Blood Composition and Functions

Blood Function

  • Fluid connective tissue distributing nutrients, oxygen, hormones, and metabolic wastes.

  • Essential for:

    • Transport of oxygen (lungs to tissues) and carbon dioxide (tissues to lungs).

    • Nutrient distribution from the digestive system or tissue storage.

    • Waste transport to kidneys.

    • Delivery of enzymes and hormones.

    • pH and electrolyte stabilization in interstitial fluids.

    • Prevention of fluid loss via clotting.

    • Defense against toxins and pathogens (white blood cells and antibodies).

    • Temperature regulation through heat distribution.

Composition of Blood

  • Blood constitutes approximately 8% of total body weight.

  • Two main components:

    • Plasma (55% by volume): consists of 91% water, 7% proteins, and 2% other solutes.

    • Formed elements (45% by volume): includes red blood cells (RBCs), white blood cells (WBCs), and platelets.

Plasma

  • Pale-yellow fluid, colloidal nature.

  • Serves as a solvent for gases, nutrients, electrolytes, and waste products.

Formed Elements

  • Red Blood Cells (RBCs or Erythrocytes):

    • Biconcave, no nucleus, high in hemoglobin.

    • Function: transport oxygen and carbon dioxide.

    • Life cycle: ~120 days; recycled by spleen and liver.

  • White Blood Cells (WBCs or Leukocytes):

    • Nucleated, combat pathogens and clean debris.

    • Various lifespans based on type (e.g., neutrophils: minutes to days).

  • Platelets (Thrombocytes):

    • Cytoplasmic fragments without a nucleus.

    • Function: clotting and preventing blood loss.

Characteristics of Blood

  • Whole blood is viscous (5x water viscosity due to plasma and formed elements).

  • Normal blood pH: 7.35 - 7.45; temperature: ~38°C.