Lecture 8 - The Heart

Mediastinum

The central compartment of the thoracic cavity where the heart is located.

Pericardium

A double-walled sac that encloses the heart and helps hold it in place.

Epicardium

The outer layer of the heart wall, which is also the visceral layer of the serous pericardium.

Myocardium

The middle muscular layer of the heart wall that is responsible for contraction.

Endocardium

The inner layer of the heart wall that lines the heart chambers.

Atria

The two upper chambers of the heart that receive blood.

Ventricles

The two lower chambers of the heart that pump blood out.

Tricuspid valve

The valve between the right atrium and right ventricle; prevents backflow.

Bicuspid (Mitral) valve

The valve between the left atrium and left ventricle; prevents backflow.

Pulmonary valve

The valve that directs blood from the right ventricle into the pulmonary artery.

Aortic valve

The valve that directs blood from the left ventricle into the aorta.

Coronary circulation

The flow of blood to and from the tissues of the heart.

Autorhythmic cells

Cells in the heart that are capable of generating their own electrical impulses.

SA node (Sinoatrial node)

The natural pacemaker of the heart located in the right atrium.

AV node (Atrioventricular node)

The node that receives impulses from the SA node and delays them before passing to the ventricles.

Bundle of His

A collection of heart muscle cells specialized for electrical conduction that transmits impulses from the AV node to the ventricles.

Purkinje fibers

Fibers that conduct electrical impulses to the muscle cells of the ventricles.

Cardiac Cycle

The sequence of events in one heartbeat, including contraction and relaxation of the heart chambers.

Cardiac output (CO)

The volume of blood ejected from the left or right ventricle into the aorta or pulmonary trunk each minute.

Stroke volume (SV)

The amount of blood pumped out of the ventricle in one beat.

Preload

The degree of stretch of the heart muscle before contraction.

Contractility

The strength of contraction of the heart muscle.

Afterload

The resistance the heart must overcome to eject blood.

Electrocardiogram (EKG or ECG)

A recording of the electrical changes that accompany each heartbeat.

Systole

The phase of the cardiac cycle when the heart muscle contracts.

Diastole

The phase of the cardiac cycle when the heart muscle relaxes.

Desmosomes

Structures that anchor cardiac muscle cells together.

Gap junctions

Specialized connections that allow electrical impulses to pass quickly between cardiac muscle cells.