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.