154
UNIT 2
Basic Tissues
SYNOPSIS 8-2
Hematopoiesis
Stem, Progenitor, and Precursor cells
Stem cells
are capable of differentiating into multiple cell lineages and can undergo proliferation indeF
nitely.
Progenitor cells
are only capable of differentiating into a single cell lineage (restricted to one or two blood cell types) and
are morphologically undifferentiated.
Precursor cells
can be recognized morphologically as undergoing differentiation along a particular blood cell lineage.
Erythropoiesis
Cytoplasm
becomes progressively less basophilic because of dilution of ribosomes during the erythropoiesis process.
Nucleus size
progressively decreases because of increased condensation of chromatin.
Cell size
progressively decreases during the erythroid differentiation.
Cytoplasm
becomes progressively more eosinophilic because of increased accumulation of hemoglobin.
The nucleus
retains a round shape and no indentation occurs before it disappears.
Granulocytopoiesis
Cell size
decreases and nucleus becomes more condensed as in erythropoiesis.
Nucleus shape
changes from round or oval (promyeloblasts) to kidney shaped/slightly indented (myelocytes) and then
changes from deeply indented (metamyelocytes) to band shaped (band cells) and F
nally to lobed (mature granulocytes).
Promyelocytes
do not have speciF
c granules (only azurophilic granules); at this stage, it is too early to tell which granular
leukocytes they will become.
Myelocytes
are the last developmental stage capable of dividing; speciF
c granules accumulate in this stage.
SYNOPSIS 8-3
Pathological and Clinical Terms for Mature and Developing Blood Cells
Gray platelet syndrome
: This condition is characterized by a deF ciency or absence of the alpha granules and contents in
blood platelets, giving platelets a gray appearance in a Wright stain smear (±ig. 8-2B).
Platelet storage pool def
ciency
: Disorder caused by a decrease or absence of platelet delta granules (dense bodies),
which normally store and release adenine nucleotides and 5HT. “Platelet-type” bleeding is common with this deF
ciency
(±ig. 8-2B).
Petechiae
: Minute red or purple spots on the skin or mucous membranes caused by capillary hemorrhage; common causes
include physical trauma and decreased platelets (thrombocytopenia).
Smudge cell
: Damaged lymphocytes seen on a peripheral blood smear caused by mechanical stress in the process of
producing the smear; although nonspeciF c, smudge cells are encountered more frequently on blood smears of patients with
chronic lymphocytic leukemia (±ig. 8-4C).
Reticulocytosis
: Increased reticulocytes in the blood, often in response to blood loss, stimulation by erythropoietin treat-
ment, or treatment of iron deF ciency anemia with iron supplementation (±ig. 8-11C).
Thrombocytosis
: Increased platelet count in the blood, which may be reactive or neoplastic, as in the disease essential
thrombocytosis (±ig. 8-12C).
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