Cardiovascular System II: Heart Anatomy, Valves, Conductivity, and Cardiac Cycle

Comprehensive vocabulary flashcards covering the structural layers of the heart, valve mechanics, conduction pathway, action potential mechanics, the cardiac cycle phases, heart sounds, and hemodynamic metrics.

Veins

Blood vessels that carry blood toward the heart; their definition is not associated with the level of oxygen contained in the blood.

Arteries

Blood vessels that carry blood away from the heart; their definition is not associated with the level of oxygen contained in the blood.

Vena Cava

The largest vein in the body, which carries oxygen-poor blood from systemic circulation into the right atrium of the heart.

Aorta

The largest artery in the body, through which oxygen-rich blood exits the left ventricle to systemic circulation.

Pulmonary Veins

Vessels that carry oxygen-rich blood returning from the lungs into the left atrium of the heart.

Pulmonary Artery

Vessel through which oxygen-poor blood leaves the right ventricle to enter pulmonary circulation.

Atrioventricular (AV) Valves

Heart valves positioned between the atria and ventricles that ensure one-way (unidirectional) blood flow from the atria into the ventricles.

Tricuspid Valve

The right atrioventricular (AV) valve consisting of three leaflets, preventing backflow of blood from the right ventricle into the right atrium.

Bicuspid (Mitral) Valve

The left atrioventricular (AV) valve consisting of two leaflets, preventing backflow of blood from the left ventricle into the left atrium.

Chordae Tendineae

Tendinous cords attached to papillary muscles that prevent the valve leaflets of the atrioventricular (AV) valves from everting back into the atria during ventricular contraction.

Semilunar Valves

Valves (aortic and pulmonary) composed of three cuplike leaflets that permit blood to flow from the ventricles into major arteries and prevent backflow into the ventricles during ventricular relaxation.

Endocardium

The innermost epithelial and endothelial layer lining the inner heart wall and chambers.

Myocardium

The middle layer of the heart wall sandwiched between the endocardium and epicardium; composed of interlacing bundles of myocardiocytes arranged spirally around the ventricles to create a wringing contraction.

Epicardium

The outer protective layer of the heart wall, which is structurally the visceral pericardium.

Intercalated Discs

Specialized cell junctions at myocardiocyte borders containing desmosomes for mechanical adhesion and gap junctions for electrical conduction.

Gap Junctions (Cardiac)

Protein channels located within intercalated discs that allow action potentials to pass directly from cell to cell across the myocardium.

Pacemaker Cells

Specialized conductivity cells in cardiac muscle that generate repetitive, self-induced action potentials without possessing a resting membrane potential, slowly depolarizing to threshold.

Sinoatrial (SA) Node

The primary heart pacemaker located in the right atrium that initiates cardiac contraction impulses.

Atrioventricular (AV) Node

A group of pacemaker cells located in the heart septum between the atria that transmits electrical impulses from the atria to the ventricles.

AV Node Delay

A brief delay of approximately $0.1\,\text{seconds}$ in electrical impulse conduction through the AV node, allowing the atria to finish contracting and filling the ventricles before ventricular systole begins.

Bundle of His (Common Bundle)

A tract of conducting tissue located in the heart septum between the left and right ventricles that relays action potentials from the AV node to the Purkinje fibers.

Purkinje Fibers

Elongated, specialized myocardial cells that form branches to rapidly propagate action potentials throughout the ventricular myocardium.

Plateau Phase (Cardiac Action Potential)

A prolonged depolarized phase in contractile cardiac muscle cells caused by slow inward $Ca^{2+}$ flux through L-type channels and reduced outward $K^+$ flux, which delays repolarization and prevents tetany.

Refractory Period (Cardiac)

The prolonged duration during and following an action potential (lasting several hundred milliseconds) where cardiac muscle cannot be re-excited, ensuring the heart alternates between contraction and filling without tetany.

Cardiac Cycle

One complete sequence of heart contraction (systole) and relaxation (diastole).

Diastole

The longest phase of the cardiac cycle, during which the heart muscle relaxes and the ventricles fill with blood.

Systole

The shorter phase of the cardiac cycle, during which the heart muscle contracts and blood is ejected from the ventricles into circulation.

Isovolumetric Ventricular Contraction

The early systole phase where the ventricles contract with all heart valves closed; ventricular pressure rises rapidly without a change in ventricular blood volume.

Ventricular Ejection

The phase of systole that occurs when ventricular pressure exceeds arterial pressure, causing the semilunar valves to open and blood to be forced into the aorta and pulmonary artery.

Isovolumetric Ventricular Relaxation

The early diastole phase where the ventricles relax with all heart valves closed; ventricular pressure drops rapidly without an alteration in blood volume.

Phonocardiogram

A diagnostic recording or instrument used to detect, time, and visualize the acoustic sounds generated by the beating heart.

First Heart Sound (S1 / LUB)

The heart sound produced by the closure of the atrioventricular (AV) valves at the onset of ventricular systole.

Second Heart Sound (S2 / DUB)

The heart sound produced by the closure of the aortic and pulmonary semilunar valves at the onset of ventricular diastole.

Heart Murmur

An abnormal heart sound that typically results from turbulent flow due to defective or abnormal valve function.

Valvular Insufficiency

A mechanical cardiac valve failure where the valve leaflets fail to close completely, allowing backflow (regurgitation) of blood.

Valvular Stenosis

A mechanical cardiac valve defect where the valve narrows or fails to open fully, creating resistance to forward blood flow.

End-Diastolic Volume (EDV)

The total volume of blood in the ventricle at the conclusion of diastole (filling), representing the maximum blood volume that can potentially be pumped during systole.

End-Systolic Volume (ESV)

The volume of blood left remaining inside a ventricle at the conclusion of ventricular systole (emptying).

Stroke Volume (SV)

The actual volume of blood ejected from a ventricle during a single contraction (systole); typically corresponds to $40\text{--}60\%$ of the end-diastolic volume.

Heart Rate (HR)

The number of cardiac cycles (heartbeats or contraction/relaxation sequences) executed per minute.

Cardiac Output (CO)

The total volume of blood pumped by the heart into the circulation per minute, calculated using the formula $\text{CO} = \text{HR} \times \text{SV}$.