Haemopoietic System – Composition and Functions of Blood
Introduction
The haemopoietic system (or blood-forming system) includes all organs and tissues involved in the production, maturation, and circulation of blood cells.
Blood is a specialized connective tissue that plays a vital role in transport, protection, and regulation throughout the body.
The major organs of the haemopoietic system include the bone marrow, spleen, liver, lymph nodes, and thymus.
Original Notes:
Composition of Blood
Blood is a red-colored fluid that circulates continuously through blood vessels.
It accounts for about 7–8% of body weight and the total blood volume in an adult is approximately 5 to 6 liters.
Blood consists of two main parts:
- Plasma (55%) – The liquid component.
- Formed Elements (45%) – The cellular components.
1. Plasma
Plasma is the fluid part of blood, which appears pale yellow in color.
It is about 90–92% water and 8–10% solids (proteins, salts, hormones, enzymes, etc.).
Main Components of Plasma:
- Water: Acts as a solvent for substances.
- Proteins: Albumin, globulin, and fibrinogen.
- Albumin – Maintains osmotic pressure.
- Globulin – Helps in immunity (antibodies).
- Fibrinogen – Helps in blood clotting.
- Mineral Salts: Sodium, potassium, calcium, etc.
- Nutrients: Glucose, amino acids, lipids, vitamins.
- Hormones and Enzymes: For regulation of body functions.
- Waste Products: Urea, uric acid, and CO₂ for excretion.
Functions of Plasma:
- Transports nutrients, hormones, and waste products.
- Maintains blood pressure and body temperature.
- Helps in blood clotting and immunity.
2. Formed Elements
These are the cellular parts of blood, suspended in plasma.
They include:
- Red Blood Cells (RBCs or Erythrocytes)
- White Blood Cells (WBCs or Leukocytes)
- Platelets (Thrombocytes)
A. Red Blood Cells (RBCs)
- Shape: Biconcave, circular, and non-nucleated (in mammals).
- Life span: About 120 days.
- Produced in: Red bone marrow.
- Pigment: Hemoglobin, which gives red color to blood.
Functions of RBCs:
- Transport oxygen from lungs to tissues.
- Carry carbon dioxide from tissues to lungs.
- Maintain acid-base balance of blood.
B. White Blood Cells (WBCs)
WBCs are colorless, nucleated cells responsible for body defense.
They are fewer in number than RBCs (about 4,000–10,000/mm³).
Types of WBCs:
- Granulocytes (with granules):
- Neutrophils: Destroy bacteria (phagocytosis).
- Eosinophils: Fight allergies and parasites.
- Basophils: Release histamine and heparin (inflammation control).
- Agranulocytes (without granules):
- Lymphocytes: Produce antibodies for immunity.
- Monocytes: Engulf foreign bodies and dead cells (phagocytes).
Functions of WBCs:
- Protect body from infection.
- Remove dead or damaged cells.
- Produce antibodies and immune reactions.
C. Platelets (Thrombocytes)
- Small, irregular-shaped cell fragments.
- Number: 1.5–4 lakh/mm³ of blood.
- Life span: 8–10 days.
- Formed in: Bone marrow (from megakaryocytes).
Functions of Platelets:
- Help in blood clotting to prevent bleeding.
- Release chemicals that repair damaged blood vessels.
Functions of Blood
1. Transport Functions
- Respiratory: Carries oxygen (by hemoglobin) and removes CO₂.
- Nutrient Transport: Distributes glucose, amino acids, fats.
- Excretory: Removes wastes like urea and uric acid to kidneys.
- Hormonal: Transports hormones from glands to target organs.
2. Protective Functions
- WBCs protect against infection.
- Platelets and plasma proteins (fibrinogen) help in clot formation.
- Antibodies neutralize harmful pathogens.
3. Regulatory Functions
- Maintains body temperature.
- Balances pH and water content.
- Regulates blood pressure and osmotic balance.
