Biomed: The Conduction System of Arteries and Veins

idk, quiz on Thursday or Friday

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

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* 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*