Bio 122 Chapter 18

18The Cardiovascular System: The HeartAnatomy

Chapter 18, Cardiovascular System

Heart AnatomyApproximately the size of your fistLocationSuperior surface of diaphragmLeft of the midlineAnterior to the vertebral column, posterior to the sternum


Heart AnatomyFigure 18.1


Coverings of the Heart: AnatomyPericardium a double-walled sac around the heart composed of:A superficial fibrous pericardiumA deep two-layer serous pericardiumThe parietal layer lines the internal surface of the fibrous pericardiumThe visceral layer or epicardium lines the surface of the heartThey are separated by the fluid-filled pericardial cavity


Coverings of the Heart: PhysiologyThe Function of the Pericardium:Protects and anchors the heartPrevents overfilling of the heart with bloodAllows for the heart to work in a relatively friction-free environment


Pericardial Layers of the HeartFigure 18.2


Heart WallEpicardium visceral layer of the serous pericardiumMyocardium cardiac muscle layer forming the bulk of the heartFibrous skeleton of the heart crisscrossing, interlacing layer of connective tissueEndocardium endothelial layer of the inner myocardial surface


External Heart: Major Vessels of the Heart (Anterior View)Vessels returning blood to the heart include:Superior and inferior venae cavaeRight and left pulmonary veinsVessels conveying blood away from the heart include:Pulmonary trunk, which splits into right and left pulmonary arteriesAscending aorta (three branches) BrachiocephalicLeft common carotidSubclavian arteries


External Heart: Vessels that Supply/Drain the Heart (Anterior View)Arteries right and left coronary (in atrioventricular groove), marginal, circumflex, and anterior interventricular arteriesVeins small cardiac, anterior cardiac, and great cardiac veins


External Heart: Anterior ViewFigure 18.4b


External Heart: Major Vessels of the Heart (Posterior View)Vessels returning blood to the heart include:Right and left pulmonary veinsSuperior and inferior venae cavaeVessels conveying blood away from the heart include:AortaRight and left pulmonary arteries


External Heart: Vessels that Supply/Drain the Heart (Posterior View)Arteries right coronary artery (in atrioventricular groove) and the posterior interventricular artery (in interventricular groove)Veins great cardiac vein, posterior vein to left ventricle, coronary sinus, and middle cardiac vein


External Heart: Posterior ViewFigure 18.4d


Gross Anatomy of Heart: Frontal SectionFigure 18.4e


Atria of the HeartAtria are the receiving chambers of the heartEach atrium has a protruding auriclePectinate muscles mark atrial wallsBlood enters right atria from superior and inferior venae cavae and coronary sinusBlood enters left atria from pulmonary veins


Ventricles of the HeartVentricles are the discharging chambers of the heartPapillary muscles and trabeculae carneae muscles mark ventricular wallsRight ventricle pumps blood into the pulmonary trunkLeft ventricle pumps blood into the aorta


Myocardial Thickness and FunctionThickness of myocardium varies according to the function of the chamberAtria are thin walled, deliver blood to adjacent ventriclesVentricle walls are much thicker and strongerright ventricle supplies blood to the lungs (little flow resistance)left ventricle wall is the thickest to supply systemic circulation


Thickness of Cardiac WallsMyocardium of left ventricle is much thicker than the right.


Atrial Septal Defect


Ventricular Septal Defect


Pathway of Blood Through the Heart and LungsRight atrium tricuspid valve right ventricleRight ventricle pulmonary semilunar valve pulmonary arteries lungsLungs pulmonary veins left atriumLeft atrium bicuspid valve left ventricleLeft ventricle aortic semilunar valve aortaAorta systemic circulation


Pathway of Blood Through the Heart and LungsFigure 18.5


Coronary CirculationCoronary circulation is the functional blood supply to the heart muscle itselfCollateral routes ensure blood delivery to heart even if major vessels are occluded


Coronary Circulation: Arterial SupplyFigure 18.7a


Coronary Circulation: Venous SupplyFigure 18.7b


Heart ValvesHeart valves ensure unidirectional blood flow through the heartAtrioventricular (AV) valves lie between the atria and the ventriclesAV valves prevent backflow into the atria when ventricles contractChordae tendineae anchor AV valves to papillary muscles


Heart ValvesSemilunar valves prevent backflow of blood into the ventricles Aortic semilunar valve lies between the left ventricle and the aorta Pulmonary semilunar valve lies between the right ventricle and pulmonary trunk


Heart ValvesFigure 18.8a, b


Heart ValvesFigure 18.8c, d


Atrioventricular Valve FunctionFigure 18.9


Semilunar Valve FunctionFigure 18.10


Mitral Valve Prolapse


Microscopic Anatomy of Heart MuscleCardiac muscle is striated, short, fat, branched, and interconnectedThe connective tissue endomysium acts as both tendon and insertionIntercalated discs anchor cardiac cells together and allow free passage of ionsHeart muscle behaves as a functional syncytiumInterActive Physiology: Cardiovascular System: Anatomy Review: The HeartPLAY


Microscopic Anatomy of Heart MuscleFigure 18.11


18The Cardiovascular System: The HeartPhysiology


Cardiac Muscle ContractionHeart muscle:Is stimulated by nerves and is self-excitable (automaticity)Contracts as a unitHas a long (250 ms) absolute refractory periodCardiac muscle contraction is similar to skeletal muscle contraction


Heart Physiology: Intrinsic Conduction SystemAutorhythmic cells:Initiate action potentials Have unstable resting potentials called pacemaker potentialsUse calcium influx (rather than sodium) for rising phase of the action potential


Pacemaker and Action Potentials of the HeartFigure 18.13


Heart Physiology: Sequence of ExcitationSinoatrial (SA) node generates impulses about 75 times/minuteAtrioventricular (AV) node delays the impulse approximately 0.1 second


Heart Physiology: Sequence of ExcitationImpulse passes from atria to ventricles via the atrioventricular bundle (bundle of His)AV bundle splits into two pathways in the interventricular septum (bundle branches)Bundle branches carry the impulse toward the apex of the heartPurkinje fibers carry the impulse to the heart apex and ventricular walls


Heart Physiology: Sequence of ExcitationFigure 18.14a


Heart Excitation Related to ECGFigure 18.17


Extrinsic Innervation of the HeartHeart is stimulated by the sympathetic cardioacceleratory center Heart is inhibited by the parasympathetic cardioinhibitory centerFigure 18.15


ElectrocardiographyElectrical activity is recorded by electrocardiogram (ECG)P wave corresponds to depolarization of SA nodeQRS complex corresponds to ventricular depolarizationT wave corresponds to ventricular repolarizationAtrial repolarization record is masked by the larger QRS complexInterActive Physiology: Cardiovascular System: Intrinsic Conduction SystemPLAY


ElectrocardiographyFigure 18.16


Heart SoundsHeart sounds (lub-dup) are associated with closing of heart valvesFirst sound occurs as AV valves close and signifies beginning of systole (contraction)Second sound occurs when SL valves close at the beginning of ventricular diastole (relaxation)


Cardiac CycleCardiac cycle refers to all events associated with blood flow through the heartSystole contraction of heart muscleDiastole relaxation of heart muscle


Phases of the Cardiac CycleVentricular filling mid-to-late diastoleHeart blood pressure is low as blood enters atria (passively) and flows into ventriclesAV valves are open, then atrial systole occurs


Phases of the Cardiac CycleVentricular systole (contraction)Atria relax Rising ventricular pressure results in closing of AV valvesIsovolumetric contraction phaseVentricular ejection phase opens semilunar valves


Phases of the Cardiac CycleIsovolumetric relaxation early diastoleVentricles relaxBackflow of blood in aorta and pulmonary trunk closes semilunar valvesDicrotic notch brief rise in aortic pressure caused by backflow of blood rebounding off semilunar valvesInterActive Physiology: Cardiovascular System: Cardiac CyclePLAY


Phases of the Cardiac CycleFigure 18.20


Cardiac Output (CO) and ReserveCardiac Output is the amount of blood pumped by each ventricle in one minuteCO is the product of heart rate (HR) and stroke volume (SV)HR is the number of heart beats per minuteSV is the amount of blood pumped out by a ventricle with each beatCardiac reserve is the difference between resting and maximal CO


Cardiac Output: ExampleCO (ml/min) = HR (75 beats/min) x SV (70 ml/beat)CO = 5250 ml/min (5.25 L/min)


Regulation of Stroke VolumeSV = end diastolic volume (EDV) minus end systolic volume (ESV)EDV = amount of blood collected in a ventricle during diastoleESV = amount of blood remaining in a ventricle after contraction


Factors Affecting Stroke VolumePreload amount ventricles are stretched by contained blood Contractility cardiac cell contractile force due to factors other than EDVAfterload back pressure exerted by blood in the large arteries leaving the heart


Frank-Starling Law of the HeartPreload, or degree of stretch, of cardiac muscle cells before they contract is the critical factor controlling stroke volumeSlow heartbeat and exercise increase venous return to the heart, increasing SVBlood loss and extremely rapid heartbeat decrease SV


Preload and AfterloadFigure 18.21


Extrinsic Factors Influencing Stroke VolumeContractility is the increase in contractile strength, independent of stretch and EDVIncrease in contractility comes from: Increased sympathetic stimuliCertain hormonesCa2+ and some drugs


Extrinsic Factors Influencing Stroke VolumeAgents/factors that decrease contractility include:AcidosisIncreased extracellular K+Calcium channel blockers


Contractility and NorepinephrineSympathetic stimulation releases norepinephrine and initiates a cyclic AMP second-messenger systemFigure 18.22


Regulation of Heart RatePositive chronotropic factors increase heart rateCaffeineNegative chronotropic factors decrease heart rateSedatives


Regulation of Heart Rate: Autonomic Nervous SystemSympathetic nervous system (SNS) stimulation is activated by stress, anxiety, excitement, or exercise Parasympathetic nervous system (PNS) stimulation is mediated by acetylcholine and opposes the SNS PNS dominates the autonomic stimulation, slowing heart rate and causing vagal toneIf the Vagus Nerver was cut, the heart would lose its tone. Thus, increasing the heart rate by 25 beats per minute.


Atrial (Bainbridge) ReflexAtrial (Bainbridge) reflex a sympathetic reflex initiated by increased blood in the atriaCauses stimulation of the SA nodeStimulates baroreceptors in the atria, causing increased SNS stimulation


Chemical Regulation of the HeartThe hormones epinephrine and thyroxine increase heart rateIntra- and extracellular ion concentrations must be maintained for normal heart functionInterActive Physiology: Cardiovascular System: Cardiac OutputPLAY


Factors Involved in Regulation of Cardiac OutputFigure 18.23


Congestive Heart Failure (CHF)Congestive heart failure (CHF) is caused by:Coronary atherosclerosisPersistent high blood pressureMultiple myocardial infarctsDilated cardiomyopathy (DCM) main pumping chambers of the heart are dilated and contract poorly


Developmental Aspects of the HeartFigure 18.24


Developmental Aspects of the HeartFetal heart structures that bypass pulmonary circulationForamen ovale connects the two atria Ductus arteriosus connects pulmonary trunk and the aorta


Examples of Congenital Heart DefectsFigure 18.25


Age-Related Changes Affecting the HeartSclerosis and thickening of valve flapsDecline in cardiac reserveFibrosis of cardiac muscleAtherosclerosis


Congestive Heart Failure Causes of CHFcoronary artery disease, hypertension, MI, valve disorders, congenital defectsLeft side heart failureless effective pump so more blood remains in ventricleheart is overstretched & even more blood remainsblood backs up into lungs as pulmonary edemasuffocation & lack of oxygen to the tissuesRight side failure fluid builds up in tissues as peripheral edema


Coronary Artery Disease Heart muscle receiving insufficient blood supplynarrowing of vessels---atherosclerosis, artery spasm or clotatherosclerosis--smooth muscle & fatty deposits in walls of arteries

Treatmentdrugs, bypass graft, angioplasty, stent


Clinical ProblemsMI = myocardial infarctiondeath of area of heart muscle from lack of O2replaced with scar tissueresults depend on size & location of damageBlood clotuse clot dissolving drugs streptokinase or t-PA & heparinballoon angioplastyAngina pectorisheart pain from ischemia (lack of blood flow and oxygen ) of cardiac muscle


By-pass Graft


Percutaneous Transluminal Coronary Angioplasty


Artificial Heart


Chapter 18, Cardiovascular System Chapter 18, Cardiovascular System

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Bio 122 Chapter 18