Chapter 18: Cardiovascular system – Heart (Part 2)

A comprehensive set of Q&A flashcards covering the key concepts from the heart (Part 2) lecture notes, including conduction system, ECG, cardiac cycle, stroke volume regulation, and related pathologies.

What two factors coordinate a coordinated heartbeat according to the intrinsic conduction system notes?

Presence of gap junctions and the intrinsic cardiac conduction system.

What are pacemaker cells and pacemaker potentials?

Auto-rhythmic non-contractile cells with unstable resting potentials that slowly depolarize (pacemaker potential) to threshold, triggering action potentials; depolarization via Ca2+ influx; repolarization via Ca2+ inactivation and K+ efflux.

What are the three parts of the pacemaker action potential?

Pacemaker potential, depolarization, and repolarization.

What is the sequence of excitation in the intrinsic conduction system and its approximate time?

SA node → AV node → AV bundle → right/left bundle branches → Purkinje fibers; about 0.22 seconds for the sequence.

Which node is the pacemaker of the heart and its intrinsic rate?

Sinoatrial (SA) node; about 100× per minute (sinus rhythm).

Where is the AV node located and what is its key function?

Located in the inferior interatrial septum; delays impulses ~0.1 s to allow atrial contraction before ventricular contraction.

What is the AV bundle (Bundle of His)?

Only electrical connection between the atria and ventricles; located in the superior interventricular septum.

What are the Purkinje fibers?

Subendocardial conducting network that depolarizes ventricles from apex to base, more elaborate on the left side.

What distinguishes pacemaker action potentials from contractile cardiac muscle APs?

Pacemaker potentials lack a true resting potential and rely on slow Na+ influx; contractile APs have a plateau from Ca2+ influx; contractile APs last about 200 ms (longer than skeletal).

What ion causes the plateau phase in contractile cardiac muscle action potentials?

Ca2+ influx through slow Ca2+ channels.

What are the main waves/intervals of the ECG and what do they represent?

P wave: atrial depolarization; QRS complex: ventricular depolarization (and atrial repolarization); T wave: ventricular repolarization; PR interval: atrial excitation to ventricular excitation; ST segment: entire ventricular myocardium depolarized; QT interval: ventricular depolarization to repolarization.

What does the QRS complex reflect?

Ventricular depolarization (and atrial repolarization).

What is the dicrotic notch?

Brief rise in aortic pressure as the aortic semilunar valve closes, marking end of systole and start of isovolumetric relaxation.

What are the three major mechanical events of the cardiac cycle?

Ventricular filling, ventricular systole (isovolumetric contraction and ejection), isovolumetric relaxation.

What are EDV and ESV?

End diastolic volume: blood in ventricles at end of diastole; End systolic volume: blood remaining after systole.

What is the Frank-Starling law of the heart?

Increased venous return increases EDV, stretches ventricles, increases contraction force, raising stroke volume and cardiac output.

What factors affect stroke volume (SV)?

Preload, contractility, and afterload.

What is preload?

Degree to which cardiac muscle cells are stretched just before contraction; primarily determined by venous return and EDV.

What is contractility?

Contractile strength at a given muscle length; positive inotropes increase contractility (e.g., epinephrine), negative inotropes decrease it.

What is afterload?

Back pressure exerted by arterial blood; higher afterload increases ESV and reduces SV.

How is heart rate regulated by the autonomic nervous system?

Sympathetic increases rate via norepinephrine; parasympathetic decreases rate via acetylcholine; vagal tone is present at rest.

Which hormones and ions influence heart rate?

Epinephrine and thyroxine increase HR; Ca2+ and K+ imbalances can be dangerous to heart function.

What is congestive heart failure (CHF) and its common causes?

CO is too low to meet tissue needs; caused by coronary atherosclerosis, chronic hypertension, myocardial infarcts, dilated cardiomyopathy, drug toxicity, or inflammation.

What are the two heart sounds and when do they occur?

Lub (AV valves close at start of ventricular systole) and Dub (SL valves close at start of ventricular diastole).

Where are heart valve sounds best heard?

Aortic: 2nd intercostal space right sternal margin; Pulmonary: 2nd intercostal space left sternal margin; Mitral: apex (5th intercostal space, midclavicular line); Tricuspid: right sternal margin (5th space).

What is a heart murmur and what causes it?

Abnormal heart sounds due to valve problems: incompetence (backflow) or stenosis (narrowing) causing swishing or clicking sounds.

What is the formula for cardiac output (CO)?

CO = Heart Rate (HR) × Stroke Volume (SV).

What are typical resting values for EDV, ESV, and SV?

EDV ~120 ml, ESV ~50 ml, SV ~70 ml/beat.

What is isovolumetric contraction and isovolumetric relaxation?

Isovolumetric contraction: all valves closed, pressure rises with no volume change; isovolumetric relaxation: ventricles relax with all valves closed before AV valves reopen.

What is a junctional rhythm?

SA node nonfunctional; AV node paces heart at 40–60 bpm; P waves may be absent.

What is ventricular fibrillation?

Disorganized electrical activity with chaotic ECG deflections; requires defibrillation.

What is tachycardia and bradycardia?

Tachycardia: HR >100 bpm; Bradycardia: HR <60 bpm; may be pathological or adaptive in athletes.