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 non contractile 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, long term 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.