Animal Histology

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Where do granular WBCs come from?
Granulopoiesis - formation of granular leukocytes (WBCs)
This process occurs in bone marrow along side erythropoiesis with each type (eosinophil, basophil, neutrophil) going through its own pathway. Two processes take place simultaneously: (1) nuclei condense to adult form (bi-lobed, multi-lobed, etc) and (2) the cell begins to synthesize and collect its specific granule population. I. Start with CFU-S WBC

1. Begin with: promyelocyte (big committed stem cell which commits right away to become either a neutrophilic myelocyte, basophilic myelocyte, or eosinophile myeocyte) a. Myelocytes have a begun nuclear changes, possessing a round nucleus or one that is flatten on one side. The cytoplasm shows a minimum of specific granules (eosinophilic or basophilic or azurophilic)

2. Metamyelocyte (MM)
b. Metamyelocytes have begun nuclear indentation (horseshoe shaped to mature morphology) and an increase in specific granules

3. Stab Cells ***EXCLUSIVE ONLY TO NEUTROPHILS***
c. Stab Cells or Band Metamyelocytes are unique to the neutrophil lineage. These cells, approximately the size of mature PMNs have a deep horseshoe or ring-like morphology to their nuclei

4. Adult Cells final nuclear morphology + specific granules - occur in bone marrow next to developing RBC
II. Back in Circulation, last type of WBC: Agranular WBC
A. Monocyte
a. 2-8% WBC
b. LANDMARK: largest circulating WBC 15-20 micron dm (3-4X RBC) c. Nucleus: irregular shaped or horseshoe shape BUT UNLIKE STAB CELLS monocytes are seen in circulation while stab cells are found only in bone marrow

d. Precursor to LCT macrophages
B. Lymphocyte
e. 2nd most common WBC (after neutrophils) 30% WBC
f. Dm: 8-10 micron (about a RBC)
g. Nucleus fills cell, leaving a royal blue rim of cytoplasm

h. Fxn: produce antibodies, secretory cell, has lost of rER,...
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