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18

The Cardiovascular System: The Heart

Part A

Human Anatomy & Physiology, Sixth Edition

Elaine N. Marieb

PowerPoint^® Lecture Slides prepared by Vince Austin, University of Kentucky

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Pathway of Blood Through the Heart and Lungs

Figure 18.5

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Heart Anatomy

Approximately the size of your fist
Location

Superior surface of diaphragm
Left of the midline
Anterior to the vertebral column, posterior to the sternum

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Heart Anatomy

Figure 18.1

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Coverings of the Heart: Anatomy

Pericardium – a double-walled sac around the heart composed of:

A superficial fibrous pericardium
A deep two-layer serous pericardium

The parietal layer lines the internal surface of the fibrous pericardium
The visceral layer or epicardium lines the surface of the heart
They are separated by the fluid-filled pericardial cavity

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Coverings of the Heart: Physiology

The pericardium:

Protects and anchors the heart
Prevents overfilling of the heart with blood
Allows for the heart to work in a relatively friction-free environment

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Pericardial Layers of the Heart

Figure 18.2

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Pericardial Layers of the Heart

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Heart Wall

Epicardium – visceral layer of the serous pericardium
Myocardium – cardiac muscle layer forming the bulk of the heart
Endocardium – endothelial layer of the inner myocardial surface

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External Heart: Major Vessels of the Heart (Anterior View)

Vessels returning blood to the heart include:

Superior and inferior venae cavae, coronary sinus
Right and left pulmonary veins

Vessels conveying blood away from the heart include:

Pulmonary trunk, which splits into right and left pulmonary arteries
Ascending aorta – coronary, brachiocephalic, left common carotid, and subclavian arteries

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External Heart: Anterior View

Figure 18.4b

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External Heart: Major Vessels of the Heart (Posterior View)

Vessels returning blood to the heart include:

Right and left pulmonary veins
Superior and inferior venae cavae

Vessels conveying blood away from the heart include:

Aorta
Right and left pulmonary arteries

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External Heart: Posterior View

Figure 18.4d

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Gross Anatomy of Heart: Frontal Section

Figure 18.4e

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Atria of the Heart

Atria are the receiving chambers of the heart
Blood enters right atria from superior and inferior venae cavae and coronary sinus
Blood enters left atria from pulmonary veins

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Ventricles of the Heart

Ventricles are the discharging chambers of the heart
Papillary muscles and trabeculae carneae muscles mark ventricular walls
Right ventricle pumps blood into the pulmonary trunk
Left ventricle pumps blood into the aorta

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Pathway of Blood Through the Heart and Lungs

Right atrium → tricuspid valve → right ventricle
Right ventricle → pulmonary semilunar valve → pulmonary arteries → lungs
Lungs → pulmonary veins → left atrium
Left atrium → bicuspid valve → left ventricle
Left ventricle → aortic semilunar valve → aorta
Aorta → systemic circulation

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Heart Valves

Heart valves ensure unidirectional blood flow through the heart
Atrioventricular (AV) valves lie between the atria and the ventricles
Prevent backflow into the atria when ventricles contract
Chordae tendineae anchor AV valves to papillary muscles

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Heart Valves

Aortic semilunar valve lies between the left ventricle and the aorta
Pulmonary semilunar valve lies between the right ventricle and pulmonary trunk
Semilunar valves prevent backflow of blood into the ventricles

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Heart Valves

Figure 18.8a, b

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Heart Valves

Figure 18.8c, d

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Atrioventricular Valve Function

Figure 18.9

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Semilunar Valve Function

Figure 18.10

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18

The Cardiovascular System: The Heart

Part B

Human Anatomy & Physiology, Sixth Edition

Elaine N. Marieb

PowerPoint^® Lecture Slides prepared by Vince Austin, University of Kentucky

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Cardiac Muscle Contraction

Heart muscle:

Is stimulated by nerves and is self-excitable (automaticity)
Contracts as a unit

Cardiac muscle contraction is similar to skeletal muscle contraction

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Heart Physiology: Sequence of Excitation

Sinoatrial (SA) node generates impulses about 75 times/minute
Atrioventricular (AV) node delays the impulse approximately 0.1 second
Impulse passes from atria to ventricles via the atrioventricular bundle (bundle of His)

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Heart Physiology: Sequence of Excitation

Figure 18.14a

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Heart Physiology: Sequence of Excitation

AV bundle splits into two pathways in the interventricular septum as the right and left bundle branches

Bundle branches carry the impulse toward the apex of the heart
Purkinje fibers carry the impulse to the heart apex and ventricular walls

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Electrocardiography

Electrical activity is recorded by electrocardiogram (ECG)
P wave corresponds to depolarization of SA node and therefore, contraction of the atria
QRS complex corresponds to depolarization of the AV node and therefore, contraction of the ventricles
T wave corresponds to ventricular repolarization
Atrial repolarization record is masked by the larger QRS complex

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Electrocardiography

Figure 18.16

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Heart Excitation Related to ECG

Figure 18.17

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Heart Sounds

Heart sounds (lub-dup) are associated with closing of heart valves

First sound occurs as AV valves close and signifies beginning of systole
Second sound occurs when SL valves close at the beginning of ventricular diastole

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Heart Sounds

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Cardiac Cycle

Cardiac cycle refers to all events associated with blood flow through the heart

Systole – contraction of heart muscle
Diastole – relaxation of heart muscle

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Phases of the Cardiac Cycle

Figure 18.20

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Cardiac Output (CO) and Reserve

CO is the amount of blood pumped by each ventricle in one minute
CO is the product of heart rate (HR) and stroke volume (SV)
HR is the number of heart beats in one minute
SV is the amount of blood pumped out by a ventricle each beat

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Cardiac Output: Example

CO (ml/min) = HR (75 beats/min) x SV (70 ml/beat)
CO = 5250 ml/min (5.25 L/min)

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Developmental Aspects of the Heart

Fetal heart structures that bypass pulmonary circulation

Foramen ovale connects the two atria

Ductus arteriosus connects pulmonary trunk and the aorta

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Patent Foramen Ovale (PFO)

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Patent Ductus Arteriosus (PDA)

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Ventricular Septal Defect

Figure 18.25

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Tetralogy of Fallot