Human Circulatory System MCQs— Class 6 Science

Quick Revision: Human Circulatory System

• Circulatory System: Transports oxygen, nutrients, hormones, and waste products throughout the body. Comprises the heart, blood vessels, and blood.
• Heart: A muscular pumping organ about the size of a fist, located in the chest cavity slightly to the left. Beats about 72 times per minute.
• Heart Chambers: Four chambers — Right Atrium (receives deoxygenated blood), Right Ventricle (pumps blood to lungs), Left Atrium (receives oxygenated blood from lungs), Left Ventricle (pumps oxygenated blood to the body).
• Heartbeat: The rhythmic contraction and relaxation of heart muscles (lub-dub sound). The number of heartbeats per minute is called the pulse rate.
• Blood Vessels — Arteries: Carry blood away from the heart. Thick, elastic walls. Carry oxygenated blood (except pulmonary artery).
• Blood Vessels — Veins: Carry blood towards the heart. Thin walls with valves to prevent backflow. Carry deoxygenated blood (except pulmonary vein).
• Blood Vessels — Capillaries: Extremely thin vessels connecting arteries and veins. Site of exchange of oxygen, nutrients, and waste between blood and body cells.
• Blood — Plasma: Pale yellow liquid, about 55% of blood. Transports nutrients, hormones, and waste proteins.
• Blood — Red Blood Cells (RBCs): Contain haemoglobin (iron-rich protein) that carries oxygen. Disc-shaped, no nucleus. Produced in bone marrow.
• Blood — White Blood Cells (WBCs): Fight infections and provide immunity. Larger than RBCs, have a nucleus. Produced in bone marrow and lymph nodes.
• Blood — Platelets: Tiny cell fragments that help in blood clotting (coagulation) at injury sites, preventing excessive blood loss.
• Double Circulation: Pulmonary circulation — blood flows between heart and lungs. Systemic circulation — blood flows between heart and the rest of the body.
• Oxygenated vs Deoxygenated Blood: Oxygenated blood is bright red (rich in O₂, carried by arteries except pulmonary artery). Deoxygenated blood is dark red (rich in CO₂, carried by veins except pulmonary vein).
• Lymphatic System: A network of lymph vessels that collects excess fluid (lymph) from tissues and returns it to the blood. Lymph nodes filter out germs.
• Lymph: A pale yellow fluid similar to plasma but with fewer proteins. Contains WBCs (lymphocytes) that fight infection.
• Spleen: An organ that filters blood, removes old RBCs, and helps produce WBCs.
• Bone Marrow: Soft tissue inside bones where RBCs, WBCs, and platelets are produced.
• Blood Groups: A, B, AB, and O (based on antigens on RBCs). Rh factor (+ or -) is also important for blood transfusion compatibility.
• Common Circulatory Disorders: Anaemia (low haemoglobin/RBCs), High Blood Pressure (hypertension), Heart Attack (blocked coronary artery), Stroke (blocked blood vessel in brain).