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Chapter 15: The Cardiovascular System
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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 thin because they
deliver blood to the ventricles.
The ventricle walls are thicker
because they pump blood greater
distances
The right ventricle walls are thinner
than the left because they pump
blood into the lungs, which are
nearby and offer very little resistance
to blood flow.
The left ventricle walls are thicker
because they pump blood through the
body where the resistance to blood
flow is greater.
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Locating the Heart
Posterior to sternum
medial to lungs
Anterior to vertebral column
Base lies beneath 2nd rib
Apex at 5th intercostal space
Lies upon diaphragm
Coverings of the Heart
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Layers of the Heart Wall
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Layers of the Heart Wall
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Heart Chambers
• Right Atrium
• receives blood from
• inferior vena cava
• superior vena cava
• coronary sinus
• Right Ventricle
• receives blood from
right atrium
• Left Atrium
• receives blood from
pulmonary veins
• Left Ventricle
• receives blood from
left atrium
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EXTERNAL HEART
Anterior View
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EXTERNAL HEART
Posterior View
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Right
Atrium
• Receives blood from 3 sources
– superior vena cava, inferior vena cava and coronary sinus
• Interatrial septum partitions the atria
• Fossa ovalis is a remnant of the fetal foramen ovale
• Tricuspid valve
– Blood flows through into right ventricle
– has three cusps composed of dense CT covered by
endocardium
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Right Ventricle
• Forms most of anterior
surface of heart
• Papillary muscles are cone
shaped trabeculae carneae
(raised bundles of cardiac
muscle)
• Chordae TENDINAE:
cords between valve cusps
and papillary muscles
• Interventricular septum:
partitions ventricles
• Pulmonary semilunar valve:
blood flows into pulmonary
trunk
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Left
Atrium
•
•
•
•
Forms most of the base of the heart
Receives blood from lungs- 4 Pulmonary VEINS
(2 right + 2 left) Red blood in a vein? Weird!
Bicuspid valve: blood passes through into left ventricle
– has two cusps
– to remember names of this valve, try the pneumonic LAMB
• Left Atrioventricular, Mitral, or Bicuspid valve
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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
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Heart Valves
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Atrioventricular Valves Open
• A-V valves open and allow blood to flow from
atria into ventricles when ventricular pressure is
lower than atrial pressure
– occurs when ventricles are relaxed, chordae tendineae
are slack and papillary muscles are relaxed
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Atrioventricular Valves Close
• A-V valves close preventing backflow of blood
into atria
– occurs when ventricles contract, pushing valve cusps
closed, chordae tendinae are pulled taut and papillary
muscles contract to pull cords and prevent cusps from
everting
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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
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valve cusps, tightly closing the SL valves
Valve Function Review
Atria contract, blood fills ventricles through A-V valves
Ventricles contract, blood pumped into aorta and
pulmonary trunk through SL valves
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Fibrous Skeleton of Heart
Dense CT rings surround the valves of the heart, fuse and
merge with the interventricular septum
Support structure for heart valves
Insertion point for cardiac muscle bundles
Electrical insulator between atria and ventricles
prevents direct propagation of AP’s to ventricles
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Path of Blood
Through the Heart
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Blood Supply to the Heart Muscle
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Heart Contraction
Atrial Systole/Ventricular Diastole
Atrial Diastole/Ventricular Systole
https://www.youtube.com/watch?v=waOSUpEHPQs
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Cardiac Cycle
• Atrial Systole/Ventricular Diastole
• blood flows passively into ventricles
• remaining 30% of blood pushed into ventricles
• A-V valves open/semilunar valves close
• ventricles relaxed
• ventricular pressure increases
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Cardiac Cycle
Ventricular Systole/Atrial diastole
• A-V valves close
• chordae tendinae prevent cusps of valves from
bulging too far into atria
• atria relaxed
• blood flows into atria
• ventricular pressure increases and opens semilunar
valves
• blood flows into pulmonary trunk and aorta
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Heart Sounds
Lubb
• first heart sound
• occurs during ventricular systole
• A-V valves closing
Dupp
• second heart sound
• occurs during ventricular diastole
• pulmonary and aortic semilunar valves closing
Murmur – abnormal heart sound
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Heart Sounds
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Cardiac Muscle Fibers
Cardiac muscle fibers form a functional
syncytium
• group of cells that function as a unit
• atrial syncytium
• ventricular syncytium
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Cardiac Conduction System
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Cardiac Conduction System
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Muscle Bundles of the Myocardium
• Cardiac muscle fibers swirl diagonally around the
heart in interlacing bundles
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Electrocardiogram
• recording of electrical changes that occur in the myocardium
• used to assess heart’s ability to conduct impulses
P wave – atrial depolarization
QRS wave – ventricular depolarization
T wave – ventricular repolarization
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Electrocardiogram
• Impulse conduction through the heart generates
electrical currents that can be detected at the
surface of the body. A recording of the electrical
changes that accompany each cardiac cycle
(heartbeat) is called an electrocardiogram (ECG
or EKG).
• The ECG helps to determine if the conduction
pathway is abnormal, if the heart is enlarged, and
if certain regions are damaged.
• Figure 20.12 shows a typical ECG.
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Electrocardiogram---ECG or EKG
• EKG
– Action potentials of all active
cells can be detected and
recorded
• P wave
– atrial depolarization
• P to Q interval
– conduction time from atrial to
ventricular excitation
• QRS complex
– ventricular depolarization
• T wave
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– ventricular repolarization
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ECG
• In a typical Lead II record, three clearly visible
waves accompany each heartbeat It consists of:.
• P wave (atrial depolarization - spread of impulse
from SA node over atria)
• QRS complex (ventricular depolarization - spread
of impulse through ventricles)
• T wave (ventricular repolarization).
• Correlation of ECG waves with atrial and
ventricular systole (Figure 20.13)
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ECG
• As atrial fibers depolarize, the P wave appears.
• After the P wave begins, the atria contract (atrial systole).
Action potential slows at the AV node giving the atria time
to contract.
• The action potential moves rapidly through the bundle
branches, Purkinje fibers, and the ventricular myocardium
producing the QRS complex.
• Ventricular contraction after the QRS complex and
continues through the ST segment.
• Repolarization of the ventricles produces the T wave.
• Both atria and ventricles repolarize and the P wave
appears.
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Regulation of Cardiac Cycle
Additional Factors that Influence HR
• physical exercise
• body temperature
• concentration of various ions
• potassium
• calcium
• parasympathetic impulses decrease heart action
• sympathetic impulses increase heart action
• cardiac center regulates autonomic impulses to the heart
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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
• Cardiac reserve is the ratio between the maximum
cardiac output a person can achieve and the cardiac
output at rest.
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Cardiac Output
• 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 maximum output/output at rest
– average is 4-5x while athlete’s is 7-8x
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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
• Afterload
– amount of pressure created by the blood in the way
– high blood pressure creates high afterload
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Stroke Volume and Heart Rate
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Preload: Effect of Stretching
• According to the Frank-Starling law of the heart,
a greater preload (stretch) on cardiac muscle fibers
just before they contract increases their force of
contraction during systole.
– Preload is proportional to EDV.
– EDV is determined by length of ventricular diastole and
venous return.
• The Frank-Starling law of the heart equalizes the
output of the right and left ventricles and keeps the
same volume of blood flowing to both the
systemic and pulmonary circulations.
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Contractility
• Myocardial contractility, the strength of
contraction at any given preload, is affected
by positive and negative inotropic agents.
– Positive inotropic agents increase contractility
– Negative inotropic agents decrease
contractility.
• For a constant preload, the stroke volume
increases when positive inotropic agents are
present and decreases when negative
inotropic agents are present.
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Afterload
• The pressure that must be overcome before
a semilunar valve can open is the afterload.
• In congestive heart failure, blood begins to
remain in the ventricles increasing the
preload and ultimately causing an
overstretching of the heart and less forceful
contraction
– Left ventricular failure results in pulmonary
edema
– Right ventricular failure results in peripheral
edema.
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Chemical regulation of heart rate
• Heart rate affected by hormones
(epinephrine, norepinephrine, thyroid
hormones).
• Cations (Na+, K+, Ca+2) also affect heart
rate.
• Other factors such as age, gender, physical
fitness, and temperature also affect heart
rate.
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Arteries and Arterioles
Artery
• thick strong wall
• endothelial lining
• middle layer of smooth
muscle and elastic tissue
• outer layer of
connective tissue
• carries blood under
relatively high pressure
Arterioles
• thinner wall than
artery
• endothelial lining
• some smooth muscle
tissue
• small amount of
connective tissue
• helps control blood
flow into a capillary
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Walls of Artery and Vein
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Arteriole
• smallest arterioles only have a few smooth muscle fibers
• capillaries lack muscle fibers
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Capillaries
• smallest diameter blood
vessels
• extensions of inner lining of
arterioles
• walls are endothelium only
• semipermeable
• sinusoids – leaky capillaries
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Exchange in the Capillaries
•
•
•
water and other substances leave capillaries because of net outward pressure at the capillaries’
arteriolar ends
water enters capillaries’ venular ends because of a net inward pressure
substances move in and out along the length of the capillaries according to their respective
concentration gradients
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Venules and Veins
• Venule
• thinner wall than arteriole
• less smooth muscle and elastic tissue than arteriole
• Vein
• thinner wall than artery
• three layers to wall but middle layer is poorly
developed
• some have flaplike valves
• carries blood under relatively low pressure
• serves as blood reservoir
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Venous Valves
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Characteristics of Blood Vessels
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Blood Volumes in Vessels
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Arterial Blood Pressure
Blood Pressure – force the blood exerts against the
inner walls of the blood vessels
Arterial Blood Pressure
• rises when ventricles contract
• falls when ventricles relax
• systolic pressure – maximum pressure
• diastolic pressure – minimum pressure
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Factors That Influence
Arterial Blood Pressure
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Control of Blood Pressure
If blood pressure rises, baroreceptors initiate the
cardioinhibitory reflex, which lowers the blood pressure
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Control of Blood Pressure
Dilating arterioles helps regulate blood pressure
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Venous Blood Flow
• not a direct result of heart
action
• dependent on
• skeletal muscle
contraction
• breathing
• venoconstriction
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Blood Flow Through Alveoli
• cells of alveolar wall are tightly joined together
• the high osmotic pressure of the interstitial fluid
draws water out of them
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Life-Span Changes
•
• cholesterol
deposition in blood vessels
•
heart enlargement
•
death of cardiac muscle cells
•
increase in fibrous connective tissue of the heart
•
increase in adipose tissue of the heart
•
increase in blood pressure
•
decrease in resting heart rate
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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
• Blood clot
– use clot dissolving drugs streptokinase or t-PA &
heparin
– balloon angioplasty
• Angina pectoris----heart pain from ischemia
of cardiac muscle
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CAD
• Coronary artery disease (CAD), or coronary heart
disease (CHD), is a condition in which the heart
muscle receives an inadequate amount of blood
due to obstruction of its blood supply. It is the
leading cause of death in the United States each
year. The principal causes of obstruction include
atherosclerosis, coronary artery spasm, or a clot in
a coronary artery.
• Risk factors for development of CAD include high
blood cholesterol levels, high blood pressure,
cigarette smoking, obesity, diabetes, “type A”
personality, and sedentary lifestyle.
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CAD
• Atherosclerosis is a process in which smooth
muscle cells proliferate and fatty substances,
especially cholesterol and triglycerides (neutral
fats), accumulate in the walls of the medium-sized
and large arteries in response to certain stimuli,
such as endothelial damage (Figure 20.18).
• Diagnosis of CAD includes such procedures as
cardiac catherization and cardiac angiography.
• Treatment options for CAD include drugs and
coronary artery bypass grafting (Figure 20.19).
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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
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Plasma Lipids and Heart Disease
• Risk factor for developing heart disease is high blood
cholesterol level.
– promotes growth of fatty plaques
– Most lipids are transported as lipoproteins
• low-density lipoproteins (LDLs)
• high-density lipoproteins (HDLs)
• very low-density lipoproteins (VLDLs)
– HDLs remove excess cholesterol from circulation
– LDLs are associated with the formation of fatty plaques
– VLDLs contribute to increased fatty plaque formation
• There are two sources of cholesterol in the body:
– in foods we ingest & formed by liver
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Desirable Levels of Blood
Cholesterol for Adults
•
•
•
•
TC (total cholesterol) under 200 mg/dl
LDL under 130 mg/dl
HDL over 40 mg/dl
Normally, triglycerides are in the range of 10190 mg/dl.
• Among the therapies used to reduce blood
cholesterol level are exercise, diet, and drugs.
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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
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By-pass Graft
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Percutaneous
Transluminal
Coronary
Angioplasty
Stent
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