What are the four chambers of the human heart? — Right atrium: Receives deoxygenated blood from the body (via vena cava). Right ventricle: Pumps deoxygenated blood to the lungs (via pulmonary artery). Left atrium: Receives oxygenated blood from the lungs (via pulmonary vein). Left ventricle: Pumps oxygenated blood to the body (via aorta).

Why is the left ventricle wall thicker than the right? — The left ventricle must pump blood around the entire body (systemic circulation) — a much greater distance and resistance than the right ventricle, which only pumps to the lungs (pulmonary circulation). Thicker muscle = greater force.

What is the cardiac cycle? — The sequence of events in one complete heartbeat: 1. Diastole — both atria and ventricles relax, blood fills atria. 2. Atrial systole — atria contract, pushing blood into ventricles. 3. Ventricular systole — ventricles contract, pumping blood to lungs and body.

What do the heart valves do and what are they? — Valves prevent backflow of blood. Atrioventricular (AV) valves: Between atria and ventricles (mitral/bicuspid — left; tricuspid — right). Semilunar valves: Between ventricles and arteries (pulmonary and aortic). The "lub-dub" heartbeat sound is valves closing.

What is the sinoatrial (SA) node? — The heart's natural pacemaker — a small cluster of cells in the right atrium that generates electrical impulses initiating each heartbeat. The impulse spreads to the AV node, then down the Bundle of His and Purkinje fibres to the ventricles.

What is the difference between arteries, veins, and capillaries? — Arteries: Thick, muscular walls; carry blood away from heart; high pressure; no valves. Veins: Thinner walls; carry blood to heart; low pressure; have valves to prevent backflow. Capillaries: One cell thick (endothelium only); site of gas and nutrient exchange.

What is pulmonary circulation vs systemic circulation? — Pulmonary circulation: Right heart → lungs → left heart. Blood is oxygenated in the lungs. Systemic circulation: Left heart → body → right heart. Blood delivers O₂ and collects CO₂ from tissues. The human heart drives both circuits simultaneously.

What are the four components of blood and their functions? — Red blood cells (erythrocytes): Carry O₂ via haemoglobin. White blood cells (leucocytes): Immune defence. Platelets (thrombocytes): Blood clotting. Plasma: Liquid matrix carrying nutrients, hormones, CO₂, proteins, waste products.

What makes red blood cells uniquely suited to carrying oxygen? — Biconcave disc shape = large surface area. No nucleus = more space for haemoglobin (~280 million molecules per cell). Flexible = can squeeze through narrow capillaries. Contain haemoglobin = binds O₂ reversibly. Short lifespan: ~120 days.

What is haemoglobin and how does it carry oxygen? — A protein in red blood cells with 4 subunits, each containing a haem group with an iron (Fe²⁺) atom. Each Fe²⁺ reversibly binds one O₂ molecule → 4 O₂ per haemoglobin. High O₂ (lungs): haemoglobin loads O₂ (becomes oxyhaemoglobin). Low O₂ (tissues): releases O₂.

What is the oxyhaemoglobin dissociation curve? — An S-shaped (sigmoid) curve showing how haemoglobin saturation varies with partial pressure of O₂. Sigmoidal shape = cooperative binding. Low pO₂ (tissues): O₂ released rapidly. High pO₂ (lungs): O₂ loaded efficiently. The Bohr effect: increased CO₂/lower pH shifts curve right → more O₂ released to active tissues.

What is the Bohr effect? — Increasing CO₂ / decreasing pH causes haemoglobin to release O₂ more readily (curve shifts right). In actively respiring tissues, high CO₂ = low pH → haemoglobin unloads more O₂. Ensures O₂ is delivered where it is most needed.

How is CO₂ transported in the blood? — ~70% as bicarbonate ions (HCO₃⁻): CO₂ + H₂O → H₂CO₃ → H⁺ + HCO₃⁻ (catalysed by carbonic anhydrase in RBCs). ~25% bound to haemoglobin (as carbaminohaemoglobin). ~5% dissolved in plasma.

What is the structure of the human lungs? — Lungs → Lobes → Bronchi → Bronchioles → Alveolar ducts → Alveoli (tiny air sacs ~0.2 mm, ~300 million per lung). Surrounded by capillary networks. Total surface area ~70 m² — the size of a singles tennis court.

What features make alveoli ideal for gas exchange? — Large surface area (~70 m²). Very thin walls (one epithelial cell thick). Moist lining (gases dissolve). Rich capillary network (maintains concentration gradient). Short diffusion distance (alveolar wall + capillary wall = ~0.5 μm).

How does breathing (ventilation) work? — Inhalation: Diaphragm flattens + intercostal muscles raise ribcage → thoracic volume increases → pressure drops → air flows in. Exhalation: Diaphragm domes up + ribcage falls → thoracic volume decreases → pressure rises → air flows out. Driven by pressure gradients.

What is tidal volume, vital capacity, and residual volume? — Tidal volume: Volume of air in each normal breath (~500 mL). Vital capacity: Maximum air exhaled after maximum inhalation (~4.5 L). Residual volume: Air remaining in lungs after maximum exhalation (~1.2 L). Total lung capacity = vital capacity + residual volume.

What is coronary heart disease (CHD) and what causes it? — Narrowing of the coronary arteries (which supply the heart muscle) due to atherosclerosis — build-up of fatty plaques (atheroma) containing cholesterol. Reduces blood flow → angina. Complete blockage → myocardial infarction (heart attack). Risk factors: high cholesterol, smoking, hypertension, obesity, inactivity.

What is atherosclerosis? — Build-up of fatty deposits (plaques/atheroma) inside arterial walls, causing narrowing and hardening. Process: LDL cholesterol → oxidised → taken up by macrophages → foam cells → fatty streak → fibrous plaque. Reduces blood flow and increases blood pressure.

What is blood pressure and what do the numbers mean? — The force of blood on artery walls. Measured in mmHg. Systolic pressure (top number): Pressure during ventricular contraction. Diastolic pressure (bottom number): Pressure during relaxation. Normal: ~120/80 mmHg. High blood pressure (>140/90) = hypertension — damages vessel walls.

What is asthma and what happens during an attack? — A chronic inflammatory condition where the bronchioles become narrowed. During an attack: bronchospasm (smooth muscle contracts), inflammation (lining swells), increased mucus secretion → airway narrows → wheeze, breathlessness, cough. Treated with bronchodilator inhalers (β₂ agonists).

What is the lymphatic system and how does it relate to circulation? — A network of vessels that returns excess interstitial fluid (tissue fluid) to the blood as lymph. Also transports dietary fats from the gut and plays a major role in immunity (lymph nodes filter pathogens). Lymph drains into the subclavian veins.

What is tissue fluid and how is it formed? — At the arterial end of capillaries, hydrostatic pressure forces plasma out of capillaries into surrounding tissues → tissue fluid. At the venous end, osmotic pressure draws most back in. Excess tissue fluid drains into lymph capillaries.

What is the difference between LDL and HDL cholesterol? — LDL ("bad" cholesterol): Carries cholesterol from liver to tissues — high levels deposit in artery walls → atherosclerosis. HDL ("good" cholesterol): Carries cholesterol from tissues back to liver for breakdown — protective against CHD.

What is the ABO blood group system? — Humans have four blood types: A (antigen A on RBCs, anti-B antibodies in plasma), B (antigen B, anti-A antibodies), AB (both antigens, no antibodies — universal recipient), O (no antigens, both antibodies — universal donor). Mismatched transfusions → agglutination → fatal.