Biomed I: Conduction System

two systems that regulate heart activity:

autonomic nervous system and intrinsic conduction system/nodal system

intrinsic conduction/nodal system

sets 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 inute

autonomic nervous system

controls voluntary movement

Sinoatrial node

located in the right atrium

serves as the heart’s pacemaker

Atrioventricular node

at the junction of the aria and ventricles

atrioventricular bundle/bundle of his

in the interventricular septum with bundle branches

Purkinje fibers spread within the ventricle wall muscles

Sinoatrial node

starts each heartbeat

impulse spreads through the atria to the AV bundle, bundle branches, and Purkinje fibers

ventricles contract; blood ejected from heart

techycardia

rapid heart rate, over 100 beats per minute

Bradycardia

slow heart rate, less than 60 beats per minutes

Cardiac cycle

refers to one complete heartbeat, when both atria and ventricles contract and relax

Systole

contraction

Diastole

relaxation

average heart rate

75 beats per minute

Length of cardiac cycle

0\.8 seconds

____ transfers blood to tissues and back from the heart

blood vessels in the closed vascular system

arteries and arterioles

vessels that carry blood away from the heart

capillary beds

vessels that are involved in exchanges between blood and tissue

venules and veins

vessels that return blood toward the heart

tunica intima

layer of the blood vessels that is friction reducing

endothelium

tunica media

smooth muscle and elastic tissue

controlled by the sympathetic nervous system

tunica externa

forms protective outermost covering

mostly fibrous connective tissue

supports and protects the vessel

arteries

heavier, stronger, and stretching tunica media than veins to withstand pressure changes

smaller lumen

veins

thinner tunica media because they operate under low pressure

have valves to prevent backflow

larger lumen

skeletal muscle contracts and pushes blood in veins toward heart

capillaries

one layer thick, tunica intima

exchanges between blood and tissue

form capillary beds, networks that consist of:

vascular shunt and true capillaries

microcirculation

blood flow through a capillary bed