Introduction to Blood Composition and Functions

Blood Composition and Functions

• Blood is a fluid that circulates in the vascular channels of the human body due to the pumping action of the heart.
• Blood consists of a liquid portion called plasma in which various types of cells are present.
• The cells suspended in the plasma are of three different types:
  • Erythrocytes (red blood cells) containing hemoglobin, which gives them their red color.
  • Leucocytes (white blood cells) of different types (5).
  • Thrombocytes (platelets) responsible for blood coagulation.

General Functions of Blood

• Respiratory function: transport of oxygen from lungs to tissues and carbon dioxide from tissues to lungs.
• Excretory function: transport of waste products to kidneys, lungs, skin, and gastrointestinal tract for excretion.
• Nutritive function: transport of digested food substances to all parts of the body.
• Defensive function: protection of the body against infections through phagocytosis by leucocytes.
• Coagulation function: formation of a clot to prevent blood loss.
• Acid-base equilibrium function: maintenance of a constant pH through buffers in the blood.
• Body temperature regulation function: maintenance of body temperature due to the high specific heat and latent heat of evaporation of blood.
• Transport of substances function: rapid circulation of blood enables easy transport of hormones, vitamins, and drugs throughout the body.
• Protein reserve function: plasma proteins can act as a protein reserve and be used in extreme protein deficiency to form cell proteins.

Blood Components

• Water: 93-95% (plasma), 65-68% (RBC), and 81-86% (whole blood).
• Electrolytes: Na+, K+, Mg2+, Cl-, HCO3-, etc.
• Proteins:
  • Albumin (40-48 g/L): carrier, buffer, and colloid osmotic pressure.
  • Globulin (15-30 g/L): immune reaction, antibody, and carrier.
  • Fibrinogen (2-4 g/L): blood coagulation.
  • Hemoglobin (Hb): 120-160 g/L (male), 110-150 g/L (female).
• Others: carbohydrates, lipids, amino acids, pigments, hormones, gases (O2, CO2), and waste products (urea, uric acid, etc.).

Plasma

• Plasma is the fluid part of the blood in which formed elements are suspended.
• Plasma contains 91-92% water and 8-9% of solid substances (organic and inorganic).
• Organic substances in plasma include:
  • Plasma proteins (6.5-8 g%): albumin, globulin, and fibrinogen.
  • Glucose (80-120 mg%).
  • Cholesterol and lipids (150-250 mg%).
  • Non-protein nitrogenous substances like urea, uric acid, creatine, and creatinine.
  • Hormones, enzymes, and blood pigments.

Plasma Proteins

• Albumin: 4-4.5 g% of plasma proteins, molecular weight 60,000, responsible for colloidal osmotic pressure.
• Globulin: 2.5 g% of plasma proteins, molecular weight 130,000, involved in antibody formation and blood coagulation.
• Fibrinogen: 0.25 g% of plasma proteins, involved in blood coagulation.

Functions of Plasma Proteins

• Colloidal osmotic pressure.
• Antibody formation.
• Coagulation.
• Transport media.
• Erythrocyte sedimentation rate (ESR).
• Viscosity.
• Buffer mechanism.
• Protein reserve.

Erythrocyte Sedimentation Rate (ESR)

• Measures the speed of sedimentation of RBC/RBC aggregates in plasma over a period of 1 hour.
• Influenced by the fibrinogen content of plasma.
• Non-specific laboratory test used to measure inflammation or disease activity.