Download The Heart The cardiovascular system is divided into two circuits The

The cardiovascular system is divided
into two circuits
• Pulmonary circuit
The Heart
– Carries blood to and from the lungs
• Systemic circuit
– Carries blood to and from the rest of the body
Chapter 20
• Vessels carry the blood through the circuits
– Arteries carry blood away from the heart
– Veins carry blood to the heart
– Capillaries permit gas, nutrient, and waste,
transfer
The Heart
• Despite its impressive workload, the heart is a small
organ, roughly the size of a clenched fist
• The heart has four chambers, two associated with
each circuit
• The
Th right
i h atrium
i
receives
i
blood
bl d from
f
the
h systemic
i
circuit and passes it to the right ventricle, which
pumps blood to the pulmonary circuit
• The left atrium receives blood from the pulmonary
circuit and passes it to the left ventricle, which pumps
blood to the systemic circuit
The Heart
• The heart is located in the anterior chest wall directly
posterior to the sternum
• The heart is surrounded by the pericardial cavity,
which is lined with the pericardium
• The pericardium is lined with a serous membrane
which can be subdivided into the visceral pericardium
and parietal pericardium
• The visceral pericardium, or epicardium, covers and
adheres closely to the surface of the heart
• The parietal pericardium lines the inner surface of the
pericardial sac, or fibrous pericardium, which
stabilizes the position of the heart
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Superficial Anatomy of the Heart
• The four chambers of the heart are two atria
and two ventricles
• The coronary sulcus is a deep groove that
marks the border between the atria and
ventricles
• The anterior interventricular sulcus and
posterior interventricular sulcus, mark the
boundary between the left and right ventricles
The Heart Wall
• Components of the heart wall include
– The epicardium, the visceral pericardium that
covers the surface of the heart
– Thee myocardium,
yoca d u , the
t e muscular
uscu a wall
wa of
o the
t e heart,
ea t,
which forms both the atria and ventricles, and also
contains blood vessels and nerves
– The endocardium, a layer of simple squamous
epithelium, that lines the inner surface of the
heart, including the valves
Internal Anatomy
• The atria are separated by the interatrial
septum, the ventricles separated by the
interventricular septum
• The atrioventricular (AV) valves are folds of
fibrous tissue that permit blood flow in only
one direction, from the atria to the ventricles
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The Right Atrium
The Right Ventricle
• The right atrium receives blood from the
systemic circuit via the superior vena cava and
inferior vena cava
p
vena cava carries blood from the
• The superior
head, neck, upper limbs, and chest
• The inferior vena cava carries blood from the
rest of the body
• The coronary veins of the heart return blood to
the heart via the coronary sinus
• Blood travels from the right atrium to the right
ventricle through the right AV or tricuspid valve
• The free edges of the fibrous flaps of the valve are
attached to the ventricular wall by the chordae
tendineae, which pprevent the flaps
p of the valve from
swinging into the atrium when the ventricle contracts
• The superior end of the right ventricle tapers to the
conus arteriosus and ends at the pulmonary semilunar
valve
• From the right ventricle blood flows into the
pulmonary trunk
The Left Atrium
The Left Ventricle
• Blood returns from the lungs via the left and
right pulmonary veins and enters the left
atrium
• From the left atrium blood passes into the left
ventricle via the left AV, bicuspid, or mitral
valve
• Despite the fact that their blood volumes are
equal, the left ventricle is much larger than the
right
• The thick muscular walls of the left ventricle
account for this size difference and enable the
left ventricle to develop sufficient pressure to
push blood through the systemic circuit
• Blood leaves the left ventricle through the
aortic semilunar valve and flows into the
ascending aorta
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Connective Tissues & The Fibrous
Skeleton of The Heart
• Connective tissue fibers of the heart
– Provide physical support and elasticity
– Distribute the force of contraction
– Prevent
P
overexpansion
i
• The fibrous skeleton
– Stabilizes the heart valves
– Physically isolates atrial from ventricular cells
Musculature of the Heart
Blood Supply to the Heart
• The coronary circulation supplies blood to the
tissues of the heart
• Arteries include the right and left coronary
arteries marginal arteries,
arteries,
arteries anterior and
posterior interventricular arteries, and the
circumflex artery
• Veins include the great cardiac vein, anterior
and posterior cardiac veins, the middle cardiac
vein, and the small cardiac vein
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The Heartbeat
• Two types of cardiac muscle cells are involved
in the normal heartbeat
– Cells of the conducting system control and
coordinate the heartbeat
– Contractile cells produce powerful contractions
that propel the blood
The Conducting System
• The conducting system is responsible for
initiating and distributing the stimulus to
contract
• It includes:
– The
h sinoatrial
i
i l (SA) node
d
– The atrioventricular (AV) node
– Conducting cells
• Atrial conducting cells are found in internodal
pathways
• Ventricular conducting cells consist of the AV bundle,
bundle branches, and Purkinje fibers
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Impulse Conduction through the
heart
• Cells in the SA node spontaneously depolarize
more rapidly than other cells of the conducting
system and thus begin the action potential
• The stimulus spreads to the AV node where it
is delayed briefly
• The impulse then travels through ventricular
conducting cells and is distributed by Purkinje
fibers
The electrocardiogram (ECG or
EKG)
• An EKG is a recording of the electrical events
occurring during the cardiac cycle
• The EKG shows several important features
– A P wave accompanies the depolarization of the atria
– The QRS complex appears as the ventricles
depolarize and contract
– The T wave indicates ventricular repolarization
Contractile Cells
• The Purkinje fibers distribute the stimulus to
the contractile cells, which form the bulk of
the atrial and ventricular walls
• Like skeletal muscle,
muscle the action potential leads
to the release of Ca2+ and the binding of Ca2+
to troponin initiates the contraction
• The contraction is of considerably longer
duration in cardiac muscle and called Plateau
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The Cardiac Cycle
• The Cardiac Cycle is the period between the
start of one heartbeat and the beginning of the
next
• During
g each cardiac cycle
y
– Each heart chamber goes through systole
(contraction) and diastole (relaxation)
– Correct pressure relationships are dependent on
the careful timing of contractions
Heart sounds
• Auscultation – listening to heart sound via
stethoscope
• There are four heart sounds
– S1 – “lubb”
lubb caused by the closing of the AV valves
– S2 – “dupp” caused by the closing of the semilunar
valves
– S3 – a faint sound associated with blood flowing into
the ventricles
– S4 – another faint sound associated with atrial
contraction
Stroke Volume and Cardiac Output
• Cardiac output – the amount of blood pumped by
each ventricle in one minute
• Cardiac output equals heart rate times stroke
volume
• When needed HR can increase by 250% and SV
can double
CO
Cardiac output
(ml/min)
=
HR
Heart rate
(beats/min)
X
SV
Stroke
volume
(ml/beat)
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Factors Affecting Cardiac Output
Factors Affecting Cardiac Output
Exercise and Cardiac Output
• Heavy exercise can increase output by 300500 percent
– Trained athletes may increase cardiac output by
700 percent
• Cardiac reserve
– The difference between resting and maximal
cardiac output
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