Cardiac Physiology

These flashcards cover key vocabulary and concepts related to cardiac physiology, including the anatomy of the heart, the conduction system, heart abnormalities, cardiac output factors, and the cardiac cycle.

ECG

Electrocardiogram; a tracing of the electrical currents created by the intrinsic conduction system.

Intrinsic conduction system

Coordinates the rhythmic excitation and contraction of cardiac muscle.

SA node

Sinoatrial node; primary pacemaker of the heart generating impulses at a rate of 70 times per minute.

AV node

Atrioventricular node; delays impulse conduction by ~0.1 seconds and fires impulses at 40-60 times per minute.

Bundle of His

Also known as atrioventricular bundle; pathway for impulses from the atria to the ventricles.

Purkinje fibers

Conduct impulses from the heart apex to the ventricular walls.

Autonomic innervation

Refers to how heart rate is modulated by the autonomic nervous system.

Tachycardia

Heart rate greater than 100 beats per minute.

Bradycardia

Heart rate less than 60 beats per minute.

Cardiac cycle

All events associated with one complete heartbeat.

Systole

Contraction phase of the heart.

Diastole

Relaxation phase of the heart.

Stroke volume (SV)

Amount of blood pumped by the heart in one heartbeat; calculated as EDV - ESV.

Cardiac output (CO)

Amount of blood pumped by the heart in one minute; CO = HR x SV.

End-diastolic volume (EDV)

Volume of blood in ventricles at the end of diastole.

End-systolic volume (ESV)

Volume of blood remaining in ventricles after contraction.

Preload

Degree of stretch of ventricles before they contract; influenced by venous return.

Afterload

Back pressure exerted by blood in arteries; the pressure the ventricles must overcome to eject blood.

Heart block

Condition where impulse traveling from atria to ventricles is impaired.

Ectopic focus

An overly excitable area that depolarizes faster than the SA node, potentially leading to premature heartbeat.

Arrhythmias

Irregular heartbeats that can result in uncoordinated contractions.

Fibrillation

Rapid, irregular twitching of the myocardium; can be atrial or ventricular.

Cardiac muscle

Striated and interconnected muscle that makes up 99% of the heart's mass.

Autorhythmic cells

Self-excitable cells in the heart that instinctively generate action potentials.

Pacemaker potentials

Unstable membrane potentials that gradually drift toward threshold in autorhythmic cells.

Funny channels

Channels that allow slow entry of Na+ contributing to pacemaker potentials.

Ion movements

Changes in membrane potential due to the movement of ions during action and pacemaker potentials.

Myocardial cells

Contractile cardiac muscle cells that generate the force of contraction.

Intercalated discs

Structures that allow free passage of ions between cardiac muscle cells.

Desmosomes

Anchoring junctions that prevent adjacent cells from being pulled apart.

S1 and S2 sounds

Heart sounds; S1 is the sound of the AV valves closing, S2 is the sound of the semilunar valves closing.

Cardiac abnormalities

Conditions that affect heart rhythm or function, such as tachycardia and bloc.

CHF

Congestive heart failure; progressive condition where the heart can't pump sufficient blood.

Pulmonary circulation

Flow of blood from the heart to the lungs and back.

Systemic circulation

Flow of blood from the heart to the rest of the body.

Gap junctions

Connections between cardiac muscle cells that allow for electrical communication.

Cardiac muscle contraction

Similar to skeletal muscle contraction; requires action potentials and calcium.

Myocardial ischemia

A condition where blood flow to the heart muscle is reduced.

Isovolumetric contraction phase

Phase where ventricles contract with no change in volume.

Ventricular ejection phase

Phase where blood is pumped out of the ventricles.

Midsternal line

Imaginary line used for anatomical reference in locating the heart.

Cardiac output factors

Include heart rate modulation influence by SNS and PNS activities.

Hormonal regulation

Hormones can influence heart rate by affecting heart muscle contraction.

Continuous electrical activity

Cardiac muscle's ability to generate its own electrical impulses.

Refractory period

Time during which a new action potential cannot be initiated in cardiac muscle.

Sarcoplasmic reticulum

Calcium storage organelle in cardiac muscle cells.

T-tubules

Invaginations that help transmit action potentials deep into muscle fibers.

Acetylcholine (ACh)

Neurotransmitter used by the parasympathetic nervous system to lower heart rate.

Norepinephrine (NE)

Neurotransmitter used by the sympathetic nervous system to increase heart rate.

Chronotropic agents

Factors that affect heart rate positively or negatively.

Resting membrane potential

The stable voltage of a cardiac cell when not being stimulated.

Electrolyte balance

Crucial for normal heart function; abnormalities can affect heart rhythm.

T-wave

Represents ventricular repolarization in an ECG.

P-R interval

Duration from the beginning of atrial depolarization to the onset of ventricular depolarization.

QRS complex

Represents ventricular depolarization, the electrical impulse moving through the ventricles.

Ventricular repolarization

Process by which the ventricles recover from depolarization.

Cardiac stressors

Factors such as exercise or emotional trauma that influence heart activity.

Electrical signals

Impulses transmitted throughout the heart to coordinate contraction.

Myocardial infarction

Heart attack due to blocked blood supply to part of the heart.

Blood pressure

The force exerted by circulating blood on the walls of blood vessels.

Troponin

Protein that binds calcium and initiates the contraction process in cardiac muscles.

Homeostasis

The body's regulatory system that maintains stable internal conditions such as temperature and blood pressure.

Ventricular filling

Phase when blood flows from the atria to the ventricles.

Dicrotic notch

Temporary dip in arterial pressure following closure of the aortic valve.

Atrial contraction

Phase where the atria contract to push blood into the ventricles.

Myocyte

Another term for a cardiac muscle cell.

Electrophysiology

Study of the electrical properties of biological cells and tissues.

Postextrasystolic potentiation

An increase in strength of subsequent contraction following an extrasystole.

Baroreceptors

Sensors that detect changes in blood pressure and help regulate heart rate.

Carotid sinus

Area in the carotid artery that contains baroreceptors.

Pacemaker potential

The gradual depolarization of autorhythmic cells leading to action potentials.

Coronary arteries

Blood vessels that supply blood to the heart muscle.

Veins

Vessels that return deoxygenated blood to the heart.

Arteries

Vessels that carry oxygenated blood away from the heart.

Cardiac remodeling

Structural changes in the heart that occur in response to chronic stressors.

Thermoregulation

Process by which the body maintains its core internal temperature.

Hemodynamic factors

Principles used to understand blood flow and pressure in relation to heart function.

Renin-angiotensin system

Hormonal system that regulates blood pressure and fluid balance.

Statins

Medications that can help control cholesterol levels and improve heart health.

What is the anatomy of the heart?

The heart consists of four chambers: the right atrium and ventricle, and the left atrium and ventricle. It is surrounded by a protective fibrous pericardium and is comprised of three layers: the epicardium (outer layer), myocardium (muscle layer), and endocardium (inner layer).

What is the difference between a myocardial cell and an autorhythmic cell?

Myocardial cells, also known as cardiac muscle cells, contract to pump blood and are responsible for the heart's contractions. Autorhythmic cells are specialized cardiac cells that generate electrical impulses and set the rhythm of the heartbeat, acting as pacemakers.

What is a pacemaker potential?

Pacemaker potential refers to the gradual depolarization of autorhythmic cells that occurs when they are at rest, leading to spontaneous action potentials that initiate heartbeats.

How do autorhythmic cells produce action potentials?

Autorhythmic cells produce action potentials through a process involving the influx of sodium ions (Na+) and calcium ions (Ca2+) which trigger depolarization, and the efflux of potassium ions (K+) during repolarization.

What ions are involved during pacemaker potentials and autorhythmic action potentials?

During pacemaker potentials, sodium ions (Na+) slowly enter the cell, while calcium ions (Ca2+) enter rapidly during action potentials, and potassium ions (K+) exit during repolarization.

What is the path of the intrinsic conduction system of the heart?

The intrinsic conduction system includes the sinoatrial (SA) node, atrioventricular (AV) node, bundle of His, right and left bundle branches, and Purkinje fibers, which coordinate the electrical impulses that trigger heart contractions.

What happens electrically and physically during each stage of intrinsic conduction?

1. SA Node: Initiates an impulse causing atrial contraction. 2. AV Node: Delays the impulse before passing it to the ventricles. 3. Bundle of His: Conducts the impulse to the bundle branches. 4. Bundle Branches: Distribute the impulse to the Purkinje fibers. 5. Purkinje Fibers: Trigger ventricular contraction.

What cardiac abnormalities can occur in relation to conduction?

Potential abnormalities include arrhythmias (irregular heartbeats), heart block (delay or disruption of impulses), and fibrillation (disorganized electrical activity leading to ineffective pumping).

How can one differentiate the degrees of heart block?

There are three degrees of heart block: 1st degree (delayed conduction with longer PR interval), 2nd degree (intermittent conduction failure), and 3rd degree (complete block where atria and ventricles beat independently).

What is an electrocardiogram (EKG)?

An electrocardiogram is a graphic representation of the electrical activity of the heart over time, reflecting the rhythm and function of the heart.

How do you read an EKG?

To read an EKG, identify the P wave (atrial depolarization), QRS complex (ventricular depolarization), and T wave (ventricular repolarization), along with measuring intervals such as PR interval and QT interval for abnormalities.

What happens electrically and physically during each wave, interval, and segment of an EKG recording?

• P Wave: Atrial depolarization; atria contract. - QRS Complex: Ventricular depolarization; ventricles contract. - T Wave: Ventricular repolarization; ventricles relax. - PR Interval: Time between atrial and ventricular depolarization. - QT Interval: Time for ventricular depolarization and repolarization.

How are myocardial cells stimulated?

Myocardial cells are stimulated by action potentials from the surrounding autorhythmic cells or through neuronal stimulation from the autonomic nervous system.

Describe an action potential of a myocardial cell.

The action potential in a myocardial cell includes depolarization (rapid influx of Na+), plateau phase (sustained influx of Ca2+), and repolarization (efflux of K+).

What are the different phases of a myocardial action potential?

1. Phase 0: Rapid depolarization due to Na+ influx. 2. Phase 1: Initial repolarization due to K+ efflux. 3. Phase 2: Plateau phase due to Ca2+ influx and K+ efflux balance. 4. Phase 3: Repolarization due to K+ efflux. 5. Phase 4: Resting membrane potential.

What is the cardiac cycle?

The cardiac cycle encompasses all events associated with one heartbeat, including the phases of contraction (systole) and relaxation (diastole) of the heart chambers.

What occurs during the cardiac cycle?

During the cardiac cycle, blood flows into the heart during diastole and is pumped out during systole, consisting of atrial and ventricular contraction and relaxation.

Define cardiac output and stroke volume.

• Cardiac Output (CO): The amount of blood the heart pumps in one minute, calculated as CO = Stroke Volume (SV) x Heart Rate (HR). - Stroke Volume (SV): The volume of blood pumped from the left ventricle with each heartbeat.

What factors influence cardiac output and stroke volume?

Factors influencing cardiac output include heart rate and myocardial contractility, while stroke volume is influenced by preload, afterload, and myocardial contractility.

What are preload and afterload?

• Preload: The degree of stretch of cardiac muscle fibers at the end of diastole. - Afterload: The resistance the heart must overcome to eject blood during systole.

What is congestive heart failure (CHF)?

Congestive heart failure is a condition where the heart is unable to pump sufficiently to maintain blood flow, potentially leading to fluid buildup, with left-sided CHF causing pulmonary congestion and right-sided CHF leading to systemic congestion