Lecture on Blood Components: Part 2

Overview

Continuation from previous lecture focusing on white blood cells (WBCs), platelets, and blood clotting.
Recap: Focus on red blood cells (RBCs) and blood typing in the last lecture.

WBCs make up a small percentage of formed elements in blood (5,000 - 10,000 per microliter).
Unlike RBCs, WBCs have nuclei and are involved in body defense.
WBCs can leave the bloodstream and enter tissues (margination and emigration/diapedesis).
Movement: Similar to amoeba movement; follows chemical trails (positive chemotaxis).
Types of WBCs: Phagocytes (three of five types can engulf pathogens).

Granulocytes: Have cytoplasmic granules; include neutrophils, eosinophils, basophils.
- Neutrophils: Most common, fast-moving, short-lived, involved in bacterial infections.
- Eosinophils: Involved in attacking larger pathogens (e.g., parasitic worms), release anti-histamines.
- Basophils: Rarest, release histamine (pro-inflammatory) and heparin (anti-coagulant).
Agranulocytes: Include monocytes and lymphocytes.
- Monocytes: Largest WBCs, known as macrophages outside blood, engage in aggressive phagocytosis.
- Lymphocytes: Common, involved in immune responses, include T cells (cell-mediated immunity), B cells (antibody-mediated immunity), NK cells (immune surveillance).

Cell fragments involved in clotting; several hundred thousand per microliter.
Produced by megakaryocytes.
Thrombocytopoiesis: Production of platelets stimulated by thrombopoietin (TPO), interleukin 6, and multi-CSF.
Functions: Release clotting chemicals, form platelet plugs, and aid in clot retraction.

Process to prevent blood loss from damaged vessels.
Three Phases:
1. Vascular Phase: Vascular spasm to reduce blood loss, endothelial cells release endothelins.
2. Platelet Phase: Platelets adhere to exposed vessel wall and to each other, forming a platelet plug.
3. Coagulation Phase: Reinforces platelet plug with fibrin threads; involves complex cascade of clotting factors.

Pathways:
- Extrinsic Pathway: Triggered by tissue factor (Factor 3) from vessel wall.
- Intrinsic Pathway: Triggered by Factor 12 and platelet factors.
- Common Pathway: Both pathways lead to activation of Factor 10 and thrombin formation.
Fibrin Formation: Thrombin converts fibrinogen to fibrin, forming a stable clot.
Role of Calcium and Vitamin K: Essential for clotting factor production and function.

Anticoagulants: Prevent excessive clotting (e.g., heparin, prostacyclin).
Clot Retraction and Removal: Platelets contract to close the wound; fibrin is broken down by plasmin (activated by TPA).
Balance in Clotting: Important to prevent disorders such as heart attacks and strokes due to inappropriate clot formation.