5-Bullet Flash Revision for Exam Day

Blood = plasma (55%) + formed elements (45%); RBC lifespan 120 days; WBC order N > L > M > E > B; platelets from megakaryocytes; basophils secrete histamine + heparin
Blood groups: O = universal donor (no antigens), AB = universal recipient (no antibodies); true universal donor = O-negative; erythroblastosis fetalis = Rh-neg mother + Rh-pos foetus (2nd pregnancy); RhoGAM within 72 hrs prevents it
Cardiac system: SAN (70-75 bpm, primary pacemaker) → AVN (0.1 s delay) → Bundle of His → Purkinje fibres → apex-upward ventricular contraction; cardiac cycle = 0.8 s (0.1 + 0.3 + 0.4 s)
ECG: P = atrial depolarization; QRS = ventricular DEPOLARIZATION (not contraction!); T = ventricular repolarization; atrial repolarization is HIDDEN within QRS; CO = SV × HR ≈ 5 L/min
CRITICAL EXCEPTION: Pulmonary ARTERIES carry DEOXYGENATED blood; pulmonary VEINS carry OXYGENATED blood — the only vessels to break the conventional artery/vein oxygenation rule