Cardiovascular System: The Heart Vocabulary

Vocabulary flashcards covering cardiac structure, action potentials, intrinsic conduction, pharmacological agents, cardiac cycle phases, stroke volume regulation, cardiac output, and nervous system control based on Chapter 18.

Pulmonary Circuit

The right side pump of the heart that receives $O_2$-poor blood from body tissues and pumps it to the lungs to eliminate $CO_2$ and pick up $O_2$.

Systemic Circuit

The left side pump of the heart that receives $O_2$-rich blood from the lungs and pumps it to the rest of the body tissues.

Contractile Fibers

Muscle cells making up $99BA$ of cardiac muscle fibers that perform the mechanical pumping work of the heart.

Autorhythmic Fibers

Specialized cells comprising $1\%$ of cardiac muscle fibers that form the intrinsic conduction system and spontaneously generate action potentials.

Intrinsic Conduction System

The specialized network of noncontractile autorhythmic cardiac cells that initiate and distribute electrical impulses throughout the heart to coordinate depolarization and contraction.

Intercalated Discs

Specialized anchoring junctions between adjacent cardiac muscle cells that contain gap junctions for electrical coupling and desmosomes to prevent cell separation during contraction.

Gap Junctions

Protein channels within intercalated discs that electrically connect adjacent cardiomyocytes, allowing ions to pass freely and enabling synchronic excitation.

Desmosomes

Cellular structures within intercalated discs that mechanically bind cardiac muscle cells together to prevent them from pulling apart during contraction.

Resting Membrane Potential (RMP) of Cardiomyocytes

The membrane potential of resting contractile cardiac muscle fibers, averaging approximately $-90\,\text{mV}$.

Plateau Phase

The period during a contractile cardiomyocyte action potential caused by $Ca^{2+}$ influx through slow $Ca^{2+}$ channels and delayed $K^{+}$ channel opening, producing a prolonged depolarization and sustained muscle contraction.

Absolute Refractory Period

The time interval during an action potential when cardiac muscle cells cannot generate another action potential, preventing tetanic contractions in the heart.

Automaticity (Autorhythmicity)

The ability of autorhythmic cardiac fibers to initiate their own electrical impulses spontaneously without requiring stimulation from the nervous system.

Pacemaker Potential

An unstable resting membrane potential in autorhythmic cardiac fibers caused by gradual $Na^{+}$ and $Ca^{2+}$ influx and decreased $K^{+}$ efflux, slowly depolarizing the cell toward threshold.

Sinoatrial (SA) Node

The primary pacemaker of the heart located in the right atrium that depolarizes fastest and establishes the sinus rhythm.

Sinus Rhythm

The normal, characteristic heart rhythm driven by impulses originating from the sinoatrial (SA) node.

Verapamil

A calcium channel blocker drug that slows depolarization of the SA node to threshold, reducing heart rate and atrial tissue automaticity to treat supraventricular tachycardia (SVT).

Procardia

A calcium channel blocker that acts primarily on smooth muscle in coronary and systemic blood vessels, causing dilation to enhance myocardial blood flow and reduce peripheral resistance.

Lidocaine

A sodium channel blocker that suppresses automaticity in ventricular conducting tissue to treat ventricular arrhythmias such as ventricular tachycardia (VT), ventricular fibrillation (V-Fib), and premature ventricular contractions (PVCs).

Digoxin

A drug derived from the foxglove plant that decreases heart rate while increasing contractile strength by elevating $Ca^{2+}$ entry, conserving myocardial energy.

Cardiac Cycle

The sequence of events encompassing blood flow through the heart during one complete heartbeat, including atrial systole and diastole followed by ventricular systole and diastole.

Systole

The contraction period of cardiac muscle during which internal chamber pressure increases and blood is ejected.

Diastole

The relaxation period of cardiac muscle during which internal chamber pressure drops and blood fills the chamber.

End Systolic Volume (ESV)

The volume of blood remaining in a ventricle at the end of its contraction phase, averaging about $50\,\text{mL/beat}$ at rest.

End Diastolic Volume (EDV)

The total volume of blood that collects in a ventricle during relaxation prior to contraction, averaging about $120\,\text{mL/beat}$ at rest.

Cardiac Output (CO)

The total volume of blood pumped by each ventricle per minute, calculated as heart rate multiplied by stroke volume ($\text{CO} = \text{HR} \times \text{SV}$).

Stroke Volume (SV)

The volume of blood pumped out by a single ventricle with each heartbeat, calculated as $\text{SV} = \text{EDV} - \text{ESV}$ (averaging $70\,\text{mL/beat}$ at rest).

Preload

The degree of stretch exerted on cardiac muscle fibers before they contract, directly related to venous return.

Frank-Starling Law of the Heart

The principle stating that increasing venous return stretches ventricular cardiac muscle fibers, which increases EDV and results in a proportional increase in stroke volume and cardiac output.

Contractility

The extrinsic contractile force developed by cardiac muscle at any given muscle length, independent of stretch and increased by enhanced $Ca^{2+}$ influx.

Afterload

The pressure that the ventricles must overcome to force open the semilunar valves and eject blood into the major arteries.

Congestive Heart Failure (CHF)

A condition in which progressive weakening of the myocardium impairs cardiac output to a level inadequate for body requirements, leading to decreased stroke volume, increased end systolic volume, and fluid retention/edema.

Cardioinhibitory Center

A neural center in the medulla oblongata that projects parasympathetic signals via the vagus nerves (using acetylcholine) to slow heart rate at the SA and AV nodes.

Cardioacceleratory Center

A neural center in the medulla oblongata that projects sympathetic signals (using norepinephrine) to increase heart rate and contractile force.

Vagal Tone

The continuous parasympathetic inhibitory effect exerted by the vagus nerve on the heart at rest, maintaining resting heart rate around $75\,\text{beats/min}$ instead of the SA node's intrinsic rate of $100\,\text{beats/min}$.