White Blood Cells Study Notes

White Blood Cells (Leukocytes)

Definition and Characteristics

• White Blood Cells: Also known as leukocytes, these are the only true blood cells due to their fully formed nucleus and ability to produce all necessary proteins.

• Size Comparison: Leukocytes are much larger than other components of blood, such as red blood cells and platelets, often 3 to 5 times larger.

• Composition in Blood: They make up less than 1% of the blood.

Main Function

• Role in Immune System: The primary function of leukocytes is to identify and attack foreign invaders in the body, including viruses, bacteria, and parasitic worms.

• Movement Dynamics: While present in the bloodstream, leukocytes do not remain there for long periods; they migrate into tissues to perform their functions.

Mechanism of Movement

• Diapedesis: This term describes the process through which leukocytes move out of the bloodstream and into the tissues.

• Amoeboid Motion: The movement mechanism adopted by leukocytes, where they use their cytoplasm to propel themselves through tissues.

  • Analogy to Octopus Movement: An analogy is given to illustrate amoeboid motion, where an octopus escapes through a narrow opening by pushing its body through gradually, mimicking how leukocytes navigate through tissue openings.

Chemotaxis

• Positive Chemotaxis: When leukocytes detect an infection, they release chemical signals that create a chemical trail (like breadcrumbs) leading to the infection site. White blood cells can move towards higher concentrations of these signals, effectively guiding them to areas of infection.

Types of White Blood Cells

• White blood cells are classified into two major categories:

  1. Granulocytes: Cells with cytoplasmic granules.

  • Types:

    • Neutrophils:

      • Account for 50-70% of white blood cells.

      • They are the primary defense against bacteria, significantly larger than red blood cells (approximately double their size).

      • Video illustration depicts a neutrophil chasing and attacking bacteria using amoeboid motion.

    • Eosinophils:

      • Comprise about 2-4% of white blood cells.

      • Primarily defend against parasitic worms and cleanup following immune responses.

    • Basophils:

      • Constitute about 0.5-1% of the white blood cell population.

      • Filled with histamine granules, crucial in inflammatory responses; they release histamine which dilates blood vessels and attracts other white blood cells.

  1. Agranulocytes: Cells that lack visible cytoplasmic granules.

  • Types:

    • Lymphocytes:

      • Make up 25-45% of white blood cells.

      • Found in lymph fluid and blood, involved in immune response.

      • Two main types:

      • T Cells: Antiviral functions and action on tumor cells.

      • B Cells: Differentiate into plasma cells which produce antibodies upon exposure to antigens, contributing to immune memory.

    • Monocytes:

      • Comprise 3-8% of white blood cells.

      • Important for dealing with chronic infections (e.g., tuberculosis) and develop into macrophages that perform phagocytosis (engulfing and breaking down pathogens).

Formation of White Blood Cells

• Leukopoiesis: The process of forming white blood cells, beginning from a precursor cell known as a hematopoietic stem cell (or hemocytoblast).

  • While the detailed steps of leukopoiesis are not elaborated upon, it is crucial to understand that leukopoiesis leads to the production of various types of white blood cells involved in immune functions.