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—— BIOL 221 Chapter 18 ——
The Heart
76 slides
1
The Heart
• The Heart: size, location, orientation:
– cone-shaped, about the size of your own fist.
– weighs 250 — 350 grams (1/2 — 3/4 of a pound).
– snugly enclosed within the mediastinum.
– is mostly under the sternum and extends from the
2nd Rib to the 5th Intercostal Space (ICS).
– 2/3 of it is to the left of midsternal line.
– 1/3 of it is to the right of midsternal line.
– Base is “top” part. Great vessels attached here.
– Apex is the pointed “bottom” part. PMI.
• Point of Maximal Intensity (PMI):
– Left 5th ICS at the mid-clavicular line (below nipple).
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The Heart
• Coverings of the Heart:
– Pericardium
• the double-walled sac around the heart
• Fibrous Pericardium
– protects heart
– anchors it to surrounding structures
– prevents heart from overfilling with blood
• Parietal Pericardium
– the serosa layer attached to the Fibrous pericardium
• Visceral Pericardium
– the serosa layer attached to the heart myocardium
– also known as the Epicardium
• Pericardial Cavity
– the space between Parietal and Visceral Pericardium.
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Heart Location
Figure 18.2a Location of the heart in the mediastinum.
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Heart Location
Figure 18.2b Location of the heart in the mediastinum.
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Heart Location
Figure 18.2c Location of the heart in the mediastinum.
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Pericardial & Heart Wall Layers
Figure 18.3 Layers of the pericardium and of the heart wall.
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The Heart
• Pericarditis
– inflammation of the pericardium
– roughens the serous layers
– normal, smooth heart beats are now rubbing up
against inflamed sac creating a sound:
• pericardial friction rub
– serous layers are innervated... this is painful.
– adhesions (sticky areas of scar tissue) form over
time, impairing proper heart contraction.
– large amounts of inflammatory fluid can accumulate
in sac causing compression of the heart... called
cardiac tamponade.
• fluid removed by pericardialcentesis.
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Layers of the Heart
• Epicardium
• outer layer
• also called the visceral pericardium
• gets infiltrated with fat as you age
• Myocardium
•
•
•
•
middle layer
is the layer of cardiac muscle cells that contracts
arranged in spiral or circular bundles (fig. 18.3)
fibrous skeleton of the heart... reinforces heart.
• Endocardium
• inner layer of squamous epithelium.
• continuous with the endothelial blood vessel lining.
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Cardiac Muscle Bundles
Figure 18.4 The circular and spiral arrangement of cardiac muscle bundles in the
myocardium of the heart.
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The 4 Heart Chambers
– Right & Left Atria
• separated by the interatrial septum
– Right & Left Ventricle
• separated by the interventricular septum
• heart is slightly rotated so that most of anterior
surface is Right Ventricle and Left Ventricle is
mostly inferior and posterior part of heart.
• coronary sulcus or atrialventricular groove is the
junction between the atria and ventricles.
• anterior interventricular sulcus
– groove on anterior surface of heart
– contains anterior interventricular artery (LAD)
– contains great cardiac vein.
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Heart: Anterior View
Figure 18.5a Gross anatomy of the heart.
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Heart: Anterior View
Figure 18.5b Gross anatomy of the heart.
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The 4 Heart Chambers
• Atria:
– posterior wall:
• is smooth on both right and left atria
– anterior wall:
• is smooth on the left
• has pectinate muscles on the right
– on top is a small extension called the auricle.
• looks like floppy dog ears.
• increases the volume capacity of both atria
– interatrial septum:
• fossa ovalis marks the spot where an opening the
foramen ovale existed in the fetal heart.
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Heart: Anterior View of Right Atrium
Figure 18.5c Gross anatomy of the heart.
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Heart: Coronal / Frontal Section
Figure 18.5e Gross anatomy of the heart.
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Heart: Coronal / Frontal Section
Figure 18.5f Gross anatomy of the heart.
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The 4 Heart Chambers
• Blood enters the Right Atria by 3 veins:
– Superior Vena Cava
• brings in blood coming from above the diaphragm
– Inferior Vena Cava
• brings in blood coming from below the diaphragm.
– Coronary Sinus
• collects blood draining from the myocardium
• Blood enters the Left Atria by 4 veins:
– 4 pulmonary veins
• bring in oxygenated blood from the lungs.
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Heart: Posterior View
Figure 18.5d Gross anatomy of the heart.
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The 4 Heart Chambers
• Ventricles:
– heart is rotated so that:
• right ventricle is located mostly anterior.
• left ventricle is located mostly posterior / inferior.
– trabeculae carneae
• “crossbars of flesh” ridges in both ventricles.
– papillary muscles
• attach to chordae tendineae which are attached to the
Tricuspid and Mitral (Bicuspid) valves.
• keep valves from prolapsing into atria during systole.
– Pulmonary Trunk is blood’s exit from right ventricle
on way to get oxygenated in lungs.
– Aorta is blood’s exit from left ventricle to body.
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Systemic & Pulmonary Circuits
Figure 18.1 The systemic and pulmonary circuits.
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Pathway of Blood through the Heart
• pulmonary circuit
– right atria and right ventricle
– sends deoxygenated blood to the lungs
– is a short, low-pressure system
• this is why walls of right ventricle are thinner.
• right ventricle is more flat and encircling in shape.
• system circuit
– left atria and left ventricle
– sends oxygenated blood to the body
– long pathway, high-pressure system.
– 5 times as much friction encountered.
• this is why walls of left ventricle are 3 times thicker.
• left ventricle is circular, making it a powerful pump.
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Walls of Right & Left Ventricles
Figure 18.9 Anatomical differences between the right and left ventricles.
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Coronary Circulation
– blood pumping through heart is too thick to make
diffusion practical for nutrient delivery.
– Coronary circulation is a system of arteries and
veins just for servicing the heart.
• left coronary artery
– very short. has two branches after about 1 inch of travel.
– Anterior Interventricular Artery
» also known as Left Anterior Descending
» also known as “widow-maker”... as it is the most common
location for Myocardial Infarction (Heart Attack) to occur.
» lies in anterior interventricular sulcus.
» supplies blood to interventricular septum
» supplies blood to the anterior wall of both ventricles.
– Circumflex Artery
» supplies blood to left atrium & posterior left ventricle.
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Coronary Circulation
– Coronary Circulation.... continued
• Right Coronary Artery
– Marginal Artery
» supplies blood to lateral right side of heart
– Posterior Interventricular Artery
» supplies blood to posterior ventricular walls.
– Coronary Circulation common variations:
• 15% of people have both Anterior and Posterior
Interventricular Artery as branches off the Left Coronary
Artery.
• 4% of people only have one coronary artery (usually the
left) supplying all blood to heart.
– Anastomoses supply additional collateral
circulation as alternate routes. (life saving).
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The Coronary Arteries
Figure 18.10a Coronary circulation.
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The Cardiac Veins
Figure 18.10b Coronary circulation.
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Coronary Circulation
• More Facts:
– vessels and branches coarse within the epicardium
and send branches inward to supply the
myocardium.
– deliver blood only during diastole.
– venous blood is collected by cardiac veins and
empties into the coronary sinus.
• this returns deoxygenated blood to the right atrium.
• has 3 feeding tributaries dumping blood into it.
– great cardiac vein from the anterior interventricular sulcus.
– middle cardiac vein from the posterior interventricular sulcus.
– small cardiac vein from heart’s right inferior margin.
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Coronary Arterial Blockages
• Angina Pectoris
– is chest pain due to a deficiency of blood to the
myocardium without cell death.
– precedes MI
• Myocardial Infarction
– prolonged blockage leading to cell death.
• Levine Sign is a clenched fist over heart while
experiencing chest pain... seen in MI and angina.
• most common cause (both) is arteriosclerosis.
• dead heart muscle is replaced by scar tissue.
– this has no contractility and will bulge out with systole and can be
seen on echocardiogram.
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Myocardial Necrosis in an MI
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Acute Myocardial Infarction of Left Ventricle
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Heart Valves
• enforces one-way flow of blood.
• pressure changes open and close them.
• two atrioventricular (AV) valves
– Tricuspid
• 3 flexible cusps between right atrium and ventricle.
– Mitral (Bicuspid)
• 2 flexible cusps between left atrium and ventricle.
– each has chordae tendineae which anchor the
cusps to papillary muscles in the ventricular wall.
Keeps cusps from prolapsing into atria during
systole.
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Heart Valves: Superior View
Figure 18.6a Heart valves.
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Heart Valves: Superior View
Figure 18.6b Heart valves.
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Tricuspid Valve
Figure 18.6c Heart valves.
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Heart: Coronal / Frontal Section
Figure 18.6d Heart valves.
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Heart Valves
• two semilunar valves:
– Aortic semilunar valve:
• blood leaving the left ventricle into the ascending aorta is
prevented from back flowing in diastole.
• open during systole, closed during diastole.
– Pulmonic semilunar valve:
• blood leaving the right ventricle into the pulmonary artery
is prevented from back flowing in diastole.
• open during systole, closed during diastole.
– Note: small amounts of blood do spurt back into the
venae cavae and pulmonary veins as they have no
valves but it is minimal.
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The AV Valves Open
Figure 18.7a The function of the atrioventricular (AV) valves.
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The AV Valves Close
Figure 18.7b The function of the atrioventricular (AV) valves.
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Semilunar Valves Open
Figure 18.8a The function of the semilunar (SL) valves.
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Semilunar Valves Close
Figure 18.8b The function of the semilunar (SL) valves.
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Valve Pathology
• an incompetent valve (a leaky one) leads to
“re-pumping” of blood
• in valvular stenosis (a stiff valve) leads to
difficulty in blood leaving the ventricles or atria.
• both conditions can lead to dilatation and
hypertrophy of the heart chamber preceding
the bad valve.
– i.e. Left ventricular hypertrophy and dilatation with
aortic valve stenosis.
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Left Ventricular Hypertrophy
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Left Ventricular Hypertrophy
With & Without Dilatation
LV Hypertrophy
without dilatation
Normal
LV Hypertrophy
with dilatation
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Cardiac Muscle Fibers
• Cardiac Muscle:
– striated.
– contracts by sliding filament mechanism.
– short, fat, branched, interconnected cells.
– only one or two centrally located nuclei.
– cells are attached to fibrous skeleton of heart
• gives the cardiac cells something to pull or exert their
forces on.
– intercalated discs lock adjacent cells together
• gap junctions and desmosome located here.
– gap junctions allow all cells to coordinate during a contraction by
allowing electrical current to flow from one cell to the next
seamlessly. This is called functional syncytium.
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Cardiac Muscle Fibers
• Cardiac Cells.... continued
– cells are 25-35% filled with mitochondria
• skeletal muscle only has 2% volume as mitochondria.
• give cardiac cells a high resistance to fatigue.
– 1% of cardiac cells are “self-excitable” or have what
is called automaticity.
• the innate rate at which a cardiac cell will fire is based on
the location of those cells.
– SA node fires the fastest at about 75 to 100 beats per minute.
– AV node fires at about 40 to 60 beats per minute.
– ventricular cells only fire at about 40 or less beats per minute.
– the heart contracts as a unit or not at all.
– very long refractory period of 250 milliseconds.
– prevents tetanic contractions (this would stop blood flow).
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Cardiac Muscle Cell
Figure 18.11 Microscopic anatomy of cardiac muscle.
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The Action Potential of Cardiac Muscle Cells
Figure 18.15 The action potential of contractile cardiac muscle cells.
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The Action Potential of Cardiac Muscle Cells
Figure 18.15 The action potential of contractile cardiac muscle cells.
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Pacemaker & Action Potentials
of Auto-rhythmic Heart Cells
Figure 18.12 Pacemaker and action potentials of typical cardiac pacemaker cells.
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Heart Physiology
• Intrinsic Conduction System
– sequence of excitation:
• Sinoatrial Node (SA Node):
– located in the right atrial wall, just inferior to the entrance of the
superior vena cava.
– inherit automaticity is about 75 to 100 bpm*
» higher end with loss of extrinsic neural & hormones.
– is the heart’s pacemaker. (i.e. determines our heart rate)
– originates our sinus rhythm.
• Inter-nodal Pathway
– pathway for electrical signal from SA to AV node.
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Heart Physiology
• Intrinsic Conduction System... continued.
• Atrioventricular Node (AV node):
– located just above the tricuspid valve.
– impulse delay of about 0.1 seconds to allow atria to respond and
contract before ventricles.
• Atrioventricular Bundle (Bundle of His)
– located in the superior part of interventricular septum.
– atria and ventricles are NOT connected by gap junctions. AV
Bundle is the only connection between them.
• Right and Left Bundle Branches
– branches that supply the ventricles with electrical signal.
• Purkinje Fibers
– from the apex, branch upward through myocardium of the
ventricles to depolarize and thus contract heart cells.
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Cardiac Intrinsic Conduction System
Figure 18.13 Intrinsic cardiac conduction system and action potential succession
during one heartbeat.
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Heart Conduction System Pathology
• arrhythmias
• abnormal heart rhythm
• fibrillation
• rapid, irregular or out-of-phase contractions
• ineffective ejection fraction.
• ectopic focus
• abnormal pacemaker that overrides AV node.
• junctional rhythm
• pace of heart is set by AV node. (40-60 bpm).
• Heart Block
• impulse transmission through AV node is impaired.
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Autonomic Innervation of the Heart
• The autonomic nervous system can adjust the
heart rate up or down.
– sympathetic nervous system
• fibers originate from cardioacceleratory center in the
medulla oblongata.
• fibers travel down spinal cord and exit at T1 to T5.
• increase the heart rate.
– parasympathetic nervous system
• fibers originate from cardioinhibitory center in the
medulla oblongata.
• fibers travel with the vagus nerve (CN X).
• decrease the heart rate.
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Autonomic Innervation of the Heart
Figure 18.14 Autonomic innervation of the heart.
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The ECG (EKG) Sequence
Figure 18.17 The sequence of depolarization and repolarization of the heart related
to the deflection waves of an ECG tracing.
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The ECG (EKG) Sequence
Figure 18.17 The sequence of depolarization and repolarization of the heart related
to the deflection waves of an ECG tracing.
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Electrocardiogram Tracing: Lead I
Figure 18.16 An electrocardiogram (ECG) tracing.
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ECG Arrhythmias
Figure 18.18 Normal and abnormal ECG tracings.
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Heart Valve Auscultation Areas
Figure 18.20 Areas of the thoracic surface where the sounds of individual valves are
heard most clearly.
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The Cardiac Cycle
• Mechanical events follow electrical ones.
• The Cardiac Cycle
– Ventricular Filling: mid-to-late diastole
• blood flows passively through atria into ventricles.
– about 80% of blood enters ventricles this way.
• both AV valves are open
• both SL valves are closed
• ends with atria contracting to shove 20% into the
ventricles. (also known as the “atrial kick”).
• max volume of blood ventricles are filled with at this point
is end diastolic volume (EDV).
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The Cardiac Cycle
– Ventricular Systole
• as the atria relax for the rest of the cycle, the ventricles
begin to contract.
• for a split-second, the pressure in the ventricles is
enough to close both AV valves, but not enough to
overcome the back pressure on the SL valves. This is
called isovolumetric contraction phase.
• after that split-second phase, ventricular contraction is
enough to open the SL valves and blood enters the lungs
and systemic circulation.
– This is known as ventricular ejection phase
– pressure in Aorta is 120 mm Hg !!!
» This is your systolic blood pressure !!!
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The Cardiac Cycle
– Isovolumetric Relaxation: early diastole
• for a split-second the ventricles are unable to squeeze
anymore blood out to the lungs and body and the SL
valves close. However, the pressure is still great enough
in the ventricles to keep the AV valves closed as well.
– this is known as isovolumetric relaxation.
• as the aortic valve closes, it causes a brief rise in the
aortic pressure wave as back-flowing blood rebounds off
the closed cusps.
– this pressure wave phenomenon is the dicrotic notch.
• pressure from blood heading toward heart to fill it again,
overcomes pressure in AV valves and they open and the
cycle starts all over again.
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The Cardiac Cycle
• Systemic pressure:
– systolic pressure normal is 120 mm Hg.
– diastolic pressure normal is 80 mm Hg.
– pressure measured with blood pressure cuff.
• Pulmonary pressure:
– systolic pressure normal is 24 mm Hg.
– diastolic pressure normal is 8 mm Hg.
– pressure measured with swan-ganz catheter.
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Cardiac Cycle Summary
Figure 18.19 Summary of events during the cardiac cycle.
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Cardiac Cycle Summary
Figure 18.19 Summary of events during the cardiac cycle.
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Cardiac Output
• Cardiac Output (CO)
– amount of blood pumped out by each ventricle in
one minute.
– entire blood supply is circulated in 1 minute at rest.
– formula:
• Heart Rate x Stroke Volume
• non athletic CO is 4 to 5 times resting at 20-25 L/min.
• athletes can increase CO to 7 times resting at 35 L/min.
• Stroke Volume (SV)
– volume of blood pumped out by one ventricle with
each beat. Normal resting value is 70 ml/beat.
• formula:
SV = EDV - ESV
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Cardiac Output
• Frank-Starling Law of the Heart:
– main variable affecting Stroke Volume is preload:
• Preload is proportional to the amount of ventricular
myocardial fiber stretch just before systole.
– i.e. the more you stretch cardiac muscle by filling the ventricles
with blood, the stronger the contraction force.
– increasing venous return to heart will fill heart more.
» slow heart rate at rest... more time for ventricle filling.
» fast heart rate with exercise (muscles squeeze blood back
toward heart).
• Afterload is the pressure the ventricles must overcome
to force open the SL valves.
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Preload vs. Afterload
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NE Increases Heart Contractility
Figure 18.22 Norepinephrine increases heart contractility via a cyclic AMP second
messenger system.
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Regulating Heart Rate Special Cases
– cut the vagal nerve to the heart and the resting
heart rate goes from 75 to 100 bpm.
• this is the vagal tone of the heart.
– remember if you have a spinal injury above T1,
then you still have adrenal medulla hormones
(epinephrine and norepinephrine) to increase
heart rate.
– high or low Ca2+ and K+ levels can easily affect
heart function.
– Tachycardia adult heart rate over 100 bpm.
– Bradycardia adult heart rate under 60 bpm.
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Diseases of Cardiac Output
• Congestive Heart Failure
– pump is ineffective at delivering blood.
– can be a result from any of the following:
• Coronary Atherosclerosis
– hypoxic hearts are bad pumps
• High Blood Pressure
– overworked hearts thicken and become bad pumps.
• Myocardial Infarction
– damaged heart walls are bad pumps.
• Dilated Cardiomyopathy
– flabby, stretched hearts are bad pump.
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Cardiac Output Regulation
Figure 18.21 Factors involved in determining cardiac output.
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Fetal Heart Anatomy Differences
• Foramen ovale
– connects the two atria
– becomes fossa ovalis in the adult.
• Ductus Arteriosus
– vessel connecting pulmonary artery and aorta.
– becomes ligamentum arteriosum in adult.
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Fetal Heart Defects
Figure 18.24 Three examples of congenital heart defects.
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