Ch 17 Blood, part 4: Leukocytes

Introduction to Leukocytes

Overview of White Blood Cells

• Leukocytes, or white blood cells, are crucial components of the immune system, making up less than 1% of total blood volume.

• They can exit capillaries to migrate into tissues, a key feature that aids in fighting infections.

• White blood cells utilize amoeboid motion and chemotaxis to locate and respond to pathogens.

Types of Leukocytes

• There are five main types of leukocytes, which can be categorized into granulocytes and agranulocytes.

• Granulocytes contain visible granules under a microscope, while agranulocytes do not.

Granulocyte Classification

Neutrophils

• Neutrophils are the most abundant leukocyte type (60-70% of white blood cell count), neutral in dye staining.

• They have multi-lobed nuclei and fine granules that stain lilac; they are highly phagocytic and act as first responders to infection.

Eosinophils

• Eosinophils make up 2-4% of white blood cells; they stain red-orange with acidic dyes and have two lobes in their nucleus.

• Their primary functions include combating parasitic infections and moderating allergic reactions through antihistamine activity.

Basophils

• Basophils are the least abundant leukocyte type (0.5%), characterized by large purple-black granules obscuring their nucleus.

• They release histamine for inflammatory responses and heparin as a natural anticoagulant during immune reactions.

Agranulocyte Classification

Lymphocytes

• Lymphocytes constitute about 20–22% of leukocyte count; they have large dark nuclei with thin cytoplasm rims.

• Key types include T cells (targeting infected or cancerous cells in tissues) and B cells (producing antibodies).

Monocytes

• Monocytes represent 3–8% of white blood cells; they possess kidney-shaped nuclei and pale blue cytoplasm.

• Upon migrating into tissues, monocytes differentiate into macrophages, which play significant roles in chronic infection response through phagocytosis.

Leukopoiesis: Formation of White Blood Cells

Process Overview

• Leukopoiesis is stimulated by chemical messengers rather than hormones; it increases during infections or allergies.

Colony Stimulating Factors

• Colony stimulating factors trigger specific types of leukocyte production based on the pathogen present (e.g., eosinophils for parasites).

Disorders Related to Leukocyte Count

Common Conditions

• Leukopenia refers to an abnormally low white blood cell count (<5000 per microliter), often resulting from chemotherapy or radiation treatments.