Studied by 19 peopleTwo systems regulate heart activity
Autonomic nervous system
Intrinsic conduction system, or the nodal system
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
Sinoatrial( SA) node
Located in the right atrium
Serves as the heart’s pacemaker
Atrioventricular (AV) node is…
at the junction of the atria and ventricles
Atrioventricular (AV) bundle (bundle of His) and bundle branches
are in the interventricular septum
Purkinje fibers spread
within the ventricle wall muscles
The sinoatrial node (SA node)
starts each heartbeat
Impulse spreads
through the atria to the AV node
Atria
contract
At the AV node,
the impulse is delayed briefly
Impulse travels
through the AV bundle, bundle branches, and Purkinje fibers
Ventricles contract;
blood is ejected from the heart
Tachycardia
rapid heart rate, over 100 beats per minute
Bradycardia
low heart rate, less than 60 beats per minutes
The cardiac cycle refers to
one complete heartbeat, in which both atria and ventricles contract and then relax
Systole = contraction
Diastole = relaxation
Average heart rate
approximately 75 beats per minute
Cardiac cycle length
normally 0.8 second
Blood vessels form
a closed vascular system that transports blood to the tissues and back to the heart
Vessels that carry blood away from the heart
Arteries and arterioles
Vessels that play a role in exchanges between tissues and blood
Capillary beds
Vessels that return blood toward the heart
Venules and veins
Three layers (tunics)
in blood vessels (except the capillaries)
Tunica intima forms a friction-reducing lining
Endothelium
Tunica media
Smooth muscle and elastic tissue
Controlled by sympathetic nervous system
Tunica externa forms protective outermost covering
Mostly fibrous connective tissue
Supports and protects the vessel
Arteries have
a heavier, stronger, stretchier tunica media than veins to withstand changes in pressure
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
Capillaries
Only one cell layer thick (tunica intima)
Allow for exchanges between blood and tissue
Form networks called capillary beds that consist of:
A vascular shunt
True capillaries
Blood flow through a capillary bed is known as
microcirculation
Note
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