Cardiovascular Physiology: Heart Anatomy, Conduction, and Mechanics

Comprehensive vocabulary flashcards covering cardiovascular anatomy, electrical conduction, myocardial action potentials, excitation-contraction coupling, electrocardiograms, and the cardiac cycle.

Portal system

A specialized vascular arrangement that joins two capillary beds in series.

Interventricular septum

The central muscular wall that divides the heart into right and left halves, preventing the mixing of deoxygenated and oxygenated blood.

Pulmonary circulation

The circuit where deoxygenated blood exits the right ventricle via the pulmonary trunk to the lungs and returns oxygenated to the left atrium via the pulmonary veins.

Systemic circulation

The circuit where oxygenated blood is pumped from the left ventricle through the aorta to body tissues and returns deoxygenated to the right atrium via the superior and inferior venae cavae.

Anastomosis

Alternative routes that blood vessels take to reach or drain the same capillary beds; endurance training may increase the number of arterial anastomoses in the heart.

Coronary circulation blood flow timing

Blood exits the aortic sinus into the coronary arteries and flows through myocardial vessels exclusively during diastole, when the heart muscle is relaxed.

Chordae tendineae

Tendinous cords referred to as "heart strings" that anchor the atrioventricular (AV) valves to prevent valve inversion during ventricular contraction.

Tricuspid valve

The right atrioventricular (AV) valve that prevents backflow of blood from the right ventricle into the right atrium.

Bicuspid (mitral) valve

The left atrioventricular (AV) valve that prevents backflow of blood from the left ventricle into the left atrium.

Semilunar (SL) valves

The aortic and pulmonary valves that prevent blood from flowing backward from the great arteries into the ventricles during ventricular diastole.

Cardiac myocytes (Contractile cells)

Striated cells organized into sarcomeres that comprise approximately $99\%$ of cardiac cells, forming the myocardium and generating the mechanical force of contraction.

Intercalated discs

Specialized cell junctions connecting cardiac muscle cells containing mechanical connections (desmosomes) and electrical connections (gap junctions).

Desmosomes

Mechanical structures within intercalated discs that physically link adjacent cardiac muscle cells together to withstand mechanical stress.

Gap junctions

Protein channels within intercalated discs that provide low-resistance electrical coupling between cells, allowing action potentials to spread rapidly so cardiac chambers contract as a single unit.

Autorhythmic cells

Non-contractile cardiac cells lacking organized sarcomeres that constitute approximately $1\%$ of cardiac cells, functioning as pacemakers to spontaneously self-generate action potentials.

Sinoatrial (SA) node

The primary pacemaker of the heart located in the right atrium that sets the heart rate at a spontaneous rhythm of $60\text{--}100\,\text{bpm}$.

Atrioventricular (AV) node

The conducting node in the right atrium that provides a conduction delay between atria and ventricles and serves as a secondary pacemaker firing at $40\text{--}60\,\text{bpm}$.

Pacemaker potential

An unstable resting membrane potential in autorhythmic cells that gradually becomes less negative until reaching a threshold of $-40\,\text{mV}$, triggering an action potential.

$I_f$ channels

Specialized ion channels in autorhythmic cells that open at hyperpolarized potentials to allow net $\text{Na}^+$ influx, driving initial pacemaker depolarization before closing as threshold approaches.

Excitation-contraction (EC) coupling in cardiac muscle

The process where an action potential triggers extracellular $\text{Ca}^{2+}$ entry via L-type channels, stimulating calcium-induced calcium release (CICR) through ryanodine receptor-channels (RyR) on the sarcoplasmic reticulum to initiate contraction.

NCX antiporter

A membrane carrier protein that removes $\text{Ca}^{2+}$ from the cytosol during relaxation by exchanging $1\,\text{Ca}^{2+}$ out of the cell for $3\,\text{Na}^+$ moving into the cell down their electrochemical gradient.

Phase 0 (Cardiac contractile action potential)

Rapid depolarization caused by the opening of voltage-gated $\text{Na}^+$ channels.

Phase 1 (Cardiac contractile action potential)

Initial brief repolarization caused by the closure of voltage-gated $\text{Na}^+$ channels.

Phase 2 (Cardiac contractile action potential)

The prolonged plateau phase maintained by the opening of voltage-gated $\text{Ca}^{2+}$ channels alongside the closure of fast $\text{K}^+$ channels.

Phase 3 (Cardiac contractile action potential)

Rapid repolarization caused by the closure of voltage-gated $\text{Ca}^{2+}$ channels and the opening of slow $\text{K}^+$ channels.

Phase 4 (Cardiac contractile action potential)

The resting membrane potential of a cardiac contractile cell, typically around $-90\,\text{mV}$.

Cardiac muscle refractory period

A period lasting $200\text{--}300\,\text{ms}$ (nearly as long as the entire muscle twitch) that prevents wave summation and tetanus in cardiac muscle fibers.

Cardiac conduction system

The specialized pathway through which electrical signals pass from the SA node through internodal pathways to the AV node, down the AV bundle (Bundle of His) and bundle branches, and through Purkinje fibers to spread upward from the apex.

Bradycardia

A heart rate slower than normal, defined as less than $60\,\text{bpm}$.

Tachycardia

A heart rate faster than normal, defined as greater than $100\,\text{bpm}$.

Fibrillation

A state of electrical and mechanical asynchrony among muscle fibers within a chamber, often described as having a "bag of worms" appearance.

Electrocardiogram (ECG)

A recording representing the summed electrical activity generated across the entire body surface by all the cells of the heart during a cardiac cycle.

P wave

The ECG wave representing electrical depolarization of the atria.

P-R segment

The isoelectric ECG segment representing electrical conduction through the AV node and AV bundle (AV nodal delay).

QRS complex

The ECG waveform representing progressive ventricular depolarization, within which atrial repolarization is simultaneously masked.

T wave

The ECG wave representing the repolarization of the ventricles.

S-T segment

The ECG segment during which the ventricles are fully depolarized and contracting (ventricular systole).

Diastole

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

Systole

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

End-diastolic volume (EDV)

The volume of blood contained within a ventricle at the end of ventricular relaxation, approximately $135\,\text{mL}$ in a resting individual.

End-systolic volume (ESV)

The volume of blood remaining in a ventricle at the end of ventricular contraction, approximately $65\,\text{mL}$ in a resting individual.

Isovolumic ventricular contraction

Early ventricular systole when AV valves close and muscle contracts, building pressure without any change in ventricular blood volume because all valves remain shut.

First heart sound ($\text{S}_1$)

The "lub" sound caused by vibrations following the closure of the atrioventricular (AV) valves at the onset of ventricular systole.

Ventricular ejection

The cardiac cycle phase where ventricular pressure exceeds arterial pressure, forcing semilunar valves open to push blood into the aorta and pulmonary trunk.

Isovolumic ventricular relaxation

The early ventricular diastole phase where semilunar valves snap shut, ventricular pressure drops, and no blood enters or exits because all valves remain closed.

Second heart sound ($\text{S}_2$)

The "dup" sound created by vibrations following the closure of the semilunar valves at the onset of ventricular diastole.

Wiggers diagram

A composite physiological diagram correlating pressure changes (aorta, left ventricle, left atrium), ventricular volume, heart sounds, and ECG events over time across a complete cardiac cycle.

Stroke volume (SV)

The volume of blood pumped out by one ventricle per contraction, calculated as $\text{SV} = \text{EDV} - \text{ESV}$ (averaging $70\,\text{mL}$ at rest).

Cardiac output (CO)

The total volume of blood pumped by one ventricle in a given period of time, defined mathematically as $\text{CO} = \text{Heart Rate} \times \text{Stroke Volume}$ (averaging $5\,\text{L/min}$).

Preload

The degree of myocardial stretch on ventricular walls at the end of diastole just before contraction begins, determined by end-diastolic volume.

Frank-Starling law of the heart

The physiological principle stating that the force created by cardiac muscle is directly related to initial sarcomere length, meaning greater stretch (EDV) produces a more forceful contraction and higher stroke volume.

Venous return

The volume of blood delivered back to the heart via the veins, which determines EDV and is aided by the skeletal muscle pump, respiratory pump, and sympathetic constriction of veins.

Inotropic agent

Any chemical substance that affects myocardial contractility; positive inotropes (such as epinephrine, norepinephrine, and digitalis) increase contractility, while negative inotropes decrease it.

Chronotropic effect

An effect that changes heart rate by modulating the rate of action potential generation in autorhythmic pacemaker cells (positive increases rate, negative slows rate).

Afterload

The combined load of end-diastolic volume and arterial resistance that the ventricles must overcome during contraction to eject blood.

Phospholamban

A regulatory protein that, when phosphorylated downstream of $\beta_1$-receptors and cAMP, enhances SR $\text{Ca}^{2+}$-ATPase activity to accelerate $\text{Ca}^{2+}$ reuptake into the sarcoplasmic reticulum, shortening contraction duration while enhancing subsequent release.

Vagus nerve (Cranial Nerve X)

The parasympathetic pathway originating from the cardioinhibitory center of the medulla that innervates the SA and AV nodes, releasing acetylcholine onto muscarinic receptors to decrease heart rate without directly affecting ventricular contractility.