Introduction
In multicellular organisms, transport of nutrients, gases, hormones, and waste products is essential for survival. This function is carried out by body fluids like blood and lymph through the circulatory system.
Body Fluids
The two main body fluids involved in circulation are:
- Blood
- Lymph (Tissue fluid)
Blood
Definition
Blood is a fluid connective tissue that circulates throughout the body.
Composition of Blood
Blood consists of:
- Plasma (55%)
- Formed elements (45%)
Plasma
- Straw-colored fluid
- Contains 90–92% water
- Contains proteins, nutrients, hormones, gases
Plasma Proteins:
- Albumin (osmotic balance)
- Globulin (immunity)
- Fibrinogen (clotting)
Formed Elements
1. Red Blood Cells (RBCs)
- Also called erythrocytes
- Contain hemoglobin
- Transport oxygen
Key Points:
- No nucleus in humans
- Lifespan: ~120 days
2. White Blood Cells (WBCs)
- Also called leukocytes
- Provide immunity
Types:
Granulocytes
- Neutrophils
- Eosinophils
- Basophils
Agranulocytes
- Lymphocytes
- Monocytes
3. Platelets (Thrombocytes)
- Help in blood clotting
- Lifespan: 7–10 days
Blood Groups
ABO Blood Group System
Based on presence of antigens:
| Blood Group | Antigen | Antibody |
|---|---|---|
| A | A | Anti-B |
| B | B | Anti-A |
| AB | A & B | None |
| O | None | Anti-A & Anti-B |
Rh Factor
- Presence of Rh antigen = Rh positive
- Absence = Rh negative
Importance
- Important in blood transfusion
- Mismatch can cause agglutination
Lymph (Tissue Fluid)
Characteristics:
- Colorless fluid
- Contains lymphocytes
- Lacks RBCs
Functions:
- Transport of fats
- Immune defense
- Returns tissue fluid to blood
Circulatory System
Types of Circulatory Systems
1. Open Circulatory System
- Blood not confined to vessels
- Example: Arthropods
2. Closed Circulatory System
- Blood flows in vessels
- Example: Humans
Human Circulatory System
Consists of:
- Heart
- Blood vessels
- Blood
Structure of Heart
- Muscular organ
- Located in thoracic cavity
Chambers of Heart
- Right atrium
- Right ventricle
- Left atrium
- Left ventricle
Valves of Heart
- Tricuspid valve (right side)
- Bicuspid/Mitral valve (left side)
- Semilunar valves
Cardiac Cycle
Sequence of events during one heartbeat.
Phases:
- Atrial systole
- Ventricular systole
- Joint diastole
Heart Sounds
- “Lub” → closing of AV valves
- “Dub” → closing of semilunar valves
Electrocardiogram (ECG)
Records electrical activity of heart.
Waves:
- P wave → atrial contraction
- QRS complex → ventricular contraction
- T wave → ventricular relaxation
Blood Vessels
1. Arteries
- Carry blood away from heart
- Thick walls
- High pressure
2. Veins
- Carry blood towards heart
- Thin walls
- Valves present
3. Capillaries
- Thin walls
- Exchange of materials
Double Circulation
Blood passes through heart twice in one cycle:
1. Pulmonary Circulation
- Heart → lungs → heart
2. Systemic Circulation
- Heart → body → heart
Disorders of Circulatory System
1. Hypertension
- High blood pressure
2. Coronary Artery Disease
- Narrowing of arteries
3. Angina
- Chest pain due to reduced blood flow
4. Heart Failure
- Inability of heart to pump efficiently
Important NEET & CBSE Points
- RBC lifespan: 120 days
- WBC → immunity
- Platelets → clotting
- Heart has 4 chambers
- Double circulation in humans
Quick Revision Notes
- Blood = transport medium
- Plasma = liquid part
- RBC = oxygen transport
- Heart = pump
- Arteries = away from heart
Frequently Asked Questions (FAQs)
Q1. What is blood?
A fluid connective tissue.
Q2. What is lymph?
Colorless fluid aiding immunity and transport.
Q3. What is double circulation?
Blood passes through heart twice.
Q4. What is ECG?
Recording of heart’s electrical activity.
Conclusion
Body fluids and circulation ensure efficient transport and coordination in the human body. This chapter is highly important for CBSE exams and NEET, especially for conceptual clarity and diagram-based questions.