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BIO 156
Chapter 6
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The Circulatory System
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The Heart
The heart is a muscular organ that pumps blood
throughout the body There are three layers in the heart walls:
The pericardium
The myocardium
The endocardium
Blood flows through two distinct circuits in the
cardiovascular system.
The pulmonary circuit, which transports blood toand from the lungs.
The systemic circuit, which delivers blood to the
body and returns it to the heart.
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The human heart consists of four chambers: two atria
and two ventricles.
The right atrium and right ventricle service the
pulmonary circuit.
The right atrium receives blood, low in oxygen and
rich in carbon dioxide, from the superiorand
inferior vena cavae.
From the right atrium, blood is pumped into the
right ventricle, then to the lungs.
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Blood, resupplied with oxygen, returns to the heart via
the pulmonary veins, which empty into the left atrium.
The left atrium and left ventricle pump blood into the
aorta and are part of the systemic circuit.
Blood from the aorta supplies cells of tissues and organs
with oxygen and picks up cellular wastes.
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Valves help control the flow of blood in the heart
Heart sounds result from the closing of heart
valves
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Heart rate is controlled primarily by an internal
pacemaker .
The sinoatrial (SA) node is located in the upperwall of the right atrium.
The cells of the SA node discharge periodically,sending impulses to all atrial muscle cells, whichcause them to contract in unison.
The impulse next travels to the ventricles, but itspassage is delayed to time for the ventricles to fill.
The impulse is channeled the atrioventricular(AV) node.
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External factors regulate thepacemaker
The SA node is curbed byimpulses transmitted by nervesthat connect the heart with acontrol center in the brain.
Hormones also play a role incontrolling heart rate.
The hearts electrical activity can
be measured on the surface of thechest.
The measurement is called anelectrocardiogram.
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Blood flows from the heart to the capillaries, then back
to the heart via veins.
Arteries and arterioles deliver oxygen-rich blood to
tissues and organs.
The aorta and many of its chief branches areelastic.
Blood pressure and flow rate are highest in the
aorta and drop considerably as the arteries branch.
This decline enhances the rate of exchangebetween the blood and the tissues.
The Blood Vessels
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Capillariespermittheexchangeofnutrientsandwastes
Capillariesformbranchingnetworks,knownascapillarybeds,amongthecellsofbodytissues
Venulesdraincapillariesandmergetoformveinsthattransportbloodbacktotheheart.
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Intheveinsabovetheheart,gravityisthechiefmeansofpropulsion.
Veinsbelowtheheartrelyonthemovementofbodypartstosqueezethebloodupwardandonvalvesthatpreventthebackflowofblood
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The lymphatic system is a
secondary system of
vessels that returns excess
fluid to the circulatory
system
The lymphatic system
includes the lymphnodes, spleen, thymus,
and tonsils.
Lymph nodes filter the
lymph. Normally, lymph is
removed from tissues at
a rate equal to its
production.
The Lymphatic System
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Cardiovascular Diseases Causes and Cures
The cardiovascular systemthe heart and bloodvesselsare subject to a variety of potentially life
threatening disease
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Myocardial infarction: blockage ofthe arteries supplying heartmusclecanleadtoheartattacks.
can occurwithout warning ormay be preceded by severalweeksofangina.
Fibrillation: anothertype ofheartattack results from a loss ofelectricalcontrol.
The cardiac muscle cells beat
independently. The heart can stop beating
altogether(cardiacarrest).
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Preventingheartattacksisthebestcure
Properdiet,exercise,andstressmanagementcanreducetheriskofheartproblem
Manymedicaltreatmentsareavailabletotreatheartattacks.
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High blood pressure (hypertension) develops gradually
over time.
Hypertension is a prolonged elevation in blood
pressure. Early detection and treatment are essential to prevent
serious problems, including heart attacks.
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Atherosclerosis results from
the buildup of cholesterol
plaque in arteries.
Arteries clogged withcholesterol force the heart
to work harder.
Blood clots can lodge in
narrowed coronary arteries.
Weakening of the arterial walls
can result in a rupture(aneurysm) of the wall.
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End of Chapter 6