Cue Column | Notes Column

What is blood? | Blood is a fluid connective tissue constituting 6-8% of body weight; plasma (55%) + formed elements (45%). Plasma = 90-92% water + albumin (osmotic pressure) + globulins (immunity) + fibrinogen (clotting).

RBC facts? | Biconcave, enucleated discs; lifespan 120 days; formed in red bone marrow; destroyed in spleen ("graveyard of RBCs"). Males: 5-5.5 million/$mm^{3}$; females: 4.5-5 million/$mm^{3}$.

WBC types? | 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). Mnemonic: Never Let Monkeys Eat Bananas.

ABO blood groups? | A: A-antigen, anti-B antibody; 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 factor? | D-antigen presence = Rh+. Rh-neg mother + Rh-pos foetus → erythroblastosis fetalis (2nd+ pregnancy). Prevention: RhoGAM within 72 hrs after first delivery.

Conducting system? | SAN (right atrium, 70-75 bpm, pacemaker) → AVN (0.1 s delay, allows atrial emptying) → Bundle of His → Purkinje fibres (apex upward ventricular contraction). SAN = primary pacemaker; AVN = secondary at 40-60 bpm.

Cardiac cycle? | 0.8 s total: atrial systole (0.1 s) + ventricular systole (0.3 s) + joint diastole (0.4 s). Valve status: atrial systole — AV valves open, semilunar valves closed. Ventricular ejection — semilunar valves open, AV valves closed. Joint diastole — AV valves open, semilunar valves closed.

ECG waves? | P = atrial depolarization; QRS = ventricular depolarization (NOT contraction!); T = ventricular repolarization. Atrial repolarization hidden within QRS.

Double circulation? | Pulmonary: RV → pulmonary artery (deoxygenated) → lungs → pulmonary veins (oxygenated) → LA. Systemic: LV → aorta → body → venae cavae → RA. KEY: pulmonary arteries carry deoxygenated blood — exception to artery rule!

Cardiac output? | CO = SV × HR ≈ 5 L/min (70 mL × 72 bpm). CO can reach 20-25 L/min during vigorous exercise.

Disorders? | Hypertension: >140/90 mmHg, "silent killer." CAD: atherosclerosis in coronary arteries. Angina: temporary ischemia, chest pain, relieved by rest/nitroglycerin. Heart failure (CHF): cannot pump effectively → breathlessness, edema.

Summary (Bottom Section)

Body fluids and circulation covers blood composition, ABO/Rh blood groups, cardiac anatomy, the conducting system (SAN→AVN→Bundle→Purkinje), the cardiac cycle (0.8 s), ECG interpretation (P-QRS-T), and double circulation. The three highest-yield NEET facts are: (1) SAN is the pacemaker at 70-75 bpm, (2) pulmonary arteries carry deoxygenated blood, and (3) QRS = ventricular depolarization (not contraction). This chapter yields 4-5 NEET questions annually.