Introduction - University of Alabama at Birmingham



IntroductionThe heart keeps the blood in motionIf blood stops moving, nutrient and oxygen supplies are exhaustedThe heart beats about 100,000 times per dayThis is about 70 beats per minuteThe heart pumps about 1.5 million gallons of blood per yearThis is about 2.9 gallons per minuteThe heart pumps between 5 and 30 liters of blood per minute—It can vary widelyAn Overview of the Cardiovascular SystemThe heart is about the size of a clenched fistThe heart consists of four chambersTwo atria Two ventriclesThe heart pumps blood into two circuitsPulmonary circuitSystemic circuitAn Overview of the Cardiovascular SystemEach circuit involves arteries, veins, and capillariesArteriesTransport blood away from the heartVeinsTransport blood toward the heartCapillariesVessels that interconnect arteries and veinsThe PericardiumPericardium is the serous membrane lining the pericardial cavityThe pericardial membrane forms two layersVisceral pericardium Also called the epicardiumParietal pericardiumThe parietal pericardium is reinforced by a layer called the fibrous pericardiumThe parietal pericardium and fibrous pericardium constitute the pericardial sacStructure of the Heart WallThe walls of the heart consist of three layers:EpicardiumExternal surfaceMyocardiumConsists of cardiac muscle cellsEndocardium Internal surfaceStructure of the Heart WallCardiac Muscle CellsMostly dependent on aerobic respirationThe circulatory supply of cardiac muscle tissue is very extensiveCardiac muscle cells contract without information coming from the CNSCardiac muscle cells are interconnected by intercalated discsStructure of the Heart WallThe Intercalated DiscsCardiac cells have specialized cell-to-cell junctionsThe sarcolemmae of two cardiac cells are bound together by desmosomesThe intercalated discs bind the myofibrils of adjacent cells togetherCardiac muscle cells are bound together by gap junctionsIons move directly from one cell to another allowing all the muscle cells to contract as one unitStructure of the Heart WallThe Fibrous SkeletonEach cardiac cell is wrapped in an elastic sheathEach muscle layer is wrapped in a fibrous sheetThe fibrous sheets separate the superficial layer from the deep layer musclesThese fibrous sheets also encircle the base of the pulmonary trunk and ascending aortaStructure of the Heart WallFunctions of the Fibrous SkeletonStabilizes the position of cardiac cells Stabilizes the position of the heart valvesProvides support for the blood vessels and nerves in the myocardiumHelps to distribute the forces of contractionHelps to prevent overexpansion of the heartProvides elasticity so the heart recoils aftercontractionIsolates atrial cells from ventricular cellsOrientation and Superficial Anatomy of HeartThe heart lies slightly to the left of midlineLocated in the mediastinumThe base is the superior portion of the heartThe apex is the inferior portion of the heartThe heart sits at an oblique angleThe right border is formed by only the right atriumThe inferior border is formed by the right ventricleOrientation and Superficial Anatomy of HeartThe heart is rotated slightly toward the leftBasically, the heart appears to be twisted just a bitThe sternocostal surface is formed by the right atrium and right ventricleThe posterior surface is formed by the left atrium Orientation and Superficial Anatomy of HeartThe four chambers of the heart can be identified by sulci on the external surfaceInteratrial groove separates the left and right atriaCoronary sulcus separates the atria and the ventriclesAnterior interventricular sulcus separates the left and right ventricles Posterior interventricular sulcus also separates the left and right ventriclesOrientation and Superficial Anatomy of HeartThe Left and Right AtriaPositioned superior to the coronary sulcusBoth have thin wallsBoth consist of expandable extensions called auriclesThe Left and Right VentriclesPositioned inferior to the coronary sulcusMuch of the left ventricle forms the diaphragmatic surfaceInternal Anatomy and Organization of the HeartA frontal section of the heart reveals:Left and right atria separated by the interatrialseptumLeft and right ventricles separated by the interventricular septumThe atrioventricular valves are formed from folds of endocardiumThe atrioventricular valves are situated between the atria and the ventriclesInternal Anatomy and Organization of the HeartThe Right AtriumReceives deoxygenated blood via the superior vena cava, inferior vena cava, and coronary sinusCoronary sinus enters the posterior side of the right atriumContains pectinate musclesContains the fossa ovalis (fetal remnant of the foramen ovale)Internal Anatomy and Organization of the HeartThe Right VentricleReceives deoxygenated blood from the right atriumBlood enters the ventricle by passing through the tricuspid valve Right atrioventricular valve—right AV valveBlood leaves the ventricle by passing through the pulmonary valveLeads to the pulmonary trunk, then to the right and left pulmonary arteriesInternal Anatomy and Organization of the HeartThe Right VentricleThe right AV valve is connected to papillary muscles via chordae tendineaeSince there are three cusps to the valve, the chordae tendineae are connected to three papillary musclesPapillary muscles and chordae tendineae prevent valve inversion when the ventricles contractInternal Anatomy and Organization of the HeartThe Right VentricleThe internal surface of the right ventricle consists of:Trabeculae carneaeModerator bandFound only in the right ventricleMuscular band that extends from the interventricular septum to the ventricular wallPrevents overexpansion of the thin-walled right ventricleInternal Anatomy and Organization of the HeartThe Left AtriumReceives oxygenated blood from the lungs via the right and left pulmonary veinsDoes not have pectinate musclesBlood passes through the bicuspid valve Left atrioventricular valveAlso called the mitral valveInternal Anatomy and Organization of the HeartThe Left VentricleHas the thickest wallNeeded for strong contractions to pump blood throughout the entire systemic circuitCompare to the right ventricle, which has a thin wall since it only pumps blood through the pulmonary circuitDoes not have a moderator bandThe AV valve has chordae tendineae connecting to the two cusps and to two papillary musclesInternal Anatomy and Organization of the HeartThe Left Ventricle (continued)Blood leaves the left ventricle by passing through the aortic valveBlood enters the ascending aortaBlood then travels to the aortic arch and then to all body parts (systemic)Internal Anatomy and Organization of the HeartStructural Differences between the Left and Right VentriclesRight ventricleThinner wallWeaker contractionHas a moderator bandLeft ventricleThicker wallPowerful contractionSix to seven times more powerful than the right ventricleInternal Anatomy and Organization of the HeartStructure and Function of the Heart ValvesThere are four valves in the heartTwo AV valvesTricuspid and bicuspid valvesTwo semilunar valvesAortic and pulmonary (pulmonic) valvesInternal Anatomy and Organization of the HeartStructure and Function of the Heart ValvesEach AV valve consists of four partsRing of connective tissue Connects to the heart tissueCusps Chordae tendineaeConnect to the cusps and papillary musclesPapillary musclesContract in such a manner to prevent AV inversionInternal Anatomy and Organization of the HeartValve Function during the Cardiac CyclePapillary muscles relaxDue to the pressure in the atria, the AV valves openWhen the ventricles contract, pressure causes the semilunar valves to openAlso upon contraction, the blood forces the AV valves closed, thus resulting in blood going through the semilunar valvesCoronary Blood VesselsOriginate at the base of the ascending aortaSupply the cardiac muscle tissueSelect coronary vessels:Right coronary artery (RCA)Right marginal branchPosterior interventricular branchLeft coronary artery (LCA)Circumflex branchLeft marginal branchAnterior interventricular branchInternal Anatomy and Organization of the HeartThe Right Coronary ArteryPasses between the right auricle and pulmonary trunkMajor branches off the right coronary artery:Atrial branchesRight marginal branchPosterior interventricular branchConducting system branchesInternal Anatomy and Organization of the HeartLeft Coronary ArteryMajor branches off the left coronary arteryCircumflex branch Branches to form the left marginal branch Branches to form the posterior left ventricular branchAnterior interventricular branch Branches that lead to the posterior interventricular branch called anastomosesInternal Anatomy and Organization of the HeartThe Coronary VeinsDrain cardiac venous blood ultimately into the right atriumSelect coronary veins:Great cardiac veinDelivers blood to the coronary sinusMiddle cardiac veinDelivers blood to the coronary sinusCoronary sinusDrains directly into the posterior aspect of the right atriumInternal Anatomy and Organization of the HeartThe Coronary VeinsSelect coronary veins (continued)Posterior vein of the left ventricleParallels the posterior left ventricular branchSmall cardiac veinParallels the right coronary arteryAnterior cardiac veinsBranches from the right ventricle cardiac cellsThe Coordination of Cardiac ContractionsThe cardiac cycle consists of alternate periods of contraction and relaxationContraction is systoleBlood is ejected into the ventriclesBlood is ejected into the pulmonary trunk and the ascending aortaRelaxation is diastoleChambers are filling with bloodThe Coordination of Cardiac ContractionsCardiac contractions are coordinated by conducting cellsThere are two kinds of conducting cellsNodal cellsSinoatrial nodes and atrioventricular nodes Establish the rate of contractionsCell membranes automatically depolarizeConducting fibersDistribute the contractile stimulus to the myocardiumThe Sinoatrial and Atrioventricular NodesSinoatrial node (SA node)Sits within the floor of the right atriumLocated in the posterior wall of the right atriumAlso called the cardiac pacemakerGenerates 80–100 action potentials per minuteAtrioventricular node (AV node)Sits within the floor of the right atriumThe Sinoatrial and Atrioventricular NodesGenerates 80–100 action potentials per minuteUpon exposure to acetylcholine (parasympathetic response)Action potential slows down (bradycardia)Upon exposure to norepinephrine (sympathetic response)Action potential speeds up (tachycardia)The Cardiac CycleSummary of Cardiac EventsImpulse travels from the SA node to the AV nodeAtrial contraction occursImpulse travels from the AV node to the AV bundleThe AV bundle travels along the interventricular septum and then divides to form the right and left bundle branchesThe bundle branches send impulses to the Purkinje fibersVentricle contraction occursAutonomic Control of Heart RateThe pacemaker sets the heart rate but can be alteredImpulses from the autonomic nervous system modify the pacemaker activityNerves associated with the ANS innervate the: SA nodeAV nodeCardiac cellsSmooth muscles in the cardiac blood vesselsAutonomic Control of Heart RateThe effects of NE and ACh on nodal tissueNorepinephrine from the ANS causes:An increase in the heart rateAn increase in the force of contractions Acetylcholine from the ANS causes:A decrease in the heart rateA decrease in the force of contractionsAutonomic Control of Heart RateCardiac centers in the medulla oblongata modify heart rateStimulation activates sympathetic neuronsCardioacceleratory center is activatedHeart rate increasesStimulation activates parasympathetic neuronsCN X is involvedCardioinhibitory center is activatedHeart rate decreases ................
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