Section 1: Blood Composition and Plasma

Blood is a fluid connective tissue constituting 6-8% of body weight. It is divided into plasma (55%) and formed elements (45%). Plasma is 90-92% water with three key proteins: albumin (maintains osmotic pressure), globulins (antibodies/immunity), and fibrinogen (blood clotting). Serum is plasma minus fibrinogen — it is the fluid remaining after a clot has formed and been removed.

Section 2: Formed Elements of Blood

Red Blood Cells (Erythrocytes): Biconcave, anucleate, ~7-8 µm diameter; lifespan 120 days; formed in red bone marrow; destroyed in spleen. Count: 5-5.5 million/$mm^{3}$ (male), 4.5-5 million/$mm^{3}$ (female). Carry $O_{2}$ via haemoglobin.

White Blood Cells (Leucocytes): Total 6000-8000/$mm^{3}$. Granulocytes: neutrophils (60-65%, phagocytosis), eosinophils (2-3%, anti-parasitic/allergy), basophils (0.5-1%, histamine + heparin). Agranulocytes: lymphocytes (20-25%, B-cell = antibody, T-cell = cell-mediated), monocytes (6-8%, → macrophages in tissues). Order by abundance: N > L > M > E > B.

Platelets (Thrombocytes): Cell fragments from megakaryocytes; count 1.5-3.5 lakh/$mm^{3}$; lifespan 5-9 days; function: blood clotting initiation.

Section 3: Blood Groups

ABO System: Based on RBC surface antigens and plasma antibodies. A: A-antigen, anti-B; B: B-antigen, anti-A; AB: both antigens, no antibodies (universal recipient); O: no antigens, both antibodies (universal donor). True universal donor = O-negative; true universal recipient = AB-positive.

Rh System: D-antigen on RBC = Rh+; absence = Rh-. Erythroblastosis fetalis: Rh- mother + Rh+ foetus → sensitization at first delivery → disease in subsequent pregnancies. Prevention: RhoGAM (anti-D IgG) within 72 hours of first delivery.

Section 4: Human Heart and Valves

Four-chambered heart in mediastinum. Valves: tricuspid (right AV), bicuspid/mitral (left AV), pulmonary semilunar (RV exit), aortic semilunar (LV exit). Left ventricle has the thickest wall (~10-15 mm) — generates ~120 mmHg for systemic circulation.

Section 5: Cardiac Conducting System

Sequence: SAN (right atrium, 70-75 bpm, primary pacemaker) → AVN (0.1 s delay) → Bundle of His → left + right bundle branches → Purkinje fibres (apex-upward ventricular activation). If SAN fails → AVN takes over at 40-60 bpm. If AVN fails → Purkinje at 20-40 bpm.

Section 6: Cardiac Cycle and ECG

Cardiac cycle = 0.8 s: atrial systole (0.1 s) + ventricular systole (0.3 s) + joint diastole (0.4 s). CO = SV × HR ≈ 5 L/min. ECG: P = atrial depolarization; QRS = ventricular depolarization; T = ventricular repolarization. Atrial repolarization hidden within QRS.

Section 7: Double Circulation and Circulatory Disorders

Pulmonary: RV → pulmonary artery (deoxygenated) → lungs → pulmonary veins (oxygenated) → LA. Systemic: LV → aorta → body → venae cavae → RA. Disorders: hypertension (>140/90 mmHg, "silent killer"), CAD (atherosclerosis in coronary arteries), angina pectoris (temporary ischemia, relieved by rest/nitroglycerin), heart failure/CHF (inadequate pump function → breathlessness, edema).