Ch 15 covers blood composition, blood groups, coagulation, heart anatomy, the cardiac cycle, the conduction system, ECG, double circulation, and the lymphatic system.
Blood: plasma (55%) + formed elements (45%). RBCs: biconcave, carry O₂ (haemoglobin), 120-day lifespan. WBCs: immunity (neutrophils, lymphocytes, monocytes, basophils, eosinophils). Platelets: blood clotting. ABO: A (anti-B), B (anti-A), AB (universal recipient, no antibodies), O (universal donor, no antigens). Rh factor: Rh+ or Rh−. Coagulation cascade: thromboplastin → prothrombin → thrombin → fibrinogen → fibrin clot.
Human heart: 4-chambered (2 atria, 2 ventricles). Valves: tricuspid (right), bicuspid/mitral (left), semilunar (aorta, pulmonary). SA node (pacemaker) → AV node → Bundle of His → Purkinje fibres. Cardiac cycle: 0.8 s (atrial systole 0.1 s, ventricular systole 0.3 s, joint diastole 0.4 s). Cardiac output = stroke volume × heart rate. ECG: P wave (atrial depolarisation), QRS (ventricular depolarisation), T wave (ventricular repolarisation).
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The left ventricle pumps oxygenated blood to the entire body (systemic circulation) through the aorta — this requires high pressure to push blood through the long circuit. The right ventricle only pumps to the nearby lungs (pulmonary circulation), requiring less pressure. So the left ventricle needs a thicker muscular wall to generate higher pressure.
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