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prepared by
Janice Meeking,
Mount Royal College
CHAPTER
18
The
Cardiovascular
System: The
Heart: Part A
Copyright © 2010 Pearson Education, Inc.
The Heart
• Beats over 100,000 times a day
• Normal Resting Heart Rate 60 – 100 beats per minute (too
slow bradycardia – too fast tachycardia)
• Approximately the size of a fist
• Location
• In the mediastinum between second rib and fifth intercostal
space
• On the superior surface of diaphragm
• Two-thirds to the left of the midsternal line
• Anterior to the vertebral column, posterior to the sternum
• Enclosed in pericardium, a double-walled sac
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Midsternal line
2nd rib
Sternum
Diaphragm
(a)
Point of
maximal
intensity
(PMI)
PMI generally found at 4th – 5th ICS at midclavicular line
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Figure 18.1a
Superior
vena cava
Aorta
Parietal
pleura (cut)
Pulmonary
trunk
Left lung
Pericardium
(cut)
Diaphragm
Apex of
heart
(c)
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Figure 18.1c
Pericardium
• Superficial fibrous pericardium
• Protects, anchors, and prevents overfilling
(overdistention)
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Pericardium
• Deep two-layered serous pericardium
• Parietal layer lines the internal surface of the
fibrous pericardium
• Visceral layer (epicardium) on external surface
of the heart
• Separated by fluid-filled pericardial cavity
(decreases friction)
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Pulmonary
trunk
Pericardium
Myocardium
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Fibrous pericardium
Parietal layer of
serous pericardium
Pericardial cavity
Epicardium
(visceral layer Heart
of serous
wall
pericardium)
Myocardium
Endocardium
Heart chamber
Figure 18.2
Layers of the Heart Wall
1. Epicardium—visceral layer of the serous
pericardium
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Layers of the Heart Wall
2. Myocardium
•
Spiral bundles of cardiac muscle cells
•
Fibrous skeleton of the heart: crisscrossing,
interlacing layer of connective tissue
•
Anchors cardiac muscle fibers
•
Supports great vessels and valves
•
Limits spread of action potentials to
specific paths
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Layers of the Heart Wall
3. Endocardium is continuous with endothelial
lining of blood vessels
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Pulmonary
trunk
Pericardium
Myocardium
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Fibrous pericardium
Parietal layer of
serous pericardium
Pericardial cavity
Epicardium
(visceral layer Heart
of serous
wall
pericardium)
Myocardium
Endocardium
Heart chamber
Figure 18.2
Cardiac
muscle
bundles
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Figure 18.3
Chambers
• Four chambers
• Two atria
• Separated internally by the interatrial
septum
• Coronary sulcus (atrioventricular groove)
encircles the junction of the atria and
ventricles
• Auricles increase atrial volume
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Chambers
• Two ventricles
• Separated by the interventricular septum
• Anterior and posterior interventricular sulci
mark the position of the septum externally
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Brachiocephalic trunk
Superior vena cava
Right pulmonary
artery
Ascending aorta
Pulmonary trunk
Right pulmonary
veins
Right atrium
Right coronary artery
(in coronary sulcus)
Anterior cardiac vein
Right ventricle
Right marginal artery
Small cardiac vein
Inferior vena cava
(b) Anterior view
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Left common carotid
artery
Left subclavian artery
Aortic arch
Ligamentum arteriosum
Left pulmonary artery
Left pulmonary veins
Auricle of
left atrium
Circumflex artery
Left coronary artery
(in coronary sulcus)
Left ventricle
Great cardiac vein
Anterior interventricular
artery (in anterior
interventricular sulcus)
Apex
Figure 18.4b
Atria: The Receiving Chambers
• Walls are ridged by pectinate muscles
• Vessels entering right atrium
• Superior vena cava
• Inferior vena cava
• Coronary sinus
• Vessels entering left atrium
• Right and left pulmonary veins
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Ventricles: The Discharging Chambers
• Walls are ridged by trabeculae carneae
• Papillary muscles project into the ventricular
cavities
• Vessel leaving the right ventricle
• Pulmonary trunk
• Vessel leaving the left ventricle
• Aorta
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Aorta
Superior vena cava
Right pulmonary
artery
Pulmonary trunk
Right atrium
Right pulmonary
veins
Fossa ovalis
Pectinate muscles
Tricuspid valve
Right ventricle
Chordae tendineae
Trabeculae carneae
Inferior vena cava
Left pulmonary
artery
Left atrium
Left pulmonary
veins
Mitral (bicuspid)
valve
Aortic valve
Pulmonary valve
Left ventricle
Papillary muscle
Interventricular
septum
Epicardium
Myocardium
Endocardium
(e) Frontal section
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Figure 18.4e
Pathway of Blood Through the Heart
• The heart is two side-by-side pumps
• Right side is the pump for the pulmonary
circuit
• Vessels that carry blood to and from the
lungs
• Left side is the pump for the systemic circuit
• Vessels that carry the blood to and from all
body tissues
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Pulmonary
Circuit
Pulmonary arteries
Venae cavae
Capillary beds
of lungs where
gas exchange
occurs
Pulmonary veins
Aorta and branches
Left atrium
Left ventricle
Right atrium
Right ventricle
Oxygen-rich,
CO2-poor blood
Oxygen-poor,
CO2-rich blood
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Heart
Systemic
Circuit
Capillary beds of all
body tissues where
gas exchange occurs
Figure 18.5
Pathway of Blood Through the Heart
• Right atrium  tricuspid valve  right
ventricle
• Right ventricle  pulmonary semilunar valve
 pulmonary trunk  pulmonary arteries 
lungs
PLAY
Animation: Rotatable heart (sectioned)
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Pathway of Blood Through the Heart
• Lungs  pulmonary veins  left atrium
• Left atrium  bicuspid valve  left ventricle
• Left ventricle  aortic semilunar valve 
aorta
• Aorta  systemic circulation
PLAY
Animation: Rotatable heart (sectioned)
Copyright © 2010 Pearson Education, Inc.
Pathway of Blood Through the Heart
• Equal volumes of blood are pumped to the
pulmonary and systemic circuits
• Pulmonary circuit is a short, low-pressure
circulation
• Systemic circuit blood encounters much
resistance in the long pathways
• Anatomy of the ventricles reflects these
differences
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Left
ventricle
Right
ventricle
Interventricular
septum
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Figure 18.6
Coronary Circulation
• The functional blood supply to the heart
muscle itself
• Arterial supply varies considerably and
contains many anastomoses (junctions)
among branches
• Collateral routes provide additional routes for
blood delivery
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Coronary Circulation
• Arteries
• Right and left coronary (in atrioventricular
groove), marginal, circumflex, and anterior
interventricular arteries
• Veins
• Small cardiac, anterior cardiac, and great
cardiac veins
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Superior
vena cava
Anastomosis
(junction of
vessels)
Right
atrium
Aorta
Pulmonary
trunk
Left atrium
Left
coronary
artery
Circumflex
artery
Right
coronary
Left
artery
ventricle
Right
ventricle
Anterior
Right
interventricular
marginal Posterior
artery
artery
interventricular
artery
(a) The major coronary arteries
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Figure 18.7a
Superior
vena cava
Anterior
cardiac
veins
Great
cardiac
vein
Coronary
sinus
Small cardiac vein
Middle cardiac vein
(b) The major cardiac veins
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Figure 18.7b
Aorta
Left pulmonary
artery
Superior vena cava
Left pulmonary
veins
Auricle of left
atrium
Left atrium
Great cardiac
vein
Right pulmonary veins
Posterior vein
of left ventricle
Left ventricle
Apex
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Right pulmonary artery
Right atrium
Inferior vena cava
Coronary sinus
Right coronary artery
(in coronary sulcus)
Posterior
interventricular
artery (in posterior
interventricular sulcus)
Middle cardiac vein
Right ventricle
(d) Posterior surface view
Figure 18.4d
Homeostatic Imbalances
• Angina pectoris
• Thoracic pain caused by a fleeting deficiency
in blood delivery to the myocardium
• Cells are weakened
• Myocardial infarction (heart attack)
• Prolonged coronary blockage
• Areas of cell death are repaired with
noncontractile scar tissue
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Heart Valves
• Ensure unidirectional blood flow through the heart
• Atrioventricular (AV) valves
• Prevent backflow into the atria when ventricles
contract
• Tricuspid valve (right)
• Mitral valve (left)
• Chordae tendineae anchor AV valve cusps to
papillary muscles
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Heart Valves
• Semilunar (SL) valves
• Prevent backflow into the ventricles when
ventricles relax
• Aortic semilunar valve
• Pulmonary semilunar valve
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Myocardium Pulmonary valve
Aortic valve
Tricuspid
Area of cutaway
(right atrioventricular)
Mitral valve
valve
Tricuspid valve
Mitral
(left atrioventricular)
valve
Aortic
valve
Myocardium
Tricuspid
(right atrioventricular)
valve
Mitral
(left atrioventricular)
valve
Aortic valve
Pulmonary
valve
Fibrous
skeleton
(a)
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Pulmonary valve
Aortic valve
Area of cutaway
(b)
Pulmonary
valve
Mitral valve
Tricuspid
valve
Anterior
Figure 18.8a
Myocardium
Tricuspid
(right atrioventricular)
valve
Mitral
(left atrioventricular)
valve
Aortic
valve
Pulmonary
valve
Pulmonary valve
Aortic valve
Area of cutaway
(b)
Mitral valve
Tricuspid valve
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Figure 18.8b
Pulmonary
valve
Aortic
valve
Area of
cutaway
Mitral
valve
Tricuspid
valve
Chordae tendineae
attached to tricuspid valve flap
(c)
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Papillary
muscle
Figure 18.8c
Opening of inferior
vena cava
Tricuspid valve
Mitral valve
Chordae
tendineae
Myocardium
of right
ventricle
Myocardium
of left ventricle
Papillary
muscles
(d)
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Interventricular
septum
Pulmonary
valve
Aortic valve
Area of
cutaway
Mitral valve
Tricuspid
valve
Figure 18.8d
1 Blood returning to the
Direction of
blood flow
heart fills atria, putting
pressure against
atrioventricular valves;
atrioventricular valves are
forced open.
Atrium
Cusp of
atrioventricular
valve (open)
2 As ventricles fill,
atrioventricular valve flaps
hang limply into ventricles.
Chordae
tendineae
3 Atria contract, forcing
additional blood into ventricles.
Ventricle
Papillary
muscle
(a) AV valves open; atrial pressure greater than ventricular pressure
Atrium
1 Ventricles contract, forcing
blood against atrioventricular
valve cusps.
2 Atrioventricular valves
close.
3 Papillary muscles
contract and chordae
tendineae tighten,
preventing valve flaps
from everting into atria.
Cusps of
atrioventricular
valve (closed)
Blood in
ventricle
(b) AV valves closed; atrial pressure less than ventricular pressure
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Figure 18.9
Aorta
Pulmonary
trunk
As ventricles
contract and
intraventricular
pressure rises,
blood is pushed up
against semilunar
valves, forcing them
open.
(a) Semilunar valves open
As ventricles relax
and intraventricular
pressure falls, blood
flows back from
arteries, filling the
cusps of semilunar
valves and forcing
them to close.
(b) Semilunar valves closed
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Figure 18.10
Histology and Physiology of Cardiac Muscle
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Requirements of Cardiac Muscle
1. Have considerable endurance – the heart
beats over 100,000 beats per day (75 beats per
minute x 1440 minutes in a day)
2. Both atria must contract as one unit and
both ventricles must contract as one unit –
even though they are made of separate
individual small cells (cells can only get so big
due to the surface to volume relationship
problem)
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Endurance
1. The cardiac muscle cells are smaller than skeletal muscle
cells giving good surface to volume relationship- thus
allowing more oxygen and nutrients to enter and waste to
leave
2. More myoglobin – red substance akin to hemoglobin that
holds reserve oxygen in the cell (more myoglobin than dark –
endurance skeletal muscle)
3. Slow ATPase – the faster ATP is broken down the more
energy that is loss as heat instead being put to good use.
Thus the slower ATP is broken down to ADP – more useful
energy that is harnessed.
4. Heart muscle uses almost exclusively aerobic metabolism
(cannot tolerate too much ischemia)– but can burn lactic acid
released by skeletal muscle
5. Lots of mitochondria
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Cardiac Muscle must have better endurance
than long endurance skeletal muscle
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Cardiac Metabolism
• The heart is so tuned to aerobic metabolism that it is unable
to pump sufficiently in ischemic conditions. At basal
metabolic rates, about 1% of energy is derived from
anaerobic metabolism. This can increase to 10% under
moderately hypoxic conditions, but, under more severe
hypoxic conditions, not enough energy can be liberated by
lactate production to sustain ventricular contractions.
• Under basal aerobic conditions, 60% of energy comes from
fat (free fatty acids and triglycerides), 35% from
carbohydrates, and 5% from amino acids and ketone bodies.
However, these proportions vary widely according to
nutritional state. For example, during starvation, lactate can
be recycled by the heart.
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Atria and Ventricles Must act as single Units
• It is essential that both atria must contract at the
same time in order to adequately squeeze the blood
into the two ventricles.
• Likewise it is important for both ventricles to contract
at the same time in order to adequately squeeze the
both into their respective outflow pipes (pulmonary
artery from right ventricle and aorta from left
ventricle)
• The problem is that the atria and ventricles must be
comprised of several small cells and not one big cell
for the atria and one for the ventricles – thus the
individual cells must physiologically lock together to
form a physiologic unit – syncytium.
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Cardiac muscle cell mechanisms to form a
syncytium
1. Cardiac muscle cells are branched – the
anatomical feature allows the action potential
signals to travel along several branches at the
same time going to several cardiac muscle cells
at the same time and those cells in turn branch
doing the same thing.
2. Hook the cells together by gap junctions – the
intercellular connection allows faster travel of
impulses between the cells.
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Microscopic Anatomy of Cardiac Muscle
• Cardiac muscle cells are striated, short, fat,
branched, and interconnected
• Connective tissue matrix (endomysium)
connects to the fibrous skeleton
• T tubules are wide but less numerous; SR is
simpler than in skeletal muscle (more
dependence on extracellular calcium)
• Numerous large mitochondria (25–35% of cell
volume)
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Table 9.3.1
Cardiac Muscle Cell Intercellular Connections
• Intercalated discs: junctions between cells
anchor cardiac cells
• Desmosomes prevent cells from separating
during contraction
• Gap junctions allow ions to pass; electrically
couple adjacent cells
• Heart muscle behaves as a functional
syncytium
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Nucleus
Intercalated discs
Cardiac muscle cell
Light microscope
see intercalated
discs
Gap junctions
Desmosomes
In Electron
Microscope
can resolute
Intercalated
Discs into
Gap junctions
And Desmosomes
(a)
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Figure 18.11a
Cardiac
muscle cell
Mitochondrion
Intercalated
disc
Nucleus
T tubule
Mitochondrion
Sarcoplasmic
reticulum
Z disc
Nucleus
Sarcolemma
(b)
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I band
A band
I band
Figure 18.11b