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"Q: What is an ECG (electrocardiogram)?"

"A: A recording of the heart’s electrical activity using electrodes attached to the chest and limbs."

"Q: How does an ECG detect the heart’s electrical signals?"

"A: The body’s fluids conduct electrical currents

"Q: What units are ECG waveforms measured in?"

"A: Milliseconds (ms) — showing timing of electrical events."

"Q: What does the SA node trigger in the ECG?"

"A: The P wave

"Q: What does the QRS complex represent?"

"A: Ventricular depolarization

"Q: Why is the QRS complex taller than the P wave?"

"A: Because the ventricles have thicker muscle walls

"Q: What does the T wave represent?"

"A: Ventricular repolarization — the ventricles reset electrically to prepare for the next beat."

"Q: Why don’t we see atrial repolarization on an ECG?"

"A: It is hidden (buried) within the QRS complex

"Q: What is the sequence of electrical activity seen on an ECG?"

"A: P wave → QRS complex → T wave"

"Q: What happens mechanically during the P wave?"

"A: The atria depolarize and then contract (systole) while the ventricles fill."

"Q: What happens during the QRS complex?"

"A: The ventricles depolarize and contract

"Q: What happens during the T wave?"

"A: The ventricles repolarize and prepare for the next contraction."

"Q: What electrical event occurs before contraction of any heart chamber?"

"A: Depolarization — it triggers the mechanical contraction that follows."

"Q: What controls our vital signs?"

"A: The autonomic nervous system through the VCR centers (vasomotor

"Q: What does the vasomotor center control?"

"A: Blood vessel tone."

"Q: What does the cardiac center control?"

"A: Heart rate — it can increase or decrease it."

"Q: What does the respiratory center control?"

"A: Breathing rate

"Q: What is cardiac output (CO)?"

"A: The amount of blood pumped by the heart per minute."

"Q: Formula for cardiac output?"

"A: Heart rate × stroke volume."

"Q: What is stroke volume?"

"A: The amount of blood pumped from the left ventricle with each beat (~70 mL)."

"Q: How often does your blood pass through your heart?"

"A: About once per minute."

"Q: What happens to stroke volume during exercise?"

"A: It increases due to better venous return."

"Q: What causes stronger heart contractions?"

"A: Increased stretch from greater venous return (Frank-Starling mechanism)."

"Q: What decreases stroke volume?"

"A: Poor venous return or high blood pressure."

"Q: What is venous return?"

"A: The amount of blood returning to the heart — it should equal what’s pumped out."

"Q: What happens to blood pressure by the time it reaches venules?"

"A: It’s mostly gone; flow slows down for gas and nutrient exchange."

"Q: What helps return blood to the heart?"

"A: Skeletal muscle contractions

"Q: How do skeletal muscles help venous return?"

"A: They squeeze veins

"Q: What prevents backflow in veins?"

"A: One-way valves."

"Q: How does breathing assist venous return?"

"A: Chest pressure changes during inhalation and exhalation help pull blood toward the heart."

"Q: What happens when abdominal organs are compressed?"

"A: Veins passing through the thoracic and abdominal cavities get squeezed

"Q: How does exercise improve venous return?"

"A: Deeper breathing and muscle contractions both enhance blood return."

"Q: What happens when the myocardium is damaged?"

"A: Contractility decreases → cardiac output drops."

"Q: What happens to contractility during exercise?"

"A: It increases

"Q: What can the sympathetic nervous system do if venous pressure is low?"

"A: Stimulate vein walls to contract (though this is rare)."

"Q: How does the left ventricle react to increased blood filling?"

"A: Myocardial fibers stretch more

"Q: What two electrolytes are most important for the heart?"

"A: Potassium and calcium."

"Q: What happens with too much potassium?"

"A: Heart rate and contraction decrease → impulse conduction may stop."

"Q: What happens with high calcium levels?"

"A: Heart rate increases → may cause prolonged contraction or cardiac arrest."

"Q: What medication treats hypercalcemia?"

"A: Calcium channel blockers."

"Q: What happens with low calcium?"

"A: Depressed heart action because there aren’t enough ions to trigger contraction."

"Q: What is Starling’s Law of the Heart?"

"A: The greater the stretch of myocardial fibers (from blood filling)