Last Updated: May 2026
NEET Biology Body Fluids and Circulation 2027 is one of the highest-ROI chapters in NCERT Class XI Unit V (Human Physiology) — typically yielding 2–3 direct questions in NEET each year, plus another 1–2 fused with cardiac physiology in NEET-PG style assertion-reason items. Across the last 5 NEET papers (2021-2025), Body Fluids & Circulation contributed an average of 3.2 questions (≈12.8 marks). With NEET 2027 expected to lean more on NCERT-line diagrams and ECG basics, this chapter is non-negotiable.
This guide locks down the complete chapter — composition of blood, lymph, cardiac cycle, ECG, double circulation, regulation, disorders — followed by 40 NEET-style practice MCQs with an answer key, an embedded interactive 10-MCQ quiz, and a NEET 2027 FAQ section. Bookmark and revise weekly.
1. Why Body Fluids Are Needed
A unicellular Amoeba exchanges materials directly with its environment. A 70 kg human cannot — diffusion across a 2 µm cell would take centuries to reach interior cells. Multicellular organisms therefore evolved a circulating fluid (blood / haemolymph) that is pumped through a network so every cell sits within ~25 µm of a capillary. This is why NCERT opens the chapter with the phrase: “Blood is a special connective tissue.”
2. Composition of Blood
Blood is a fluid connective tissue with a fluid matrix called plasma (55%) and formed elements (45%) — RBCs, WBCs and platelets.
Plasma
- Water: 90–92%
- Proteins: 6–8% — fibrinogen (clotting), globulins (immunity), albumins (osmotic balance)
- Minerals: Na+, Ca2+, Mg2+, HCO3-, Cl- etc.
- Glucose, amino acids, lipids — in transit
- Factors for coagulation in inactive form
Plasma minus clotting factors = serum. This 1-line distinction is a recurring NEET item.
Formed Elements
| Cell | Count / mm³ | Lifespan | Key facts |
|---|---|---|---|
| RBC (Erythrocyte) | 5.0–5.5 million (M), 4.5–5.0 million (F) | 120 days | Anucleate in mammals, biconcave; haemoglobin 12–16 g/100 mL; formed in red bone marrow; destroyed in spleen (“graveyard of RBCs”) |
| WBC (Leucocyte) | 6,000–8,000 | Days–years | Nucleated, colourless; granulocytes (neutrophils 60–65%, eosinophils 2–3%, basophils 0.5–1%) + agranulocytes (lymphocytes 20–25%, monocytes 6–8%) |
| Platelet (Thrombocyte) | 1.5–3.5 lakh | ~8 days | Cell fragments from megakaryocytes; release clotting factors |
Blood Groups
Two systems are NCERT-mandatory: ABO (Landsteiner, 1900) and Rh.
| Group | Antigen on RBC | Antibody in plasma | Donor to | Recipient from |
|---|---|---|---|---|
| A | A | anti-B | A, AB | A, O |
| B | B | anti-A | B, AB | B, O |
| AB | A and B | nil | AB | A, B, AB, O (Universal recipient) |
| O | nil | anti-A and anti-B | A, B, AB, O (Universal donor) | O |
Rh: 80% Indians are Rh+. Erythroblastosis fetalis = Rh- mother carrying Rh+ baby a second time; antibodies cross placenta and lyse foetal RBCs.
Coagulation of Blood
NCERT cascade: tissue injury → thromboplastin (from platelets/tissue) + Ca2+ converts inactive prothrombin → thrombin; thrombin then converts fibrinogen → fibrin; fibrin meshes trap blood cells = clot.
3. Lymph (Tissue Fluid)
As blood passes through capillaries, water plus small soluble substances move out at the arterial end (hydrostatic > osmotic) — this interstitial fluid / tissue fluid is the actual exchange medium. Most of it returns at the venous end; the rest enters lymphatic capillaries as lymph. Lymph contains lymphocytes, fewer proteins, no RBCs, no platelets. Lymphatic vessels drain into subclavian veins.
4. Circulatory Pathways
Two patterns: open (arthropods, molluscs — blood pumped into open spaces called sinuses) and closed (annelids, all vertebrates — blood remains within blood vessels). Closed is more efficient: precise regulation of flow possible.
- Single circulation: fishes (heart → gills → body → heart, deoxy throughout heart)
- Incomplete double circulation: amphibians, reptiles (3-chambered heart; mixing in ventricle, except crocodile which has 4 chambers)
- Complete double circulation: birds, mammals (4-chambered heart; full separation; oxy and deoxy never mix)
5. Human Heart — Anatomy
Mesodermally-derived, fist-sized, located between the lungs slightly tilted to the left, enclosed in a double-walled pericardium with pericardial fluid for lubrication. Four chambers: 2 atria (thin walled, separated by inter-atrial septum) and 2 ventricles (thick walled, separated by inter-ventricular septum). Atrium and ventricle of the same side are separated by an atrio-ventricular septum bearing an opening guarded by a valve.
| Valve | Location | Cusps |
|---|---|---|
| Tricuspid | Right AV opening | 3 |
| Bicuspid (Mitral) | Left AV opening | 2 |
| Semilunar (Pulmonary + Aortic) | Openings of pulmonary artery & aorta | 3 each |
Valves prevent backflow. The whole heart is myogenic — contraction is initiated within the heart itself, not by nerves.
Conducting System — The “Pacemaker” Nodes
- Sinoatrial node (SAN): in upper-right atrium wall — pacemaker, initiates 70–75 action potentials/min.
- Atrioventricular node (AVN): at lower-left of right atrium near the inter-atrial septum.
- Bundle of His: from AVN through atrio-ventricular septum, splits into left + right bundle branches.
- Purkinje fibres: terminal network reaching ventricular musculature.
6. Cardiac Cycle
Sequential events in one heartbeat. Resting human heart: 72 bpm → cycle duration = 60/72 ≈ 0.8 s.
| Phase | Duration | Event |
|---|---|---|
| Joint diastole | 0.4 s | All chambers relaxed; tricuspid + bicuspid open; blood flows passively from atria to ventricles |
| Atrial systole | 0.1 s | SAN fires → atria contract → push remaining ~30% blood into ventricles |
| Ventricular systole | 0.3 s | AV valves close (LUB), pressure rises, semilunar valves open, blood ejected |
| Ventricular diastole | — | Semilunar valves close (DUB), AV valves open |
Stroke volume = blood pumped out per beat per ventricle ≈ 70 mL.
Cardiac output = stroke volume × heart rate ≈ 70 × 72 = 5,040 mL ≈ 5 L/min.
An athlete can push CO to 25–30 L/min during heavy exercise (Frank-Starling law).
7. ECG (Electrocardiogram)
A graphic record of the electrical activity of the heart obtained via leads on the wrists and left ankle (standard limb leads).
- P wave: depolarisation of atria → atrial contraction
- QRS complex: depolarisation of ventricles → ventricular contraction
- T wave: repolarisation of ventricles → return to normal state
Counting QRS complexes per unit time gives heart rate. Width/timing changes diagnose blocks, infarcts, arrhythmias. Atrial repolarisation is hidden under QRS — rarely seen.
8. Double Circulation in Humans
Pulmonary circulation: Right ventricle → pulmonary artery → lungs → pulmonary veins → left atrium. (artery carries deoxy, vein carries oxy — the only exception in the body apart from umbilical vessels in foetus).
Systemic circulation: Left ventricle → aorta → body tissues → vena cavae → right atrium.
Hepatic portal system: connects intestine to liver via hepatic portal vein — ensures absorbed substances are processed before reaching general circulation. Coronary circulation supplies the cardiac muscle itself.
9. Regulation of Cardiac Activity
Heart is myogenic but rate is modulated by:
- Medulla oblongata via autonomic nervous system: sympathetic ↑ rate & force, parasympathetic (vagus) ↓ rate.
- Adrenal medullary hormones: adrenaline & noradrenaline ↑ rate.
10. Disorders of Circulation
| Disorder | Cause / Definition |
|---|---|
| Hypertension | BP > 140/90 mm Hg consistently → kidney, brain, heart damage |
| Coronary Artery Disease (CAD / atherosclerosis) | Lumen narrowed by deposition of Ca, fat, fibrous tissue, cholesterol |
| Angina pectoris | Acute chest pain due to inadequate O2 to heart muscle |
| Heart failure | Heart unable to pump enough to meet body needs (≠ cardiac arrest, ≠ heart attack) |
Useful internal links to deepen prep: all NEET 2027 courses · NEET 2027 syllabus & strategy · free NCERT-line notes · NEET 2027 FAQ · join Drishti NEET Bio batch.
40 NEET Practice MCQs — Body Fluids & Circulation
- Plasma without clotting factors is called: (a) Serum (b) Lymph (c) Tissue fluid (d) Whole blood
- Mature mammalian RBCs lack: (a) Cell membrane (b) Cytoplasm (c) Nucleus (d) Haemoglobin
- Lifespan of human RBC is: (a) 100 days (b) 120 days (c) 60 days (d) 24 hours
- Universal recipient blood group: (a) A (b) B (c) AB (d) O
- SA node is located in: (a) Left atrium (b) Right atrium upper wall (c) Inter-ventricular septum (d) Left ventricle apex
- The pacemaker initiates ____ action potentials/min: (a) 25–30 (b) 40–60 (c) 70–75 (d) 100–110
- Width of QRS complex represents: (a) Atrial depolarisation (b) Ventricular depolarisation (c) Ventricular repolarisation (d) Atrial repolarisation
- Stroke volume × heart rate = (a) Cardiac output (b) Blood pressure (c) Cardiac index (d) Mean arterial pressure
- Tricuspid valve is located between: (a) LA and LV (b) RA and RV (c) RV and pulmonary artery (d) LV and aorta
- “LUB” sound is produced by: (a) Closing of semilunar valves (b) Closing of AV valves (c) Opening of AV valves (d) SA node discharge
- Cardiac muscle is: (a) Voluntary, striated (b) Involuntary, non-striated (c) Involuntary, striated (d) Voluntary, non-striated
- Erythroblastosis fetalis occurs when: (a) Rh+ mother, Rh- foetus (b) Rh- mother, Rh+ foetus (c) Both Rh+ (d) Both Rh-
- Spleen is called: (a) Graveyard of RBCs (b) Cradle of RBCs (c) RBC factory (d) WBC nursery
- Most abundant WBC: (a) Lymphocyte (b) Monocyte (c) Neutrophil (d) Eosinophil
- Heparin is secreted by: (a) Eosinophils (b) Basophils (c) Neutrophils (d) Lymphocytes
- Thromboplastin is released by: (a) Plasma (b) RBCs (c) Damaged tissue & platelets (d) Lymph nodes
- Albumin maintains: (a) Immunity (b) pH (c) Osmotic pressure of plasma (d) Coagulation
- Pulmonary artery carries: (a) Oxygenated blood (b) Deoxygenated blood (c) Mixed blood (d) Lymph
- Pericardial fluid acts as: (a) Lubricant (b) Antiseptic (c) Anticoagulant (d) Buffer
- Bundle of His is found in: (a) Atria only (b) Ventricles only (c) Inter-ventricular septum (d) AV valve
- Cardiac cycle duration in a person with HR 72 bpm: (a) 0.5 s (b) 0.6 s (c) 0.8 s (d) 1.2 s
- Atrial systole lasts: (a) 0.1 s (b) 0.3 s (c) 0.4 s (d) 0.8 s
- Plasma proteins with clotting role: (a) Globulin (b) Albumin (c) Fibrinogen (d) Insulin
- RBC count in adult human male per mm³: (a) 1–2 lakh (b) 5.0–5.5 million (c) 6–8 thousand (d) 1.5 million
- Lymph contains: (a) Lymphocytes only (b) RBCs and platelets (c) Lymphocytes and tissue fluid (d) Plasma without WBC
- The chambers of frog heart: (a) 2 (b) 3 (c) 4 (d) 1
- Vagus nerve effect on heart rate: (a) Increase (b) Decrease (c) No effect (d) Stops it
- Hepatic portal system connects: (a) Liver to heart (b) Intestine to liver (c) Kidney to liver (d) Lung to liver
- Frank-Starling law relates to: (a) Stretch of cardiac muscle vs force (b) Heart rate vs BP (c) ECG and pulse (d) Coronary perfusion
- Closed circulation is found in: (a) Cockroach (b) Earthworm (c) Snail (d) Prawn
- Blood pressure normal value: (a) 90/60 (b) 120/80 (c) 140/90 (d) 160/100
- Foetal haemoglobin compared to adult Hb has: (a) Lower O2 affinity (b) Higher O2 affinity (c) Same affinity (d) No affinity
- P-wave in ECG corresponds to: (a) Ventricular contraction (b) Ventricular relaxation (c) Atrial depolarisation (d) Atrial repolarisation
- Bicuspid valve is also called: (a) Mitral (b) Tricuspid (c) Pulmonary (d) Aortic
- Cardiac output of normal resting adult: (a) 2 L/min (b) 5 L/min (c) 10 L/min (d) 25 L/min
- Atherosclerosis is narrowing due to: (a) Iron (b) Cholesterol & Ca deposits (c) Glucose (d) Bilirubin
- The valve between LV and aorta: (a) Tricuspid (b) Bicuspid (c) Aortic semilunar (d) Pulmonary semilunar
- Adrenaline on heart: (a) ↓ rate (b) ↑ rate and force (c) No effect (d) Stops contraction
- Universal donor blood group: (a) A+ (b) AB+ (c) O- (d) B-
- Heart of crocodile has chambers: (a) 2 (b) 3 (c) 4 (d) 5
Answer Key (NEET Practice — Body Fluids & Circulation)
| 1-a | 2-c | 3-b | 4-c | 5-b | 6-c | 7-b | 8-a |
| 9-b | 10-b | 11-c | 12-b | 13-a | 14-c | 15-b | 16-c |
| 17-c | 18-b | 19-a | 20-c | 21-c | 22-a | 23-c | 24-b |
| 25-c | 26-b | 27-b | 28-b | 29-a | 30-b | 31-b | 32-b |
| 33-c | 34-a | 35-b | 36-b | 37-c | 38-b | 39-c | 40-c |
Interactive 10-MCQ Quiz
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FAQ — NEET Biology Body Fluids and Circulation 2027
How many questions from Body Fluids & Circulation appear in NEET?
Across NEET 2021–2025, the chapter has averaged 3.2 questions (~12 marks). NEET 2027 is expected to maintain this weight given the chapter’s heavy NCERT diagram count (heart, ECG, cardiac cycle).
Which diagrams from this chapter are most asked?
(1) Standard ECG with P, QRS, T waves; (2) Internal anatomy of human heart with valves labelled; (3) Conducting system of the heart (SAN, AVN, Bundle of His, Purkinje fibres); (4) Cardiac cycle phase diagram with valve states.
Is double circulation considered “complete” in all amphibians?
No. Amphibians and most reptiles have incomplete double circulation due to mixing in a single ventricle. Only crocodiles among reptiles, plus all birds and mammals, have complete double circulation.
What is the difference between cardiac arrest, heart attack and heart failure?
Cardiac arrest = sudden stop of heart’s pumping action. Heart attack (myocardial infarction) = death of heart muscle from blocked coronary artery. Heart failure = chronic inability to pump enough blood to meet body needs. NCERT-line distinction.
Where are RBCs formed and destroyed?
Formed in the red bone marrow (after birth) and destroyed in the spleen (“graveyard of RBCs”) and Kupffer cells of liver. Lifespan ≈ 120 days.
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