Transcript Slide 1

The Circulatory System
rev 6-10
•The circulatory system consists of the heart,
blood vessels and the blood itself.
•The circulatory system is essential
•to supply all cells with what they need and
•remove substances they no longer need.
•This system maintains homeostasis.
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Types of Blood Vessels
 Arteries—carry blood away from the heart
 Veins—carry blood toward the heart
 Capillaries—carry blood from the arterioles
to the venules. Exchange of nutrients, wastes
and respiratory gases takes place here because
capillaries have only one layer.
Bigggest Artery, Biggest Vein
• Aorta: carries blood out of the left ventricle of
the heart
• Inferior and Superior Vena Cava return
blood to the right atrium of the heart after the
blood has circulated throughout the body.
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Structure--Arteries
 inner layer of endothelial cells
 middle: smooth muscle tissue
 This layer is thicker in arteries than in veins
 outermost layer of connective tissue
Structure—Veins
 Inner: layer of endothelial cells
 Valves prevent backward movement of blood
 Middle: smooth muscle tissue
 thinner layer in veins than in arteries
 outermost layer of connective tissue
 can be thicker than in arteries
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Functions
 Arteries—take blood away from the heart to the body
 distribute nutrients and gases;
 movement of blood is under higher pressure than in
veins;
 assist in maintaining blood pressure
 Veins---return blood to the heart;
 lower pressure than in arteries;
 can act as a blood volume reservoir for blood
because they can expand
 veins have larger diameters (lumen) than arteries
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• the larger diameter of veins allows them to
stretch to accommodate large volumes of
blood at low pressures
– because veins can stretch, it is more difficult for
them to return blood to the heart against the force
of gravity
– people who spend a lot of time on their feet may
get varicose veins because of this
Factors which help veins to return blood to heart
• Contraction of skeletal muscles—skeletal
muscle pump
– as we move, muscles contract and relax and they
press against veins and help push blood to the
heart
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– One-way valves—blood can only flow in
one direction
• Open passively to allow blood to move toward
the heart and close whenever blood begins to
flow backward
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Pressure changes associated with breathing
– movements associated with breathing also help
pump blood. This is called a respiratory pump
and helps to push blood from the abdomen to the
chest and to the heart.
• when we breathe, there are pressure changes
in the thoracic and abdominal cavities
• during inhalation, abdominal pressure
increases and squeezes abdominal veins
• simultaneously, pressure within the thoracic
cavity decreases which dilates the thoracic
veins and thus propels the blood.
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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 (skeletal muscle pump), and
• changing pressures in the chest cavity
caused by breathing (respiratory pump)
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The Heart
Structure: composed of cardiac muscle enclosed
by pericardium, a fibrous sac
• located in mediastinum
– is approximately the size of a closed fist
Pericardium protects the heart, anchors it to
surrounding structures, prevents it from
overfilling with blood
– Pericardial cavity separates it from heart muscle itself
and contains a tiny amount of fluid to allow heart and
pericardium to glide smoothly every time the heart
contracts
– Rate of pumping usually controlled by brain
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Anatomy
Heart chambers
 The two upper chambers are called the right
and left atria and are the chambers which
receive blood
 The two lower chambers are the right and left
ventricles; these are the chambers which eject
blood
 The wall of each heart chamber is composed of
cardiac muscle tissue called myocardium
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

 In order to keep the blood moving in a
forward direction, there are valves in between
each area the blood must go.
Valves of the heart
 Atrioventricular or AV valves are located
between the atria and the ventricles
 Left side: bicuspid or mitral valve
 Right side: tricuspid valve
Chordae tendineae
 are located inferiorly to the AV valves and
attach the valves to the heart wall
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• Semilunar Valves are located between the 2
ventricles and the arteries that carry blood away
from the heart when a contraction begins.
– Pulmonary semilunar valve is located at the
beginning of the pulmonary artery
– Aortic semilunar valve is located at the beginning of
the aorta
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Blood flow through the heart
 venous blood enters the right atrium through the
superior and inferior venae cavae (biggest vein)
 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
 from the lungs blood flows to the left atrium through
the pulmonary vein
 passes through the bicuspid (mitral) valve to the left
ventricle;
 blood in the left ventricle is pumped through the
aortic semilunar valve into the aorta (biggest artery)
and is distributed to the entire body
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• There are actually 2 circulations through the
heart:
• The pulmonary circulation involves movement of
blood from the right ventricle to the pulmonary
arteries to the lungs and then through the
pulmonary veins back to the left atria.
• The systemic circulation involves movement of
the blood from the left ventricle throughout the
body.
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• Part of the systemic circulation includes the
coronary circulation: blood supply to the
heart muscle itself
 Blood, which supplies oxygen and nutrients
to the myocardium of the heart, flows from
the first branch off the aorta through the
right and left coronary arteries
 Blockage of blood flow through the coronary
arteries can cause a myocardial infarction
(heart attack)
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Types of Circulation
Systemic circulation


Carries blood throughout the body
Path goes from left ventricle through aorta, smaller
arteries, arterioles, capillaries, venules, inferior and
superior venae cavae, to right atrium
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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Hepatic portal circulation (blood route through the liver)
• Veins from the spleen, stomach, pancreas,
gallbladder and intestines detour their blood to the
liver via the hepatic portal vein
• Blood then goes through the capillaries of the liver
where excess glucose from our meals is removed
and stored as glycogen
– Blood is also detoxified---poisonous substances, alcohol,
drugs are removed
• Then the blood enters into the systemic circulation
via the inferior vena cava
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Heart pumping
– The contraction of the heart is called systole;
relaxation is diastole
– When the heart beats, the atria contract first
and force blood into the ventricles
– Once filled, the ventricles contract and force
blood out of the heart
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Electrical Conduction System of the Heart
 Intercalated disks are electrical connectors that
join all the cardiac muscle fibers in a region
together so that they receive their impulse and
then contract at about the same time
 4 structures are located in the wall of the heart.
These are specialized to initiate strong impulses
and rapidly conduct them to certain regions in
the wall of the heart. This ensures that first the
atria contract and then the ventricles contract in
an efficient pattern
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Cardiac Anatomy Quiz
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Blood Pressure
• Blood pressure measures the force of blood in the
blood vessels
• Highest in arteries, lowest in veins
• Blood pressure causes blood to circulate—liquids
can flow only from the area where pressure is
higher to where it is lower
• Top number= systolic reading—force the heart
uses to pump the blood
• Bottom number= diastolic reading—heart at rest
or relaxing
• Normal is approximately 120/70-80
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• Blood volume, heartbeat, and viscosity (thickness) are
the main factors that produce blood pressure
• Blood pressure varies within normal range from time
to time
Pulse
• Definition—alternate expansion and recoil
of the blood vessel wall
• Places where the pulse is typically taken:
 carotid artery, brachial artery, radial artery
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Cardiovascular Disorders
 Angina pectoris: chest pain caused by
inadequate oxygen to the heart
 Pericarditis: layer of the coverings of the
heart becomes inflamed. This causes pain
each time the heart beats
 Heart murmur is created by obstructions
the blood must flow over or if the valves
don’t function properly
 Coronary bypass surgery: veins from
other parts of the body are used to bypass
blockages in coronary arteries
 Aneurysm: the arterial wall has a weakness
and blood pushes it out into a balloon shape
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• Hypertension: high blood pressure
– Signs: headache, blurred vision
– Causes: kidney disorders, smoking, overweight,
stress
• Hypotension: blood pressure too low so blood can’t be
pushed throughout the body and back to the heart;
generally thought of as reducing blood flow to the brain
– Signs: dizziness, fainting
– Causes: orthostatic, severe burns, blood loss
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• Myocardial infarction/heart attack: permanent cardiac
damage
• Congestive heart failure: decrease in pumping
efficiency
• Embolism: blockage of blood vessels
– Thrombus=clot that doesn’t move
– Embolus=clot that travels through the circulatory system
• Stroke or Cerebrovascular Accident or brain attack:
impaired blood flow with subsequent damage to the
brain
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Disorders of Blood Clotting
• Thrombus: clot forms in the blood vessel
• Embolus: clot which breaks off and circulates through
the blood
– Medications to dissolve clots:
• Streptokinase and recombinant tissue
plasminogen activator
• Hemophilia: Inherited condition caused by a deficiency
of one or more clotting factors (known as clotting factor
VIII)
– When a blood vessel is damaged, blood either clots
very slowly or not at all
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Reducing the Risks of Heart Disease
• Smoking: don’t
• Weight: maintain a normal weight (weighing too much
will increase the risk of a heart attack or stroke)
• Monitor cholesterol levels, HDL, LDL, triglycerides
• Regular exercise
• Blood pressure: treat hypertension
• Control of diabetes mellitus
• Stress: avoid chronic stress
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