White Blood Cells Overview

White Blood Cells (WBC)

• WBCs, also known as leukocytes or leucocytes, contain nuclei and lack hemoglobin
• Their count in blood ranges from 4,000 to 11,000 per mm³
• WBCs are less than 1% of total blood volume

Types of WBCs

• Granulocytes
  • Contain numerous granules
  • Nuclei are lobed
  • Include:
    • Neutrophils (40-70%), diameter 10-15 µm
    • Eosinophils (1-4%), diameter 10-15 µm
    • Basophils (0-2%), diameter 10-15 µm
• Agranulocytes
  • Few or no granules
  • Nuclei are large and spherical
  • Include:
    • Lymphocytes (20-40%), diameter 11-15 µm (large) or 7-10 µm (small)
    • Monocytes (3-8%), diameter 14-18 µm

Leukopoiesis

• Production of WBCs
• Sites:
  • Bone marrow (granulocytes, monocytes, and some lymphocytes)
  • Lymph tissue (lymphocytes and plasma cells)
• Stimulators:
  • Chemical messengers from bone marrow and mature WBCs (in areas of inflammation)
  • Interleukins (e.g., IL-1, IL-2)
  • Colony-stimulating factors (CSFs) (named for the WBC type they stimulate)
• Steps:
  • Hemocytoblasts differentiate into myeloid and lymphoid stem cells
  • Myeloid stem cells become myeloblasts or monoblasts
  • Lymphoid stem cells become lymphoblasts
  • Myeloblasts form eosinophils, neutrophils, and basophils
  • Monoblasts develop into monocytes
  • Lymphoblasts develop into lymphocytes

Leukocytosis and Leukopenia

• Leukocytosis: Increased WBC count (above 11,000/mm³)
  • Physiological causes (e.g., extreme exercise, adrenaline injection, after meals, hot baths)
  • Pathological causes (e.g., acute infection, acute hemorrhage, post-operative, tissue damage)
• Leukopenia: Decreased WBC count (below 4,000/mm³)
  • Causes (e.g., toxicity of some drugs, typhoid fever, vitamin B12 and folic acid deficiency, bone marrow hypoplasia)

Neutrophils

• Lifespan: 6-12 hours
• First line of defense against bacteria and foreign particles
• Important roles: phagocytosis and inflammation
• Key characteristics:
  • Margination
  • Diapedesis
  • Amoeboid movement
  • Chemotaxis
  • Opsonization
  • Phagocytosis
  • Degranulation

Granulocyte Degranulation

• Lysosomal enzymes in neutrophils fuse with phagocytic vesicles
• Destroy bacteria and neutrophils
• Removed by monocyte macrophages (reticuloendothelial system)

Other WBCs (Eosinophils, Basophils, Monocytes, Lymphocytes)

• Eosinophils:
  • Fighting parasites
  • Allergic inflammatory response
  • Release plasminogen (dissolves blood clots)
• Basophils:
  • Synthesize histamine (allergic/inflammatory mediator)
  • Synthesize heparin (anticoagulant)
• Monocytes:
  • Largest WBC type
  • Function: Phagocytosis. Mature into macrophages in tissues
• Lymphocytes:
  • Key cells of the immune system
  • Two types:
    • T Cells (helper, cytotoxic, suppressor and memory)
    • B Cells (produce antibodies)

Tissue Macrophages

• Derived from monocytes
• Many types in various tissues (Kupffer cells in liver, alveolar macrophages in lungs)
• Important role in phagocytosis, filtering out bacteria and debris

Immunity

• The ability of the body to resist organisms and toxins that cause damage
• Two types of immunity
• Innate immunity (non-specific)
  • First line of defense
  • Does not require "prior exposure" to the antigen
• Acquired immunity (specific)
  • Humoral immunity (antibodies)
  • Cellular immunity (Tc lymphocytes)

Antibodies (Immunoglobulins)

• Gamma globulin plasma proteins
• Produced by B cells in response to antigens
• Five types: IgG, IgM, IgA, IgE, IgD.

Preprocessing of Lymphocytes

• Lymphocyte stem cells develop in bone marrow or fetal liver
• Processed in the thymus gland (T lymphocytes) and other lymphatic tissues (B lymphocytes).

Quiz Questions

• (Answers are not provided, but this section contains the questions from the supplied documents.)*

Explore the fascinating world of white blood cells (WBCs), their types, and their critical role in the immune system. This quiz covers the characteristics of granulocytes and agranulocytes, as well as the process of leukopoiesis. Test your knowledge on WBCs and their functions in the human body.