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Lecture 13

§  The Heart

§  Coronary Circulation

§  The Cardiac Cycle

§  Blood Pressure

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Coronary circulation nourishes the heart.

§  Coronary arteries (2) branch directly off of the aorta and supply blood to the heart.

§  After blood passes through the capillarybed it enters the coronary veins (2) and isdrained to the right atrium.

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Coronary circulation nourishes the heart.

LeftCoronaryArtery

RightCoronary

 Artery

RightCoronary

Vein

LeftCoronaryVein

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Coronary circulation nourishes the heart.

LeftCoronaryVein

RightCoronary

Vein

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Coronary circulation nourishes the heart.

§  Coronary arteries branch off of the aortaand supply blood to the heart.

§  Coronary veins drained blood away fromthe heart and into the right atrium.

§  Obstructed flow through the coronaryarteries can lead to a heart attack.

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The cardiac cycle

§  The 2 sides of the heart beat in unison.§  The order of events during a single

heartbeat is called the cardiac cycle.

§  Two key words…

Contraction is called systole

Relaxation is called diastole

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The cardiac cycle

1.  All four chambers relax and blood drains

into the heart (diastole).

2.  Atria contract (atrial systole)

3.  Ventricles contract (ventricular systole)

4.  All chambers relax…cycle begins again

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EarlyDiastole

LateDiastole

AtrialSystole

VentricularSystole

1

1

2

3

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Internal conduction system of the heart

§  Heart muscles contract in unison becauseelectrical signals spread from cell to cell.

§  Electrical signals in the heart travel from:1.  Sinoatrial Node

2.  Atrioventricular Node

3.  Atrioventricular Bundle

4.  Purkinje Fibers

Pacemaker

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Internal conduction system of the heart

Sinoatrial Node

 Atrioventricular Node

 Atrioventricular Bundle

Purkinje Fibers

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Internal Conduction System: In Summary… 

1.  The sinoatrial (SA) node is located in theright atrium and generates an electrical

signal that causes the atria to contract.

2.  Electrical signals spread to the AV node,then the AV bundle, then the Purkinje

fibers.

3.  The Purkinje fibers spread electrical

signals to ventricles and they contract.

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Disorders of the Internal Conduction System

§  Ventricular  fibrillation

§  Weak contraction of the ventricles

§  Can be treated by shock or a defibrillator.

§  Damage to the SA Node (Heart Attack)

§  Abnormal heart rate.

§  Can be treated by an implanted pacemaker.

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EKG measures the heart’s electrical signals

The EKG records 3 waves of activity.

1.  P Wave: Atrial Systole

2.  QRS Wave: Ventricular Systole

3.  T Wave: Diastole

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EKG measures the heart’s electrical signals

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Structure and Function of Heart: In Summary… 

§  Coronary Circulation nourishes the heart.

§  Order of events during the cardiac cycle.

1.  Diastole

2.   Atrial Systole3.  Ventricular Systole

§  Electrical signals in the heart travel from:

1.  SA Node (Pacemaker)2.  AV Node

3.  AV Bundle

4.  Purkinje fibers

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Blood Pressure

§ The force exerted by the blood against thewalls of the blood vessels.

§  Measured by a sphygmomanometer .

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Blood Pressure

Systolic pressure§  During ventricular systole (contraction)

§  ~ 120 mm Hg in a healthy adult

Diastolic pressure§  During ventricular diastole (relaxation)

§  ~ 80 mm Hg in a healthy adult

Typical Blood Pressure: 120/80 

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Blood PressureMeasuring Blood Pressure

§ BP is measured with a sphygmomanometer.

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Blood PressureMeasuring Blood Pressure

§ BP is measured with a sphygmomanometer.

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Blood Pressure

§  In the US 1/3 adults has high bloodpressure (hypertension).

§  While there may be no symptoms, highblood pressure slowly damages the body.

§ Stresses the heart

§ Can lead to aneurysm

§ Increases the risk of atherosclerosis