Chapter 9 Notes: Leukopoiesis, WBC Differential, and Lymphocyte Function

Leukopoiesis

The process of forming white blood cells (leukocytes) to defend against bacteria, viruses, fungi, and other foreign substances.

WBC Production Rate

Approximately 1.5 \times 10^9 white blood cells per day in the bone marrow.

M:E Ratio

Myeloid:erythroid ratio in bone marrow, typically 3:1 to 4:1, indicating about 3-4 WBCs for each RBC.

Myeloid Stem Cell

Originates granulocytes (neutrophils, eosinophils, basophils), erythrocytes, monocytes/macrophages, and megakaryocytes.

Lymphoid Stem Cell

Originates lymphocytes (T cells, B cells, NK cells).

Granulocytes

White blood cells containing granules (e.g., neutrophils, eosinophils, basophils) with enzymes to digest/destroy foreign substances.

Neutrophil Maturation Sequence

Myeloblast → Promyelocyte → Myelocyte → Metamyelocyte → Band → Segmented Neutrophil.

Myeloblast

Least mature neutrophil precursor, characterized by very uniform, smooth chromatin, multiple visible nucleoli (2–5), and blue–red azurophilic (primary) granules.

Segmented Neutrophil

Most mature neutrophil, characterized by a nucleus with 2-5 lobes (filaments) and pale lilac cytoplasm with fine, dusty secondary granules.

Eosinophil

A granulocyte with usually bilobed nuclei and large, distinctive red–orange (eosinophilic) granules, increased in parasitic infections or allergic reactions.

Basophil

A granulocyte with a bilobed or bilobed-like nucleus often obscured by large purple–black granules.

Monocyte

The most mature cell in the monocytic series, characterized by a highly variable (lobulated, convoluted, or oval) nucleus, loose/lacy chromatin, grayish-blue cytoplasm, and often vacuoles; size 12–28 μm.

Lymphocyte

A type of white blood cell responsible for recognizing foreign bodies and generating antibodies/building immunity; matures from lymphoblast and prolymphocyte stages.

Small Lymphocyte

Mature lymphocyte (7–12 μm) with dense, clumped chromatin often wrapped around the nuclear membrane and scant cytoplasm.

Primary Lymphoid Tissues

Sites where lymphocytes originate and mature, including bone marrow (for B cells and precursors) and thymus (for T cell maturation).

Secondary Lymphoid Tissues

Sites where mature lymphocytes encounter antigens and mount immune responses, including spleen, lymph nodes, Peyer's patches, and tonsils.

Flow Cytometry

A technique used to differentiate lymphocyte subpopulations (e.g., B cells, T cells, NK cells) by surface CD markers, as they are indistinct by routine smear morphology.

Manual Differential Trigger

Situations warranting a manual review of WBCs, such as first-time patient samples, automated system flags for blasts/unusual findings, or markedly high lymphocyte counts.

Critical Values

Any lab result deemed critical, requiring immediate notification of appropriate personnel and documentation.

Delta Checks

Automated system flags for results that differ markedly from a patient’s prior results, requiring technologist investigation and verification.

Absolute WBC Count

Calculated as (relative fraction of specific cell type) × (total WBC count); e.g., \text{Absolute Count} = \frac{\text{P}}{100} \times \text{Total WBC Count} where P is the percentage.