Cardiovascular system

CARDIOVASCULAR SYSTEM
prepared by Guesh M.
3/18/2017 1

Outline
• Overview of the cardiovascular system
• Mechanical properties of the heart
• Electrical properties of the heart
• The vascular system
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Introduction
• Overview of the Cardiovascular System
– The cardiovascular system transports materials
throughout the body
– The cardiovascular system consists of the heart,
blood vessels, and blood
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Functional components of the cardiovascular
system in man
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Fig. Overview of the cardiovascular system. The right side of the heart, pulmonary
circulation, left side of the heart, and systemic circulation are arranged in series. RA, right
atrium; RV, right ventricle; PA, pulmonary artery; Ao, aorta; LA, left atrium; LV, left ventricle.
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Functional anatomy of the heart
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The Heart
• The heart for the average human will contract about 3 billion
times;
– Never resting,
– Never stopping to take a break except for a fraction of a
second between beats.
• Many believe that the heart is the first organ to become
functional.
• Within weeks of conception the heart starts its mission of
supplying the body with nutrients
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The Heart cont’d…
• The primary function of the heart is to pump blood
through the arteries, capillaries, and veins.
– There is an estimated 60,000 miles of vessels
throughout an adult body.
• The heart is the pump that keeps blood circulating
properly.
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• The heart is a pump that receives blood from venous
blood vessels at a low pressure, imparts energy to the
blood (raises it to a higher pressure) by contracting
around the blood within the cardiac chambers, and then
ejects the blood into the arterial blood vessels.
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Blood flow within the heart. Venous blood returns to the right atrium (RA) via the superior
(SVC) and inferior vena cava (IVC). Blood passes from the RA into the right ventricle (RV),
which ejects the blood into the pulmonary artery (PA). After passing through the lungs, the
blood flows into the left atrium (LA) and then fills the left ventricle (LV), which ejects the
blood into the aorta (A) for distribution to the different organs of the body.
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• Pump blood through the blood vessels by repeated, rhythmic
contractions.
• The heart is composed of cardiac muscle, an involuntary muscle
tissue that is found only within this organ.
• The term "cardiac" (as in cardiology) means "related to the heart”
and comes from the Greek word kardia, for "heart."
• It has a four chambered, double pump and is located in the
thoracic cavity between the lungs.
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• The heart is actually two separate pumps:
– a right heart that pumps blood through the lungs, and
– a left heart that pumps blood through the peripheral
organs.
• In turn, each of these hearts is a pulsatile two-chamber
pump composed of an atrium and a ventricle.
• Each atrium is a weak primer pump for the ventricle, helping
to move blood into the ventricle.
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• The ventricles then supply the main pumping force that
propels the blood either
1. through the pulmonary circulation by the right ventricle or
2. through the peripheral circulation by the left ventricle.
• Special mechanisms in the heart cause a continuing
succession of heart contractions called cardiac rhythmicity,
transmitting action potentials throughout the heart muscle
to cause the heart’s rhythmical beat.
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Fig. Functional anatomy of the heart3/18/2017 21

Fig. Structure of the heart, and course of blood flow through the
heart chambers and heart valves.3/18/2017 22

• The Atria:
– Two thin-walled overlying muscular sheaths
– Serve as reservoirs and pumps
• The Ventricles:
– Thicker-walled portion of the heart
– Pumps blood from the low-pressure venous system
into the higher pressure arterial system.
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• The heart has four chambers
• Heart valves ensure one-way flow in the heart
• Cardiac muscle cells contract without innervation
• Calcium entry is a feature of cardiac EC coupling
• Cardiac muscle contraction can be graded
• Myocardial action potentials vary
• Autonomic neurotransmitters modulate heart rate
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• The Heart as a Pump
– Electrical conduction in the heart coordinates contraction
– Pacemakers set the heart rate
– The electrocardiogram reflects electrical activity
– The heart contracts and relaxes during a cardiac cycle
– Pressure-volume curves represent one cardiac cycle
– Stroke volume is the volume of blood pumped per
contraction
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• Cardiac output is a measure of cardiac performance
• Heart rate is modulated by autonomic neurons and
catecholamines
• Multiple factors influence stroke volume
• Contractility is controlled by the nervous and
endocrine systems
• EDV and arterial blood pressure determine afterload
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• Pressures in the cardiovascular system are expressed in
millimeters of mercury (mm Hg) above atmospheric
pressure.
• One millimeter of mercury is the pressure exerted by a 1-
mm vertical column of mercury (1 mm Hg is the equivalent
of 1.36 cm H2O hydrostatic pressure).
• Vascular resistance is determined by the size of blood
vessels, the arrangement of the vascular network, and the
viscosity of the blood flowing within the vasculature.
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• The right atrium receives systemic venous blood (venous
return) at very low pressures (near 0 mm Hg).
• This venous return then passes through the right atrium
and fills the right ventricle; atrial contraction also
contributes to the ventricular filling.
• Right ventricular contraction ejects blood from the right
ventricle into the pulmonary artery.
• This generates a maximal pressure (systolic pressure) that
ranges from 20 to 30 mm Hg within the pulmonary artery.
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• As the blood passes through the pulmonary circulation, the blood
pressure falls to about 10 mm Hg.
• The left atrium receives the pulmonary venous blood, which then
flows passively into the left ventricle; atrial contraction provides a
small amount additional filling of the left ventricle.
• As the left ventricle contracts and ejects blood into the systemic
arterial system, a relatively high pressure is generated (100–140
mm Hg maximal or systolic pressure).
• Therefore, the left ventricle is a high-pressure pump, in contrast to
the right ventricle, which is a low-pressure pump.
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Heart Valves
• Ensure one-way flow in the heart preventing the
backward flow of blood.
• Two sets of heart valves ensure this one way flow:
– one set (the atrioventricular valves) between the atria and
ventricles, and
– the second set (the semilunar valves, named for their crescent-
moon shape) between the ventricles and the arteries.
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Heart valves cont’d…
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• The opening between each atrium and its ventricle is guarded by
an atrioventricular (AV) valve.
• The AV valve is formed from thin flaps of tissue joined at the base
to a connective tissue ring.
• The flaps are slightly thickened at the edge and connect on the
ventricular side to collagenous tendons, the chordae tendineae
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• When a ventricle contracts, blood pushes against the bottom side
of its AV valve and forces it upward into a closed position.
• The chordae tendineae prevent the valve from being pushed back
into the atrium, just as the struts on an umbrella keep the umbrella
from turning inside out in a high wind.
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• The two AV valves are not identical.
• The valve that separates the right atrium and right ventricle has
three flaps and is called the tricuspid valve [cuspis, point]
• The valve between the left atrium and left ventricle has only two
flaps and is called the bicuspid valve.
• The bicuspid is also called the mitral valve because of its
resemblance to the tall headdress, known as a miter, worn by
popes and bishops.
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• The semilunar valves separate the ventricles from the major
arteries.
• The aortic valve is between the left ventricle and the aorta, and the
pulmonary valve lies between the right ventricle and the
pulmonary trunk.
• Each semilunar valve has three cuplike leaflets that snap closed
when blood attempting to flow
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Heart valves create one-way ow through the heart. Views (a) and (c) show the AV
valves as viewed from the atria, and the semilunar valves as viewed from inside the
arteries.
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Heart sound and the cardiac cycle
• how are heart sounds produced?
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HEART SOUNDS
• Two sounds are normally heard through a
stethoscope during each cardiac cycle.
• First sound
– is a low, slightly prolonged “lub”
– caused by vibrations set up by the sudden closure of
the AV valves at the start of ventricular systole
– has a duration of about 0.15 s and a frequency of 25
to 45 Hz.
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Heart sounds cont’d …
• It is soft when the heart rate is low, because the
ventricles are well filled with blood and the leaflets of the
AV valves float together before systole.
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• Second sound
– is a shorter, high-pitched “dup”
– caused by vibrations associated with closure of the aortic
and pulmonary valves just after the end of ventricular
systole.
– lasts about 0.12 s, with a frequency of 50 Hz.
– It is loud and sharp when the diastolic pressure in the
aorta or pulmonary artery is elevated, causing the
respective valves to shut briskly at the end of systole.
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• The interval between aortic and pulmonary valve closure
during inspiration is frequently long enough for the
second sound to be reduplicated (physiologic splitting of
the second sound).
• Splitting also occurs in various diseases.
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• Third sound
– A soft, low-pitched third sound is heard about one
third of the way through diastole in many normal
young individuals.
– It coincides with the period of rapid ventricular filling
and is probably due to vibrations set up by the inrush
of blood.
– The third sound, when present, has a duration of 0.1 s.
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• Fourth sound
– A fourth sound can sometimes be heard immediately
before the first sound when atrial pressure is high or
the ventricle is stiff in conditions such as ventricular
hypertrophy.
– It is due to ventricular filling and is rarely heard in
normal adults.
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MURMURS
• Murmurs, or bruits, are abnormal sounds heard in various parts of
the vascular system.
• The two terms are used interchangeably, though “murmur” is
more commonly used to denote noise heard over the heart than
over blood vessels.
• Blood flow is laminar, nonturbulent, and silent up to a critical
velocity; above this velocity and beyond an obstruction, blood flow
is turbulent and creates sounds.
• Blood flow speeds up when an artery or a heart valve is narrowed.
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Murmurs cont’d …
• Examples of vascular sounds outside the heart are
– the bruit heard over a large, highly vascular goiter,
– the bruit heard over a carotid artery when its lumen is
narrowed and distorted by atherosclerosis, and
– the murmurs heard over an aneurysmal dilation of one of the
large arteries,
– an arteriovenous (A-V) fistula, or a patent ductus arteriosus.
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Cardiac Cycle
• Each cardiac cycle has two phases:
–diastole, the time during which cardiac
muscle relaxes, and
–systole, the time during which the muscle is
contracting [diastole, dilation; systole,
contraction].
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Systole and diastole are the mechanical events of the
cardiac cycle.
1. Late diastole both sets of chambers are relaxed and
ventricles fill passively.
2. Atrial systole atrial contraction forces a small
amount of additional blood into ventricles.
3. Isovolumic ventricular contraction first phase of
ventricular contraction pushes AV valves closed but
does not create enough pressure to open semilunar
valves.
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4. Ventricular ejection as ventricular pressure rises
and exceeds pressure in the arteries, the
semilunar valves open and blood is ejected.
5. Isovolumic ventricular relaxation as ventricles
relax, pressure in ventricles falls, blood flows
back into cusps of semilunar valves and snaps
them closed.
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Cardiac output and its regulation
• Cardiac output (CO)
– Is the volume of blood pumped by one ventricle in a
given period of time.
– Is an indicator of total blood flow through the body.
– can be calculated by multiplying heart rate (beats per
minute) by stroke volume (mL per beat, or per
contraction) (CO = SV . HR)
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Cardiac output and its regulation con’d…
• However, cardiac output does not tell us how
blood is distributed to various tissues.
• That aspect of blood flow is regulated at the
tissue level.
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Cardiac output and its regulation con’d…
• At rest, one side of the heart pumps all the blood in the body
through it in only one minute!
• Normally, cardiac output is the same for both ventricles.
• However, if one side of the heart begins to fail for some reason
and is unable to pump efficiently, cardiac output becomes
mismatched.
• In that situation, blood pools in the circulation behind the weaker
side of the heart.
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Electrophysiological properties of the
heart
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• The heart is endowed with a special system for
1. Generating rhythmical electrical impulses to
cause rhythmical contraction of the heart muscle
and
2. Conducting these impulses rapidly through the
heart.
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• The action potentials generated by these pacemaker cells
are conducted throughout the heart and trigger
contraction of cardiac myocytes.
• This results in ventricular contraction and ejection of
blood.
• The force of ventricular contraction, and therefore stroke
volume, is regulated by mechanisms intrinsic to the
heart, by autonomic nerves and hormones
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• When this system functions normally, the atria contract about one
sixth of a second ahead of ventricular contraction, which allows
filling of the ventricles before they pump the blood through the
lungs and peripheral circulation.
• Another special importance of the system is that it allows all
portions of the ventricles to contract almost simultaneously, which
is essential for most effective pressure generation in the
ventricular chambers.
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Specialized Excitatory and Conductive System of the Heart
• The sinus node ( sinoatrial or S-A node),
– in which the normal rhythmical impulse is generated
• The internodal pathways that conduct the impulse
from the sinus node to the atrioventricular (A-V)
node
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Specialized Excitatory and Conductive System of the Heart cont’d …
• The A-V node,
– in which the impulse from the atria is delayed before passing
into the ventricles
• The A-V bundle,
– which conducts the impulse from the atria into the ventricles
and
• The left and right bundle branches of Purkinje fibers,
– which conduct the cardiac impulse to all parts of the
ventricles.
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Electrical conduction in the heart
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Electrocardiography (ECG) and its
application
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Fig. Correlation between an ECG and electrical events in the heart. The figure shows the
correspondence between electrical events in the ECG and depolarizing (purple) and repolarizing
(peach) regions of the heart
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Fig Comparison of an ECG and myocardial AP
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Abnormalities of cardiac conduction,
rhythm and rate
• Reading assignment
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• The pumping activity of the heart is usually expressed in terms of
its cardiac output, which is the amount of blood ejected with each
contraction
• (i.e., stroke volume) multiplied by the heart rate. Any factor that
alters heart rate or stroke volume will alter the cardiac output.
• The heart rate is determined by groups of cells within the heart
that act as electrical pacemakers, and their activity is increased or
decreased by autonomic nerves and hormones
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• Vascular System
– Blood vessels constrict and dilate to regulate arterial blood
pressure, alter blood flow within organs, regulate capillary
blood pressure, and distribute blood volume within the body.
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• The systemic arteries are a pressure reservoir that
maintains blood flow during ventricular relaxation.
• The arterioles are the site of variable resistance.
• Exchange between the blood and cells takes place only at
the capillaries.
• Veins serve as an expandable volume reservoir.
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• Blood pressure is highest in the arteries and decreases
continuously as blood flows through the circulatory
system.
• The decrease in pressure occurs because energy is lost
as a result of the resistance to flow offered by the
vessels.
• Resistance to blood flow also results from friction
between the blood cells.
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• In the systemic circulation, the highest pressure occurs in
the aorta and results from pressure created by the left
ventricle.
• Aortic pressure reaches an average high of 120 mm Hg
during ventricular systole (systolic pressure), then falls
steadily to a low of 80 mm Hg during ventricular diastole
(diastolic pressure).
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• pressure in the ventricle falls to 0 mm Hg as the ventricle
relaxes, but diastolic pressure in the large arteries
remains relatively high.
• The high diastolic pressure in arteries reflects the ability
of those vessels to capture and store energy in their
elastic walls.
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• The rapid pressure increase that occurs when the left
ventricle pushes blood into the aorta can be felt as a
pulse, or pressure wave, transmitted through the fluid
filled arteries.
• The pressure wave travels about 10 times faster than the
blood itself.
• Even so, a pulse felt in the arm is occurring slightly after
the ventricular contraction that created the wave.
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• The amplitude of the pressure wave decreases over
distance because of friction, and the wave finally
disappears at the capillaries.
• Pulse pressure, a measure of the strength of the
pressure wave, is defined as systolic pressure minus
diastolic pressure:
• Systolic pressure - diastolic pressure = pulse pressure
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• Pressure, Volume, Flow, and Resistance
– The pressure of fluid in motion decreases over
distance
– Pressure changes in liquids without a change in
volume
– Blood flows from higher pressure to lower pressure
– Resistance opposes flow
– Velocity depends on the flow rate and the cross-
sectional area
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• It is important to understand that organ blood flow is not driven
by the output of the heart per se, but rather by the pressure
generated within the arterial system as the heart pumps blood
into the vasculature, which serves as a resistance network.
• Organ blood flow is determined by the arterial pressure minus the
venous pressure, divided by the vascular resistance of the organ
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Parallel arrangement of organs within the body. One major exception is the hepatic (liver)
circulation, which is both in series with the gastrointestinal circulation (GI) by the hepatic
portal circulation and in parallel by the hepatic artery, which supplies part of the hepatic
circulation. SVC, superior vena cava; IVC, inferior vena cava.
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Arterial blood pressure and its regulation
• In the systemic system,
– normal systolic pressure is about 120 mm Hg and
– normal diastolic pressure is about 80 mm Hg.
• In the pulmonary system,
– the normal systolic pressure is about 25 mm Hg and
– the normal diastolic pressure is about 8 mm Hg.
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• The maximum pressure generated during ventricular
contraction is the systolic pressure.
• When the ventricles relax (ventricular diastole), the
arterial pressure drops.
• The lowest pressure that remains in the arteries prior to
the next ventricular contraction is the diastolic pressure
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Fig. Mean intraluminal blood pressure at various points in the
pulmonary and systemic vascular systems.
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• Changes in vascular diameters are brought about
by
– activation of vascular smooth muscle within the
vascular wall by autonomic nerves,
– metabolic and biochemical signals from outside of the
blood vessel, and
– vasoactive substances released by cells that line the
blood vessels (i.e., the vascular endothelium)
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• Blood vessels have another function besides
distribution of blood flow and exchange.
• The endothelial lining of blood vessels produces
several substances
e.g.,
– nitric oxide [NO],
– endothelin-1 [ET-1], and
– prostacyclin [PGI2]) modulate cardiac and vascular
function, hemostasis (blood clotting), and inflammatory
responses
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• Interdependence of circulatory and organ function
• Cardiovascular function is closely linked to the function of
other organs.
– For example,
– 1. The brain not only receives blood flow to support its metabolism,
but it also acts as a control center for regulating cardiovascular
function.
– 2. A second example of the interdependence between organ function
and the circulation is the kidney.
– The kidneys excrete varying amounts of sodium, water, and other
molecules to maintain fluid and electrolyte homeostasis.
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• Blood passing through the kidneys is filtered and the
kidneys then modify the composition of the filtrate to
form urine.
• Reduced blood flow to the kidneys can have detrimental
effects on kidney function and therefore on circulation
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Mean intraluminal blood pressure at various points in the pulmonary
and systemic vascular systems.
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Clinical correlates
• Reading assignment
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Cardiovascular system

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