Cardiac Cycle and Heart Output — NEET Biology
📚 Practice ConceptAll vertebrates and a few invertebrates have a closed circulatory system. Our circulatory system consists of a muscular pumping organ, heart, a network of vessels and a fluid, blood. Heart has four chambers, two atria and two ventricles. The sino-atrial node (SAN) generates the maximum number of action potentials per minute (70-75/min) and therefore, it sets the pace of the activities of the heart. Hence it is called the Pacemaker. The cardiac cycle consists of systole (contraction) and diastole (relaxation) corresponding to their relaxation (diastole). The systole forces the blood to move from the atria to the ventricles and to the pulmonary artery and the aorta. The cardiac cycle is formed by sequential events in the heart which is cyclically repeated and is called the cardiac cycle. A healthy person shows 72 such cycles per minute. About 70 mL of blood is pumped out by each ventricle during a cardiac cycle and it is called the stroke volume. The stroke volume multiplied by the heart rate gives the cardiac output and it is equal to the product of stroke volume and heart rate (approx 5 litres). The electrical activity of the heart can be recorded from
(A) Arrange the ECG events in the correct sequence during a cardiac cycle: 1. QRS complex – ventricular depolarisation, systole begins 2. P-wave – atrial depolarisation, atrial contraction 3. T-wave – ventricular repolarisation, systole ends (B) Match the terms with their values/definitions: Column I A. Stroke Volume B. Cardiac Output Column II i. 70 mL blood pumped per ventricle per beat ii. ~5000 mL blood pumped per ventricle per minute
View solution & NCERT explanation
Correct answer: B — (A) 2 → 1 → 3 ; (B) A–i, B–ii
ECG: P-wave → QRS → T-wave (sequence = 2 → 1 → 3). Stroke volume = 70 mL/beat/ventricle. Cardiac output = stroke volume × heart rate ≈ 5000 mL/min.
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Through deep analysis of NEET and NTA, 176 of the 180 ReNEET 2026 (June 21) questions were already in the MedicNEET question bank before the exam.
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