Chapter 19: Circulatory System - The Heart

Comprehensive vocabulary flashcards covering the anatomy, histology, conduction physiology, electrocardiogram features, hemodynamics, and regulation of the heart.

Pulmonary Circuit

The major division of the circulatory system that carries oxygen-poor blood from the right side of the heart to the lungs for gas exchange and returns oxygenated blood to the left side of the heart.

Systemic Circuit

The major division of the circulatory system that receives fully oxygenated blood from the lungs via pulmonary veins and pumps it from the left side of the heart to all tissues of the body before returning it to the right side of the heart.

Base (of the Heart)

The wide, superior portion of the heart where the great blood vessels attach.

Apex (of the Heart)

The tapered inferior end of the heart that tilts toward the left side of the body.

Pericardium

The double-walled sac that encloses the heart to decrease friction, allow room to expand, and resist excessive expansion.

Parietal Pericardium

The outer pericardial sac consisting of a superficial fibrous layer of connective tissue and a deep, thin serous layer.

Epicardium

The visceral pericardium, consisting of a serous membrane covering the outer surface of the heart through which coronary blood vessels travel.

Pericardial Cavity

The space between the parietal and visceral pericardia that is filled with pericardial (serous) fluid.

Endocardium

The smooth inner epithelial lining of the heart and blood vessels that covers valve surfaces and is continuous with the endothelium of blood vessels.

Myocardium

The middle layer of the heart wall composed of cardiac muscle that spirals around the heart to produce a wringing motion during contraction.

Fibrous Skeleton of the Heart

A framework of collagenous and elastic fibers that provides structural support, muscle attachment, valve anchoring, and electrical insulation between the atria and ventricles.

Cardiomyocytes

Striated, short, thick, branched muscle cells containing a single central nucleus surrounded by glycogen, repairing almost entirely by fibrosis (scarring).

Intercalated Discs

Specialized end-to-end junctional complexes that link cardiomyocytes mechanically through desmosomes and electrically through gap junctions.

Desmosomes

Mechanical linkages within intercalated discs that prevent contracting cardiomyocytes from pulling apart from one another.

Gap Junctions (Cardiac)

Electrical junctions within intercalated discs that allow ions to flow directly between cells, enabling the myocardium of the atria or ventricles to act as a unified cell.

Auricles

Ear-like flap extensions visible on the external surface of the heart that enlarge the capacity of the atria.

Interatrial Septum

The wall of tissue that separates the right and left atria.

Interventricular Septum

The thick muscular wall that separates the right and left ventricles.

Atrioventricular (AV) Valves

Valves that regulate blood flow between the atria and ventricles, comprising the tricuspid valve (right AV valve with three cusps) and the mitral valve (left AV valve with two cusps).

Chordae Tendineae

Tendinous cords that connect the cusps of the AV valves to papillary muscles on the floor of the ventricles, preventing the valves from flipping or bulging into the atria during ventricular contraction.

Semilunar Valves

Pocket-like valves that control blood flow from the ventricles into great arteries, comprising the pulmonary semilunar valve (into the pulmonary trunk) and the aortic semilunar valve (into the aorta).

Left Coronary Artery (LCA)

A major coronary vessel branching off the ascending aorta that divides into the anterior interventricular branch and the circumflex branch.

Right Coronary Artery (RCA)

A major coronary vessel branching off the ascending aorta that divides into the right marginal branch and the posterior interventricular branch.

Coronary Sinus

A large vein situated on the posterior side of the heart that collects deoxygenated coronary blood and drains directly into the right atrium.

Angina Pectoris

Chest pain resulting from ischemia due to partial obstruction of coronary blood flow, forcing myocardium into anaerobic fermentation that generates lactic acid.

Myocardial Infarction (MI)

The sudden death of a patch of myocardium resulting from long-term obstruction of the coronary circulation.

Sinoatrial (SA) Node

The primary pacemaker of the heart consisting of modified cardiomyocytes in the right atrium near the base of the superior vena cava that initiates each heartbeat and sets heart rate.

Pacemaker Potential

The gradual membrane depolarization of the SA node toward threshold driven by a slow, constant influx of $\text{Na}^+$.

Atrioventricular (AV) Node

An electrical gateway located at the lower end of the interatrial septum that delays signal transmission to allow the ventricles adequate time to fill with blood.

Atrioventricular (AV) Bundle

The conducting pathway (bundle of His) that originates at the AV node and forks into right and left bundle branches passing through the interventricular septum toward the apex.

Purkinje Fibers

The subendocardial conducting network that distributes electrical excitation rapidly throughout the ventricular myocardium.

Systole

The contraction phase of a heart chamber, most commonly referring to the contraction of the ventricles.

Diastole

The relaxation phase of a heart chamber, most commonly referring to the relaxation of the ventricles.

Sinus Rhythm

The normal, regular heartbeat triggered by the SA node, typically ranging from $70\text{ to }80\text{ bpm}$ in a resting adult.

Ectopic Focus

Any region of spontaneous electrical firing in the heart located outside of the sinoatrial (SA) node.

Nodal Rhythm

An ectopic heart rhythm set by the AV node when the SA node is damaged, typically producing a rate of $40\text{ to }50\text{ bpm}$.

P Wave

The electrocardiogram deflection produced when the SA node fires and both atria undergo depolarization.

QRS Complex

The complex spike deflection on an ECG representing ventricular depolarization, shaped by the differing wall thickness and shape of the two ventricles.

ST Segment

The ECG segment representing ventricular systole, corresponding directly to the plateau phase of the myocardial action potential.

T Wave

The ECG deflection representing ventricular repolarization occurring immediately before ventricular diastole.

Ventricular Fibrillation

A severe cardiac arrhythmia in which electrical signals travel randomly through the ventricles, preventing pumping, coronary perfusion, and rapidly causing death.

Defibrillation

The application of a strong electrical shock intended to depolarize the entire myocardium simultaneously, resetting the heart back to a normal sinus rhythm.

Asystole

The complete cessation of electrical and mechanical activity in the heart, characterized by the absence of a heartbeat.

First Heart Sound ($S_1$)

The louder, longer "lubb" sound occurring with the closure of the AV valves, blood turbulence, and movement of the atrial heart wall at the start of ventricular systole.

Second Heart Sound ($S_2$)

The softer, sharper "dupp" sound occurring with the closure of the semilunar valves, blood turbulence, and movements of the ventricular heart wall.

Isovolumetric Contraction

The early systolic phase where ventricles depolarize and contract while all four valves remain closed, raising pressure without ejecting blood volume.

Ventricular Ejection

The phase of the cardiac cycle when ventricular pressure exceeds arterial pressure, opening semilunar valves and ejecting approximately $70\text{ mL}$ of blood.

Isovolumetric Relaxation

The early diastolic phase where ventricles expand, blood closes the semilunar valves ($S_2$), and all four valves are closed with no volume change.

Cardiac Output (CO)

The volume of blood ejected by each ventricle per minute, calculated as $\text{Cardiac Output} = \text{Heart Rate} \times \text{Stroke Volume}$, averaging $4\text{ to }6\text{ L/min}$ at rest.

Stroke Volume (SV)

The volume of blood ejected from a ventricle in a single contraction, measuring about $70\text{ mL}$ in a resting adult.

Pulse

The surge of pressure produced by each heartbeat that can be palpated at a superficial artery.

Tachycardia

A persistent resting adult heart rate exceeding $100\text{ bpm}$.

Bradycardia

A persistent resting adult heart rate below $60\text{ bpm}$.

Preload

The amount of tension or stretch in the ventricular myocardium immediately prior to contraction, where increased stretch increases the force of contraction.

Contractility

The contractile force generated by the myocardium for a given preload, independent of stretch.

Afterload

The sum of all forces opposing the ejection of blood from a ventricle, primarily driven by blood pressure in the aorta and pulmonary trunk.

Ventricular Hypertrophy

An enlargement of the ventricular myocardium induced by sustained exercise training that increases stroke volume and allows a lower resting heart rate.