* Anchored the cusps in place by chordae tendineae to the walls of the ventricles * Open during heart relaxation, when blood passively fills the chambers * Closed during ventricular contraction
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Semilunar valves
* Closed during heart relaxation * Open during ventricular contraction
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Valves open and close in response…
* to pressure changes in the heart
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Blood in the heart chambers…
* does not nourish the myocardium
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The heart has its own nourishing circulatory system consisting of:
* —branch from the aorta to supply the heart muscle with oxygenated blood
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Cardiac veins
* drain the myocardium of blood
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Coronary sinus
a large vein on the posterior of the heart; receives blood from cardiac veins
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Blood empties into…
* the right atrium via the coronary sinus
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Two systems regulate heart activity
* Autonomic nervous system * Intrinsic conduction system, or the nodal system
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Atrioventricular (AV) node is…
* at the junction of the atria and ventricles
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Tachycardia
rapid heart rate, over 100 beats per minute
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Tunica intima forms a friction-reducing lining
Endothelium
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Tunica externa forms protective outermost covering
* Mostly fibrous connective tissue * Supports and protects the vessel
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Intrinsic conduction system, or the nodal system does
* Sets the heart rhythm * Composed of special nervous tissue * Ensures heart muscle depolarization in one direction only (atria to ventricles) * Enforces a heart rate of 75 beats per minute
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Sinoatrial( SA) node
* Located in the right atrium * Serves as the heart’s pacemaker
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Atrioventricular (AV) bundle (bundle of His) and bundle branches
\
* are in the interventricular septum
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Purkinje fibers spread
* within the ventricle wall muscles
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The sinoatrial node (SA node)
* starts each heartbeat
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Impulse spreads
through the atria to the AV node
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Atria
\
* contract
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At the AV node,
the impulse is delayed briefly
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Impulse travels
* through the AV bundle, bundle branches, and Purkinje fibers
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Ventricles contract
* blood is ejected from the heart
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Bradycardia
* low heart rate, less than 60 beats per minutes
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The *cardiac cycle* refers to
\
* one complete heartbeat, in which both atria and ventricles contract and then relax * Systole = contraction * Diastole = relaxation
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Average heart rate
* approximately 75 beats per minute
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Cardiac cycle length
* normally 0.8 second
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Blood vessels form
* a closed vascular system that transports blood to the tissues and back to the heart
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Vessels that carry blood away from the heart
* Arteries and arterioles
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Vessels that play a role in exchanges between tissues and blood
* Capillary beds
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Vessels that return blood toward the heart
* Venules and veins
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Three layers (tunics)
* in blood vessels (except the capillaries)
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Tunica media
* Smooth muscle and elastic tissue * Controlled by sympathetic nervous system
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Arteries have
a heavier, stronger, stretchier tunica media than veins to withstand changes in pressure
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Veins have
* a thinner tunica media than arteries and operate under low pressure * Veins also have valves to prevent backflow of blood * Lumen of veins is larger than that of arteries * Skeletal muscle “milks” blood in veins toward the heart
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Capillaries
* Only one cell layer thick (tunica intima) * Allow for exchanges between blood and tissue
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Form networks called *capillary* *beds* that consist of: