Presentation on theme: "The Cardiovascular System: The Heart"— Presentation transcript:
1 The Cardiovascular System: The Heart 18P A R T AThe Cardiovascular System: The Heart
2 Approximately the size of your fist Location Heart AnatomyApproximately the size of your fistLocationSuperior surface of diaphragmLeft of the midlineAnterior to the vertebral column, posterior to the sternum
7 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
8 Aorta Superior vena cava Left Right pulmonary artery pulmonary artery Left atriumPulmonary trunkLeftpulmonary veinsRight atriumRightpulmonary veinsMitral(bicuspid) valveFossaovalisAorticvalvePectinatemusclesPulmonaryvalveTricuspidvalveLeft ventriclePapillarymuscleRight ventricleChordaetendineaeInterventricularseptumMyocardiumTrabeculaecarneaeVisceralpericardiumInferiorvena cavaEndocardium(e)Figure 18.4e
18 Microscopic Anatomy of Heart Muscle Cardiac 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 ®:Anatomy Review: The Heart, pages 3–7
19 Microscopic Anatomy of Cardiac Muscle Figure 18.11
20 The Cardiovascular System: The Heart 18P A R T BThe Cardiovascular System: The Heart
21 Cardiac Muscle Contraction Heart 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
22 Heart Physiology: Intrinsic Conduction System Autorhythmic cells:Initiate action potentialsHave unstable resting potentials called pacemaker potentialsUse calcium influx (rather than sodium) for rising phase of the action potential
23 Pacemaker and Action Potentials of the Heart Figure 18.13
26 Heart Physiology: Sequence of Excitation Sinoatrial (SA) node generates impulses about 75 times/minuteAtrioventricular (AV) node delays the impulse approximately 0.1 secondImpulse passes from atria to ventricles via the atrioventricular bundle (bundle of His)
27 Heart Physiology: Sequence of Excitation 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
37 Electrical activity is recorded by electrocardiogram (ECG) 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 complexPLAYInterActive Physiology ®:Intrinsic Conduction System, pages 3–6
38 Defective heart valves: Heart MurmursAbnormal heart sounds produced by abnormal patterns of blood flow in the heart.Defective heart valves:Valves become damaged by antibodies made in response to an infection, or congenital defects.Mitral stenosis:Mitral valve becomes thickened and calcified.Impairs blood flow from left atrium to left ventricle.Accumulation of blood in left ventricle may cause pulmonary HTN.Incompetent valves:Damage to papillary muscles.Valves do not close properly.Murmurs produced as blood regurgitates through valve flaps.
39 Septal defects: Heart Murmurs Usually congenital. Holes in septum between the left and right sides of the heart.May occur either in interatrial or interventricular septum.Blood passes from left to right.
40 Electrocardiogram (ECG/EKG) The body is a good conductor of electricity.Tissue fluids have a high [ions] that move in response to potential differences.Electrocardiogram:Measure of the electrical activity of the heart per unit time.Potential differences generated by heart are conducted to body surface where they can be recorded on electrodes on the skin.Does NOT measure the flow of blood through the heart.
41 Ischemic Heart Disease Ischemia:Oxygen supply to tissue is deficient.Most common cause is atherosclerosis of coronary arteries.Increased [lactic acid] produced by anaerobic respiration.Angina pectoris:Substernal pain.Myocardial infarction (MI):Changes in T segment of ECG.Increased CPK and LDH.
42 Arrhythmias Detected on ECG Abnormal heart rhythms.Flutter:Extremely rapid rates of excitation and contraction of atria or ventricles.Atrial flutter degenerates into atrial fibrillation.Fibrillation:Contractions of different groups of myocardial cells at different times.Coordination of pumping impossible.Ventricular fibrillation is life-threatening.
43 Arrhythmias Detected on ECG (continued) Bradycardia:HR slower < 60 beats/min.Tachycardia:HR > 100 beats/min.First–degree AV nodal block:Rate of impulse conduction through AV node exceeds 0.2 sec.P-R interval.Second-degree AV nodal block:AV node is damaged so that only 1 out of 2-4 atrial APs can pass to the ventricles.P wave without QRS.
44 Arrhythmias Detected on ECG (continued) Third-degree (complete) AV nodal block:None of the atrial waves can pass through the AV node.Ventricles paced by ectopic pacemaker.
48 Heart sounds (lub-dup) are associated with closing of heart valves First sound occurs as AV valves close and signifies beginning of systoleSecond sound occurs when SL valves close at the beginning of ventricular diastole
49 Cardiac CycleCardiac cycle refers to all events associated with blood flow through the heartSystole – contraction of heart muscleDiastole – relaxation of heart muscle
50 Phases of the Cardiac Cycle Ventricular filling – mid-to-late diastoleHeart blood pressure is low as blood enters atria and flows into ventriclesAV valves are open, then atrial systole occurs
51 Phases of the Cardiac Cycle Ventricular systoleAtria relaxRising ventricular pressure results in closing of AV valvesIsovolumetric contraction phaseVentricular ejection phase opens semilunar valves
52 Phases of the Cardiac Cycle Isovolumetric 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 valvesPLAYInterActive Physiology ®: Cardiac Cycle, pages 3–18
53 Phase of contraction. Phase of relaxation. Cardiac Cycle Refers to the repeating pattern of contraction and relaxation of the heart.Systole:Phase of contraction.Diastole:Phase of relaxation.End-diastolic volume (EDV):Total volume of blood in the ventricles at the end of diastole.Stroke volume (SV):Amount of blood ejected from ventricles during systole.End-systolic volume (ESV):Amount of blood left in the ventricles at the end of systole.
55 Cardiac Cycle (continued) Step 1: Isovolumetric contraction:QRS just occurred.Contraction of the ventricle causes ventricular pressure to rise above atrial pressure.AV valves close.Ventricular pressure is less than aortic pressure.Semilunar valves are closed.Volume of blood in ventricle is EDV.Step 2: Ejection:Contraction of the ventricle causes ventricular pressure to rise above aortic pressure.Semilunar valves open.Ventricular pressure is greater than atrial pressure.AV valves are closed.Volume of blood ejected: SV.
56 Cardiac Cycle (continued) Step 3: T wave occurs:Ventricular pressure drops below aortic pressure.Step 4: Isovolumetric relaxation:Back pressure causes semilunar valves to close.AV valves are still closed.Volume of blood in the ventricle: ESV.Step 5: Rapid filling of ventricles:Ventricular pressure decreases below atrial pressure.AV valves open.Rapid ventricular filling occurs.
57 Cardiac Cycle (continued) Step 6: Atrial systole:P wave occurs.Atrial contraction.Push 10-30% more blood into the ventricle.
59 Correlation of ECG with Heart Sounds First heart sound:Produced immediately after QRS wave.Rise of intraventricular pressure causes AV valves to close.Second heart sound:Produced after T wave begins.Fall in intraventricular pressure causes semilunar valves to close.
61 Cardiac Output (CO) and Reserve CO 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
62 Cardiac Output: Example CO (ml/min) = HR (75 beats/min) x SV (70 ml/beat)CO = 5250 ml/min (5.25 L/min)
63 Regulation of Stroke Volume SV = 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
64 Factors Affecting Stroke Volume Preload – amount ventricles are stretched by contained bloodContractility – cardiac cell contractile force due to factors other than EDVAfterload – back pressure exerted by blood in the large arteries leaving the heart
65 Cardiac Output (CO) Volume of blood pumped/min. by each ventricle. Pumping ability of the heart is a function of the beats/ min. and the volume of blood ejected per beat.CO = SV x HRTotal blood volume averages about 5.5 liters.Each ventricle pumps the equivalent of the total blood volume each min. (resting conditions).
66 Frank-Starling Law of the Heart Preload, 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
68 Extrinsic Factors Influencing Stroke Volume Contractility is the increase in contractile strength, independent of stretch and EDVIncrease in contractility comes from:Increased sympathetic stimuliCertain hormonesCa2+ and some drugs
72 Circulatory Changes During Exercise (continued)
73 Regulation of Heart Rate: Autonomic Nervous System Sympathetic nervous system (SNS) stimulation is activated by stress, anxiety, excitement, or exerciseParasympathetic nervous system (PNS) stimulation is mediated by acetylcholine and opposes the SNSPNS dominates the autonomic stimulation, slowing heart rate and causing vagal tone
74 Atrial (Bainbridge) Reflex Atrial (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
75 Chemical Regulation of the Heart The hormones epinephrine and thyroxine increase heart rateIntra- and extracellular ion concentrations must be maintained for normal heart functionInterActive Physiology ®: Cardiac Output, pages 3–9
79 Renin-Angiotension-Aldosterone System (continued)
80 Dehydration or excess salt intake: Regulation by ADHReleased by posterior pituitary when osmoreceptors detect an increase in plasma osmolality.Dehydration or excess salt intake:Produces sensation of thirst.Stimulates H20 reabsorption from urine.