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Human Anatomy,
First Edition
McKinley & O'Loughlin
Chapter 22 Lecture Outline:
Heart
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Functions of the Heart
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Center of the cardiovascular system, the heart.
Connects to blood vessels that transport blood
between the heart and other body tissues.
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Arteries carry blood high in oxygen.
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(except for the pulmonary arteries)
Veins carry blood low in oxygen.
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arteries carry blood away from the heart
veins carry blood back to the heart
(except for the pulmonary veins)
Arteries and veins entering and leaving the heart are
called the great vessels.
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Characteristics and Functions
of the Heart
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Ensures the unidirectional flow of blood through both the heart
and the blood vessels.
Backflow of blood is prevented by valves within the heart.
Acts like two independent, side-by-side pumps that work
independently but at the same rate.
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one directs blood to the lungs for gas exchange
the other directs blood to body tissues for nutrient delivery
Develops blood pressure through alternate cycles of heart wall
contraction and relaxation.
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
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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.
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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.
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carries blood to all the peripheral organs and tissues of the body
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Pulmonary and Systemic
Circuits
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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 from 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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Anatomy of the Heart
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Relatively small, conical organ approximately the size
of a person’s clenched fist.
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it weighs about 250 to 350 grams
Located left of the body midline posterior to the
sternum in the middle mediastinum.
Rotated such that its right side or border (right
atrium and ventricle) is located more anteriorly, while
its left side or border (left atrium and ventricle) is
located more posteriorly.
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Anatomy of the Heart
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The posterosuperior surface of the heart, formed
primarily by the left atrium, is called the base.
The pulmonary veins that enter the left atrium border
this base.
The inferior, conical end is called the apex.
It projects slightly anteroinferiorly toward the left
side of the body.
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Pericardium
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Heart is contained 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 so that it doesn’t bounce and move
about in the thoracic cavity, 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
 visceral layer
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Heart Wall Structure
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Heart wall consists of three distinctive layers:
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external epicardium
middle myocardium, and
internal endocardium
Epicardium is the outermost heart layer and is also
known as the visceral layer of serous pericardium.
As we age, more fat is deposited in the epicardium,
and so this layer becomes thicker and more fatty.
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Heart Wall Structure
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Myocardium is the middle layer of the heart wall and is
composed chiefly of cardiac muscle tissue.
Myocardium is the thickest of the three heart wall layers.
 it lies deep to the epicardium and superficial to the
endocardium
Internal surface of the heart and the external surfaces of the
heart valves are covered by a thin endothelium called the
endocardium.
 between the endocardium and myocardium lies a
subendocardial layer, which is composed of areolar
connective tissue
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Cardiac Muscle Tissue
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Fibers are relatively short, branched fibers that usually house
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 in that fibers in both muscles are
striated, with extensive capillary networks that supply needed
nutrients and oxygen.
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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External Anatomy of the Heart
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Composed of 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 Anatomy of the Heart
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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 Anatomy of the Heart
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Atria are separated from the ventricles externally by a
relatively deep coronary sulcus (or atrioventricular
sulcus) that extends around the circumference of the
heart.
On both the anterior and posterior surfaces of the
heart, the anterior interventricular sulcus and the
posterior interventricular sulcus are located between
the left and right ventricles.
These sulci extend inferiorly from the coronary sulcus
toward the heart apex.
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Functions of the Fibrous
Skeleton of the Heart
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The fibrous heart skeleton is located between the
atria and the ventricles, and is formed from dense
irregular connective tissue.
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separates the atria and ventricles
anchors heart valves by forming supportive rings at their
attachment points
provides electrical insulation between atria and ventricles
insulation ensures that muscle impulses are not spread
randomly throughout the heart, 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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Internal Anatomy of the Heart
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There are four heart chambers:
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right atrium
right ventricle
left atrium
left ventricle
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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Right Atrium
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Receives venous blood from the systemic circuit and
the heart muscle itself.
Three major vessels empty into the right atrium.
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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.
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Right Atrioventricular (AV) Valve
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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.
Is forced closed when the right ventricle begins to contract,
preventing blood backflow into the right atrium.
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Right Ventricle
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Receives deoxygenated venous blood from the right atrium.
An interventricular septum forms a wall between the right and
left ventricles.
The internal wall surface of each ventricle has three coneshaped, 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
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Pulmonary Trunk
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At its superior end it narrows into a smooth-walled, conical
region called the conus arteriosus.
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
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Semilunar Valves
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Located within the walls of both ventricles immediately before
the connection of the ventricle to the pulmonary trunk and
aorta.
Each is 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 is prevented from
flowing back into the ventricles from the arterial trunk by first
entering the pockets of the semilunar valves between the cusp
and the chamber wall.
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causes the cusps to “inflate” and meet at the artery center,
effectively blocking blood backflow
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Left Atrium
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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 approximately four pulmonary veins.
Has pectinate muscles along its anterior wall as well
as an auricle.
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Left Atrioventricular (AV) Valve
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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.
Is forced closed when the left ventricle begins to
contract
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prevents blood backflow into the left atrium
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Left Ventricle
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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.
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right ventricle only has to pump blood to the nearby lungs
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Left Ventricle
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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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Cardiac Cycle
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The inclusive period of time from the start of one heartbeat to
the initiation of the next.
All chambers within the heart experience alternate periods of
contraction and relaxation.
Contraction of a heart chamber is called systole.
 forces blood either into another chamber (from atrium to
ventricle) or into a blood vessel (from a ventricle into the
attached large artery)
Relaxation phase of a heart chamber is termed diastole.
 myocardium of each chamber relaxes between contraction
phases, and the chamber fills with blood
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Conduction System of the
Heart
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Exhibits autorhythmicity, meaning that the heart itself
(not external nerves) is responsible for initiating the
heartbeat.
Certain cardiac muscle fibers 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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Conduction System of the
Heart – Sinoatrial (SA) Node
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Heartbeat is initiated by the cardiac muscle
fibers of the sinoatrial (SA) node.
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Act as the pacemaker.
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located in the posterior wall of the right atrium,
adjacent to the entrance of the superior vena cava
rhythmic center that establishes the pace for
cardiac activity
Initiates impulses 70 - 80 times per minute.
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Conduction System of the Heart –
Atrioventricular (AV) Node
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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.
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located in the floor of the right atrium between the right AV
valve and the coronary sinus
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Conduction System of the Heart –
Atrioventricular (AV) Bundle
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Cardiac impulse then travels from the AV node to the
atrioventricular (AV) bundle(bundle of His).
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extends into the interventricular septum and then divides into one
right and two left bundle branches.
Conduct the impulse 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.
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Innervation of the Heart
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Innervated by the autonomic nervous system.
Consists of both sympathetic and parasympathetic components.
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referred to as the coronary plexus
Autonomic innervation by autonomic centers in the hindbrain
doesn’t initiate heartbeat, but it can increase or decrease the
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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Coronary Circulation
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Left and right coronary arteries travel in the coronary
sulcus (atrioventricular groove) of the heart to supply
the heart wall.
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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
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marginal artery
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supplies the right border of the heart
posterior interventricular artery
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supplies both the left and right ventricles
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Coronary Circulation
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Left coronary artery typically branches into
the anterior interventricular artery.
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Circumflex artery.
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also called the left anterior descending artery
supplies the anterior surface of both ventricles and
most of the interventricular septum
supplies the left atrium and ventricle
Arterial pattern can vary greatly among
individuals.
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