Key Concepts on Blood: White Blood Cells, Platelets, Plasma, Hemostasis & Blood Typing

Introduction to Blood

  • Focus on white blood cells (WBCs).

White Blood Cells (WBCs)

  • Normal count: 5,000 to 10,000 cells per microliter.
  • Leukocytopenia: Decreased white cell count (below normal).
  • Leukocytosis: Increased white cell count (above normal).
    • Indicates possible infections or diseases.

Differential Count of WBCs

  • Identifies which type of white blood cell has increased:
    • Neutrophils: Increase during bacterial infections.
    • Basophils: Increase during allergic reactions.
    • Eosinophils: Increase during parasite infestations.

Implications of WBC Count Changes

  • High counts of immature WBCs can decrease resistance to infection (e.g., leukemia).
  • Signs and symptoms of inflammation: redness, swelling, pain, heat, and pus formation.

Septicemia vs. Bacteremia

  • Bacteremia: Presence of bacteria in the blood;
  • Septicemia: Severe form leading to systemic infection, can be fatal.

Platelets

  • Size: 2 to 4 micrometers; smaller than red blood cells (RBCs).
  • Origin: Fragmentation of megakaryocytes in the bone marrow.
  • Lifespan: 5 to 10 days.
  • Functions: Essential for blood clotting.
    • Activated platelets change shape and release chemicals (e.g., serotonin).
Platelet Count and Related Disorders
  • Normal platelet count: 150,000 to 400,000 cells per microliter.
  • Platelet distribution: 80% in blood, 20% in spleen.
  • Thrombocytopenia: Decreased platelet count;
    • Causes include certain drugs (e.g., aspirin), HIV, or long-term IV therapy (plasma expanders).
  • Idiopathic Thrombocytopenic Purpura (ITP): Unexplained decrease in platelets leading to bleeding risks.

Plasma Composition

  • Water: 91.5% of plasma composition; essential for dissolving solutes.
  • Proteins: 7% (most produced by the liver), including:
    • Albumin: Maintains osmotic pressure.
    • Globulins: Three types: alpha, beta, gamma (immunoglobulins).
  • Fibrinogen: Important for clotting; converted to fibrin during clotting.
  • Remaining solutes: Include electrolytes, nutrients, waste products, vitamins, lipid transporters, and clotting factors.

Lipoproteins in Plasma

  • Types include Triglycerides, Phospholipids, and Cholesterol.
  • Lipoproteins transport these lipids, classified by density:
    • Very Low Density Lipoprotein (VLDL): High triglycerides.
    • Low Density Lipoprotein (LDL): High cholesterol, associated with heart disease.
    • High Density Lipoprotein (HDL): Low cholesterol content, considered protective against heart disease.

Hemostasis Process (Stopping Bleeding)

  • Distinct from homeostasis (which maintains stable internal conditions).
  • Stages of Hemostasis:
    1. Vascular spasm: Immediate constriction of blood vessels.
    2. Platelet plug formation: Activated platelets adhere to the injury, forming a plug.
    3. Coagulation (clot formation): Fibrin meshes trap cells to stabilize the plug.
    4. Clot retraction: The clot shrinks to bring tissue edges closer together.
Detailed Steps in Coagulation
  • Involves intrinsic and extrinsic pathways.
    • Intrinsic pathway: Activated by injury to blood vessels; relies on factors like Factor XII.
    • Extrinsic pathway: Triggered by external trauma; relies on Tissue Factor.
  • Thrombin converts fibrinogen to fibrin, forming a solid mesh.
Vitamin K and Coagulation
  • Essential for synthesizing certain clotting factors (II, VII, IX, X).
  • Deficiency leads to bleeding disorders.

Blood Typing and Transfusions

  • Determined by antigens present on RBC surfaces:
    • Type A: Antigen A, antibodies against B.
    • Type B: Antigen B, antibodies against A.
    • Type AB: Antigens A and B, no antibodies (universal recipient).
    • Type O: No antigens, both anti-A and anti-B antibodies (universal donor).
  • Rh factor impacts transfusions (Rh negative mother with Rh positive baby may lead to hemolytic disease).

Clinical Applications

  • Coumadin: Blocks vitamin K, reduces clotting factors,
  • DIC (Disseminated Intravascular Coagulation): Concurrent clotting and bleeding in severe conditions.
  • Clot-busting medications: FDA-approved for managing myocardial infarctions and strokes.

Conclusion

  • Understanding blood components, their functions, and related disorders is crucial for the management of diseases and clinical scenarios.