Introduction

Body fluids and circulation are vital for maintaining homeostasis in animals, transporting nutrients, gases, and waste products. NEET emphasizes blood, lymph, heart anatomy, cardiac cycle, ECG, cardiac output, and blood pressure.

Understanding this topic is essential for questions on physiology, formulas, and diagram-based problems.

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1. Composition of Blood

Blood is a connective tissue composed of plasma and formed elements:

• Plasma (55%): Water (90%), proteins (albumin, globulin, fibrinogen), hormones, electrolytes

• Formed Elements (45%):

  • Red Blood Cells (RBCs): Transport O₂ via hemoglobin

  • White Blood Cells (WBCs): Immune defense → Neutrophils, lymphocytes, monocytes, eosinophils, basophils

  • Platelets: Blood clotting

NEET Formula / Fact:

• Hematocrit (PCV) = (Volume of RBC / Total Blood Volume) × 100

2. Functions of Blood

• Transport of oxygen, carbon dioxide, nutrients, hormones, and waste

• Regulation of body temperature and pH

• Defense against infections (WBCs)

• Blood clotting (platelets & fibrinogen)

NEET Tip:

• Prepare a table of blood components and their functions for quick revision

3. Lymph and Its Functions

• Definition: Colorless fluid similar to plasma

• Function: Returns tissue fluid to blood, absorbs fats, and participates in immune response

• Difference from Blood: Contains no RBCs, less protein, contains lymphocytes

4. Structure of Heart

• Four chambers: Right atrium (RA), Right ventricle (RV), Left atrium (LA), Left ventricle (LV)

• Valves: Tricuspid (RA-RV), Mitral/Bicuspid (LA-LV), Pulmonary (RV-Pulmonary artery), Aortic (LV-Aorta)

• Major vessels: Aorta, Pulmonary artery, Pulmonary vein, Superior & Inferior vena cava

NEET Tip:

• Memorize flow of blood in heart diagram

5. Cardiac Cycle

• Definition: Sequence of events in one heartbeat (systole + diastole)

• Phases:

  1. Atrial systole → Ventricular filling

  2. Ventricular systole → Blood pumped to arteries

  3. Complete diastole → Heart relaxes

NEET Formulas:

1. Cardiac Output (CO) = Stroke Volume (SV) × Heart Rate (HR)

2. Stroke Volume (SV) = EDV – ESV

   • EDV: End-Diastolic Volume

   • ESV: End-Systolic Volume

NEET Tip:

• Remember heart rate × stroke volume = cardiac output

6. Heart Sounds

• “Lub” (S1): Closure of AV valves (Tricuspid & Mitral)

• “Dub” (S2): Closure of semilunar valves (Aortic & Pulmonary)

7. Electrocardiogram (ECG / EKG)

• Definition: Graphical representation of heart’s electrical activity

• Components:

  • P-wave: Atrial depolarization

  • QRS complex: Ventricular depolarization

  • T-wave: Ventricular repolarization

NEET Tip:

• ECG diagrams are frequently asked in NEET diagrams

8. Blood Pressure and Regulation

• Blood Pressure (BP): Force of blood on vessel walls

• Normal BP: 120/80 mmHg (Systolic/Diastolic)

• Regulation:

  • Neural: Autonomic nervous system (Sympathetic ↑, Parasympathetic ↓)

  • Hormonal: Renin-Angiotensin system, ADH, Aldosterone

NEET Formulas / Facts:

1. Mean Arterial Pressure (MAP) ≈ Diastolic BP + 1/3(Systolic BP – Diastolic BP)

2. Cardiac Output (CO) × Total Peripheral Resistance (TPR) = BP

9. Circulatory Pathways

1. Pulmonary Circulation: Right ventricle → Lungs → Left atrium

2. Systemic Circulation: Left ventricle → Body → Right atrium

3. Coronary Circulation: Supplies heart muscles with oxygenated blood

4. Portal Circulation: Digestive organs → Liver (Hepatic portal vein)

NEET Tip:

• Prepare diagram showing all circulatory pathways

10. NEET Important Formulas / Memory Aids

1. Cardiac Output → CO = SV × HR

2. Stroke Volume → SV = EDV – ESV

3. Mean Arterial Pressure → MAP = DBP + 1/3(SBP – DBP)

4. Hematocrit → PCV = (RBC volume / Total blood volume) × 100

Mnemonic for heart valves:

• “Try Pulling My Aorta” → Tricuspid, Pulmonary, Mitral, Aortic

11. NEET Exam Tips

• Memorize blood composition, lymph, heart anatomy, valves, cardiac cycle, and ECG

• Focus on formulas: cardiac output, stroke volume, mean arterial pressure

• Diagram-based questions → Heart structure, flow of blood, ECG graph

• Understand difference between systemic, pulmonary, coronary, and portal circulation

Conclusion

Body Fluids and Circulation is a high-yield NEET topic. Mastery of blood composition, lymph, heart structure, cardiac cycle, cardiac output, ECG, blood pressure, and circulatory pathways is essential for scoring in MCQs, diagrams, and numerical questions.

With this StudentBro.in guide, students can efficiently revise circulation formulas, diagrams, and physiology concepts, enhancing speed and accuracy during NEET exams.

Remember: Circulation = Blood + Lymph + Heart + Cardiac Cycle + Cardiac Output + Blood Pressure + Circulatory Pathways → Core for human physiology questions.