Cardiac cycle
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💓 Cardiac Conduction & ECG
Q: What controls the heartbeat?
A: The cardiac conduction system (electrical system of the heart).
Q: What does the ECG show?
A: Electrical signals as waves representing heart muscle contraction/relaxation.
🔄 Cardiac Cycle Overview
Q: What are the two phases of the cardiac cycle?
A: Systole (contraction) and Diastole (relaxation).
Q: What happens first in the cycle?
A: Atria contract → then ventricles contract.
📈 Phases of the Cardiac Cycle
Q: What happens during atrial systole?
A: Atria contract, topping off ventricles (AV valves open, semilunar valves closed).
Q: What is isovolumetric ventricular contraction?
A: Ventricles start to contract with all valves closed; pressure builds (1st heart sound).
Q: What happens during ejection phase?
A: Semilunar valves open, blood exits; marked by T wave (ventricular repolarization).
Q: What is isovolumetric relaxation?
A: Ventricles relax, all valves closed again (2nd heart sound).
Q: What is passive ventricular filling?
A: Atria passively fill ventricles as AV valves reopen (no contraction yet).
🔊 Heart Sounds
Q: What causes the "lubb" sound?
A: AV valves closing at the start of ventricular systole.
Q: What causes the "dupp" sound?
A: Semilunar valves closing at the start of diastole.
Q: What is a murmur?
A: An abnormal heart sound due to valve issues (e.g., regurgitation, stenosis).
💧 Cardiac Output (CO)
Q: How is cardiac output calculated?
A: CO = Stroke Volume (SV) × Heart Rate (HR)
Q: What is a normal CO?
A: 4–6 L/min
Q: What happens if HR or SV increases?
A: CO increases.
🧠 Controls of HR and SV
Q: What are the 3 controls of heart activity?
A:
Chronotropic = heart rate
Inotropic = contraction strength
Dromotropic = signal conduction speed
🧪 Heart Rate Regulation
Q: What part of the brain regulates HR?
A: Medulla’s cardiac center.
Q: What does the sympathetic nervous system do to HR?
A: Increases it (via norepinephrine).
Q: What does the parasympathetic nervous system do?
A: Decreases it (via acetylcholine and vagus nerve).
Q: What do baroreceptors do?
A: Detect blood pressure changes to adjust HR (e.g., drop = HR increases).
Q: What do chemoreceptors do?
A: Detect low O2, high CO2, or acidosis → increase HR.
⚡️ Factors That Affect HR
Emotions (stress = ↑ HR)
Exercise (↑ HR via epi & nerves)
Temperature (heat ↑, cold ↓)
Pain (can ↓ HR → fainting)
💪 Stroke Volume (SV)
Q: What is stroke volume?
A: Amount of blood pumped by one ventricle per beat (~70 mL).
Q: What affects SV?
A:
Nervous & hormonal signals
Blood return/stretch (preload)
Electrolyte balance
Inotropic drugs
🧬 Starling’s Law
Q: What is Starling’s Law?
A: The more the heart fills (stretches), the stronger it contracts (to a point).
Q: What is preload?
A: Volume of blood in ventricles before contraction.
Q: What is afterload?
A: The pressure the heart must pump against (e.g., high BP = ↑ afterload).
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