Transcript Heart - Institut Teknologi Bandung

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2010
 The heart is located in the thoracic cavity between the lungs,
within the mediastinum.
 It is a hollow, cone-shaped, muscular organ, about the
size of a fist.
 The base (the widest part) of the heart is superior to its
apex (the pointed tip), which rests on the diaphragm.
 Also, the heart is on a slant; the base is directed toward the
right shoulder, and the apex points to the left hip.
 The base is deep to the second rib, and the apex is at the
level of the fifth intercostal space.
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Size and Location, Position of the Heart
and Associated Blood Vessels
• Size: Nine (9) inches long x three
(3) inches wide.
 Located within the mediastinum,
bordered laterally by the lungs,
posteriorly by the backbone, and
anteriorly by the sternum.
 Base  attached to several
large blood vessels and lies
beneath the second rib.
• Apex at the fifth intercostal
space
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• As the heart pumps the blood through the
pulmonary and systemic vessels, it performs
these functions:
1. keeps O2-poor blood separate from O2-rich
blood;
2. keeps the blood flowing in one direction —
blood flows away from and then back to the
heart in each circuit;
3. creates blood pressure, which moves the
blood through the circuits;
4. regulates the blood supply based on the
current needs of the body
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 The right side of the heart
pumps blood through
vessels of the pulmonary
circuit.
The heart is called double pump.
- Pulmonary circuit
- Systemic circuit
 The left side of the
heart pumps blood through
vessels of the systemic
circuit.
 Gas exchange occurs as
blood passes through lung
(pulmonary) capillaries.
 Gas exchange and nutrientfor-waste exchange occur
as blood passes through
tissue (systemic)
capillaries.
In this illustration, red vessels
carry O2-rich blood, and blue
vessels carry O2-poor blood.
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Wall of the Heart
The wall of the heart consists of three layers.
 an outer : epicardium or visceral pericardium
 a middle: myocardium  thick is composed of cardiac
muscle tissue.
 an inner : endocardium
 External to the epicardium is the double-layered 
parietal pericardium, composed of an inner serous
membrane and an outer fibrous membrane.
• The pericardial cavity, lies between the epicardium and
parietal pericardium containing pericardial fluid
• Fluid secreted by the serous membranes reduces friction,
enabling the heart to move freely within the pericardial sac.
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Anterior view of exterior heart anatomy
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Chambers and valves of the heart
The heart has four hollow chambers
• The upper (superior):
– thin-walled chambers, the left and right atria, which receive blood
returning to the heart.
– Atria send blood into the adjacent ventricles.
• The lower (inferior),
– thick-walled chambers are the left and right ventricles, which
pump blood into the arteries leaving the heart.
– the left ventricle has a thicker wall than the right ventricle;
– the right ventricle pumps blood to the lungs, which are nearby.
– The left ventricle pumps blood to all the other parts of the body.
 Internally, the atria are separated by the interatrial septum, and
the ventricles are separated by the interventricular septum.
 Therefore, the heart has a left and a right side.
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• The heart has 4 valves:
– two atrioventricular valves
– two semilunar valves.
 The Atrioventricular valves
 The valves prevent a backflow of blood from the ventricles into
the atria during systole - the contraction phase of the heart
cycle.
 The cusps have thin cords, the chordae tendineae, that
anchor them to papillary muscles on the walls of the ventricles
and prevent the valve cusps from being forced into the atria
during contraction.
 The tricuspid av-valve, has three flaps or cusps and
occurs between the right atrium and ventricle.
 The mitral or bicuspid av-valve has only two cusps,
and occurs between the left atrium and ventricle.
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 The semilunar valves
 the pulmonary semilunar valve
 located at the base of the pulmonary artery
 the aortic semilunar valve
 located at the base of the aorta
 They each have three cusps
 Prevent the backflow of blood from the arteries
into the ventricles during diastole - the
relaxation phase of the heart cycle.
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Internal heart anatomy
Semilunar valve
Bicuspid (mitral)
valve (AV valve)
Tricuspid valve
(AV valve)
Intraventricular septum
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Coronary Circuit
Cardiac muscle fibers and the other types of cells in the wall of the
heart are not nourished by the blood in the chambers;
Instead,
these cells receive nutrients and rid themselves of wastes at
capillaries embedded in the heart wall.
 coronary
arteries,
the left and right coronary arteries, branch from the aorta
just beyond the aortic semilunar valve.
• Each of these arteries branches then rebranches  encircled
by small arterial blood vessels  capillary bed in the heart  the
coronary veins (specifically called cardiac veins).
• The cardiac veins enter a coronary sinus,
• The coronary sinus enters the right ventricle.
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Coronary Circuit Disorders
• Heart diseases are especially associated with atherosclerosis, a
degenerative disorder of arterial walls.
First, soft masses of fatty materials, particularly cholesterol,
accumulate in the arterial wall.  Further changes result in
plaque, protrusions that interfere with blood flow.
If the coronary artery is partially occluded (blocked) by atherosclerosis,
the individual may suffer from ischemic heart disease.
 the person experiences insufficiency during exercise or stress.
 This may lead to angina pectoris, chest pain that is often
accompanied by a radiating pain in the left arm.
The blood may clot in an unbroken blood vessel, particularly if plaque is
present  thromboembolism is present when a blood clot breaks
away from its place of origin and is carried to a new location.
Thromboembolism leads to heart attacks when the embolus blocks a
coronary artery and a portion of the heart dies due to lack of oxygen.
Dead tissue is called an infarct, and therefore, a heart attack is
termed a myocardial infarction.
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The physiology of the heart pertains to its pumping action—
that is, the heartbeat.
It is estimated that the heart beats two and-a-half billion
times in a lifetime, continuously recycling some 5 liters (L) of
blood to keep us alive.
In this section, we will consider what causes the heartbeat,
what it consists of, and its consequences.
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Conduction System of the Heart
 The conduction system of the heart is a route of
specialized cardiac muscle fibers that initiate and
stimulate contraction of the atria and ventricles.
 The conduction system is said to be intrinsic, meaning
that the heart beats automatically without the need for
external nervous stimulation.
 The conduction system coordinates the contraction of
the atria and ventricles, so that the heart is an effective
pump.
 Without this conduction system, the atria and ventricles
would contract at different rates.
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Conduction System of the Heart
The SA node is called the pacemaker because it usually keeps
the heartbeat regular.
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Nodal system,
intrinsic conducting
system Components
 Sinoatrial (S-A) Node
(pacemaker)
 Atrioventricular node
(A-V node)
 A-V bundle
(Bundle of His)
 right and left bundle
branches
 down, the branches
give rise to enlarged
Purkinje fibers
Sinoatrial
(SA) node
(AV) node
AV bundle
Left bundle
branch
Right bundle
branch
Purkinje
fibers
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 An area other than the SA node can become the
pacemaker when it develops a rate of contraction that is
faster than the SA node.
 This site, called an ectopic pacemaker, may cause
an extra beat, if it operates only occasionally, or it
can even pace the heart for a while.
• Caffeine and nicotine are two substances that can
stimulate an ectopic pacemaker.
A rate of fewer than 60 heartbeats per minute is called
bradycardia, and more than 100 heartbeats per minute is
called tachycardia.
Another type of arrhythmia is fibrillation, in which the heart
beats rapidly but the contractions are uncoordinated.
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Electrocardiogram (ECG)
• Impulse transmission
through the conduction
system generated
electrical currents that
can be detected on the
body's surface.
• A graph that records the
electrical activity of the
myocardium during
a cardiac cycle is called
an electrocardiogram,
or ECG.
An ECG consists of a
set of waves:
 the P wave,
 a QRS complex,
 a T wave.
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• P-Wave
– Indicates atrial depolarization.
• The spread of the impulse from the S-A node through the two
atria.
• the atria are going to be in systole and that the atrial myocardium
is about to contract.
• QRS-Wave or Complex
– Represents ventricular depolarization
– the spread of the electrical impulse through the ventricles.
– Shortly after the QRS wave begins, the ventricles undergo
contraction.
• T-Wave
– Indicates ventricular repolarization
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Cardiac Cycle and Heart Sounds
 A cardiac cycle includes all the events that occur during one
heartbeat.
 On average, the heart beats about 70 times a minute,
although a normal adult heart rate can vary from 60 to 100
beats per minute.
 The right and left sides of the heart beat independently of
one another, but actually, they contract together.
 First the two atria contract simultaneously; then the two
ventricles contract together.
 The term systole refers to contraction of heart muscle, and
the term diastole refers to relaxation of heart muscle.
 During the cardiac cycle, atrial systole is followed by
ventricular systole.
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three phases of the cardiac cycle
Phase 1: Atrial Systole.
Phase 2: Ventricular Systole.
Phase 3: Atrial and Ventricular Diastole.
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Phase 1: Atrial Systole.
- Time
0.15 sec.
- During this phase, both atria are in systole (contracted),
while the ventricles are in diastole (relaxed).
- Rising blood pressure in the atria forces the blood to enter
the two ventricles through the AV valves.
- At this time, both atrioventricular valves are open, and the
semilunar valves are closed.
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Phase 2: Ventricular Systole.
- Time
0.30 sec.
- During this phase, both ventricles are in systole
(contracted), while the atria are in diastole (relaxed).
- Rising blood pressure in the ventricles forces the blood to
enter the pulmonary trunk leading to the pulmonary
arteries and aorta through the semilunar valves.
- At this time, both semilunar valves are open, and the
atrioventricular valves are closed.
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Phase 3: Atrial and Ventricular Diastole.
- Time
0.40 sec.
- During this period, both atria and both ventricles are in
diastole (relaxed).
- At this point, pressure in all the heart chambers is low.
- Blood returning to the heart from the superior and inferior
vena cava and the pulmonary veins fills the right
and left atria and flows passively into the ventricles.
- At this time, both atrioventricular valves are open, and
the semilunar valves are closed.
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Phase 1: atrial systole
Phase 3: atrial & ventricular diastole
Phase 2: ventricular systole
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Heart Sounds
• A heartbeat produces the familiar “LUB-DUP” sounds as
the chambers contract and the valves close.
• Lub sound
– The first heart sound, “lub,” is heard when the
ventricles contract and the atrioventricular valves
close.
– This sound lasts longest and has a lower pitch.
• Dup sound
– The second heart sound, “dup,” is heard when the
relaxation of the ventricles allows the semilunar valves
to close.
• The third sound seems to be caused by the vibration of
the ventricular walls and the atrio-ventricular valve cusps
during systole.
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Heart murmurs,
 which are clicking or swishing sounds heard after the
“lub,” are often due to ineffective valves.
• These leaky valves allow blood to pass back into the
atria after the atrioventricular valves have closed, or
back into the ventricles after the semilunar valves have
closed.
– A trained physician or health professional can diagnose heart
murmurs from their sound and timing.
– It is possible to replace the defective valve with an artificial valve.
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Cardiac Output
• Cardiac output (CO)
– is the volume of blood pumped out of a ventricle in one
minute.
• Cardiac output is dependent on two factors:
– heart rate (HR), which is the beats per minute;
– stroke volume (SV), which is the amount of blood
pumped by a ventricle each time it contracts.
• The CO of an average human is 5,250 ml (or 5.25 L) per minute,
which equates to about the total volume of blood in the human
body.
– Each minute, the right ventricle pumps about 5.25 L through the
pulmonary circuit, while the left ventricle pumps about 5.25 L through
the systemic circuit.
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Heart Rate
• A cardioregulatory center in the medulla oblongata of the brain
can alter the heart rate by way of the autonomic nervous
system (ANS)
– Parasympathetic motor impulses conducted by the vagus
nerve cause the heart rate to slow,
– Sympathetic motor impulses conducted by sympathetic motor
fibers cause the heart rate to increase.
• The cardioregulatory center is under the influence of the
cerebrum and the hypothalamus.
– when we feel anxious,
• the sympathetic motor nerves are activated, and the
adrenal medulla releases the hormones norepinephrine
and epinephrine.
 The result is an increase in heartbeat rate.
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 Activities such as yoga and meditation lead to
activation of the vagus nerve, which slows the
heartbeat rate.
• low body temperature  slows the rate.
• proper electrolyte concentrations are needed to keep the
heart rate regular.
• Exercise?
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Stroke Volume
• SV - which is the amount of blood that leaves a ventricle,
depends on the strength of contraction.
• The degree of contraction depends on
– the blood electrolyte concentration
– the activity of the autonomic system.
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Venous Return
Venous return is the amount of blood entering the heart by
way of the vena cava (right side of heart) or pulmonary
veins (left side of heart).
Any event that decreases or increases the volume or speed
of blood entering the heart will affect the strength of
contraction—called Starling’s Law.
• A slow heart rate allows more time for the ventricles to
fill and therefore increases the strength of contraction.
• A low venous return, as might happen if there is blood
loss, decreases the strength of contraction.
– Exercise increases the strength of contraction because
skeletal muscle contraction puts pressure on the veins and
speeds venous return.
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Regulation of blood
pressure and volume
Bottom:
When the blood sodium (Na) level
is low, a low blood pressure causes
the kidneys to secrete renin. Renin
leads to the secretion of
aldosterone from the adrenal
cortex. Aldosterone causes the
kidneys to reabsorb Na, and water
follows, so that blood volume and
pressure return to normal.
Top:
When the blood Na is high, a high
blood volume causes the heart to
secrete atrial natriuretic hormone
(ANH). ANH causes the kidneys to
excrete Na, and water follows. The
blood volume and pressure return
to normal.
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