myeloid tissue, myeloid, histology, histo, microanatomy, micrana

1. MYELOID TISSUE

2. Hematopoiesis
process
specialized blood cells develop from pluripotent stem cells of
myeloid tissue in the bone marrow
result of simultaneous,
continuous proliferation and
differentiation – reduction in
the potential of the cells
Site - occurs in myeloid and lymphatic tissue.
Myeloid tissue
bone marrow
Lymphatic tissue
lymphatic organs
- not a rigidly compartmentalized process;
blood cells usually associated with myeloid tissue can
arise in lymphoid tissue, and vice versa

5. Prenatal Hematopoiesis
occurs successively in the yolk sac, liver, spleen and bone
marrow

7. Structural Organization Of Hematopoietic Marrow
Cancellous bone – bony spicules or trabeculae lined by
endosteum and marrow filled with
hematopoietic and non-hematopoietic cells
Blood vessels of the marrow compartment
1. Nutrient arteries
periosteum pass through the compact bone to enter
the marrow space.
2. Longitudinal arteries
formed by the division of a nutrient artery - run
parallel to the long axis of a bone.
3. Radial arteries
spoke-like branches that arise from longitudinal
arteries to form thin-walled sinusoids in the
hematopoietic tissue.

11. Bone marrow
very large and complex organ
cavities of the skeleton
total mass, adult – 1600 to 3000 grams
½ - hematopoietically inactive fatty (yellow) marrow
few microscopic foci of hematopoietic cells
½ - hematopoietically active (red) marrow
function - based on a high degree of structural organization
(organization - labile, altering rapidly in response to
many stimuli)
hematopoietic marrow
formation and release - blood cells
phagocytosis and degradation - microorganisms
and abnormal or senescent rbcs
antibody production
non-hematopoietic marrow
large store of reserve lipids

12. Sinusoids
endothelial cells
no basement membrane,
overlapping and may interdigitate extensively
adventitial layer
external discontinuous layer
Stroma of the Marrow
Cells
3-dimensional meshwork of reticular cells and a delicate
web of containing hematopoietic cells, macrophages, mast
cells, fat cells, lymphocytes and plasma cells.
reticular cells - form a loose net of reticular fibers
reinforce the sinusoidal capillaries and
internal support for the stroma
cytoplasmic processes – lie along the sinusoidal
surface and protrude outward in- between
hematopoietic cells

15. Matrix
contains collagen types I and III, fibronectin, laminin, and
proteoglycans. Laminin, fibronectin, and hemonectin - cell
binding substance
interact with cell receptors to bind cells
to the matrix
Other cells
osteoblast and osteoclast
fat cells
newborn - 0%
2 week-old infant – 15%
children between 18 months to 11 year-old – 20% to 65%
adult – 30% to 70%
70 year-old - >70%
Marrow cellularity - proportion of the area occupied by cells
other than fat cells
normocellular, hypocellular or
hypercellular

16. Macrophages
intracytoplasmic inclusion - refractile yellow-brown
hemosiderin - iron (+)granules
marrow fragments or smear semi-quantitatively to
assess total iron store
long cytoplasmic processes – protrude into the sinusoids and
phagocytozed senescent or damage rbcs, progranulocytes
and circulating microorganism
present in the erythroblastic islands, plasma cell island and
lymphatic nodules but may also occurs elsewhere
generate various neutrophilic growth factors
Mast cells
progenitor cells occur in the marrow, but proliferation and
maturation and acquisition of granules occurs in the tissues
associated with lymphoid nodule, wall of the arterioles,
adjacent to the endothelium of sinusoids and endosteal
cells of bone trabeculae

17. Characterization of Hematopoietic tissue
microscopically by differentiating blood cells.
1. Stained smear of bone marrow reveals a complex population
comprising several types of blood cells and their precursors
2. These cell types can be sorted into several developmental
sequences, each sequence culminating in one of the several
types of mature blood cells – M:E ratio
3. Bone marrow biopsy
cellularity
architecture – structural relationship of the components
tumor

18. Hematopoietic Cords - Cell Associations in Red Bone Marrow
Histologic sections of bone marrow show the following
relationships.
a. Nests of erythroblasts and myelocytes.
developing blood cells are often seen clumped into nests or
islets - cells clump when mitotic events increase their
numbers and the daughter cells remain restricted to
the immediate vicinity.
b. Normoblasts
orthochromatic erythroblasts and macrophages.
Macrophages are found in close association
with nests of normoblasts, where they
phagocytize nuclei expelled by the
normoblasts during erythropoiesis.
c. Megakaryocytes and the sinusoidal wall.
Megakaryocytes are found in close proximity to the walls of
marrow blood capillaries(sinusoids) - facilitates the release of
platelets into the blood stream

19. During preparation of a bone marrow smear,
these normal cellular relationships are demolished.

22. Abnormal Increase in Hematopoiesis
Young children – rapid increase in hematpoietic tissue
accomodated mainly by a
reduction in the proportion of marrow space
occupied by sinusoids
skeletal abnormalities –
frontal and parietal bossing, dental
deformation, and malocclusion of the teeth,
thinning of the cortex – fracture
if the increase is substantial - extramedullary
hematopoies
Adult
initially associated with the replacement of fat cells in the red
marrow by hematopoietic cells and also with the spread of red
marrow into marrow cavities normally containing yellow marrow
if the increase is gross – extramedullary hematopoiesis

23. Postnatal Hematopoiesis
involved three classes of cells
1. Pluripotent stem cells - primitive hematopoietic
two properties – undergo enormous proliferation
a. differentiate into multiple cell lineage - ability to mature
into several types of blood cells
give rise to progenitor cells
lymphoid progenitor cells
multipotent myeloid progenitor cells
b. self- renewal - extensive capacity to generate new stem
cells
present – blood circulation and BM
no identifiable morphologic feature – resemble large
lymphocytes

24. 2. Progenitor cells
proliferating and differentiating stem cells to form daughter cell
with reduced potentiality.
committed to a single cell lineage
unipotential or bipotential progenitor cell generate
precursor cells (blasts)
produce both progenitor and precursor cells,
morphologically indistinguishable from stem cells
3. Precursor cells
display distinct morphologic characteristics
produce only mature blood cells.

25. Hematopoiesis depends on favorable
1. Microenvironmental conditions
2. Presence of growth factors.
Microenvironmental conditions
furnished by cells of the stroma of hematopoietic organs,
which produce an adequate extracellular matrix.
conditions are present
development of blood cells depend on factors that affect cell
proliferation and differentiation.
Growth factors,
act mainly
by stimulating proliferation (mitogenic activity) of
immature
(mostly progenitor and precursor) cell
supporting the differentiation of
maturing cells and enhancing the functions of mature cells.

28. Rate of cell division is accelerated
in both progenitor cells and precursor cells,
and
large numbers of differentiated, mature cells are produced
3 X 10 erythrocytes
0.85 X 10 granulocytes/kg/day in human bone marrow).

30. Initial steps in Blood Formation
Pluripotent hematopoietic stem cells
give rise to multipotent hematopoietic stem cells
Multipotent hematopoietic stem cells
two type - proliferate and differentiate – progenitor cells
CFU-S – colony forming unit–spleen
erythrocytes, granulocytes, monocytes and platelets
CFU-Ly – colony forming unit-lymphocytes
T, B, and NK cells
Erythropoiesis – yield 1 trillion daily in adult
CFU-S
begins with the formation of progenitor cells
BFU-E – burst forming unit-erythroid
high rate of mitotic activity,
high conc. of erythropoietin
CFU-E – colony forming unit erythroid
low conc. of erythropoietin
first recognizable – precursor cell - proerythroblast

31. Granulopoiesis – yields about 1million granulocytes daily in adult
CFU-S
begins with production of three unipotential or
bipotential cells – progenitor cells
CFU-Eo – is the progenitor of eosinophil lineage
CFU-Ba – is the progenitor of basophils
CFU-NM – is the common progenitor of neutrophils and
monocytes - give rise to CFU-N and CFU-M
give rise to histologically identical - in the early stage of all three
lineages
myeloblast (precursor) and promyelocytes - develop
characteristic granules unique to each cell type
during the myelocytes stage and a distinctive
nuclear shape during stab stage
CFU-NM – give rise to CFU-N – progenitor cells of neutrophils
give rise to precursor cells

32. Monocytopoiesis – yields about 10 trillion daily in adult
CFU-NM – progenitor for both neutrophils and monocytes
begins with the formation of
CFU-M – progenitor of monoocyte
give rise to monoblast – precursor cell
Thrombocytopoiesis
CFU-S
begins with the progenitor cells
CFU-Meg
give rise to precursor cells
megakaryoblast

35. Lymphopoiesis
CFU-Ly
begins with differentiation into immunoincompetent
progenitor cells
CFU-LyB and CFU-LyT
give rise to progenitor cells
pre-B pre-T
lymphocytes lymphocytes
stay migrate
Bone marrow Thymus
lymphoblast –precursor cells
proliferation and differentiation
immunocompetent – mature lymphocytes
leave and circulate to the Peripheral lymphatic tissues and
organs

37. Release of mature bone cells from the marrow
controlled by releasing factors produced in response to
the needs of the organism.
Substances with releasing activity
C3 component of complement, some bacterial toxins.
hormones (glucocorticoids and androgens),

38. Two processes involved in the formation of all types of blood cells
Cytodifferentiation (maturation) - all stages of hematopoiesis
progressive acquisition of the morphologic , biochemical,
and functional characteristics of the particular cell type
Cell proliferation
stem cells, progenitor cells and immature recognizable
precursor cells except megakaryocytic lineage
Morphologic criteria of blood cell development.
indicators
1.Changes in cell size and nuclear structure,
2.Presence of differentiation products
( cytoplasmic granules and hemoglobin),
Cell size.
Less mature cells tend to be larger in overall diameter.
Nuclear structure
1. Chromatin configuration.
Less mature cells have euchromatic (transcriptionally active)
nuclei.
Nuclei usually become heterochromatic (transcriptionally inactive)
later in development.
2. Nuclear lobulation.
Granulocytes, during development, acquire characteristically lobed
nuclei

39. 3. Nuclear loss.
Erythrocytes, during development, extrude the nucleus that is
present in an immature cell.
4. Nucleolar loss.
intranuclear organelle may be visible in immature blood cells but
disappears from cells nearing completion of development.
Differentiation Products
Cytoplasmic granules.
In granulocytes,
presence and staining characteristics of azurophilic granules
and specific granules are important developmental criteria.
In erythrocytes,
gradual changes in cytoplasmic staining caused by accumulating
hemoglobin are important developmental criteria

41. ERYTHROPOIESIS.
red blood cells develop through
several well-defined stages from
a progenitor cell to a mature
erythrocyte.
Proerythroblast.
first developmental stage
not an easily recognized cell
Morphologic characteristics
Size - large cell (18-25 um)
Nucleus - euchromatic and
usually has one or
two nucleoli.
Cytoplasm - exhibits
basophilia.

42. Basophilic erythroblast
Morphologic characteristics
Size - (15-18 um) smaller than
a proerythroblast.
Nucleus - spheroidal and
becomes increasingly
heterochromatic with successive
mitoses.
Cytoplasm - distinctly
basophilic
Significance of cytoplasmic
basophilia - large number of
polyribosomes, assembled in
preparation for the synthesis of
hemoglobin.

43. Polychromatophilic erythroblast.
(normoblast)
shows evidence of Hgb accumulation.
Morphologic characteristics
Size - (12-15 um) slightly smaller
than a basophilic erythroblast.
Nucleus - Coarse heterochromatin
and alternating euchromatic regions
"checkerboard" arrangement in a
spherical nucleus - useful identifying
feature.
Cytoplasm - acquires a
polychromatophilic staining
characteristic- acidophilic and
basophilic.
Significance of cytoplasmic
polychromatophilia
Polyribosomes- basophilic component
Hemoglobin - acidophilic component
- accumulates in stainable
amounts - Acidophilia of accumulating
hemoglobin gradually dilutes the
basophilia of the polyribosomes

44. Orthochromatic
erythroblast
last stage of
erythropoiesis in which a
nucleus can be
identified.
Morphologic
characteristics
Size - smaller than a
polychromatophilic and
slightly larger than a
mature erythrocyte.
Nucleus - pyknotic
and is intensely
heterochromatic; little
evidence of euchromatin
is visible.
Cytoplasm -
acidophilic because of
the high concentration
of recently synthesized
hemoglobin.

45. Expulsion of the nucleus from the cell
a. normoblast stage ends when the condensed, kernel-like nucleus is cast out
of the cell.
b. nucleus is not viable - phagocytized in the macrophage-rich hematopoietic
compartment.
Reticulocyte
nearly mature red cells
found in circulating blood.
Morphologic characteristics
Size - is approximately the same size as the mature erythrocyte.
Nucleus - does not have a nucleus.
Cytoplasm
routine blood stains - strongly acidophilic and has essentially the same
staining characteristics as the mature erythrocyte.
supravital staining by brilliant cresyl blue - stains the remaining
polyribosomes of the cell, producing the basophilic
reticulum
Circulating reticulocytes
released into the peripheral blood; therefore, developing red blood cells circulate
before erythropoiesis is completed.
peripheral blood
comprise about 1% to 2% of the circulating red blood cells

46. Reticulocytes mature into erythrocytes
after about 24 hours in circulation.
Hemoglobin synthesis continues during
this period.

47. Kinetics of red blood cell development
Mitotic and postmitotic phases of erythropoiesis
mitosis occurs
erythroblasts up to and including the polychromatophilic erythroblast.
postmitotic cells
orthochromatophilic , reticulocytes, and mature erythrocytes
Distribution of the erythrocyte population
Virtually all erythrocytes are released into the circulation as soon as they are
formed.
Normally released into circulation are reticulocytes, not fully mature cells
Erythropoiesis - completed as the cells circulate through the body.
Bone marrow - not a site of red blood cell storage
Apparently mature erythrocytes observed in routinely stained bone marrow smears
are either
1. reticulocytes about to be released into the circulation
or
2. intravascular cells that were passing through the marrow at the time of biopsy

48. Duration of erythropoiesis and Life-span of the mature erythrocyte
Basophilic erythroblast
appear as mature erythrocytes in about 1 week.
Mature erythrocyte
functions in the peripheral blood for about 120 days before it is removed
by macrophages in the spleen

49. Erytrocytes
maturation

51. GRANULOPOIESIS.
Dev. of granulocytes
(neutrophils, eosinophils,
and basophils) passes
through several well-defined
stages.
Myeloblast
first developmental
stage
not an easily recognized
cell
Morphologic
characteristic
Size- large cell (about
14-18 um in
diameter),
approximately twice
the
diameter of an
erythrocyte.
Nucleus - euchromatic
and nucleoli are usually

52. Promyelocyte
Morphologic
characteristics
Size - (18-20 um)
slightly larger than the
myeloblast and is much
larger than an RBC
Nucleus - large and
euchromatic, and nucleoli
may
be identified.
No indentation of the
nuclear
surface
Cytoplasmic granules
(1) Azurophilic, or
primary, granules are
present important
indicator of this stage of
granulopoiesis.
These granules are stained
by the azure dye that is
one of the components of

53. Characteristics of promyelocyte granules
Azurophilic granules (and in later granulocyte stages)
Type of lysosome,
contain both lysosomal enzymes and peroxidase – myeloperoxidase to
emphasize its presence in myeloid cells.
synthesized only by promyelocytes, and not by cells in later stages of
granulopoiesis.
Hence,
number of azurophilic granules per developing granulocyte
diminishes with each cell division of the promyelocyte and its
progeny.
Multipotential nature of promyelocytes
a. Promyelocytes cannot be divided into neutrophilic, eosinophilic, or
basophilic subtypes.
become recognizable at the myelocyte stage - specific granules

54. Myelocyte.
commonly encountered
cell type in bone marrow.
Neutrophilic myelocytes,
eosinophilic myelocytes,
basophilic myelocytes
recognized on the basis of
the staining of their specific
granules.
These secondary granules
are first seen at this stage of
granulopoiesis.
Morphologic characteristics
Size - iapproximately the
size of the mature
granulocyte (12-15 um).
Nucleus
acquires an indentation
on its surface facing the
interior of the cell.
becomes more
heterochromatic, and
nucleoli are usually not
visible.

55. Cytoplasmic granules
Two populations of granules - recognized in myelocytes.
Specific granules
characteristic staining reactions (neutrophilia, acidophilia, or basophilia),
first appear in myelocytes.
Azurophilic granules
form a decreasing fraction of the total number of granules in the
developing granulocyte.
eosinophils and basophils tend to be obscured by the larger, more
numerous, more intensely stained, and more electron-opaque
specific granules.
"dawn of neutrophilia"
characteristic of the developing neutrophilic myelocyte.

56. Specificity of secondary granules - Specific granules
impart to the developing granulocyte.
functional specificity AND morphologic specificity
a. Neutrophilic specific granules
contain bacteriostatic and bactericidal substances such as lysozyme,
lactoferrin, and alkaline phosphatase
act in concert with the lysosomal azurophilic granules during the
phagocytic function of neutrophils.
b. Eosinophilic specific granules
containing a paracrystalline, arginine-rich protein.
gives the granule its characteristic acidophilia,
its refractility, and its unique fine structure
c. Basophilic specific granules
contain histamine and heparan sulfate

59. Metamyelocyte
next developmental stage beyond the myelocyte.
Nucleus
a. indentation of the nucleus deepens
and the nucleus becomes kidney-shaped.
b. chromatin - slightly more condensed
(heterochromatic) than in the myelocyte stage.
Cytoplasmic granules
a. few hundred granules with specific granules outnumbering
azurophilic granules by 3 or 4 to 1.
b. No new azurophilic or specific granules are formed

61. Band cell
developmentally closest to the mature neutrophil.
stab cell
no comparable stage for developing eosinophils and basophils.
Morphologic characteristics
Nuclear shape - band-like, horseshoe-shaped structure.
Nuclear lobulation
(1) first indications of nuclear lobe formation
(2) Only when nuclear lobulation is complete and when, typically, 3-5
distinct segmented lobes are apparent is the cell considered a
mature polymorphonuclear leukocyte (PMN - neutrophil)

65. KINETIC OF NEUTROPHIL PRODUCTION
total time taken for a myeloblast to emerge as a mature neutrophil in
the circulation is about 11days.
Under normal circumstances,
5 mitotic divisions occur in the myeloblast, promyelocyte, and
neutrophilic myelocyte stages of development.
Neutrophils Pass Through Several Functionally and Anatomically Defined
Compartments
Medullary Formation Compartment
subdivided into a
1.Mitotic compartment (-3 days) and a
2.Maturation compartment (-4 days).
Remain in this compartment for about 4 days.
Medullary Storage Compartment
acts as a Buffer System, capable of releasing large numbers of
mature neutrophils on demand.

66. Circulating Compartment
consists of neutrophils suspended in plasma and circulating in blood
vessels.
Marginating Compartment
composed of neutrophils that are present in blood but do not circulate,
are in capillaries and are temporarily excluded from the circulation
by vasoconstriction, or especially in the lungs – they may be at the
periphery of vessels, adhering to the endothelium, and not in the
main bloodstream.
Marginating and Circulating compartments
are of about equal size, and there is a constant interchange of cells
between them.
half-life of a neutrophil in these two compartments is 6-7 hours.

67. Medullary Formation and Storage Compartments
together are about 10 times as large as the Circulating and Marginating
compartments.
Neutrophils and Other Granulocytes
enter the connective tissues by passing through intercellular junctions
found between endothelial cells of capillaries and postcapilIary venules
(diapedesis).
Connective Tissues Compartment
size is not known.
Neutrophils reside here for 1-4 days and then die by apoptosis, whether
or not they have performed their major function of phagocytosis.

68. medullary
Medullary
Formation

69. Circulating Band Cells.
small number of band cells may be found in normal blood smears.
number in peripheral blood is elevated under conditions that place demands
on the neutrophil population.
Kinetics of neutrophil development
1. Mitotic and postmitotic phases of granulopoiesis
a. Cell divisions cease by the late myelocyte stage.
b. Postmitotic cells.
Metamyelocytes, band cells, and mature neutrophils
do not divide.
2. Distribution of the neutrophil population
a. Approximately 15 times more mature neutrophils and nearly mature
neutrophils (band cells) are found in the Marrow than in the
Peripheral blood.
b. Large numbers are stored in the marrow and enter the circulation
in response to injury and infection.
c. leave the circulation to enter the perivascular connective tissue.

70. Duration of granulopoiesis and life-span of a mature peripheral neutrophil
a. mitotic phase,
myeloblast to late myelocyte - lasts about 1 week.
b. postmitotic phase
late myelocyte to mature neutrophil - lasts about 1 week.
c. Neutrophils
circulate for 6 to 12 hours in peripheral blood before they enter the
perivascular connective tissue.
After 1 to 2 days in the perivascular compartment
neutrophils are phagocytized and destroyed by macrophages.

71. Numbers of neutrophils and erythropoietic cells in bone marrow
1. Neutrophils are the predominant cell type in bone marrow.
a. Immature neutrophils (metamyelocytes and band cells) and mature
neutrophils account for approximately 50% of the cells in a bone
marrow smear.
b. Erythropoietic cells, from early basophilic erythroblasts to
normoblasts, account for only about 18% of the cells in a marrow
smear.
2. Therefore, while erythrocytes vastly outnumber granulocytes in
circulating blood, their immature forms are a distinct minority in
the marrow compartment.

72. MEGAKARYOCYTOPOIESIS.
Megakaryocytes
bone marrow cells that give rise to platelets.
Megakaryoblast
immature cell derived from the pluripotential CFC.
Morphologic characteristics
large cell (about 30 um in diameter) with a nonlobulated nucleus.
No evidence is seen of platelet formation by the megakaryoblast.
Megakaryoblast-megakaryocyte transition
1. Successive endomitoses occur in the megakaryoblast.
a. DNA replicates and the number of chromosomes increases.
b. Neither karyokinesis nor cytokinesis takes place, however, so that
the chromosomes remain within one enlarging nucleus and
ploidy increases from 2N to 32N or 64N.
2. Once the cell becomes large and polyploid - considered a
megakaryocyte.

74. Megakaryocyte.
mature, platelet-forming cell.
Chromosome replication does not occur - postendomitotic cell.
Morphologic characteristics
Size
(1) vary in size from 50 to 100 um in diameter.
largest cell in normal marrow.
(2) Both the cell and its nucleus have increased in size over the
megakaryoblast, in proportion to the ploidy of the cell.
Cytoplasm.
electron microscope,
superficial cytoplasm - divided into small compartments by
multiple invaginations of the plasma
membrane.
platelet demarcation channels and
they define future platelets.

75. Cell surface.
smears of bone marrow examined by light microscopy,
clusters of platelets, about to be released, are often seen at the surface of
megakaryocytes.
Platelet formation and release
a. Each cytoplasmic compartment
defined by platelet demarcation channels in the megakaryocyte,
corresponds to a developing platelet.
b. platelet is released from the megakaryocyte when its surrounding
demarcation channels become continuous with one another.
c. Platelets are shed from the surface of the megakaryocyte as small,
membrane-bounded cytoplasmic packets.

78. MONOCYTOPOIESIS.
development of the monocyte-macrophage cell line takes place in
three sites.
Bone Marrow,
monocyte develops from the CFC through intermediate stages.
monoblasts and promonocytes,
Peripheral Blood,
monocytes can be recognized in this location, however, they are
not fully differentiated cells.
Perivascular Connective Tissue,
final differentiation occurs.
Monocytes leave the blood by crossing the vessel wall to
enter the connective tissue around the blood vessel.
differentiate several types of Mononuclear - Phagocytic Cells
macrophage - final stage of development of a monocyte.