Blood Components: Focus on Platelets

Blood Components and Their Functions-2

• The presentation is about blood components and their functions, specifically focusing on platelets.
• Platelets (Thrombocytes):
  • Shape: Minute round or oval discs (2-4 μm), non-nucleated, size can increase to 6 μm after activation.
  • Number: 150,000 – 400,000/mm³.
  • Formation: Formed in the bone marrow as buds on the surface of megakaryocytes, released into the bloodstream under the influence of thrombopoietin from the kidney.
  • Life span: 8-12 days, then removed by tissue macrophages.
• Platelet Structure:
  • Outer coat: Mucopolysaccharide surface coat, crucial for adhesion and aggregation. Glycoproteins bind to Von Willebrand Factor (vWF), necessary for adhesion to damaged endothelial cells; also acts as fibrinogen receptors.
  • Plasma membrane: Basis structure of platelet factor 3 (PF3).
  • Cytoskeleton (under the membrane):
    • Microfilaments: Composed of actin, myosin, and thrombasthenin.
    • Microtubules: Maintain the disc shape of the platelets.
  • Granules: Three types:
    • Dense granules: Small, contain nucleotides (ADP), serotonin, and calcium.
    • Specific (Alpha) granules: Large, contain platelet factors responsible for hemostasis.
    • Dense tubular system: Contains calcium; site for prostaglandin and thromboxane A2 synthesis; regulates platelet activation by sequestering or releasing calcium.
  • Other components: Mitochondria, glycogen, and lysosomes containing hydrolytic enzymes.

Functions of Blood Platelets

• Form temporary hemostatic plugs (platelet adhesion, activation, and aggregation).
• Release serotonin and thromboxane A2.
• Crucial for blood coagulation (supplying platelet factor III and factor XIII).
• Cause clot retraction.
• Release platelet-derived growth factor (PDGF) for healing injured endothelium.

Hemostasis

• Stoppage of bleeding by forming blood clots and maintaining blood fluidity in the vascular system.
• Three main components:
  • Vasoconstriction: Contraction of smooth muscle in vessel walls (vascular spasm).
  • Platelet aggregation: Platelets adhere to exposed collagen fibers in damaged blood vessels, releasing chemicals to cause aggregation (temporary platelet plug).
  • Coagulation (blood clotting): Occurs via clotting factors (proteins, mostly synthesized in the liver).

Blood Coagulation

• Essential process because aggregation and vasoconstriction alone are not enough to stop bleeding entirely.
• Involves clotting factors that work together to transform fibrinogen into fibrin, forming a clot.
• Two pathways to blood clot formation: Intrinsic and extrinsic pathways.

White Blood Cells (WBCs)

• Circulate briefly in the bloodstream, predominantly migrating through body tissues.
• Migrate from blood vessels through extravasation.
• Some WBCs (neutrophils, eosinophils, monocytes) exhibit phagocytosis.

Types of White Blood Cells (WBCs)

• Classified into granulocytes (include neutrophils, eosinophils, basophils) and agranulocytes (include lymphocytes—B and T lymphocytes and natural killer cells, and monocytes).

This quiz explores the essential components of blood with a particular focus on platelets (thrombocytes). Learn about their structure, formation, lifespan, and functions in the body. Discover how platelets play a crucial role in the healing process and blood clotting.