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Chapter 20
The Cardiovascular System: The Heart
• Heart pumps over
1 million gallons
per year
• Over 60,000 miles
of blood vessels
20-1
Heart Location
Anterior surface
of heart
• Heart is located in the mediastinum
– area from the sternum to the vertebral column and
between the lungs
20-2
Heart Orientation
• Apex - directed anteriorly, inferiorly and to the left
• Base - directed posteriorly, superiorly and to the
right
• Anterior surface - deep to the sternum and ribs
• Inferior surface - rests on the diaphragm
• Right border - faces right lung
• Left border (pulmonary border) - faces left lung
20-3
Heart Orientation
• Heart has 2 surfaces: anterior and inferior,
and 2 borders: right and left
20-4
Surface Projection of the Heart
• Superior right point at the superior border of the 3rd right
costal cartilage
• Superior left point at the inferior border of the 2nd left
costal cartilage 3cm to the left of midline
• Inferior left point at the 5th intercostal space, 9 cm from
the midline
• Inferior right point at superior border of the 6th right costal
cartilage, 3 cm from the midline
20-5
Pericardium
• Fibrous pericardium
– dense irregular CT
– protects and anchors
the heart, prevents
overstretching
• Serous pericardium
– thin delicate membrane
– contains
• parietal layer-outer layer
• pericardial cavity with
pericardial fluid
• visceral layer
(epicardium) 20-6
Layers of Heart Wall
• Epicardium
– visceral layer of
serous pericardium
• Myocardium
– cardiac muscle layer
is the bulk of the
heart
• Endocardium
– chamber lining &
valves
20-7
Muscle Bundles of the Myocardium
• Cardiac muscle fibers swirl diagonally around the
heart in interlacing bundles
20-8
Chambers and Sulci of the Heart
• Four chambers
– 2 upper atria
– 2 lower ventricles
• Sulci - grooves on surface of heart
containing coronary blood vessels and fat
– coronary sulcus
• encircles heart and marks the boundary between the
atria and the ventricles
– anterior interventricular sulcus
• marks the boundary between the ventricles
anteriorly
– posterior interventricular sulcus
• marks the boundary between the ventricles
posteriorly
20-9
Chambers and Sulci
Anterior View
20-10
Chambers and Sulci
Posterior View
20-11
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
20-12
Right Ventricle
• Forms most of anterior surface of heart
• Papillary muscles are cone shaped trabeculae carneae (raised
bundles of cardiac muscle)
• Chordae tendineae: cords between valve cusps and papillary
muscles
• Interventricular septum: partitions ventricles
• Pulmonary semilunar valve: blood flows into pulmonary trunk
20-13
Left Atrium
• Forms most of the base of the heart
• Receives blood from lungs - 4 pulmonary veins (2 right +
2 left)
• 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
20-14
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
20-15
Myocardial Thickness and Function
• Thickness of myocardium varies according to the function
of the chamber
• Atria are thin walled, deliver blood to adjacent ventricles
• Ventricle walls are much thicker and stronger
– right ventricle supplies blood to the lungs (little flow resistance)
– left ventricle wall is the thickest to supply systemic circulation
20-16
Thickness of Cardiac Walls
Myocardium of left ventricle is much thicker than the right.
20-17
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
20-18
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
20-19
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
20-20
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
20-21
Valve Function Review
Atria contract, blood fills
ventricles through A-V
valves
Ventricles contract, blood
pumped into aorta and
pulmonary trunk through
SL valves
20-22
Blood Circulation
• Two closed circuits, the systemic and pulmonic
• Systemic circulation
–
–
–
–
–
left side of heart pumps blood through body
left ventricle pumps oxygenated blood into aorta
aorta branches into many arteries that travel to organs
arteries branch into many arterioles in tissue
arterioles branch into thin-walled capillaries for
exchange of gases and nutrients
– deoxygenated blood begins its return in venules
– venules merge into veins and return to right atrium
20-23
Blood Circulation (cont.)
• Pulmonary circulation
–
–
–
–
right side of heart pumps deoxygenated blood to lungs
right ventricle pumps blood to pulmonary trunk
pulmonary trunk branches into pulmonary arteries
pulmonary arteries carry blood to lungs for exchange
of gases
– oxygenated blood returns to heart in pulmonary veins
20-24
Blood Circulation
• Blood flow
– blue = deoxygenated
– red = oxygenated
– www.sitcomsonline.com/
themesonglyrics.html
20-25
Coronary Circulation
• Coronary circulation is blood supply to the heart
• Heart as a very active muscle needs lots of O2
• When the heart relaxes high pressure of blood in
aorta pushes blood into coronary vessels
• Many anastomoses
– connections between arteries supplying blood to the
same region, provide alternate routes if one artery
becomes occluded
20-26
Coronary Arteries
• Branches off aorta above
aortic semilunar valve
• Left coronary artery
– circumflex branch
• in coronary sulcus, supplies
left atrium and left ventricle
– LAD.
• supplies both ventricles
• Right coronary artery
– marginal branch
• in coronary sulcus, supplies
right ventricle
– posterior interventricular art.
• supplies both ventricles
20-27
Coronary Veins
• Collects wastes from cardiac muscle
• Drains into a large sinus on posterior surface of heart
called the coronary sinus
• Coronary sinus empties into right atrium
20-28
Conduction System of Heart
Coordinates contraction of heart muscle.
20-29
Conduction System of Heart
• Autorhythmic Cells
– Cells fire spontaneously, act as pacemaker and form
conduction system for the heart
• SA node
– cluster of cells in wall of Rt. Atria
– begins heart activity that spreads to both atria
– excitation spreads to AV node
• AV node
– in atrial septum, transmits signal to bundle of His
• AV bundle of His
– the connection between atria and ventricles
– divides into bundle branches & purkinje fibers, large
diameter fibers that conduct signals quickly
20-30
Rhythm of Conduction System
• SA node fires spontaneously 80-100 times per
minute
• AV node fires at 40-60 times per minute
• If both nodes are suppressed fibers in ventricles by
themselves fire only 20-40 times per minute
• Artificial pacemaker needed if pace is too slow
• Extra beats forming at other sites are called
ectopic pacemakers
– caffeine & nicotine increase activity
20-31
Timing of Atrial &
Ventricular Excitation
• SA node setting pace since is the fastest
• In 50 msec excitation spreads through both atria
and down to AV node
• 100 msec delay at AV node due to smaller
diameter fibers- allows atria to fully contract filling
ventricles before ventricles contract
• In 50 msec excitation spreads through both
ventricles simultaneously
20-32
Physiology of Contraction
• Depolarization, plateau, repolarization
20-33
Depolarization & Repolarization
• Depolarization
– Cardiac cell resting membrane potential is -90mv
– excitation spreads through gap junctions
– fast Na+ channels open for rapid depolarization
• Plateau phase
– 250 msec (only 1msec in neuron)
– 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 & tension development
• Repolarization
– Ca+2 channels close and K+ channels open & -90mv is restored as
potassium leaves the cell
• Refractory period
– very long so heart can fill
20-34
Action Potential in Cardiac Muscle
Changes in cell membrane permeability.
20-35
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
– ventricular repolarization
20-36
One Cardiac Cycle
• At 75 beats/min, one cycle requires 0.8 sec.
– systole (contraction) and diastole (relaxation) of
both atria, plus the systole and diastole of both
ventricles
• End diastolic volume (EDV)
– volume in ventricle at end of diastole, about 130ml
• End systolic volume (ESV)
– volume in ventricle at end of systole, about 60ml
• Stroke volume (SV)
– the volume ejected per beat from each ventricle,
about 70ml
– SV = EDV - ESV
20-37
CO Cardio Output
• CO = HR x SV
• BP = CO X SVR
20-38
Phases of Cardiac Cycle
• Isovolumetric relaxation
– brief period when volume in ventricles does not
change--as ventricles relax, pressure drops and AV
valves open
• Ventricular filling
– rapid ventricular filling:as blood flows from full atria
– diastasis: as blood flows from atria in smaller
volume
– atrial systole pushes final 20-25 ml blood into
ventricle
• Ventricular systole
– ventricular systole
– isovolumetric contraction
• brief period, AV valves close before SL valves open
– ventricular ejection: as SL valves open and blood is
ejected
20-39
Cardiac Cycle
20-40
Ventricular Pressures
• Blood pressure in aorta is 120mm Hg
• Blood pressure in pulmonary trunk is 30mm Hg
• Differences in ventricle wall thickness allows heart
to push the same amount of blood with more force
from the left ventricle
• The volume of blood ejected from each ventricle is
70ml (stroke volume)
• Why do both stroke volumes need to be same?
20-41
Auscultation
• Stethoscope
• Sounds of heartbeat are from turbulence in
blood flow caused by valve closure
– first heart sound (lubb) is created with the closing
of the atrioventricular valves
– second heart sound (dupp) is created with the
closing of semilunar valves
20-42
Heart Sounds
Where to listen on chest wall for heart sounds.
20-43
Cardiac Output
• Amount of blood pushed into aorta or
pulmonary trunk by ventricle
• Determined by stroke volume and heart rate
• 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 4-5 while athlete is 7-8
20-44
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
20-45
Congestive Heart Failure
• 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
20-46
Regulation of Heart Rate
• Nervous control from the cardiovascular
center in the medulla
– Sympathetic impulses increase heart rate and
force of contraction
– parasympathetic impulses decrease heart rate.
– Baroreceptors (pressure receptors) detect
change in BP and send info to the cardiovascular
center
• located in the arch of the aorta and carotid arteries
• Heart rate is also affected by hormones
– epinephrine, norepinephrine, thyroid hormones
– ions (Na+, K+, Ca2+)
– age, gender, physical fitness, and temperature
20-47
Regulation of Heart Rate
20-48
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
20-49
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
20-50
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.
20-51
Exercise and the Heart
• Sustained exercise increases oxygen demand
in muscles.
• Benefits of aerobic exercise (any activity that
works large body muscles for at least 20
minutes, preferably 3-5 times per week) are;
–
–
–
–
–
increased cardiac output
increased HDL and decreased triglycerides
improved lung function
decreased blood pressure
weight control.
20-52
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 TNKor t-PA &
heparin
– balloon angioplasty
• Angina pectoris----heart pain from ischemia
of cardiac muscle
20-53
By-pass Graft
20-54
Homework: Chapter 20
• A2, A4, A5, A7, B1, B2, B6, B7, C3
• PLEASE LOOK AT Wiley Plus THAT
ACCOMPANY YOUR TEXT
• WORK THROUGH THE ENTIRE
INTERACTIONS
20-55