Cardiovascular System:
The Heart
Dr. Michael P. Gillespie
Cardiovascular System
 Blood
 Heart
 Blood vessels
Heart
 Propels the blood through the blood vessels to reach all of cells of
the body.
 It circulates the blood through an estimated 100,000 km (60,000
miles) of blood vessels.
Heart
 It beats 100,000 times every day (35 million beats / year).
 It pumps about 5 liters (5.3 qt) each minute and 14,000 liters
(3,600 gal) each day.
 Cardiology – the study of the normal heart and diseases associated
with it.
Size And Shape
 About the size of a closed fist.
 Cone-shaped.
 12cm (5 in.) Long, 9cm (3.5 in.) Wide, and 6cm (2.5 in.) Thick.
 250g (8 oz) in adult females and 300g (10 oz) in adult males.
Location
 Lies in the mediastinum (a mass of tissue between the sternum and
the vertebral column).
 2/3 of the mass is left of midline.
 A cone lying on its side.
Anatomical Landmarks
 The apex (pointed end) is directed anteriorly, inferiorly, and to the
left.
 The base (broad portion) is directed posteriorly, superiorly, and to
the right.
 Anterior surface – deep to sternum & ribs.
Anatomical Landmarks
 Inferior surface – rests upon diaphragm.
 Right border – faces the right lung.
 Left border (pulmonary border) – faces the left lung.
Cardiopulmonary Resuscitation
(CPR)
 External pressure (compression) can be used to force
blood out of the heart and into the circulation.
 CPR is utilized when the heart suddenly stops beating.
 Cardiac compressions with artificial ventilation of the
lungs keeps oxygenated blood circulating until the heart
can be restarted.
 Self CPR (coughing).
Pericardium
 Pericardium – membrane that surrounds and protects
the heart.
 Fibrous pericardium – tough, inelastic, dense irregular CT.
Prevents overstretching of the heart.
 Serous pericardium – thinner, more delicate layer.
 Parietal layer.
 Visceral layer (epicardium) – adheres to the heart.
 Pericardial fluid lies in between these two layers in the pericardial
cavity.
Layers Of The Heart Wall
 Epicardium (visceral layer of the serous pericardium).
 Myocardium – cardiac muscle tissue.
 Endocardium – smooth lining of the chambers of the heart and
valves (continuous with blood vessels).
Chambers Of The Heart
 Atria – superior chambers.
 Auricle – pouchlike structure.
 Ventricles – inferior chambers.
 Sulci – grooves on the surface of the heart that contain blood
vessels.
Chambers Of The Heart
 Right atrium – receives blood from three veins: superior vena cava,
inferior vena cava, and coronary sinus.
 Tricuspid valve.
 Pectinate muscles.
 Interatrial septum.
 Fossa ovalis – depression (remnant of foramen ovale).
Chambers Of The Heart
 Right ventricle – receives blood from right atrium.
 Trabeculae carneae – bundles of cardiac muscle tissue.
 Chordae tendineae – connects to the cusps of the tricuspid valve which
are connected to papillary muscles.
 Interventricular septum.
 Pulmonary valve into pulmonary arteries.
Chambers Of The Heart
 Left atrium – receives blood from the lungs through the
pulmonary veins.
 Bicuspid (mitral) valve.
 Left ventricle – receives blood from left atrium.
 Trabeculae carneae – bundles of cardiac muscle tissue.
 Chordae tendineae – connects to the cusps of the bicuspid valve which
are connected to papillary muscles.
 Aortic valve into the ascending aorta (largest artery).
Myocardial Thickness
 The function of the individual chambers determines their thickness.
 The atria pump blood a short distance and consequently have
thinner walls than the ventricles.
 The left ventricle pumps blood a greater distance than the right at
higher pressures and has a thicker wall.
Fibrous Skeleton Of The Heart
 Dense CT rings that surround the valves and prevent overstretching.
 Provides insertion points for bundles of cardiac muscle fibers.
Atrioventricular (AV) Valves
 Tricuspid and bicuspid valves.
 When the valve is open, the pointed cusps point into the ventricle.
Atrioventricular (AV) Valves
 When atrial pressure is higher than ventricular pressure
the valves open (the papillary muscles are relaxed and the
chordae tendinae is slack.
 When the ventricles contract the pressure forces the AV
valves closed. The papillary muscles close concurrently.
 Damaged valves allow regurgitation (flow back).
Semilunar (SL) Valves
 The aortic and pulmonary valves.
 The SL valves open when the pressure in the ventricles exceeds the
pressure in the arteries.
Heart Valve Disorders
 Stenosis (narrowing) – failure of the heart valve to open fully.
 Insufficiency (incompetence) – failure of a valve to close fully.
 Mitral stenosis – due to scar formation of a congenital defect.
Heart Valve Disorders
 Mitral insufficiency – backflow of blood from the left ventricle to
the left atrium.
 Mitral valve prolapse (MVP) – one or both cusps protrude into the left
atrium during ventricular contraction.
 Aortic stenosis – the aortic valve is narrowed.
Heart Valve Disorders
 Aortic insufficiency – backflow of blood from the aorta into the left
ventricle.
 Rheumatic fever – an acute systemic inflammatory disease.
Antibodies produced to destroy the bacteria attack and inflame the
CT of joints, heart valves and other organs.
Systemic And Pulmonary
Circulations
 Two closed systems.
 The output of one becomes the input of another with each beat of
the heart.
Coronary Circulation
 The myocardium has its own blood vessels, the coronary
circulation.
 The coronary arteries branch from the ascending aorta
and encircle the heart.
 When the heart is contracting the coronary arteries are
squeezed shut.
 When the heart is relaxed, the high pressure from the
aorta pushes blood into the coronary arteries and from the
arteries to the coronary veins.
Coronary Arteries
 Two coronary arteries, right and left coronary arteries, branch from
the ascending aorta and supply oxygenated blood to the
myocardium.
Coronary Arteries
 Left coronary artery branches into:
 Anterior interventricular or left anterior descending LAD (supplies
ventricle walls).
 Circumflex branches (supplies left ventricle and left atrium).
Coronary Arteries
 Right coronary artery branches into:
 Atrial branches (supplies right atrium).
 Posterior interventricular branch (supplies the two ventricles).
 Right marginal branch (supplies the right ventricle).
Coronary Veins
 The great cardiac vein (anterior) and the middle cardiac vein
(posterior) drain into the coronary sinus.
 Coronary Sinus – a large bascular sinus on the posterior surface of
the heart.
Reperfusion Damage
 Reperfusion is reestablishing the blood flow to the heart muscle
after a blockage of a coronary artery.
 Reperfusion damages the tissue further due to the formation of
oxygen free radicals from the reintroduced oxygen.
Histology Of Cardiac Muscle
Tissue
 Cardiac muscle fibers are shorter in length and less circular than
skeletal muscle fibers.
 Cardiac muscle fibers exhibit branching.
Histology Of Cardiac Muscle
Tissue
 Usually one centrally located nucleus is present, although
it may occasionally have two nuclei.
 Intercalated disc connect neighboring fibers.
 The discs contain desmosomes, which hold the fibers together.
 Mitochondria are larger and more numerous in cardiac
muscle fiber.
 Gap junctions allow for propagation of action potentials.
Regeneration Of Heart Cells
 Infarcted (dead) cardiac muscle tissue is replaced with noncontractile fibrous scar tissue.
 A lack of stem cells limits the ability of the heart to repair damage.
 Some stem cells from the blood migrate into the heart tissues and
differentiate into functional muscle cells and endothelial cells.
Autorhythmic Fibers: The
Conduction System
 Autorhythmic fibers are self-excitable and maintain the heart’s
continuous beating.
 Act as a pacemaker, setting the rhythm of electrical excitation that
causes contraction of a heart.
 Form a conduction system, that provides a path for the cycle of
cardiac excitation through the heart.
Sequence Of Cardiac
Conduction
 Sinoatrial (SA) node – undergo spontaneous depolarization
(pacemaker potential) – propagates through the atria through gap
junctions.
 Atrioventricular (AV) node (bundle of his) – site where action
potentials are conducted from the atria to the ventricles.
Sequence Of Cardiac
Conduction
 Right and left bundle branches – propagate action potentials
through the ventricles and the interventricular septum to the apex
of the heart.
 Purkinje fibers – conduct the action potentials from the apex,
through the remainder of the ventricles stimulating contraction.
Pacemaker
 The SA node regulates the pace of the heart.
 At rest, it contracts approximately 100 time per minute.
 Nerve impulses from the ANS and blood born hormones
(epinephrine) modify the timing and strength of each heartbeat.
Pacemaker
 Acetylcholine from the ANS slows the heart rate to about 75 bpm.
 If the SA node becomes damaged, the AV node can pick up the job;
However, at a slower rate (40 – 60 bpm).
 If both nodes are damaged, an artificial pacemaker sends out
electrical currents to stimulate the heart to contract.
Ectopic Pacemaker
 If a site other than the SA node becomes self-excitable, it becomes
an ectopic pacemaker.
 It make operate occasionally, producing extra beats, or for a period
of time.
 Triggers:
 Caffeine, nicotine, electrolyte imbalances, hypoxia, and toxic reactions
to drugs.
Refractory Period
 In cardiac muscle tissue, the refractory period lasts longer than the
contraction period.
 This prevents tetanus (maintained contraction).
Electrocardiogram (ECG or EKG)
 As action potentials propagate through the heart, they generate
electrical currents that can be detected on the surface of the body.
 An electrocardiogram is a recording of these signals.
 An electrocardiograph is the instrument used to record the signals.
Electrocardiogram (ECG or EKG)
 Electrodes are positioned on the arms and legs (limb leads) and at
six positions on the chest (chest leads).
 12 different tracings are produced from different combinations of
leads.
Electrocardiogram (ECG or EKG)
 If these tracings are compared to one another and to a normal
tracing, it is possible to determine the following:
 If the conducting pathway is abnormal.
 If the heart is enlarged.
 If certain regions of the heart are damaged.
Typical Lead II Record
 Three clearly recognizable waves appear with each heartbeat.
 P wave – atrial depolarization.
 QRS complex – rapid ventricular depolarization.
 T wave – ventricular repolarization.
Changes In Wave Size
 Large P waves – enlargement of the atrium.
 Large Q waves – myocardial infarction.
 Large R waves – enlarged ventricles.
 Flat T wave – insufficient oxygen.
 Large T wave – hyperkalemia (high blood K+ levels).
Stress Electrocardiogram
(Stress Test)
 Elevate the heart’s response to stress.
 Narrowed coronary arteries may carry adequate blood supply at
rest, but not during exercise.
Changes In Time Span Between
Waves
 Time spans between waves are called intervals or
segments.
 P-Q interval – time between the beginning of the P wave
and the beginning of the QRS complex.
 The P-Q interval represents the time required for an
action potential to travel through the atria, AV node and
remaining fibers of the conduction system.
Changes In Time Span Between
Waves
 The P-Q interval lengthens when the action potentials
must travel around scar tissue from rheumatic fever.
 The S-T segement is elevated in acute myocardial
infarction and depressed when the heart receives
insufficient oxygen.
 The Q-T interval may be lengthened by myocardial
damage, myocardial ischemia, or conduction
abnormalities.
Terminology
 Systole – the phase of contraction.
 Diastole – the phase of relaxation.
 Cardiac cycle – all of the events associated with one heartbeat
(systole and diastole of the atria and systole and diastole of the
ventricles).
Heart Sounds
 Auscultation – listening to sounds within the body (performed with
a stethoscope).
 During each cardiac cycle there are 4 heart sounds, but in a normal
heart, only the first and second heart sounds (S1 and S2) are loud
enough to be heard with a stethoscope.
Heart Sounds
 The first sound (S1), described as a lubb sound, is louder and longer
than the second.
 Caused by closure of the AV valves after ventricular systole begins.
 The second sound (S2), described as dupp sound, is shorter and not
as loud as S1.
 Caused by closure of the semilunar valves as ventricular diastole
begins.
Heart Sounds
 S3 is due to blood turbulence from rapid ventricular filling.
 S4 is due to blood turbulence during atrial systole.
 S3 and S4 are not normally heard.
Heart Murmurs
 A heart murmur is an abnormal sound consisting of a clicking,
rushing, or gurgling noise that is heard before, between, or after the
normal heart sounds. It can also mask the normal heart sounds.
 Some heart murmurs are “innocent”; However, they usually
represent a valve disorder.
Congestive Heart Failure
 In CHF, the heart is a failing pump.
 Causes include coronary artery disease, congenital defects, longterm high blood pressure (increases afterload), myocardial
infarctions, valve disorders.
 Pulmonary edema – left ventricle fails first.
 Peripheral edema – right ventricle fails first.
Regulation Of Heart Rate
 Autonomic regulation of heart rate.
 Proprioceptors, chemoreceptors, baroreceptors.
 Cardiac accelerator nerves.
 Chemical regulation of heart rate.
 Hormones (epinephrine, norepinephrine, and thyroid hormones)
accelerate the heart rate.
 Cations.
Terminology
 Tachycardia – elevated resting heart rate.
 Bradycardia – a resting heart rate under 60 bpm.
 Hypothermia – lowering of the body temperature, which slows the
heart rate.
Disorders Of The Heart
 Coronary artery disease (CAD).
 Arteriosclerosis and atherosclerosis.
Disorders Of The Heart
 Myocardial ischemia and infarction.
 Hypoxia.
 Angina pectoris.
Disorders Of The Heart
 Congenital defects.
 Coarctation of the aorta.
 Patent ductus arteriosus.
 Septal defect.
 Atrial and ventricular.
 Tetralogy of Fallot.
Disorders Of The Heart
 Arrhythmias – irregularity of the heart rhythm.
 Heart block.
 Flutter and fibrillation.
 Ventricular premature contraction.
Medical Terminology
 Angiocardiography – x-ray examination of the heart and
great vessels with radiopaque dye.
 Cardiac arrest.
 Cardiomegaly.
 Cor pulmonale (CP) – ventricular hypertrophy from
disorders that bring about hypertension in the pulmonary
circulation.
 Palpitation.