Module 1 - Heart Definitions

Cardiums

The three layers of the heart: epicardium, myocardium, and endocardium.

Epicardium

The outermost layer of the heart.

Myocardium

The middle and thickest layer of the heart; it is the muscle of the heart.

Endocardium

The innermost and very thin layer of the heart.

Atria

The two upper chambers of the heart.

Ventricles

The two lower chambers of the heart.

Interatrial septum (IAS)

Thin partition separating the right atrium from the left atrium.

Interventricular septum (IVS)

Partition separating the right ventricle from the left ventricle.

Atrioventricular (AV) valves

Valves located between the atria and ventricles.

Semilunar valves

Valves that prevent blood in the arteries from flowing back into the heart.

Tricuspid valve

AV valve between the right atrium and right ventricle.

Bicuspid/mitral valve

AV valve between the left atrium and left ventricle.

Pulmonary semilunar valve

Valve between the right ventricle and pulmonary artery.

Aortic semilunar valve

Valve between the left ventricle and aorta.

SA node

Structure in the right atrial wall that begins cardiac excitation.

Natural pacemaker of the heart

The sinoatrial (SA) node.

AV node

Structure located in the interatrial septum where the action potential slows considerably.

ECG/EKG

Recording of the electrical changes that accompany the heartbeat.

P wave

Small upward deflection representing atrial depolarization.

QRS complex

ECG wave representing the onset of ventricular depolarization and ventricular contraction.

Q wave

Downward deflection at the beginning of the QRS complex.

R wave

Large, upright, triangular wave in the QRS complex.

S wave

Downward wave at the end of the QRS complex.

T wave

Dome-shaped upward deflection representing ventricular repolarization.

Cardiac output (CO)

The amount of blood ejected by each ventricle in one minute.

Pulse

Surge of pressure produced by a heartbeat that can be felt by palpating a superficial artery.

Tachycardia

Resting adult heart rate above 100 bpm.

Bradycardia

Resting adult heart rate below 60 bpm.

Positive chronotropic agents

Factors that raise heart rate.

Negative chronotropic agents

Factors that lower heart rate.

Cardiostimulatory effect

Effect produced by the sympathetic pathway that increases heart rate.

Cardioinhibitory effect

Effect produced by the parasympathetic pathway that decreases heart rate.

Sympathetic postganglionic fibers

Adrenergic fibers that release norepinephrine.

Stroke volume (SV)

The other major factor, besides heart rate, that determines cardiac output.

Preload

Amount of tension in the ventricular myocardium immediately before it begins to contract.

Contractility

How hard the myocardium contracts for a given preload.

Positive inotropic agents

Agents that increase contractility.

Negative inotropic agents

Agents that reduce contractility.

Afterload

The sum of all forces opposing ejection of blood from the ventricle.