CRITICAL FACTS (Verify before entering exam hall)
Blood Composition
- Blood = 6-8% body weight; Plasma = 55%; Formed elements = 45%
- Plasma = 90-92% water + albumin (osmotic) + globulins (immunity) + fibrinogen (clotting)
- RBC lifespan = 120 days | Formation = red bone marrow | Destruction = spleen
WBC Order (% abundance) N > L > M > E > B (Never Let Monkeys Eat Bananas) Neutrophils 60-65% | Lymphocytes 20-25% | Monocytes 6-8% | Eosinophils 2-3% | Basophils 0.5-1% Basophils → histamine + heparin | Eosinophils → allergy + parasites | Neutrophils → phagocytosis Lymphocytes → B = antibody; T = cell-mediated (T matures in Thymus)
Blood Groups O: no antigens, anti-A + anti-B → UNIVERSAL DONOR (O-negative = TRUE universal donor) AB: both antigens, no antibodies → UNIVERSAL RECIPIENT (AB-positive = TRUE universal recipient) Rule: antibody is AGAINST antigen you DON'T have
Rh Factor and Erythroblastosis Fetalis Rh factor = D antigen | Rh+ = D antigen present Erythroblastosis fetalis = Rh-neg mother + Rh-pos foetus → 2nd+ pregnancy danger Prevention = RhoGAM (anti-D IgG) within 72 hours of first delivery
Cardiac Conducting System SAN (right atrium, 70-75 bpm, pacemaker) → AVN (delay 0.1 s) → Bundle of His → Purkinje fibres If SAN fails → AVN takes over at 40-60 bpm (secondary pacemaker)
Cardiac Cycle (0.8 s at 75 bpm) Atrial systole = 0.1 s | Ventricular systole = 0.3 s | Joint diastole = 0.4 s (LONGEST) All valves closed = isovolumetric contraction (brief phase at start of ventricular systole) Joint diastole: AV valves OPEN, semilunar valves CLOSED
ECG P = atrial DEPOLARIZATION | QRS = ventricular DEPOLARIZATION (NOT contraction!) | T = ventricular REPOLARIZATION Atrial repolarization = HIDDEN in QRS complex PR interval = AVN conduction time (normal 0.12-0.20 s; prolonged = 1st degree block)
Double Circulation EXCEPTIONS Pulmonary ARTERY → carries DEOXYGENATED blood (RV → lungs) Pulmonary VEIN → carries OXYGENATED blood (lungs → LA) This is the most tested NEET exception in this chapter!
Cardiac Output CO = SV × HR | Rest ≈ 5 L/min (70 mL × 72 bpm) Exercise: CO can reach 20-25 L/min
Disorders Hypertension: >140/90 mmHg, "silent killer" Angina: temporary ischemia, reversible, relieved by nitroglycerin MI: permanent cell death (prolonged coronary occlusion) CHF: cannot pump effectively → dyspnea + edema
NEVER CONFUSE THESE PAIRS
- SAN (pacemaker) vs AVN (delay relay)
- QRS = depolarization vs contraction (mechanical)
- Spleen = destruction vs bone marrow = formation
- O = donor vs AB = recipient
- Pulmonary artery = deoxygenated vs pulmonary vein = oxygenated
- Serum = plasma minus fibrinogen vs plasma = complete liquid