Body Fluids and Circulation: Complete Guide for Class 11 NCERT Biology

Composition and Functions of Blood

Blood is a vital fluid connective tissue in humans, responsible for transporting oxygen, carbon dioxide, nutrients, hormones, and waste products. It maintains homeostasis and protects the body from infections.

Blood consists of two main components:

• Plasma: The fluid matrix, making up about 55% of blood volume. It is a straw-coloured viscous fluid, mainly water (90-92%) with dissolved proteins (6-8%) like fibrinogen (for clotting), globulins (immune defense), and albumins (osmotic balance). Plasma also contains minerals (Na⁺, Ca²⁺, Mg²⁺), nutrients (glucose, amino acids), and inactive clotting factors.

• Formed Elements: These are cellular components, about 45% of blood volume, including:
• Red Blood Cells (RBCs): Biconcave, anucleate cells containing haemoglobin that transports oxygen. RBC count is about 5 to 5.5 million/mm³.
• White Blood Cells (WBCs): Nucleated cells defending against infections. Count ranges from 6000 to 8000/mm³.
• Platelets: Cell fragments aiding blood clotting, numbering 1,500,000 to 3,500,000/mm³.

Understanding these components is essential for grasping how blood functions as a connective tissue.

Detailed Study of Plasma and Its Importance

Plasma is the liquid part of blood and plays several critical roles:

• Water (90-92%): Acts as a solvent and medium for transport.
• Proteins (6-8%):
• Albumins: Maintain osmotic pressure, preventing fluid loss from blood vessels.
• Globulins: Act as antibodies and transport proteins.
• Fibrinogen: Essential for blood clotting.
• Minerals and Electrolytes: Sodium (Na⁺), calcium (Ca²⁺), magnesium (Mg²⁺), bicarbonate (HCO₃⁻), and chloride (Cl⁻) help in maintaining pH and muscle function.
• Nutrients: Glucose, amino acids, and lipids are transported to cells.
• Waste Products: Carbon dioxide and urea are carried away from cells.

Plasma without clotting factors is called serum. It is important for diagnostic tests and understanding immune responses.

Key Functions of Plasma Proteins:

• Maintaining osmotic pressure
• Transporting hormones and drugs
• Participating in immune responses
• Blood clotting

This knowledge is crucial for Class 11 NCERT students to understand blood’s fluid matrix.

Formed Elements: RBCs, WBCs, and Platelets Explained

The formed elements in blood perform specialized functions:

• Red Blood Cells (RBCs):
• Shape: Biconcave discs without nucleus
• Function: Transport oxygen using haemoglobin
• Lifespan: About 120 days
• Count: 5 to 5.5 million/mm³

• White Blood Cells (WBCs):
• Types: Granulocytes (neutrophils, eosinophils, basophils) and agranulocytes (lymphocytes, monocytes)
• Function: Defend against infections
• Count: 6000 to 8000/mm³

• Platelets:
• Cell fragments from megakaryocytes
• Function: Blood clotting by releasing clotting factors
• Count: 1,500,000 to 3,500,000/mm³

Understanding these elements helps explain how blood supports life and immunity.

Circulatory System and Blood Circulation Process

The circulatory system transports blood throughout the body, delivering oxygen and nutrients and removing wastes.

• Heart: A muscular organ that pumps blood. It has four chambers: two atria and two ventricles.
• Blood Vessels:
• Arteries: Carry oxygenated blood away from the heart (except pulmonary artery).
• Veins: Carry deoxygenated blood to the heart (except pulmonary vein).
• Capillaries: Tiny vessels where exchange of gases and nutrients occurs.

Blood Circulation Types:

• Pulmonary Circulation: Heart to lungs and back, for oxygenation of blood.
• Systemic Circulation: Heart to body tissues and back, supplying oxygen and nutrients.

Heartbeat Phases:

• Systole: Contraction phase, pumping blood out.
• Diastole: Relaxation phase, heart fills with blood.

Worked Example: Calculate the volume of blood pumped by the heart per minute (Cardiac Output) if stroke volume is 70 ml and heart rate is 72 beats per minute.

$$ Cardiac\ Output = Stroke\ Volume \times Heart\ Rate = 70\ ml \times 72 = 5040\ ml/min = 5.04\ litres/min $$

This circulation ensures all body cells receive necessary substances and maintain homeostasis.

Differences Between Blood and Lymph

Blood and lymph are both body fluids involved in transport but differ in composition and function.

Lymph helps maintain fluid balance and immunity, complementing blood functions.

Importance of Blood as a Connective Tissue

Blood is classified as a connective tissue because:

• It has a fluid extracellular matrix called plasma.
• It connects different body parts by transporting substances.
• It originates from mesenchymal cells during development.
• It contains cells (formed elements) suspended in plasma.

This classification helps understand blood’s role beyond just transport — it supports tissue function, immunity, and healing. For Class 11 NCERT students, recognizing blood as connective tissue links it to broader biological concepts.