Download Chapter 20 Heart

Anatomy & Physiology 2
Chapter 20 - The Heart
Albert Grazia, M.S., N.D.
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The Cardiovascular System: The Heart
• Heart pumps over
1 million gallons
per year
• Over 60,000 miles
of blood vessels
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Heart Location
Anterior surface
of heart
• Heart is located in the mediastinum
– area from the sternum to the vertebral column and
between the lungs Albert Grazia, M.S., N.D.
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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
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Heart Orientation
• Heart has 2 surfaces: anterior and inferior, and
2 borders: right and left
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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
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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)
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Layers of Heart Wall
• Epicardium
– visceral layer of
serous pericardium
• Myocardium
– cardiac muscle layer
is the bulk of the
heart
• Endocardium
– chamber lining &
valves
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Muscle Bundles of the Myocardium
• Cardiac muscle fibers swirl diagonally around the
heart in interlacingAlbert
bundles
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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
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Chambers and Sulci
Anterior
View
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Chambers and Sulci
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 tendineae: 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)
• 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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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
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Thickness of Cardiac Walls
Myocardium of left ventricle is much thicker than the right.
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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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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 valve
cusps, tightly closing the SL valves
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Valve Function Review
What are the ventricles doing?
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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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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
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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
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Blood Circulation
• Blood flow
– blue = deoxygenated
– red = oxygenated
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• The Right Atrium, receives "used blood" from the body. Blood
will be pushed through the tricuspid valve to the
• Right Ventricle, the chamber which will pump to the lungs
through the pulmonic valve to the
• Pulmonary Arteries, providing blood to both lungs. Blood is
circulated through the lungs where carbon dioxide is removed
and oxygen added. It returns through the
• Pulmonary Veins, which empty into the
• Left Atrium, a chamber which will push the Mitral Valve open.
Blood then passes into the
• Left Ventricle is the largest and most important chamber in the
heart. It pumps to the rest of the body. As it pumps, the pressure
will close the mitral valve and open the aortic valve, with blood
passing through to the
• Aorta, where it will be delivered to the rest of the body.
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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
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• The heart needs its own reliable blood supply in order
to keep beating- the coronary circulation.
• There are two main coronary arteries, the left and
right coronary arteries, and these branch further to
form several major branches.
• The coronary arteries lie in grooves (sulci) running
over the surface of the myocardium, covered over by
the epicardium, and have many branches which
terminate in arterioles supplying the vast capillary
network of the myocardium.
• Even though these vessels have multiple
anastomoses, significant obstruction to one or other
of the main branches will lead to ischaemia in the
area supplied by that branch.
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Coronary Arteries
• Branches off aorta above
aortic semilunar valve
• Left coronary artery
– circumflex branch
• in coronary sulcus, supplies
left atrium and left ventricle
– anterior interventricular art.
• supplies both ventricles
• Right coronary artery
– marginal branch
• in coronary sulcus, supplies
right ventricle
– posterior interventricular art.
• supplies both ventricles
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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
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Cardiac Muscle Histology
• Branching, intercalated discs with gap junctions,
involuntary, striated, single central nucleus per cell
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Cardiac Myofibril
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Conduction System of Heart
Coordinates contraction of heart muscle.
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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
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Rhythm of Conduction System
• SA node fires spontaneously 90-100 times per
minute
• AV node fires at 40-50 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
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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
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Physiology of Contraction
• Depolarization, plateau, repolarization
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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
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Action Potential in Cardiac Muscle
Changes in cell membrane permeability.
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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
– ventricular repolarization
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• The P wave represents atrial depolarization- there is
little muscle in the atrium so the deflection is small.
• The Q wave represents depolarization at the bundle of
His; again, this is small as there is little muscle there.
• The R wave represents the main spread of
depolarization, from the inside out, through the base of
the ventricles. This involves large amounts of muscle
so the deflection is large.
• The S wave shows the subsequent depolarization of
the rest of the ventricles upwards from the base of the
ventricles.
• The T wave represents Repolarization of the
myocardium after systole is complete. This is a
relatively slow process- hence the smooth curved
deflection.
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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
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– SV = EDV - ESVAlbert
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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
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Cardiac Cycle
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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)
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Auscultation
• Stethoscope
• Sounds of heartbeat are from turbulence in
blood flow caused by valve closure
– first heart sound (lub) is created with the closing
of the atrioventricular valves
– second heart sound (dup) is created with the
closing of semilunar valves
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Heart Sounds
Where to listen on chest wall for heart sounds.
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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 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
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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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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
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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
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Regulation of Heart Rate
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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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Important Blood Tests:
• Homocysteine
• C-Reactive Protein (C-RP)
• Lipoprotein (a)
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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
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– drugs, bypass graft,
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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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Unusual Sweating Predicts
Oncoming Heart Attack
• When individuals begin perspiring, after little or no exertion, while
experiencing discomfort in their chest, arm, neck or jaw, it could indicate
the onset of a heart attack.
• Time is of the Essence
• Time is of the essence during a heart attack. Doctors have urged people
who experience common symptoms to get to a hospital as quickly as
possible. These symptoms can include shortness of breath, cold sweats,
nausea, lightheadedness, or discomfort in the chest, arm, neck or jaw.
• Sweating is a Key Factor
• Many seek treatment when they experience a high number of these
symptoms; however, those who only experience a few may delay seeking
treatment, which can be dangerous. Sweating may be a key factor in the
symptoms that prompt individuals to seek treatment.
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Percutaneous Transluminal
Coronary Angioplasty
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Stent in an Artery
• Maintains patency of blood vessel
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By-pass Graft
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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.
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