Download Chapter 12 The Circulatory System

Chapter 12
The Circulatory System
HEART
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Location, size, and position
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Triangular organ located in mediastinum with two thirds
of the mass to the left of the body midline and one third
to the right; the apex on the diaphragm; shape and size
of a closed fist (Figure 12-1)
Cardiopulmonary resuscitation (CPR)—the heart lies
between the sternum in front and the bodies of the
thoracic vertebrae behind; rhythmic compression of the
heart between the sternum and vertebrae can maintain
blood flow during cardiac arrest; if combined with
artificial respiration procedure, it can be life saving
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HEART
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Anatomy
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Heart chambers (Figure 12-2)
• Two upper chambers called atria (receiving chambers)—
right and left atria
• Two lower chambers called ventricles (discharging
chambers)—right and left ventricles
• Wall of each heart chamber is composed of cardiac muscle
tissue called myocardium
• Endocardium—smooth lining of heart chambers—
inflammation of endocardium called endocarditis
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Covering sac, or pericardium
• Pericardium is a two-layered fibrous sac with a lubricated
space between the two layers
• Inner layer called visceral pericardium or epicardium
• Outer layer called parietal pericardium
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HEART
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Anatomy
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Heart action
• Contraction of the heart is called systole
• Relaxation is called diastole
Heart valves (Figure 12-3)
• Valves keep blood flowing through the heart and prevent
backflow
• Consist of two atrioventricular, or AV, and two semilunar
(SL) valves
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Tricuspid—at the opening of the right atrium into the ventricle
Bicuspid (mitral)—at the opening of the left atrium into the
ventricle
Pulmonary semilunar—at the beginning of the pulmonary
artery
Aortic semilunar—at the beginning of the aorta
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HEART
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Heart sounds
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Two distinct heart sounds in every heartbeat or
cycle—“lub-dub”
First sound (lub) is caused by the vibration and
closure of AV valves during contraction of the
ventricles
Second sound (dub) is caused by the closure
of the semilunar valves during relaxation of the
ventricles
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HEART

Blood flow through the heart (Figure 12-4)
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The heart acts as two separate pumps—the right atrium
and ventricle performing different functions from the left
atrium and ventricle
Sequence of blood flow: venous blood enters the right
atrium through the superior and inferior venae cavae—
passes from the right atrium through the tricuspid valve
to the right ventricle; from the right ventricle it passes
through the pulmonary semilunar valve to the pulmonary
artery to the lungs—blood moves from the lungs to the
left atrium, passing through the bicuspid (mitral) valve to
the left ventricle; blood in the left ventricle is pumped
through the aortic semilunar valve into the aorta and is
distributed to the body as a whole
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HEART
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Blood supply to the heart muscle
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Blood, which supplies oxygen and nutrients to the
myocardium of the heart, flows through the right and left
coronary arteries (Figure 12-5); called coronary
circulation
Blockage of blood flow through the coronary arteries is
called myocardial infarction (heart attack)
Angina pectoris—chest pain caused by inadequate
oxygen to the heart
Coronary bypass surgery—veins from other parts of the
body are used to bypass blockages in coronary arteries
(Figure 12-6)
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HEART
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Cardiac cycle
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Heartbeat is regular and rhythmic—each complete beat
is called a cardiac cycle—average is about 72 beats per
minute
Each cycle, about 0.8 seconds long, is subdivided into
systole (contraction phase) and diastole (relaxation
phase)
Stroke volume—volume of blood ejected from one
ventricle with each beat
Cardiac output—amount of blood that one ventricle can
pump each minute; average is about 5 L per minute at
rest
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HEART
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Conduction system of the heart (Figure 12-7)
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Intercalated disks are electrical connectors that join all
the cardiac muscle fibers in a region together so that
they receive their impulse, and thus contract, at about
the same time
SA (sinoatrial) node, the pacemaker—located in the wall
of the right atrium near the opening of the superior vena
cava
AV (atrioventricular) node—located in the right atrium
along the lower part of the interatrial septum
AV bundle (bundle of His)—located in the septum of the
ventricle
Purkinje fibers—located in the walls of the ventricles
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HEART
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Electrocardiogram (Figure 12-8)
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Specialized conduction system structures generate and
transmit the electrical impulses that result in contraction
of the heart
These tiny electrical impulses can be picked up on the
surface of the body and transformed into visible tracings
by a machine called an electrocardiograph
The visible tracing of these electrical signals is called an
electrocardiogram, or ECG
The normal ECG has three deflections or waves
• P wave—associated with depolarization of the atria
• QRS complex—associated with depolarization of the
ventricles
• T wave—associated with repolarization of the ventricles
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BLOOD VESSELS
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Types
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Arteries—carry blood away from the heart
Veins—carry blood toward the heart
Capillaries—carry blood from the arterioles to
the venules
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BLOOD VESSELS
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Structure (Figure 12-9)
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Arteries
• Tunica intima—inner layer of endothelial cells
• Tunica media—smooth muscle with some elastic tissue,
thick in arteries; important in blood pressure regulation
• Tunica externa—thin layer of fibrous elastic connective
tissue
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Capillaries—microscopic vessels with only one layer—
tunica intima
Veins
• Tunica intima—inner layer; valves prevent retrograde
movement of blood
• Tunica media—smooth muscle; thin in veins
• Tunica externa—heavy layer of fibrous connective tissue in
many veins
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BLOOD VESSELS
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Functions
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Arteries—distribution of nutrients, gases, etc., with
movement of blood under high pressure; assist in
maintaining the arterial blood pressure
Capillaries—serve as exchange vessels for nutrients,
wastes, and fluids
Veins—collect blood for return to the heart; low pressure
vessels
Names of main arteries—see Figure 12-10 and
Table 12-1
Names of main veins—see Figures 12-11 and 1212 and Table 12-2
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CIRCULATION
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Systemic and pulmonary circulation—refers to the
blood flow through the vessels arranged to form a
circuit or circular pattern (Figure 12-13)
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Systemic circulation
• Carries blood throughout the body
• Path goes from left ventricle through aorta, smaller
arteries, arterioles, capillaries, venules, venae cavae, to
right atrium
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Pulmonary circulation
• Carries blood to and from the lungs; arteries deliver
deoxygenated blood to the lungs for gas exchange
• Path goes from right ventricle through pulmonary arteries,
lungs, pulmonary veins, to left atrium
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CIRCULATION
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Hepatic portal circulation (Figure 12-14)
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Unique blood route through the liver
 Vein (hepatic portal vein) exists between two
capillary beds
 Assists with homeostasis of blood glucose
levels
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CIRCULATION
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Fetal circulation (Figure 12-15)
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Refers to circulation before birth
Modifications required for fetus to efficiently
secure oxygen and nutrients from the maternal
blood
Unique structures include the placenta,
umbilical arteries and vein, ductus venosus,
ductus arteriosus, and foramen ovale
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BLOOD PRESSURE
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Defining blood pressure—push, or force,
of blood in the blood vessels
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Highest in arteries, lowest in veins (Figure 1216)
 Blood pressure gradient causes blood to
circulate—liquids can flow only from the area
where pressure is higher to where it is lower
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BLOOD PRESSURE
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Factors that influence blood pressure
(Figure 12-17)
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Blood volume
 Strength of contractions
 Blood viscosity
 Resistance to blood flow
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BLOOD PRESSURE
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Fluctuations in blood pressure
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Blood pressure varies within normal range
Normal average arterial blood pressure is 120/80
Venous blood pressure within right atrium called central
venous pressure
Venous return of blood to the heart depends on five
mechanisms—a strongly beating heart, adequate arterial
blood pressure, valves in the veins, pumping action of
skeletal muscles as they contract, and changing
pressures in the chest cavity caused by breathing
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PULSE
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Definition—alternate expansion and recoil
of the blood vessel wall
Nine major "pulse points" named after
arteries over which they are felt (Figure
12-18)
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