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© 2012 Pearson Education, Inc.

21 The Cardiovascular

System: The Heart


Introduction

• The heart keeps the blood in motion

• beats about 100,000 times per day

• pumps about 1.5 millions gallons of blood per year

• pumps between 5 and 30 liters of blood per minute


An Overview of the Cardiovascular System

• The heart is about the

size of one’s clenched

fist

• The heart consists of

four chambers

• Two atria

• Two ventricles

• The heart pumps

blood into two circuits

• Pulmonary circuit

• Systemic circuit


Figure 21.2a Location of the Heart in the Thoracic Cavity

Anterior view of the open chest cavity showing the position

of the heart and major vessels relative to the lungs. The

sectional plane indicates the orientation of part (c).

Apex of

heart

Parietal pericardium

(cut)

Base of

heart

Diaphragm

Right lung

Trachea

Thyroid gland

First rib (cut)

Left lung


The Pericardium

• Pericardium is the serous membrane lining the pericardial cavity

• The pericardial membrane forms two layers • Visceral pericardium (also called the epicardium)

• Parietal pericardium • The parietal pericardium is reinforced by a layer

called the fibrous pericardium

• The parietal pericardium and fibrous pericardium constitute the pericardial sac


Structure of the Heart Wall

• The walls of the heart

consist of three layers:

• Epicardium

• External surface

• Myocardium

• Consists of cardiac

muscle cells

• Endocardium

• Internal surface


Orientation and Superficial Anatomy of Heart

• The heart lies slightly to the left of midline

• Located in the mediastinum

• The base is the superior portion of the heart

• The apex is the inferior portion of the heart

• The heart sits at an oblique angle

• The heart is rotated slightly toward the left



• The four chambers of the heart can be

identified by sulci on the external surface

• Interatrial sulcus separates the left and right

atria

• Coronary sulcus separates the atria and the

ventricles

• Anterior interventricular sulcus separates the

left and right ventricles

• Posterior interventricular sulcus also

separates the left and right ventricles


Figure 21.5a Superficial Anatomy of the Heart, Part I

Anterior view of the heart and great

vessels

Fat in

anterior

interventricular

sulcus LEFT

VENTRICLE

RIGHT

VENTRICLE

RIGHT

ATRIUM

Fat in

coronary

sulcus

Auricle

of right

atrium

Superior

vena cava

Ascending

aorta

Brachiocephalic trunk

Left common carotid artery

Auricle of

left atrium

Pulmonary

trunk

Left pulmonary

artery

Descending

aorta

Ligamentum

arteriosum

Arch of aorta

Left subclavian artery


Figure 21.5b Superficial Anatomy of the Heart, Part I

Posterior view of the heart and great

vessels

LEFT

VENTRICLE

Fat in

coronary

sulcus

Coronary

sinus

Left pulmonary artery

Left pulmonary veins

RIGHT

VENTRICLE

LEFT

ATRIUM

RIGHT

ATRIUM

Arch of aorta

Right pulmonary

artery

Superior

vena cava

Right

pulmonary

veins (superior

and inferior)

Inferior

vena cava

Fat in posterior

interventricular sulcus



• The left and right atria

• Positioned superior to the coronary sulcus

• Both have thin walls

• Both consist of expandable extensions called

auricles

• The left and right ventricles

• Positioned inferior to the coronary sulcus

• Both have thicker walls


Internal Anatomy and Organization of the

Heart

• The Right Atrium

• Receives

deoxygenated blood

via the superior vena

cava, inferior vena

cava, and coronary

sinus

• Consists of pectinate

muscles

• Contains the fossa

ovalis (fetal remnant of

the foramen ovale)



Heart

• The Right Ventricle

• Receives deoxygenated

blood from the right atrium

• Blood enters the right

ventricle by passing

through the tricuspid

valve

• The AV valve has chordae

tendineae connecting to the

three cusps and to three

papillary muscles

• Trabeculae carneae



Heart

• The internal surface of the right ventricle consists of:

• Right ventricle has a thin wall since it only pumps blood through the pulmonary circuit

• Blood leaves the right ventricle by passing through the pulmonary semilunar valves

• Blood leads to the pulmonary trunk, then to the right and left pulmonary arteries

• Blood enters the lungs



Heart

• The Left Atrium

• Receives oxygenated

blood from the lungs

via the right and left

pulmonary veins

• Does not have

pectinate muscles



Heart

• The Left Ventricle • Receives oxygenated

blood from the left atrium

• Blood passes through the bicuspid valve

• The AV valve has chordae tendineae connecting to the two cusps and to two papillary muscles

• Trabeculae carneae



Heart

• The Left Ventricle • Has the thickest wall

• Needed for strong

contractions to pump

blood throughout the

entire systemic circuit

• Blood leaves the left

ventricle by passing

through the aortic

semilunar valves and

enters the ascending aorta

• Blood then travels to the

aortic arch and then to all

body parts (systemic)


Pathway of blood flow • (from tissues) dO2 blood

enters R. atrium via superior & inferior vena cava tricuspid valve R. ventricle pulmonary semilunar valve pulmonary (trunk) arteries lungs drop off dO2 blood & pick up O2 blood

• (from lungs) O2 blood enters L. atrium via pulmonary veins bicuspid valve L. ventricle aortic semilunar valve aorta rest of the body


Figure 21.7b Sectional Anatomy of the Heart, Part I

Diagrammatic frontal section through the relaxed heart shows the major

landmarks and the path of blood flow through the atria and ventricles (arrows).

Inferior vena cava

RIGHT VENTRICLE

Papillary muscle

Chordae tendineae

Cusp of right AV

(tricuspid) valve

Conus arteriosus

Pectinate muscles

RIGHT ATRIUM

Opening of

coronary sinus

Ascending

aorta

Right

pulmonary

arteries

Fossa ovalis

Superior

vena cava

Brachiocephalic

trunk

Aortic arch

LEFT

ATRIUM

Left common carotid artery

Left subclavian artery

Ligamentum arteriosum

Pulmonary trunk

Pulmonary valve

Left pulmonary

arteries

Left pulmonary

veins

Interatrial septum

Aortic valve

Cusp of left AV

(mitral) valve

LEFT VENTRICLE

Interventricular

septum

Trabeculae

carneae

Moderator

band

Descending

aorta



Heart

• Function of the Atrioventricular Valves

• Each AV valve lie between the atria and the ventricles

• AV valves prevent backflow into the atria when ventricles contract

• Chordae tendineae anchor AV valves to papillary muscles



Heart

• Function of the Semilunar

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



Heart

• Function of the Heart

Valves

• When the ventricles

are relaxed, the AV

valves are opened and

the semilunar valves

are closed. The

chordae tendineae are

loose, and the

papillary muscles are

relaxed.



Heart

• Function of the Heart

Valves

• When the ventricles

are contracting, the AV

valves are closed and

the semilunar valves

are opened.



Heart

• Coronary Blood

Vessels

• Supplies blood to the

heart muscles

• Major coronary

vessels

• Right coronary artery

(RCA)

• Left coronary artery

(LCA)

• Cardiac veins



Heart

• Right Coronary Artery

• Passes between the

right auricle and

pulmonary trunk

• Major branches off the

right coronary artery:

• Atrial branches

• Right marginal branch

• Posterior

interventricular

branch (back)



Heart

• Left Coronary Artery

• Major branches off the

left coronary artery

• Circumflex branch

• Anterior

interventricular

branch



Heart

• The Cardiac Veins

• Posterior vein of the

left ventricle

• Middle cardiac vein

• Small cardiac vein

• Anterior cardiac

veins (front)

• All the above drain into

the great cardiac vein

• Great cardiac vein

drains into the

coronary sinus


The Cardiac Cycle

• The cardiac cycle consists of alternate

periods of contraction and relaxation

• Contraction is systole

• Blood is ejected into the ventricles

• Blood is ejected into the pulmonary trunk and the

ascending aorta

• Relaxation is diastole

• Chambers are filling with blood

• Normal BP ~ 120/80

• Bradycardia: slow heart rate

• Tachycardia: rapid heart rate


Intrinsic Conduction System

• Nerve signals to the heart controlling heart contraction

• Sinoatrial node (SA node) = pacemaker

• Atrioventricular node (AV node) via internodal pathways

• AV bundle

• Right and Left bundle branches

• Purkinje fibers

• Impulses are then conveyed to the ventricular myocardium


Figure 21.12b The Conducting System of the Heart

The movement of the contractile stimulus through the heart is shown in STEPS 1–5.

SA node activity and atrial activation begin.

SA node

Time 0

Stimulus spreads across the atrial surfaces and reaches the AV node. AV node

Elapsed time 50 msec


AV bundle

Bundle branches

There is a 100 msec delay at the AV node. Atrial contraction begins.

The impulse travels along the interventricular septum within the AV bundle and the bundle branches to the Purkinje fibers and, via the moderator band, to the papillary muscles of the right ventricle.

Moderator band Elapsed time 175 msec


The impulse is distributed by Purkinje fibers and relayed throughout the ventricular myocardium. Atrial contraction is completed, and ventricular contraction begins.

Purkinje fibers


The Cardiac Cycle

• Autonomic Control of Heart Rate

• The pacemaker sets the heart rate but can be

altered

• Impulses from the autonomic nervous system

modify the pacemaker activity

• Nerves associated with the ANS innervate the:

• SA node

• AV node

• Cardiac cells

• Smooth muscles in the cardiac blood vessels


The Cardiac Cycle

• Autonomic Control of

Heart Rate • Norepinephrine from the

Sympathetic system of the

ANS causes:

• An increase in the heart

rate

• An increase in the force

of contractions

• Acetylcholine from the

Parasympathetic system of

the ANS causes:

• A decrease in the heart

rate

• A decrease in the force

of contractions

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