tube fails to close completelyCan result in partial paralysis and risk of infectionHydrocephalusBuildup of excess CSF in the brain ................
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