Clinical Applications and Physiological Connections

Emergency transfusion: O-negative blood is given when patient's blood type is unknown — it carries no A, B, or Rh antigens that could trigger a reaction
Erythroblastosis fetalis prevention: RhoGAM (anti-D immunoglobulin) must be given within 72 hours of first delivery, miscarriage, or any event causing foetal-maternal haemorrhage; this destroys foetal Rh+ RBCs before the mother's immune system creates anti-Rh memory B-cells
Atherosclerosis → CAD: LDL cholesterol infiltrates damaged arterial endothelium → macrophages engulf LDL → foam cells → fatty streak → fibrous plaque → plaque rupture → thrombus → myocardial infarction or stroke
Angina vs. MI: Angina = temporary myocardial ischemia (inadequate $O_{2}$ ), reversed by rest or nitroglycerin; MI = prolonged complete coronary occlusion causing irreversible cardiac muscle cell death; ST-segment elevation on ECG indicates MI
Heart failure types: Left-sided failure → pulmonary congestion → breathlessness/dyspnea; right-sided failure → systemic venous backup → peripheral edema, elevated JVP, ascites
Hypertension complications: Damages arterial endothelium (accelerates atherosclerosis), stresses left ventricle (causes left ventricular hypertrophy), damages kidney glomeruli (causes chronic kidney disease), increases risk of stroke (cerebral vessel rupture)
Blood count clinical clues: Neutrophilia = bacterial infection; lymphocytosis = viral infection; eosinophilia = allergy or parasites; thrombocytopenia = dengue/ITP (bleeding risk); anaemia = iron/B12 deficiency, haemolysis
Artificial pacemakers: Implanted when SAN fails or complete heart block occurs; provides the electrical stimulus that the damaged SAN/AVN connection cannot; fires at a programmed rate (typically 60-80 bpm)
ECG in heart block: First-degree = prolonged PR interval; second-degree = some P waves not followed by QRS; third-degree (complete) = complete AV dissociation — P and QRS independent rates
Nitroglycerin mechanism: Vasodilator that dilates coronary arteries (increases $O_{2}$ supply) and dilates systemic veins (reduces preload and cardiac workload), resolving the ischemic imbalance causing angina