Cardiovascular System: The Heart

Dr. Michael P. Gillespie

Cardiovascular System: The Heart

Cardiovascular SystemBloodHeartBlood vessels

HeartPropels 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.

HeartIt 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 ShapeAbout 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.

LocationLies 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 LandmarksThe 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 LandmarksInferior 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).

PericardiumPericardium – 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 WallEpicardium (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 HeartAtria – superior chambers.

Auricle – pouchlike structure.Ventricles – inferior chambers.Sulci – grooves on the surface of the heart

that contain blood vessels.

Chambers Of The HeartRight 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 HeartRight 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 HeartLeft 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 ThicknessThe 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 HeartDense CT rings that surround the valves

and prevent overstretching.Provides insertion points for bundles of

cardiac muscle fibers.

Atrioventricular (AV) ValvesTricuspid and bicuspid valves.When the valve is open, the pointed cusps

point into the ventricle.

Atrioventricular (AV) ValvesWhen 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) ValvesThe aortic and pulmonary valves.The SL valves open when the pressure in

the ventricles exceeds the pressure in the arteries.

Heart Valve DisordersStenosis (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 DisordersMitral 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 DisordersAortic 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 CirculationsTwo closed systems.The output of one becomes the input of

another with each beat of the heart.

Coronary CirculationThe 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 ArteriesTwo coronary arteries, right and left

coronary arteries, branch from the ascending aorta and supply oxygenated blood to the myocardium.

Coronary ArteriesLeft coronary artery branches into:

Anterior interventricular or left anterior descending LAD (supplies ventricle walls).

Circumflex branches (supplies left ventricle and left atrium).

Coronary ArteriesRight coronary artery branches into:

Atrial branches (supplies right atrium).Posterior interventricular branch (supplies

the two ventricles).Right marginal branch (supplies the right

ventricle).

Coronary VeinsThe 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 DamageReperfusion 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 TissueCardiac muscle fibers are shorter in length

and less circular than skeletal muscle fibers.

Cardiac muscle fibers exhibit branching.

Histology Of Cardiac Muscle TissueUsually 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 CellsInfarcted (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 SystemAutorhythmic 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 ConductionSinoatrial (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 ConductionRight 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.

PacemakerThe 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.

PacemakerAcetylcholine 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 PacemakerIf 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 PeriodIn 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 RecordThree clearly recognizable waves appear

with each heartbeat.P wave – atrial depolarization.QRS complex – rapid ventricular

depolarization.T wave – ventricular repolarization.

Changes In Wave SizeLarge 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 WavesTime 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 WavesThe 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.

TerminologySystole – 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 SoundsAuscultation – 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 SoundsThe 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 SoundsS3 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 MurmursA 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 FailureIn 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 RateAutonomic 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.

TerminologyTachycardia – 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 HeartCoronary artery disease (CAD).Arteriosclerosis and atherosclerosis.

Disorders Of The HeartMyocardial ischemia and infarction.

Hypoxia.Angina pectoris.

Disorders Of The HeartCongenital defects.

Coarctation of the aorta.Patent ductus arteriosus.Septal defect.

Atrial and ventricular.Tetralogy of Fallot.

Disorders Of The HeartArrhythmias – irregularity of the heart

rhythm.Heart block.Flutter and fibrillation.Ventricular premature contraction.

Medical TerminologyAngiocardiography – 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.