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Body Fluids and Circulation

NCERT Class 11 Biology Chapter 15

Body Fluids and Circulation for Class 11 Biology and NEET: blood, blood groups, clotting, lymph, human heart, cardiac cycle, ECG and circulatory disorders.

6 topics Updated 8 Nov 2026

For: Class 11 and NEET

In the syllabus: NEET Class 11 syllabus

With your textbook

NCERT Biology (Class 11), Chapter 15 “Body Fluids and Circulation”, reprint 2026-27.

Open the official NCERT chapter (PDF, 3.1 MB, ncert.nic.in)

Checked on 19 Oct 2026.

Learn in this order

  1. Blood: plasma, cells, blood groups, clotting

    Plasma and serum, RBC, WBC and platelet counts, ABO and Rh blood groups, and how blood clots.

    NCERT Section 15.1 14 min read 6 solved examples 8 practice questions

  2. Lymph and tissue fluid

    Composition of lymph, how tissue fluid forms, the lymphatic system, functions of lymph, and lymph vs blood and plasma.

    NCERT Section 15.2 7 min read 3 solved examples 6 practice questions

  3. Heart, cardiac cycle and ECG

    Open vs closed circulation, chambers and valves with a labelled diagram, the SAN, cardiac cycle, cardiac output and ECG.

    NCERT Section 15.3 16 min read 7 solved examples 7 practice questions

  4. Double circulation

    Pulmonary and systemic circulation with a diagram, arteries vs veins, the hepatic portal and coronary systems.

    NCERT Section 15.4 8 min read 4 solved examples 6 practice questions

  5. Regulation of cardiac activity

    Myogenic vs neurogenic heart, sympathetic and parasympathetic control, adrenal medullary hormones.

    NCERT Section 15.5 10 min read 5 solved examples 6 practice questions

  6. Disorders of the circulatory system

    Hypertension (120/80, 140/90), coronary artery disease, angina vs heart attack, heart failure.

    NCERT Section 15.6 11 min read 6 solved examples 6 practice questions

Key formulas in this chapter

Blood

  • blood = plasma (about 55%) + formed elements (about 45%)
  • RBC 5–5.5 million per mm; WBC 6000–8000 per mm; platelets 150 000–350 000 per mm
  • haemoglobin 12–16 g per 100 mL; RBC life 120 days
  • red cells, ABO/RhD: O negative universal donor; AB positive universal recipient
  • prothrombin → thrombin; fibrinogen → fibrin (thrombokinase, calcium ions)

Lymph (tissue fluid)

  • tissue fluid: water + small solutes from capillaries; same minerals as plasma
  • lymphatic system: collects tissue fluid → major veins
  • lymph: colourless; lymphocytes; carries nutrients, hormones; fats via lacteals

Circulatory pathways

  • cardiac output = stroke volume × heart rate = 70 mL × 72 ≈ 5000 mL a minute
  • cardiac cycle = 60 ÷ 72 ≈ 0.8 s
  • lub: tricuspid and bicuspid close; dub: semilunar valves close
  • P: atrial depolarisation; QRS: ventricular depolarisation; T: ventricular repolarisation
  • SAN → AVN → AV bundle → right and left bundles → Purkinje fibres

Double circulation

  • pulmonary: RV → pulmonary artery → lungs → pulmonary veins → LA
  • systemic: LV → aorta → tissues → vena cava → RA
  • vessel wall: tunica intima, tunica media, tunica externa
  • hepatic portal vein: intestine → liver

Regulation of cardiac activity

  • cardiac output = stroke volume × heart rate
  • sympathetic: heart rate ↑, contraction strength ↑, cardiac output ↑
  • parasympathetic: heart rate ↓, conduction speed ↓, cardiac output ↓
  • adrenal medullary hormones: cardiac output ↑

Disorders of the circulatory system

  • normal blood pressure = 120/80 mm Hg (systolic/diastolic)
  • WHO hypertension threshold: repeated systolic ≥140 OR diastolic ≥90 mm Hg
  • CAD: deposits narrow the coronary lumen → less oxygen to the heart muscle → angina
  • heart failure ≠ cardiac arrest ≠ heart attack

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