E2 PATHO WEEK 6 10.06

Blood Composition

  • Erythrocytes (Red Blood Cells)

    • Comprise approximately 45% of blood volume.

    • Lifespan of 120 days.

    • Undergo apoptosis after 120 days.

  • Leukocytes (White Blood Cells)

    • Comprise about 1% of blood volume.

    • Important for immune response.

  • Plasma

    • Makes up about 55% of blood volume.

Role of Red Blood Cells

  • Function: Carry oxygen throughout the body.

  • A1C and Diabetes:

    • Life cycle of red blood cells is critical in measuring blood glucose levels over time.

    • A1C test reflects average glucose levels over approximately 120 days, aligning with the lifespan of erythrocytes.

Types of White Blood Cells

  • Granulocytes

    • Include:

    • Neutrophils: First responders to infection.

    • Eosinophils: Combat parasites and allergic responses.

    • Basophils: Release histamine and play a role in inflammatory responses.

  • Agranulocytes

    • Include:

    • Lymphocytes: Key players in the immune response.

    • Monocytes: Differentiate into macrophages and dendritic cells upon reaching tissues.

Macrophages

  • Kupffer Cells: Specialized macrophages located in the liver.

  • Microglial Cells: Specialized macrophages in the brain.

Platelet Function and Lifespan

  • Platelets: Important for clotting (hemostasis).

  • Lifespan: Approximately 10 days.

    • Undergo apoptosis if unused during this period.

Hematopoiesis

  • Definition: The production of blood cells.

    • Types:

    • Medullary Hematopoiesis: Occurs in the bone marrow.

    • Extramedullary Hematopoiesis: Occurs outside the bone marrow (e.g., spleen, liver).

Diagnostic Tools for Blood Assessment

  • Complete Blood Count (CBC)

    • Provides information about the levels and types of cells in blood.

    • CBC with differential examines types of white blood cells to indicate infections.

  • Erythrocyte Sedimentation Rate (ESR):

    • Measures how quickly blood cells settle in a test tube, indicating inflammation.

    • Normal range: 0-15 mm/hr for men; 0-20 mm/hr for women.

    • Elevated rates may suggest inflammatory processes.

Clot Formation and Hemostasis

  • Process of Hemostasis: Involves clot formation and dissolution.

    1. Vascular Constriction (Vasospasm):

    • Blood vessels constrict to reduce blood flow through the injured area.

    1. Platelet Activation:

    • Inactive platelets become activated, changing shape and forming receptor sites (e.g., GP IIb/IIIa).

    1. Platelet Plug Formation:

    • Activation leads to aggregation where platelets bind together via von Willebrand factor (vWF) and fibrinogen.

Important Factors in Clotting

  • Vitamin K: Essential for synthesizing clotting factors such as II, VII, IX, X, prothrombin, and protein C.

  • Intrinsic and Extrinsic Pathways:

    • Intrinsic Pathway: Activated by blood exposure to the damaged vessel. Slower, taking about 1-6 minutes to form a clot.

    • Extrinsic Pathway: Activated by external factors from tissue injury, often quicker, forming clots within 15 seconds.

    • Both pathways convert inactive factor X to active factor Xa.

  • Thrombin Production:

    • Activated factor Xa converts prothrombin to thrombin, which then converts fibrinogen to fibrin, completing clot formation.

Clot Retraction and Dissolution

  • Clot Retraction: The process by which a clot contracts to reduce its size and promote healing, squeezing out serum and facilitating tissue repair.

  • Fibrinolysis: Breakdown of the clot, occurring through the conversion of plasminogen to plasmin, which digests fibrin strands.

Disorders Related to Clotting

  • Hypercoagulability: Condition with excessive clot formation.

  • Thromboembolic Disorders: Can occur due to conditions affecting blood flow, such as turbulence (e.g., atheromatous plaques).

  • Bleeding Disorders: Resulting from insufficient platelets or dysfunctions in clotting mechanisms, such as:

    • Hemophilia A: Caused by defect in clotting factor VIII (X-linked recessive).

    • Von Willebrand Disease: Deficiency in vWF, impairing platelet adherence.

  • Disseminated Intravascular Coagulation (DIC):

    • Simultaneous clot formation and bleeding, can lead to multiple organ failure due to depletion of clotting factors.

    • Symptoms include petechiae, purpura, and severe bleeding.

Anemia Types and Causes

  • Vitamin Deficiencies:

    • Folate and vitamin B12 deficiencies lead to improper red blood cell formation; folate aid in DNA synthesis.

  • Aplastic Anemia: Bone marrow failure resulting in reduced production of all blood cells.

  • Sickle Cell Disease: Genetic disorder causing malformed red blood cells that can lead to vaso-occlusive crises.

    • Result of point mutation substituting glutamic acid with valine in the hemoglobin chain.

  • Thalassemias: Genetic disorders affecting synthesis of globin chains, having regional prevalence.

Polycythemia

  • Definition: Refers to increased number of red blood cells, leading to increased hematocrit.

    • Can also lead to increased blood viscosity and potential hypoxia despite increased red blood cells.

  • Causes: Fluid loss or other factors leading to relative polycythemia.

Summary of Key Concepts

  • Understand the importance of various blood components, their functions, and diagnostic significance.

  • Recognize the mechanisms of hemostasis, including clot formation, retraction, and dissolution.

  • Be aware of the consequences of imbalances in blood components leading to disorders of coagulation and bleeding.