Biomed: The Conduction System of Arteries and Veins

Two 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