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The Heart
Chapter 20
INTRODUCTION
• The cardiovascular system consists of the
blood, heart, and blood vessels.
• Cardiology - is the Branch of Science involved
in the study of the heart and the diseases
associated with it .
Size, Shape and Location of
the heart
• Size: equivalent to a person’s closed fist.
• Shape: cone-shaped, pointed apex is inferior in
position, flat base is superior.
• Location: sits above the diaphragm, two-thirds of its
mass is to the left of the midline.
Location of the heart (contd)
•Heart is situated between the lungs in
the mediastinum.
•Heart is protected on the anterior side
the by the sternum and on the posterior
side by the vertebrae.
Protective layers of the heart
• Pericardium – 2 layered sac that surrounds and
protects the heart.
• outer fibrous pericardium - made up of dense irregular
connective tissue, protects and anchors the heart, prevents
overstretching
• inner serous pericardium- is composed of
• Outer parietal layer and
• inner visceral layer (also known as epicardium)
Pericardium
Between the parietal and visceral layers of the
serous pericardium is the pericardial cavity,
filled with pericardial fluid that reduces
friction between the two membranes.
An inflammation of the pericardium is known as
pericarditis.
Layers of Heart Wall
Wall of the heart
has three layers:
1. Epicardium
– visceral layer of
serous
pericardium
2. Myocardium
– cardiac muscle
layer is the bulk
of the heart
3. Endocardium
– chamber lining &
valves
Exernal Anatomy of the Heart
Chambers and Sulci of the Heart
• Four chambers
– 2 upper atria
– 2 lower ventricles
• Sulci - grooves on surface of heart containing
blood vessels and fat
– coronary sulcus
• Separates the atria from the ventricles
– anterior interventricular sulcus
• marks the boundary between the
ventricles anteriorly
– posterior interventricular sulcus
• marks the boundary between the
ventricles posteriorly
Chambers and Sulci
Anterior View
Posterior View
Cardiac Muscle Histology
• Cardiac muscle fibers are
long, parallel and
branched.
• Single centrally located
nucleus
• Striations present
• Intercalated discs with
gap junctions
• involuntary
Right
Atrium
• Has a flap like extension called auricle which increase surface
area.
• Receives blood from 3 veins
– superior vena cava, inferior vena cava and coronary sinus
• Separated from the left atrium by the interatrial septum
– fetus has an opening called foramen ovale in the interatrial
septum which closes after birth and is called the fossa
ovalis.
• Blood flows through the right atrioventricular valve (AV valve or
the tricuspid valve) into the right ventricle.
Right
Ventricle
• Inside of the right ventricle is composed of ridges called trabeculae
carneae (raised bundles of cardiac muscle), cone shaped
traberculae carnae are called papillary muscles.
• Cusps of the AV valves are connected to the papillary muscles by
cords called chordae tendineae
• Interventricular septum: partitions the right and left ventricles
• Blood flows from the right ventricle into the pulmonary trunk by
Pulmonary semilunar valve.
Left
Atrium
• Forms most of the base of the heart
• Receives blood from lungs via 4 pulmonary veins (2
right + 2 left)
• Blood flows into the left atrioventricular valve (AV
valve or the bicuspid valve) into the left ventricle.
– has two cusps
– Also known as the mitral valve.
Left
Ventricle
• Forms the apex of heart
• Chordae tendineae anchor bicuspid valve to papillary muscles (also has
trabeculae carneae like right ventricle)
• Aortic semilunar valve:
– blood passes through valve into the ascending aorta
– just above valve are the openings to the coronary arteries
– In fetus, a temporary blood vessel called ductus arteriosus, connects
pulmonary trunk to aorta. The ductus arteriosus closes shortly after
birth, leaving a remnant ligamentum arteriosum.
Myocardial
Thickness and
Function
• The thickness of the myocardium of the four chambers varies
according to the function of each chamber.
– The atria walls are thinner in contrast to the ventricles because
they deliver blood short distance.
– The left ventricle walls are thicker than the right ventricle because
they pump blood through the body where the resistance to blood
flow is greater.
HEART VALVES AND CIRCULATION
OF BLOOD
• Valves open and close in response to
pressure changes as the heart contracts and
relaxes.
• Prevent backflow of blood into heart
chambers.
• Valves have 2-3 flaps or cusps. The cusps of
the AV valve are connected to tendon like
cords called chordae tendinae which in turn
are connected to the traberculae carnae by
papillary muscles.
• Two types: Atrioventricular valves and
Semilunar valves.
Atrioventricular Valves
• When Atria contract, the ventricular pressure is lower than
atrial pressure,
– chordae tendineae to slack and papillary muscles are
relaxed.
– the AV valves open.
• when ventricles contract:
– valve cusps closed, chordae tendinae are pulled taut
and papillary muscles contract to pull cords and
prevent cusps from everting
– A-V valves close preventing backflow of blood into atria
Semilunar Valves
• SL valves open with ventricular contraction
– allow blood to flow into pulmonary trunk and aorta
• SL valves close with ventricular relaxation
– prevents blood from returning to ventricles, blood fills
valve cusps, tightly closing the SL valves
Heart valve disorders
• Stenosis is a narrowing of a heart valve which
restricts blood flow.
• Insufficiency or incompetence is a failure of a
valve to close completely.
REVIEW!!!
Now that you have reviewed the anatomy of the heart, try
to answer the following questions:
• From superficial to deep, name the layers of the heart
wall.
• Define mediastinum.
• Describe the heart's location?
• What is cardiac tamponade?
• Name the four chambers of the heart.
• List the arteries and veins of the heart.
• What structures prevent backflow of blood in the heart?
• Name the four valves of the heart and their location.
• Compare arteriosclerosis with atherosclerosis.
If you are comfortable with this material, move on to the
next section on cardiac Physiology.
Blood Circulation
•
•
Two closed circuits, the systemic and pulmonic
Systemic circulation
– left side of heart pumps blood through body
– Receives oxygenated blood from the lungs and distributes
it to body cells
left ventricle  aorta  arteries  arterioles  capillaries 
gas and nutrient exchange  venules  veins  right
atrium
Blood Circulation (cont.)
• Pulmonary
circulation
– right side of
heart pumps
deoxygenated
blood to lungs
for oxygenation.
right ventricle  pulmonary trunk  pulmonary arteries  lungs
 exchange of gases  pulmonary veins  left atrium
Blood Circulation (cont.)
• Coronary Circulation
– Is the flow of blood through the many
vessels that supply blood to the cardiac
muscle cells of the heart.
– It delivers oxygenated blood and nutrients
to and removes carbon dioxide and wastes
from the myocardium.
– Many connections (anastomoses) are
seen between arteries supplying blood to
the same region. This provides alternate
routes if one artery becomes blocked.
Coronary Circulation
• Left Ventricle - Aorta  left and right coronary
arteries  supply blood to the atrium and the ventricles
 large coronary sinus  right atrium.
• Sinus - large vein without smooth muscle layer.
Conduction System of Heart
Autorhythmic Cells:
Generate action potential spontaneously, act as
pacemaker and form conduction system for the heart
•
SA node
–
–
–
•
AV node
–
•
in atrial septum, Slows the transmission of the action potential
by 0.15 seconds. transmits signal to bundle of His
Bundle of His
–
–
•
cluster of cells in wall of Right Atria
begins heart activity that spreads to both atria
excitation spreads to AV node
the connection between atria and ventricles
The AV bundle divides into right and left bundle branches,
and action potentials descend to the apex of the heart.
Action potentials are carried by the Purkinje fibers from
the bundle branches to the ventricular walls.
Conduction
System of Heart
Signals from the
autonomic nervous
system and hormones,
such as epinephrine,
do modify the heartbeat
(in terms of rate and
strength of contraction),
but they do not
establish the
fundamental rhythm.
Action potential and
contraction of contractile fibers
• An impulse in a ventricular contractile fiber is characterized
by rapid depolarization, plateau, and repolarization.
• Depolarization
– Cardiac cell resting membrane potential is -90mv
– fast Na+ channels open for rapid depolarization
• Plateau phase
– Period of maintained depolarization
– slow Ca+2 channels open, let Ca +2 enter from outside cell and
from storage in sarcoplasmic reticulum, while K+ channels
close
– Ca +2 binds to troponin to allow for actin-myosin cross-bridge
formation & muscle contraction.
• Repolarization
– Ca+2 channels close and K+ channels open & -90mv is
restored as potassium leaves the cell
• Refractory period
– the time interval when a second contraction cannot be
triggered
– very long so heart can fill
Physiology of Contraction
Electrocardiogram---ECG or EKG
A recording of the
electrical changes
that accompany
each cardiac cycle
(heartbeat) is called
an
electrocardiogram
(ECG or EKG).
– P wave
• atrial depolarization
– P to Q interval
• conduction time from atrial to
ventricular excitation
– QRS complex
• ventricular depolarization
– T wave
• ventricular repolarization
The ECG helps to
determine if the
conduction pathway
is abnormal, if the
heart is enlarged,
and if certain
regions are
damaged.
ECG (Contd.)
• Figure shows
the relation
between the
ECG and
changes in
atrial pressure,
ventricular
pressure, aortic
pressure, and
ventricular
volume during
the cardiac
cycle.
THE CARDIAC CYCLE
• A cardiac cycle includes all the events
occurring in a single heart beat.
• It consists of repetitive contraction (systole)
and relaxation (diastole) of heart chambers
• During a cardiac cycle atria and ventricles
alternately contract and relax forcing blood
from areas of high pressure to areas of lower
pressure.
Phases of Cardiac Cycle
1.
Atrial Systole: The atria contract, increasing pressure
forces the AV valves to open.
–
The amount of blood in the ventricle at the end of
diastole is the End Diastolic Volume (EDV)
2.
Ventricular systole/atrial diastole
–
Ventricles contract and increasing pressure
forces the AV valves to close.
–
AV and SL valves are all closed (isovolumetric
contraction).
–
Pressure continues to rise opening the SL valves
leading to ventricular ejection.
–
The amount of blood in the left ventrical at the
end of systole is End Systolic Volume (ESV).
Stroke volume (SV) is the volume of blood
ejected from the left ventricle SV = EDV-ESV.
Phases of Cardiac Cycle
(Contd.)
3.
Relaxation period: Both atria and ventricles
are relaxed. Pressure in the ventricles fall
and the SL valves close. Brief time all four
valves are closed is the isovolumetric
relaxation. Pressure in the ventricles
continues to fall, the AV valves open, and
ventricular filling begins.
Cardiac Cycle
Heart Sounds
• The sound of a heartbeat comes primarily from
the turbulence in blood flow caused by the
closure of the valves.
• The act of listening to sounds within the body is
called auscultation, and it is usually done with a
stethoscope.
• The first heart sound (lubb) is created by blood
turbulence associated with the closing of the
atrioventricular valves soon after ventricular
systole begins.
• The second heart sound (dupp) represents the
closing of the semilunar valves close to the
end of the ventricular systole.
Murmurs
• A heart murmur is an abnormal sound that
consists of a flow noise that is heard before,
between, or after the lubb-dupp or that may
mask the normal sounds entirely.
• Not all murmurs are abnormal or
symptomatic, but most indicate a valve
disorder.
Heart Sounds
Cardiodynamics
• Refers to movements and forces generated
during muscle contractions.
• End-diastolic volume (EDV):volume of blood
in the ventricles at the end of ventricular
diastole.
• End-systolic volume (ESV): volume of blood
remaining in each ventricle at the end of
ventricular systole.
• Stroke volume (SV): EDV – ESV
CARDIAC OUTPUT
• Cardiac output (CO) is the volume of blood ejected from
the left ventricle (or the right ventricle) into the aorta (or
pulmonary trunk) each minute.
– Cardiac output equals the stroke volume (the volume
of blood ejected by the ventricle with each contraction)
multiplied by the heart rate (the number of beats per
minute).
CO = SV X HR
– at 70ml stroke volume & 75 beat/min----5 and 1/4
liters/min
– entire blood supply passes through circulatory system
every minute
• Cardiac reserve is the ratio between the maximum cardiac
output a person can achieve and the cardiac output at
rest.
– average is 4-5x while athlete’s is 7-8x
Factors Affecting Cardiac Output
• Cardiac output
– Adjusted by
changes in heart
rate or stroke
volume
• Heart rate
– Adjusted by
autonomic
nervous system
or hormones
• Stroke volume
– Adjusted by
changing EDV or
ESV
Regulation of Heart Rate
• Several Factors affect heart rate
– Intrinsic regulation: Results from normal functional
characteristics, not on neural or hormonal regulation
– Extrinsic regulation: Involves neural and hormonal
control
• Parasympathetic stimulation
– Supplied by vagus nerve, decreases heart rate,
acetylcholine is secreted and hyperpolarizes the
heart
– Can decrease the heart rate to 20-30 bpm.
• Sympathetic stimulation
– Supplied by cardiac nerves. Innervate the SA and
AV nodes, coronary vessels and the atrial and
ventricular myocardium. Increases heart rate and
force of contraction. Epinephrine and
norepinephrine released.
– Can increase the heart rate to as high as 250-300
bpm.
Regulation of Heart Rate (Contd)
– Hormonal Control.
• Epinephrine and norepinephrine from
the adrenal medulla. Occurs in
response to increased physical
activity.
– Cations (Na+, K+, Ca+2) also affect
heart rate.
– age, gender, physical fitness, and
temperature, emotional excitement,
stress.
Factors affecting Stroke Volume
• Stroke volume is measured as the difference
between end diastolic volume and end
systolic volume.
• Therefore any changes in either EDV or ESV
will have an impact on stroke volume. Some
of these factors that impact stroke volume are:
Factors affecting Stroke Volume
• EDV: is the amount of blood in a ventricle
after diastole. Two factors influence this
volume:
– Filling time: is the duration of the ventricular
diastole, which is entirely dependent on heart rate.
– Venous return: varies in response to changes in
cardiac output, blood volume, patterns of peripheral
circulation etc.
– Preload: the degree of stretch in the heart before it
contracts. Greater the preload on fibers just before
they contract greater is the force of contraction
(Frank-Starling law of the heart). This law equalizes
the volume of blood flowing to both systemic and
pulmonary circulations.
Factors affecting Stroke Volume
(contd.)
• ESV: is the amount of blood left behind in the
ventricle after ventricular systole. Three factors
affect ESV:
– Preload: discussed earlier.
– Contractility: is the forcefulness of myocardial
contraction. Substances that increase contractility are
positive inotropic agents (e.g. epinephrine,
norepinephrine, stimulation of sympathetic nervous
system) and those that decrease contractility are
negative inotropic agents (e.g. inhibition of
sympathetic division, acidosis and anesthetics).
– Afterload: the pressure that must be overcome before
a semilunar valve can open. An increase in afterload
causes the stroke volume to decrease.
Influences on Stroke Volume
• Preload (affect of stretching)
– Frank-Starling Law of Heart
– more muscle is stretched, greater force of contraction
– more blood more force of contraction results
• Contractility
– autonomic nerves, hormones, Ca+2 or K+ levels
– Positive inotropic agents increase contractility
– Negati ve inotropic agents decrease contractility.
• Afterload
– amount of pressure created by the blood in the way
– high blood pressure creates high afterload
Factors affecting Stroke Volume
(contd)
Regulation
of Heart
Rate
Risk Factors for Heart Disease
• Risk factors in heart disease:
–
–
–
–
high blood cholesterol level
high blood pressure
cigarette smoking
obesity & lack of regular exercise.
• Other factors include:
–
–
–
–
–
diabetes mellitus
genetic predisposition
male gender
high blood levels of fibrinogen
left ventricular hypertrophy
Clinical Problems
• MI = myocardial infarction
– death of area of heart muscle from lack of O2
– replaced with scar tissue
– results depend on size & location of damage
– A myocardial infarction can usually be
diagnosed with an ECG and blood studies
• Angina pectoris----heart pain from ischemia of
cardiac muscle
Clinical Problems (Contd)
Coronary Artery Disease
• Heart muscle receiving insufficient blood supply
– narrowing of vessels---atherosclerosis, artery spasm or clot
– atherosclerosis--smooth muscle & fatty deposits in walls of
arteries
• Treatment
– drugs, bypass graft, angioplasty, stent
Clinical Problems (Contd)
• Congenital Heart Defect is a defect that exists
at birth, and usually before birth.
– Congenital defects of the heart include coarctation
of the aorta, patent ductus arteriosus, septal defects
(interatrial or interventricular), valvular stenosis, and
tetralogy of Fallot.
• Arrhythmia (disrhythmia) is an irregularity in
heart rhythm resulting from a defect in the
conduction system of the heart.
– Categories are bradycardia, tachycardia, and
fibrillation.
Clinical Problems (Contd)
• Congestive heart failure is a chronic or acute
state that results when the heart is not capable of
supplying the oxygen demands of the body.
• Causes of CHF
– coronary artery disease, hypertension, MI, valve
disorders, congenital defects
• Left side heart failure
–
–
–
–
less effective pump so more blood remains in ventricle
heart is overstretched & even more blood remains
blood backs up into lungs as pulmonary edema
suffocation & lack of oxygen to the tissues
• Right side failure
– fluid builds up in tissues as peripheral edema
REVIEW
Now that you have reviewed the cardiac
physiology, try to answer the following
questions. Feel free to review any section
again that you have difficulty with.
What do the terms systole and diastole
mean?
• List the phases of the cardiac cycle?
• if the cells of the SA node failed to function,
how would the heart rate be affected?
• Why is it important for impulses to be delayed
at the AV node before they pass into the
ventricles?
• Compare badycardia with tachycardia.
REVIEW (Contd)
• Define end-diasystolic volume and endsystolic volume.
• List the factors that affect the stroke volume.
• Define electrocardiogram.
• Identify the main components of the ECG, and
indicate what each represents.
• Define blood flow, and describe its
relationship to blood pressure and peripheral
resistance.
• Define edema.
• Identify the hormones affecting the blood
pressure.