BODY FLUIDS & CIRCULATION
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├── BLOOD
│   ├── Composition
│   │   ├── Plasma (55%) — water 90-92%, albumin, globulins, fibrinogen
│   │   └── Formed elements (45%) — RBC, WBC, platelets
│   ├── RBC
│   │   ├── Biconcave, enucleated; lifespan 120 days
│   │   ├── Formed: red bone marrow; Destroyed: spleen
│   │   └── Function: $O_{2}$/C$O_{2}$ transport via haemoglobin
│   ├── WBC (granulocytes + agranulocytes)
│   │   ├── Neutrophils: 60-65%, phagocytosis
│   │   ├── Eosinophils: 2-3%, allergy + parasites
│   │   ├── Basophils: 0.5-1%, histamine + heparin
│   │   ├── Lymphocytes: 20-25%, B-cell (antibody), T-cell (cell-mediated)
│   │   └── Monocytes: 6-8%, → macrophages
│   └── Platelets: 1.5-3.5 lakh/$mm^{3}$, from megakaryocytes, clotting
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├── BLOOD GROUPS
│   ├── ABO System
│   │   ├── A: A-antigen, anti-B antibody
│   │   ├── B: B-antigen, anti-A antibody
│   │   ├── AB: both antigens, no antibodies — universal RECIPIENT (AB+)
│   │   └── O: no antigens, both antibodies — universal DONOR (O-)
│   └── Rh System
│       ├── Rh+: D-antigen present
│       ├── Rh-: D-antigen absent
│       └── Erythroblastosis fetalis: Rh- mother + Rh+ foetus (2nd pregnancy)
│           └── Prevention: RhoGAM within 72h after first delivery
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├── HUMAN HEART
│   ├── Location: mediastinum, slightly left-tilted
│   ├── Chambers: 2 atria (thin) + 2 ventricles (thick)
│   ├── Valves
│   │   ├── AV valves: tricuspid (right), bicuspid/mitral (left)
│   │   └── Semilunar: pulmonary (RV→PA), aortic (LV→aorta)
│   └── Conducting System
│       ├── SAN → 70-75 bpm (pacemaker)
│       ├── AVN → delay 0.1 s (allows atrial emptying)
│       ├── Bundle of His → through interventricular septum
│       └── Purkinje fibres → apex-upward ventricular contraction
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├── CARDIAC CYCLE (0.8 s at 75 bpm)
│   ├── Atrial systole: 0.1 s (AV valves open, semilunar closed)
│   ├── Ventricular systole: 0.3 s
│   │   ├── Isovolumetric contraction (all valves closed)
│   │   └── Ejection phase (semilunar open, AV closed)
│   └── Joint diastole: 0.4 s (AV valves open, semilunar closed) — LONGEST
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├── ECG
│   ├── P wave: atrial depolarization
│   ├── QRS complex: ventricular depolarization (NOT contraction!)
│   ├── T wave: ventricular repolarization
│   └── Atrial repolarization: hidden within QRS complex
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├── DOUBLE CIRCULATION
│   ├── Pulmonary: RV → pulm. artery (deoxy) → lungs → pulm. veins (oxy) → LA
│   └── Systemic: LV → aorta → body → venae cavae → RA
│       └── KEY: pulm. arteries = deoxy; pulm. veins = oxy (EXCEPTIONS!)
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├── CARDIAC OUTPUT
│   ├── Formula: CO = SV × HR
│   ├── Rest: ~5 L/min (70 mL × 72 bpm)
│   └── Exercise: up to 20-25 L/min
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└── DISORDERS
    ├── Hypertension: >140/90 mmHg, "silent killer"
    ├── CAD: atherosclerosis in coronary arteries
    ├── Angina pectoris: temporary ischemia, chest pain
    └── Heart failure (CHF): cannot pump effectively → breathlessness, edema