Chapter 22, sp 10

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Human Anatomy, Second Edition

McKinley & O'Loughlin

Chapter 22 Lecture Outline: Heart

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Overview of the Cardiovascular System The pump, the heart, connects to blood vessels that

transport blood between the heart and other body tissues. arteries carry blood away from the

heart high in oxygen except for the pulmonary

arteries veins carry blood back to the heart

low in oxygen (except for the pulmonary veins)

The arteries and veins entering and leaving the heart are called the great vessels.

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Overview of the Cardiovascular System

There is a unidirectional flow of blood through both the heart and the blood vessels.

Acts like two independent, side-by-side pumps that work independently but at the same rate.

one directs blood to the lungs for gas exchange the other directs blood to body tissues for

nutrient delivery Alternate cycles of heart wall contraction (systole)

and relaxation (diastole) develop blood pressure. Minimum blood pressure is essential to push blood

through blood vessels to the body tissues for nutrient and waste exchange.

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Pulmonary and Systemic Circuits The pulmonary circuit consists of the chambers on

the right side of the heart (right atrium and ventricle) as well as the pulmonary arteries and veins.

conveys blood to the lungs via pulmonary arteries to reduce carbon dioxide and replenish oxygen levels in the blood before returning to the heart in pulmonary veins

Blood returns to the left side of the heart, where it then enters the systemic circuit.

The systemic circuit consists of the chambers on the left side of the heart (left atrium and ventricle), along with all the other named blood vessels.

carries blood to all the peripheral organs and tissues of the body

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Pulmonary and Systemic Circuits Oxygenated blood from the left side of the heart is

pumped into the aorta, the largest systemic artery in the body, and then into smaller systemic arteries.

Gas exchange in tissues occurs in capillaries. Systemic veins then carry deoxygenated blood

(high in carbon dioxide) and waste products. Most veins merge and drain into the superior

and inferior venae cavae, which drain blood into the right atrium.

There, the blood enters the pulmonary circuit, and the cycle repeats.

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Postition of the Heart Approximately the size of a fist (about 250 to

350 g) Located left of the midline posterior to the

sternum in the middle mediastinum. Rotated such that the right atrium and

ventricle are located more anteriorly, while the left atrium and ventricle are located more posteriorly.

CPR - heart between the sternum and the vertebrae - allows compression

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Position of the Heart The posterosuperior surface is the base. The pulmonary veins that enter the left

atrium border this base. The inferior end is the apex. It projects slightly toward the left

side of the body.

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Characteristics of the Pericardium The heart is in a fibrous, serous sac held in place within

the mediastinum by connective tissue that supports the great vessels’ external walls superior to the heart and the diaphragm inferior to it.

Restricts heart movements and prevents the heart from overfilling with blood.

Outer portion is a tough, dense connective tissue layer called the fibrous pericardium.

attached to both the sternum and the diaphragm Inner portion is a thin, double-layered serous membrane

called the serous pericardium. parietal layer (fused to fibrous pericardium) visceral layer (epicardium) produces serous fluid

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Pericarditis Inflammation of the pericardium Possible causes: viruses, bacteria, or fungi Blood vessels become leaky and blood

accumulates in the pericardial cavity Severe case: cardiac tamponade can

lead to heart failure (drain with a needle) Piercing pain-not crushing pain of heart

attack Also friction rub in pericarditis helps to

distinguish the two

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Anatomy of the Heart

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Heart Wall Structure Three distinctive layers:

external epicardium middle myocardium internal endocardium

Epicardium, the outermost heart layer, is also known as the visceral layer of serous pericardium.

As we age, the epicardium becomes thicker and more fatty.

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Heart Wall Structure Myocardium, the middle layer, is

composed chiefly of cardiac muscle tissue and is the thickest layer.

Internal surface of the heart and the external surfaces of the heart valves are covered by a thin endothelium called the endocardium.

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External Heart Anatomy Four hollow chambers: two smaller atria and two

larger ventricles. Atria are thin-walled chambers that are located

superiorly. anterior part of each atrium is a wrinkled,

flaplike extension called an auricle Atria receive blood returning to the heart

through both circulatory circuits. right atrium receives blood from the systemic

circuit left atrium receives blood from the pulmonary

circuit

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External Heart Anatomy Blood that enters an atrium is passed to the

ventricle on the same side of the heart. Ventricles are the inferior chambers. Two large arteries, the pulmonary

trunk and the aorta exit the heart at the basal surface.

The pulmonary trunk carries blood from the right ventricle into the pulmonary circuit.

The aorta conducts blood from the left ventricle into the systemic circuit.

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External Heart Anatomy Atria are separated from the ventricles

externally by a relatively deep coronary sulcus (or atrioventricular sulcus) around the circumference of the heart.

The anterior interventricular sulcus and the posterior interventricular sulcus are located between the left and right ventricles on the surfaces of the heart.

These sulci extend toward the heart apex.

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Internal Heart Anatomy: Chambers and Valves There are four heart chambers: each plays

a role in the continuous process of blood circulation.

Valves permit the passage of blood in one direction and prevent its backflow.

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Fibrous Skeleton Dense irregular connective tissue.

separates the atria and ventricles anchors heart valves by forming supportive

rings (like handcuffs) at their attachment points and prevents overdilation of valve openings

provides electrical insulation between atria and ventricles

and thus prevents all of the heart chambers from beating at the same time

Provides a rigid framework for the attachment of cardiac muscle tissue.

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Right Atrium Receives venous blood from the systemic circuit

and the heart muscle itself. Three major vessels empty into the right atrium.

superior vena cava drains blood from the head, upper limbs, and superior regions of the trunk

inferior vena cava drains blood from the lower limbs and trunk

coronary sinus drains blood from the heart wall The interatrial septum forms a wall between the

right and left atria. Fossa ovalis in the wall was the foramen ovale

before birth Has pectinate muscles

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Separates the right atrium from the right ventricle.

Also called the tricuspid valve. has three triangular flaps

Venous blood flows from the right atrium, through the valve into the right ventricle.

It is forced closed when the right ventricle begins to contract, preventing blood backflow into the right atrium.

Right A-V Valve

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Right Ventricle Receives deoxygenated venous blood from the right

atrium. An interventricular septum separates the right and

left ventricles. The internal wall surface of each ventricle has cone-

shaped, muscular projections called papillary muscles, which: anchor chordae tendineae

attach to the cusp of the right AV valve and prevent everting and flipping into the atrium when contracting

Trabeculae carneae are muscular ridges in both ventricles

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Right Ventricle The pulmonary semilunar valve marks the

end of the right ventricle and the entrance into the pulmonary trunk.

Pulmonary trunk divides shortly into right and left pulmonary arteries. carry deoxygenated blood to the lungs

Between the pulmonary trunk and the aorta is the ligamentum arteriosum. Before birth, it was the ductus arteriosus, a bypass of the lungs and the left side of the heart.

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Right Ventricle: Pulmonary Semilunar Valve Within the walls of the ventricles immediately

before the connection of the ventricle to the pulmonary trunk and aorta.

Composed of three thin, pocketlike semilunar cusps. As blood is pumped into the arterial trunks, it

pushes against the cusps, forcing the valves open. When ventricular contraction ceases, blood enters

the pockets of the semilunar valves between the cusp and the chamber wall. causes the cusps to “inflate” and meet at the

artery center, effectively blocking blood backflow

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Left Atrium Once gas exchange occurs in the lungs,

the oxygenated blood travels through the pulmonary veins to the left atrium.

Smooth posterior wall of the left atrium contains openings for four pulmonary veins.

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Left A-V Valve Separates the left atrium from the left

ventricle. Also called the bicuspid valve or the mitral

valve. Left AV valve has chordae tendineae similar to

those of the right AV valve. Oxygenated blood flows from the left atrium

into the left ventricle. It is forced closed when the left ventricle

begins to contract prevents blood backflow into the left atrium

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Left Ventricle Largest of the four heart chambers. Wall is typically three times thicker than

the right ventricular wall. Requires thick walls in order to

generate enough pressure to force the oxygenated blood from the lungs into the aorta and then through the entire systemic circuit. right ventricle only has to pump blood

to the nearby lungs

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Left Ventricle Trabeculae carneae in the left ventricle

are more prominent. Two large papillary muscles attach to

the chordae tendineae that help support the left AV valve.

At the superior end of the ventricular cavity, the aortic semilunar valve marks the end of the left ventricle and the entrance into the aorta.

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Valve Defects and Their Effects on Circulation Valvular insufficiency or valvular incompetence

Leaky valves from inflammation or disease can lead to regurgitation

Heart working hard to overcome may lead to further heart enlargement with possible bad consequences

A primary cause is rheumatic heart disease Valvular stenosis

Narrowing of valve resists flow and output of affected chamber decreases and may hypertrophy and dilate

Rheumatic heart disease When antibodies against strep cross-react with connective

tissue Most effected are the endocardium, the valve leaflets, and

the left AV valve

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Heart Sounds Four normal heart sounds: lubb-dupp Lubb due to turbulance of blood from

closing of AV valves (long, booming sound)

Pause Dupp due to turbulance of blood from

closing of semilunar valves (short, sharp sound)

Longer pause Sounds are not heard exactly over valves

(surface projection)

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Heart Murmurs Abnormal sounds usually from turbulance

from faulty valves May be innocent or often a valve disorder Serious valve problems reduce the pumping

efficiency of the heart Common cause: carditis, esp., rheumatic fever

from streptococcal infection. 10-20 years later may lead to rheumatic heart disorder

Examples Mitral stenosis Mitral valve prolapse

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Coronary Circulation Left and right coronary arteries travel in the

coronary sulcus to supply the heart wall. the only branches of the ascending aorta

Openings for these arteries are located immediately superior to the aortic semilunar valve.

The right coronary artery typically branches into the

marginal artery supplies the right border of the heart

posterior interventricular artery supplies both the left and right ventricles

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Coronary Circulation Left coronary artery typically branches into the

anterior interventricular artery. also called the left anterior descending artery (or “widow

maker”) supplies the anterior surface of both ventricles and most

of the interventricular septum Circumflex artery.

supplies the left atrium and ventricle Arterial pattern can vary greatly among

individuals. Anastomoses are small so these arteries are

functional end arteries. Heart muscle can survive with 10-15% of normal supply.

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Coronary Circulation Veins parallel arteries generally. Great cardiac vein is beside the anterior

interventricular artery The middle cardiac vein is beside the

posterior interventricular artery The small cardiac vein is beside the right

marginal artery All these cardiac veins drain into the

coronary sinus, a large vein with no smooth muscle in the posterior coronary sulcus, that drains into the right atrium.

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Angina Pectoris and Myocardial Infarction Coronary atherosclerosis or coronary

heart disease is the most common cause of death in the US - narrows coronary blood vessels and decreases blood flow and causes chest pain

Angina pectoris Pain with exertion - follows sympathetic

pathways Nitroglycerin may temporarily dilate vessels Prognosis and long-term therapy depend upon

severity of narrowing

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Angina Pectoris and Myocardial Infarction Myocardial infarction (MI) or heart attack

May be from a thrombus (blood clot) or an embolus (a traveling blood clot).

Sudden blockage, infarct, of a coronary artery leads to a dead area. The result is a scar and/or conduction problems.

Deprivation of oxygen may lead to necrosis Symptoms: excruciating, crushing pain; weakness;

shortness or breath; sweating. Some have little pain. May have sudden death if ventricular fibrillation. If

person survives, then scar tissue because little or no regeneration. May weaken heart and lead to death. If person survives, heart muscle may get stronger due to hypertrophy.

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Treatment of Myocardial Infarction Clot busting drugs

Streptokinase tPA Aspirin

May help during an attack Also decreases MI risk but has risks:

cerebral bleeding and GI bleeding (consult doctor)

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Congestive Heart Failure Progressive usually from atherosclerosis,

high blood pressure, multiple infarcts Right sided failure causes

peripheral edema Left sided failure caused pulmonary

edema Eventually leads to right sided failure as well Cor pulmonale

Right ventricular hypertrophy from hypertension in pulmonary circulation

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Risk Factors in Heart Disease 1/5 of those who reach 60 yrs. have a MI 1/4 30-60 yrs. have the potential for MI Major risk factors

High blood cholesterol level High blood pressure Cigarette smoking Obesity Lack of regular exercise Diabetes mellitus Genetic predisposition Male up to 70 yrs.

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Help for Failing Hearts Coronary artery bypass grafting Angioplasty and stents Latissimus dorsi muscle HeartMate LVAD (left ventricular

assist device) Heart transplant

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Prevention

Aerobic exercise, diet, and drugs

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How the Heart Beats: Electrical Properites of Cardiac Tissue The efficient pumping of blood through

the heart and blood vessels requires coordinated contractions of the heart chambers made possible by the properties of cardiac muscle tissue and by specialized cells in the heart, the conducting system.

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Characteristics of Cardiac Muscle Tissue Fibers are relatively short, branched fibers with one

or two central nuclei and numerous mitochondria for ATP supply.

Fibers are arranged in spiral bundles and wrapped around and between the heart chambers.

Resembles skeletal muscle: fibers are striated, with extensive capillary networks that supply needed nutrients and oxygen.

Cardiac muscle differs from skeletal muscle in certain ways

The sarcoplasmic reticulum is less extensive and organized

No terminal cisternae

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Contraction of Heart Muscle Fibers contract as a single unit because

muscle impulses are distributed immediately and simultaneously throughout all fibers either of the atria or of the ventricles.

Specialized cell–cell contacts called intercalated discs electrically and mechanically link the fibers together and permit the immediate passage of nerve impulses.

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The Heart’s Conducting System Autorhythmicity. Some of the cells

spontaneously depolarize. Certain cardiac muscle fibers (1%) are

specialized to conduct muscle impulses to the contractile muscle cells of the myocardium.

Specialized cells are part of the heart’s conduction system.

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The Heart’s Conducting System Heartbeat is initiated by the cardiac

muscle fibers of the sinoatrial (SA) node. near the entrance of the superior vena cava

Act as the pacemaker (fastest part of the heart).

Initiates impulses 70 - 80 times per minute.

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The Heart’s Conducting System Impulse travels to both atria,

stimulating atrial systole. And via an internodal conduction

pathway through an opening in the fibrous skeleton to the atrioventricular (AV) node between the right AV valve and the coronary sinus Delay at the AV node

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The Heart’s Conducting System From the AV node to the atrioventricular (AV)

bundle (bundle of His). into the interventricular septum and then divides

into one right and two left bundle branches. To conduction fibers called Purkinje fibers in the

heart apex. Purkinje fibers are larger than other cardiac muscle

fibers. Muscle impulse conduction along the Purkinje fibers is

extremely rapid, consistent with the large size of the cells.

The impulse spreads immediately throughout the ventricular myocardium and the ventricles contract.

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The Heart’s Conducting System Fastest part of the heart sets the

rhythm If the SA node is damaged, then the

rhythm is set by the atria, the next fastest part of the heart

If the AV node is blocked, then the ventricles will beat at a slow rate (about 40 beats/min) and independently of the atria

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Summary of Blood Flow During the Cardiac Cycle Blood flows continuously into both atria

under low pressure. Blood flows into the ventricles if the AV

valves are open. Most of the ventricular filling is passive (70%). Atrial systole pushes in the final 30%.

During ventricular systole, the AV valves close, and the semilunar valves open to allow blood to enter the large arterial trunks.

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The Electrocardiogram (ECG or EKG) Composite tracing of all muscle

impulses generated by myocardial cells 3 principle deflections

P wave corresponds to atrial depolarization QRS complex corresponds to the beginning

of depolarization of the ventricles (and repolarization of the atria)

T wave corresponds to repolarization of the ventricles

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Atrial flutter 200-400 beats/min - stimulates atria and AV node

repeatedly May last for years and may degenerate to

fibrillation Atrial fibrillation

Chaotic and leads to an irregular heart rate Ventricles respond by increasing and decreasing

contraction activities and may lead to serious dysrhythmia

May increase likelihood of blood clots Decreased efficiency of the heart (20-30%)

Cardiac Arrhythmia (Dysrhythmia)

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Premature ventricular contractions (PVCs) Often from stress, stimulants such as caffeine,

or sleep deprivation May be single or in bursts Common and not a problem unless in great

numbers Ventricular fibrillation

Uncoordinated contractions, life-threatening - leads to cardiac arrest

Paddle electrodes depolarize the heart and puts it in refractory period (stops it), hope that normal sinus rhythm will start up

Cardiac Arrhythmia (Dysrhythmia)

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Innervation of the Heart Innervated by the autonomic nervous

system, the coronary plexus Autonomic innervation by autonomic

centers in the brainstem don’t initiate heartbeat.

Sympathetic innervation increases the rate and the force of heart contractions.

Parasympathetic innervation decreases heart rate, but tends to have no effect on the force of contractions, except in special circumstances.

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Tying It All Together: The Cardiac Cycle The time of one complete heartbeat. Contraction phase is called systole

forces blood either into another chamber or into a blood vessel

Relaxation phase is termed diastole. the chamber fills with blood

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Steps in the Cardiac Cycle

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Decreased flexibility and elasticity of the connective tissue can cause the valves to become slightly inflexible and a murmur may develop and blood flow through the heart may be altered.

Decreased conduction system efficiency reduces the ability to pump the extra blood needed during stress and exercise.

Aging and the Heart

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The muscular wall of the ventricle increases in thickness when high blood pressure causes the ventricles to work harder.

That leads to hypertrophy and, therefore, thickening of the cardiac muscle fibers and a change in the normal arrangement of formed fiber bundles. The heart is enlarged, but it works less efficiently.

Aging and the Heart

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Starts to develop in the third week when diffusion is not enough.

During weeks 5-8, the single heart tube becomes partitioned into four chambers and the main vessels entering the leaving the heart form. This partitioning is complex, and errors in development lead to many of the more common congenital heart malformations.

Development of the Heart

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Congenital Heart Defects Ventricular septal defect Transposition of the great vessels Coarctation of the aorta Tetralogy of Fallot Pulmonary stenosis Patent foramen ovale Patent ductus arteriosus