ICSE Class 10 Biology: Circulatory System — Complete Notes 2026

Components of Blood

• Plasma (55%): water, proteins, glucose, urea, hormones, CO₂
• Red blood cells (erythrocytes): biconcave, no nucleus, haemoglobin carries O₂
• White blood cells (leucocytes): 5 types; neutrophils (phagocytosis), lymphocytes (antibodies)

Heart — Structure

• 4-chambered heart: 2 atria (receiving), 2 ventricles (pumping)
• Bicuspid (mitral) valve between left atrium and ventricle; tricuspid between right atrium and ventricle
• Semilunar valves at exits of aorta and pulmonary artery; prevent backflow

Cardiac Cycle

• Diastole: heart muscle relaxes; chambers fill with blood
• Systole: atria contract first → blood to ventricles; then ventricles contract → blood to lungs/body
• Heart rate: ~70 beats/min; stroke volume × heart rate = cardiac output (~5 L/min)

Blood Vessels

• Arteries: thick muscular walls; carry oxygenated blood away from heart (except pulmonary artery)
• Veins: thin walls; carry deoxygenated blood to heart; have valves to prevent backflow
• Capillaries: single cell wall; site of exchange of O₂, CO₂, nutrients, waste between blood and tissues

Double Circulation

• Pulmonary circuit: right heart → lungs → left heart (deoxygenated → oxygenated)
• Systemic circuit: left heart → body → right heart (oxygenated → deoxygenated)
• Advantage: complete separation maintains pressure; efficient oxygen delivery

Lymphatic System

• Lymph: excess tissue fluid collected by lymph capillaries; similar to plasma but less protein
• Lymph nodes filter lymph; contain lymphocytes; site of immune response
• Returns lymph to blood at left subclavian vein; transports dietary fat from intestines

ICSE Exam — Circulatory System

• Draw and label a diagram of the human heart showing major blood vessels
• Distinguish between arteries and veins (tabular form)
• State the function of each type of white blood cell