Body Fluids and Circulation covers the composition of blood and lymph, ABO and Rh blood grouping, the mechanism of coagulation, the structure and functioning of the human heart, the cardiac cycle and its ECG correlates, and the concept of double circulation. NEET consistently asks 3–4 questions from this chapter — the ABO table, ECG waves, and the SA node as pacemaker are perennial MCQ favourites.
Blood is a fluid connective tissue consisting of plasma (55%) and formed elements (45%). It transports respiratory gases, nutrients, hormones, and metabolic wastes.
Plasma is a straw-coloured fluid containing water (~92%), proteins (fibrinogen, globulins, albumins), glucose, amino acids, lipids, and inorganic salts.
Formed elements:
ABO blood groups — based on presence or absence of antigens A and B on RBC surface:
| Blood Group | Antigen on RBC | Antibody in Plasma | Can donate to |
|---|---|---|---|
| A | A | Anti-B | A, AB |
| B | B | Anti-A | B, AB |
| AB | A and B | None | AB only (universal recipient) |
| O | None | Anti-A and Anti-B | All groups (universal donor) |
Rh factor — Rh antigen present in ~80% of humans (Rh⁺). Rh incompatibility during pregnancy can cause erythroblastosis foetalis.
Blood coagulation: Injury → platelets aggregate → release thromboplastin → prothrombin → thrombin → fibrinogen → fibrin (clot).
The human heart is a myogenic (self-generating) muscular organ located in the thoracic cavity between the lungs. It has four chambers: two atria (thin-walled, receiving) and two ventricles (thick-walled, pumping).
Valves:
Nodal tissue (conduction system):
The cardiac cycle is the sequence of events in one heartbeat (~0.8 seconds at 72 beats/min):
Cardiac output = Stroke volume × Heart rate = ~70 mL × 72 beats/min = ~5 L/min.
ECG (Electrocardiograph):
Double circulation means blood passes through the heart twice per complete circuit — once through the pulmonary circuit and once through the systemic circuit. This ensures oxygenated and deoxygenated blood never mix.
Lymphatic system — returns excess tissue fluid to blood via lymph capillaries and lymph vessels. Lymph nodes filter lymph and are sites of immune response.
Disorders:
Use this section after the first reading. It connects facts into mechanisms, comparisons, and NEET-style decision rules.
ABO questions become simple if you separate antigen and antibody. The antigen is on RBC; the antibody is in plasma. Group A has A antigen and anti-B antibody. Group B has B antigen and anti-A antibody. Group AB has both antigens and no anti-A/anti-B antibodies. Group O has no antigen and both antibodies.
Blood flow sequence: body -> right atrium -> right ventricle -> lungs -> left atrium -> left ventricle -> body. Valves enforce one-way flow. SA node starts the impulse, AV node delays it, and Purkinje fibres spread it through ventricles.
ECG: P wave = atrial depolarisation, QRS = ventricular depolarisation, T wave = ventricular repolarisation.
Use this process after reading the notes. It turns NCERT lines into exam-ready recall, diagrams, and MCQ decisions.
Memory mistake: make a two-column comparison table.
Diagram mistake: redraw the labelled structure from memory.
Process mistake: rewrite the sequence with arrows.
Assertion-reason mistake: check truth of each statement first, then relation.
Practice these before starting MCQs. They are designed to lock core concepts with minimum theory load.
SA node.
Ventricular depolarisation.
O group is universal donor; AB group is universal recipient for ABO matching.
Bicuspid or mitral valve.
Cardiac output = stroke volume x heart rate.
Chapter note placement for Body Fluids and Circulation.
Test your understanding of Body Fluids and Circulation with focused sectional tests and a full-length NEET-style module test. Each chapter now runs 5 practice tests of 25 questions each, and every question has a 90-second timer — matching real NEET exam pacing.
5 focused sessions: blood composition & RBC/WBC, ABO groups & clotting, heart anatomy & valves, cardiac cycle & ECG, and double circulation & disorders — 15 MCQs each.
Open Session TestsNEET-style 125-question module test on Body Fluids and Circulation with timer, palette, review, and subtopic accuracy breakdown.
Open Full MockInline banner shown in the practice section — high-intent placement for test-prep and coaching campaigns.
Move straight from chapter-wise questions into a subject test, then loop back into weaker areas instead of ending the session here.