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1. CHAPTER 2
CHAPTER 2
Composition, Formation and
Function of Blood
, Formation and Function of
Blood

2. Acknowledgements
 Addisa Ababa University
 Jimma University
 Hawassa University
 Haramaya University
 University of Gondar
 American Society for Clinical Pathology
 Center for Disease Control and Prevention-Ethiopia

3. Objectives
Upon completion of this chapter the student will be able to:
 Explain the composition of blood
 Describe the morphology and functions of the formed
elements of blood
 Discuss the functions of plasma
 Define hemopoiesis and explain the process of blood cell
origin and development
 Indicate the sites of hemopoiesis in infancy, childhood and
adulthood
 List at least three hemopoietic growth factors
 Name the cells in the development order that will mature
into erythrocytes, thrombocytes and the five leukocytes

4. Objectives cont’d
 Discuss how hemopoiesis is regulated
 Describe the morphology of the red blood cell, white
blood cell, and platelet precursors
 Define extramedullary hemopoiesis
 Differentiate between intramedulary and extramedulary
hemopoiesis
 Define erythropoiesis
 Explain how erythropiesis is regulated and list the effects
of the hormone erythropoietin on erythropoiesis
 Define megaloblastic erythropoiesis
 Define ineffective erythropoiesis
 Define myeloid erythroid ratio

5. Outline
 Composition of Blood
 Characteristics of Blood
 Hematopoiesis
 The Hemopoietic Microenvironment
 Regulation of Hematopoiesis
 Maturational characteristics of hemopoietic cells

6. 2.1 Composition of Blood
 Blood
 is the only fluid tissue
 constitutes 6-8% of the total body weight
 consists of cells suspended in a fluid called plasma.
 about 45% cells; 55% plasma

7. Composition of Blood cont’d
(WBC + platelets)

8. Composition cont’d
 Plasma
 part of the extracellular fluid
 a complex solution of proteins, salts and numerous
metabolic substances
 acts as a transport medium carrying its constituents to
specialized organs of the body.
 Consists of:
 about 91.5% water
 about 8.5% solutes of which about 7% are proteins
 Out of the 7% protein:
54% albumin
38% globulins
7% fibrinogen

9. Composition of Plasma
Constituent Percentage of plasma
Water 90-92 %
Protein 6-8%
Inorganic ions <1% (0.9%)
Organic ions <1% (0.5-0.9%)
Plasma Proteins Plasma concentration
Albumin 4.5 %
Globulin 2.5%
Fibrinogen 0.25%

10. Formed Elements
 The three main blood cells/formed elements are:
 red blood cells (erythrocytes)
 white blood cells (leucocytes)
 platelets (thrombocytes)

11. Erythrocytes (Red Blood Cells)
 Are the most numerous cells in the blood
 The normal RBC count is approximately 4.5 to 6
million cells per microliter.
 Their primary function is gas exchange.
 carry oxygen from the lungs to the tissues
 return carbon dioxide (CO2), a waste product of
metabolism, from the tissues to the lungs to be
exhaled
 are anucleated cells containing few organelles
 a large proportion of their cytoplasm consists of the
iron containing oxygen transport molecule
hemoglobin.

12. Erythrocytes cont’d
 shaped like biconcave disks approximately 7 to 8 m in
diameter with a thickness of 1.7-2.4m
 The biconcave disk shape gives red blood cells (RBCs) the
flexibility to squeeze their way through capillaries and other
small blood vessels.
 In stained smears, RBCs look like a circle with a central
hole, or central pallor, which is approximately one-third
the diameter of the cell
 normally survives in the blood stream for approximately
120 days
 after finishing its life span, it is removed by the phagocytic
cells of the reticuloendothelial system, broken down and
some of its constituents re utilized for the formation of new
cells.

13. Erythrocytes
 Note that the size of the erythrocytes is about
the same as the nucleus of the small resting
lymphocyte.

14. Leukocytes (White Blood Cells)
 Leukocytes are :
 a heterogeneous group of nucleated cells
 responsible for the body’s defenses
 transported by the blood to the various tissues where
they exert their physiologic role, e.g. phagocytosis.
 The normal WBC count is ~4,000 to 10,000/L (4.0–10.0 x
103/L)
 Leukocytes are usually divided into:
 Granulocytes, which have specific granules, and
 Agranulocytes, which lack specific granules

15. Leukocytes (White Blood Cells)
 Granulocytes/ Polymorphonuclear leukocytes are divided
into:
 Neutrophils (with faintly staining granules),
 Eosinophils (with large reddish or eosinophilic
granules), and
 Basophils (with large dark blue or basophilic granules).
 Agranulocytes/mononuclear leukocytes are divided into:
 Lymphocytes and
 Monocytes.
 Although they are called white blood cells, leukocytes
predominantly function in tissues.
 They are only in the blood transiently, while they travel to
their site of action.

16. Neutrophils
 are the most common type of WBCs in adults
 The segmented neutrophils “segs,” also called
polymorphonuclear neutrophil leukocytes
[PMNs or “polys”]
 are the primary defense against bacterial
infection
 Their size ranges from 10-12m in diameter.
 They are capable of amoeboid movement.
 There are 2-5 lobes to their nucleus that stain
purple violet.
 The cytoplasm stains light pink with pinkish
dust like granules.

17. Neutrophils cont’d
 Normal range: 2.0-7.5 x 103/l.
 Increased in acute bacterial infections.
Band Neutrphil

18. Eosinophils
 Have the same size as neutrophils or may be a
bit larger (12-14m).
 The nucleus:
 is often bilobed with a "spectacle"
arrangement.
 stains a little paler than that of neutrophils.
 Cytoplasm contains many, large, round/oval
orange pink granules.
 They are involved in allergic reactions and in
combating helminthic infections.
 Normal range: 40-400/l.
 Increase in their number (eosinophilia) is
associated with allergic reactions and
helminthiasis.

19. Basophils
 Size: 10-12m in diameter.
 are the least common type of leukocytes,
normally ≤1% of total WBCs.
 Have a kidney shaped nucleus often obscured
by a mass of large deep purple/dark blue
staining (basophilic) granules.
 The granules contain:
 heparin (an anticoagulant),
 histamine (a fast vasodilator),
 the slow-reacting substance of anaphylaxis
(a slow vasodilator), and other compounds.

20. Basophils cont’d
 involved in immediate hypersensitivity reactions
related to immunoglobulin class E (IgE)
 Normal range: 20-200/l. Basophilia is rare except in
cases of chronic myeloid leukemia.

21. Lymphocytes
 are the second most common type of leukocytes
in adults (~20–40% of WBC)
 The average number of lymphocytes in the
peripheral blood is 2500/l.
 The lymphocyte number is higher in children and
also increases with viral infections

22. Lymphocytes cont’d
1. Small Lymphocytes/Resting
lymphocytes:
 are usually small (7-10m in diameter)
 has a dark round to oval nucleus, and
 only a rim of pale blue staining cytoplasm
 nucleus is about the same diameter as a
normal erythrocyte & occupies most of the
cell
 are the predominant forms found in the blood.

23. 2. Large Lymphocyte
 A small number of lymphocytes in the blood
 Slightly larger than resting lymphocytes, with
reddish purple (azurophilic) granules. This
appearance generally corresponds to natural
killer (NK) cells
 Size: 12-14m in diameter
 Nucleus:
 a little paler than small lymphocytes
 is usually eccentrically placed in the cell
 Cytoplasm:
 Is more plentiful
 stains pale blue and may contain a few
reddish (azurophilic) granules.

24. Monocytes
 Are the largest white cells measuring 14-18m in
diameter.
 Normally comprise ~2 to 8% of leukocytes
 After 8 to 14 hours in the blood, they enter tissue to
become tissue macrophages (also called histiocytes)
 Cytoplasm:
 abundant staining light gray to light blue
 finely granular
 Nucleus has very finely granular chromatin and is often
folded, bean shaped, oval, or irregular

25. Monocytes cont’d
 Monocytes have two functions:
 Phagocytosis of microorganisms (particularly
fungi and mycobacteria) and debris
 Antigen processing and presentation. In this role,
they are critical in initiation of immune reactions
 Normal range: 700-1500/l.
 Monocytosis is seen in bacterial infections (e.g.,
tuberculosis) and protozoan infections.

26.  *Values given are for adults; children tend to have a
higher proportion of lymphocytes. The exact ranges will
vary slightly between different laboratories.

27. Platelets (Thrombocytes)
 are small, non nucleated (anucleated), round/oval
cells/cell fragments
 Their size ranges 1-4m in diameter
 The cytoplasm stain pale blue and contain many pink
granules
 They are produced in the bone marrow by
fragmentation of megakaryocytes, which are large and
multinucleated cells
 Their primary function is preventing blood loss from
hemorrhage by forming a platelet plug

28. Platelets
 Platelets have a life span of approximately 10 days.
 Senescent platelets are removed by the spleen
 Normal range: 150-400 x 103 /l.

29. 2.2. Characteristics of Blood
1. Temperature
 Roughly 38°C (100.4 °F)
2. Viscosity
 Five times that of H2O due to interactions among
dissolved proteins, formed elements, & surrounding
H2O molecules
 Sticky, cohesive, and resistant to flow
3. pH
 Ranges from 7.35- 7.45, averaging 7.4

30. Characteristics of Blood cont’d
4. Volume
 5-6 liters in adult male
 4-5 liters in adult female
 differences between genders reflect differences in
body size
 Blood volume (BV) can be estimated by calculating
7% of the body wt in Kg
 E.g. 75 Kg individual would have a BV of
approximately 5.25 liters (~1.4 gallons)
 Hypovolemic = below normal
 Normovolemic = normal
 Hypervolemic = above normal
 Abnormally high BV can place severe stress on
the heart

31. 2.3. Function of Blood
 Transportation
 O2 to tissues & CO2 from tissues to lung
 Nutrients from GIT to cells
 Heat and waste products from cells for excretion
 Hormones from endocrine glands to other body cells
 Regulation
 pH
 Temperature
 Osmotic pressure (influence water and ion content of
cells)

32. Function of Blood cont’d
 Protection
 From bleeding (by the clotting mechanism)
 Immunity (phagocytes, lymphocytes, antibodies,
complement proteins, etc)

33. 2.4. Formation and Regulation of Blood
Cells production
 Hematopoiesis / Hemopoiesis
 is the process of blood cell formation, differentiation
and development
 Origin of Blood cells
 There have been two theories
 Monophyletic theory – all blood cells originate from
a single mother cell
 Polyphyletic theory – several mother cells give rise
to the different cell lineages
 monophyletic theory is accepted by many
hematologists

34. Flow diagram of the monophyletic theory

35. Hematopoiesis cont’d
 According to this theory:
 all blood cells (RBC, WBC, PLT) originated from a
Pluripotent stem cell (PSC)
 PSC is the first in a sequence of regular and orderly
steps of cell growth and maturation
 Depending on the conditioning stimuli and mediators
(colony-stimulating factors, erythropoietin, interleukin,
etc.), PSCs mature along morphologically and
functionally diverse lines

36. Hematopoiesis cont’d
 PSCs:
 Produce other stem cells and self-regenerate
maintaining their original numbers (self renewal), or
 Differentiate into:
 Lymphoid cell line for lymphopoiesis
 Myeloid cell line for myelopoiesis
 is a multipotent stem cell (MSC) capable of
granulopoiesis, erythropoiesis and
thrombopoiesis.
 The MSC will first give rise to CFU-GEMM

37. Hemopoiesis cont’d
 In response to specific cytokines, CFU-GEMM produces
erythroid, granulocytic (Eos, Baso, Neut),
Monocyte/macrophage and megakaryotic cells.
 The Lymphoid stem cell (LSC) differentiates into a
committed pre-B and Pre-T cells that from B & T
lymphocytes

39. Stages in hemopoietic cell development

40. 2.4.1. Sites of Hemopoiesis
 The sites of blood cell development follow a definite
sequence from embryonic life to fetal life, to childhood, and
to adult life.
 Fetus:
1. Embryonic Yolk sac
 Is the site where mesoblastic phase of hemopoiesis
occurs
 Dominates during the first 2-8 weeks of life
 the earliest hemopoietic cells to be produced are the
primitive erythroid precursors (in 2 weeks old
embryo)
 Stops at 8 -10 weeks of gestation

41. Sites of Hemopoiesis cont’d
2. Liver and spleen:
 gradually replace yolk sac
 are the sites where the hepatic phase of
hemopoiesis takes place
 Liver is major site by the 2nd month
 appearance of granulocytes and megakaryocytes.
 Liver and spleen predominate 2-5 months
 Production in the liver tails off within 1-2 weeks of
delivery
3. Bone marrow:
 begins in the 4th month
 After 5th month, it is the primary site of hemopoiesis

42. Site of hemopoiesis

43. Stages/Phases of hemopoiesis in the
embryo and fetus
 Stages of hemopoiesis in the embryo and fetus, indicating the
comparative participation of the chief centers of hematopoiesis and
the approximate times at which the different types of cells make their
appearance
Months

44. The Bone marrow during infancy,
childhood and adulthood
 In infancy
 Red & hematopoietic (active)
 During childhood
 Replacement of red marrow with fatty tissue
 During Adulthood
 The marrow of the central skeleton (vertebrae,
sternum) & proximal ends of long bones (femurus,
humurus) consist of 50% fatty space
 BM cavities in body contain non-hematopoietic fatty
marrow

45. Medullary hemopoiesis
 Blood cell production within the bone marrow
(medulla)

46. Extramedulary hemopoiesis
 Formation of apparently normal blood cells outside the
confines of the bone marrow mainly in the liver and
spleen in post fetal life is known as Extramedullary
Hemopoiesis.
 Occurs when the bone marrow becomes
dysfunctional e.g., aplastic anemia, infiltration by
malignant cells, or over proliferation of a certain cell
(e.g. leukemia)
 When the bone marrow is unable to meet increased
demand for cells, e.g., hemolytic anemia
 If extramedulary hemopoiesis develops, the liver
and spleen are enlarged (hepatosplenomegaly)

47. Extramedulary hemopoiesis

48. 2.4.2. The Hemopoietic Microenvironment
 Hemopoiesis occurs in a microenvironment in the bone
marrow:
 in the presence of fat cells, fibroblasts and
macrophages
 on a bed of endothelial cells
 The medullary cavities contain:
 vascular spaces (sinuses)
 hematopoietic cells , and
 specialized stromal cells of various types.
 All the cells form a complex microenvironment, with
numerous intricate and interdependent relationships
between stromal cells and hematopoietic cells (see
fig).

49. Hemopoietic Microenvironment cont’d
 an extracellular matrix of fibronectin, collagen and
laminin combines with these cells to provide a setting in
which stem cells can grow and divide.

50. Bone marrow biopsy
 The clear space is an adipocyte
 the large cells with abundant pink cytoplasm and folded
nuclei are megakaryocytes;
 the small cells with opaque dark nuclei are late-stage
erythroid precursors;
 the cells with folded or bent nuclei are granulocytes.

51. Bone Marrow Microenvironment cont’d
 Hemopoietic Cords (parenchyma) are the
extravascular portions of the bone marrow and the site of
blood cell production
 Sinuses (vascular spaces) of the marrow are lined
with specialized endothelial cells, which prevent the
premature escape of immature cells into the peripheral
blood.
 The basal lamina is incomplete, allowing mature cells to
pass through the wall of the sinuses.

52. Bone Marrow Microenvironment cont’d
 Stromal Cells compose the supportive tissues of the
bone marrow. Some of these cells produce hemopoietic
growth factors. Examples include:
 Adventitial (reticular) cells:
 Are modified fibroblasts that produce the reticulin
framework of the bone marrow
 Macrophages:
 Produce hemopoietic growth factors
 store iron for hemoglobin production, and
 carry out phagocytosis of debris
 Adipocytes: Store energy in the form of fat

53. 2.4.3. Regulation of Hemopoiesis
 hemopoiesis is maintained in a steady state in
which production of mature cells equals cell loss
 Increased demands for cells as a consequence
of disease or physiologic change are met by
increased cell production.
 system subject to some form of feedback control
which could be exerted by humoral factors, e.g.,
 erythropoietin
 colony-stimulating factors
 growth factors

54. Feed back control e.g.
Increased destruction of red blood cells
(as in hemolytic anemia)
Low blood hemoglobin level
Tissue hypoxia
stimulation of increased erythropoietin
production by the kidneys
Increase in the rate at which committed
progenitor cells divide and differentiate
Hemoglobin level brought to normal

55. Hemopoietic Growth Factors
Factor Function
Stem Cell Growth
Factor (Steel factor)
Stimulates pluripotent hematopoietic stem cells (hemocytoblasts)
Interleukin-3
(multi-CSF*)
Stimulates pluripotent hematopoietic stem cells and progenitors
of eosinophils, neutrophils, basophils, monocytes, and platelets
Granulocyte-
Macrophage CSF
(GM-CSF)
Stimulates development of erythrocytes, platelets, granulocytes
(eosinophils, neutrophils, and basophiles,), and monocytes.
Macrophage CSF
(M-CSF)
Stimulates development of monocytes and macrophages
Granulocyte CSF
(G-CSF)
Stimulates development of neutrophils
Interleukin-5 Stimulates development of eosinophils
Interleukin-7 Stimulates development of B lymphocytes
*CSF=Colony stimulating factor

56. Hemopoietic Growth Factors and site
of action

57. Summary of Hematopoiesis showing site of action of
growth factors
 GEMM=
Granulocyte/erythroid/m
onocyte/megakaryocyte
precursor
 GM=
Granulocyte/monocyte
precursor
 GM-CSF= Granulocyte-
macrophage colony-
stimulating factor
 G-CSF= Granulocyte
colony stimulating factor
 IL-2= Interleukin 2
 IL-3= Interleukin 3
 IL-5= Interleukin 5
 IL-6= Interleukin 6

58. 2.4.4. Maturation Characteristics
 Blood cells go through maturation stages in the bone
marrow and are released into the blood at maturity to
perform their function
 In any cell series, a progression of cells exists between
the most immature ‘blast’ cell and the mature cells
 Sometimes, it is difficult to know what stage is
represented by a particular cell
 The general rule is to identify the cell as the most
mature form.

59. Identification of cells
 Main features to identify cells on a Wright’s- stained
smear are:
 Size of the cell
 Nuclear-cytoplasmic ratio
 Nuclear characteristics
 Chromatin pattern
 Nuclear shape
 Presence of nucleoli
 Cytoplasmic characteristics
 Color
 Granulation
 Vacuoles
 Shape

60. Identification of cells cont’d
Changes With maturation:
 Size of the cell decreases
 Nuclear:cytoplasmic ratio decreases from 4:1 or 3:1 to
2:1 or 1:1 in most cases
 Exceptions:
 erythrocytes and thrombocytes have no nuclei
 Small lymphocytes frequently retain the original
ratio
 Nuclear characteristics
 Chromatin pattern becomes more coarse and dense
 Nuclear shape changes to many lobes or segments
(in Granulocytes)
 Nucleoli disappear

61. Changes With maturation cont’d
 Cytoplasmic characteristics
 Color changes from deep blue color in the blast
stage to:
 lighter blue (e.g. lymphocytes)
 blue-gray (e.g. moncytes) or
 pink (e.g. RBC)
 Granulation: in the granulocytic series changes
from no granules in the blast stage to non-specific
granules then to specific granules

62. Changes With maturation cont’d
 Cytoplasmic characteristics cont’d
 Vacuoles: vacuolation increases as the white cells
age (except for monocytes which frequently have
vacuoles throughout their life cycle)
 Shape: change of shape seen in the
megakaryocyte. It has more irregular outline
 In identifying of cells, examine more systematically
by assessing various maturational features

63. Blast Cell Characteristics
 In blood cells developmental stages, the earliest
morphologically identifiable precursor is the blast cell
 Blast cell:
 is a large cell
 has round nucleus with fine chromatin and nucleoli,
 has small amount of dark blue (Wright’s stain)
cytoplasm,
 is10-20 μm in diameter with high nuclear/cytoplasmic
(N/C) ratio
 Additional tests are needed to identify blasts in malignant
situations, such as the leukemias.
 The number of nucleoli varies depending on the cell type,
as in the following examples:

64. Blast Cell Characteristics cont’d
 Myeloblast: contains 1-5 nucleoli
 Lymphoblast: 1-2 nucleoli
 Monoblast: 1-2 nucleoli, but occasionally 3-4
 Erythroblast may have up to 2 that may stain darker
than other types of blast cells
 Megakaryoblast: has 1-5 nucleoli

65. Production Of Specific Cell Lines:
Erythrocyte Production (Erythropoiesis)
 Erythropoiesis is the production of red cells
 Begins with the development of primitive erythrocytes in
the embryonic yolk sac
 Basic substances needed: are amino acids (proteins),
iron, Vit B12, Vit B6, folic acid and the trace minerals
cobalt and nickel
 Regulated by erythropoietin, a glycoprotein primarily
produced by the kidneys in response to tissue hypoxia.
(10-15% production of erythropoietin occurs in the liver)
 Androgen and thyroid hormones can also stimulate
erythropoiesis

66. Erythropoiesis cont’d
 Erythroid precursors are derived from the CFU-GEMM
 The earliest progenitor committed exclusively to
erythroid lineage is the burst-forming unit–erythroid
(BFU-E)
 This stage is followed by the colony-forming unit–
erythroid (CFU-E)
 The earliest recognizable RBC precursor is the
proerythroblast, which is characterized by fine
nuclear chromatin and intensely blue cytoplasm

67. Pronormoblast/Proerythroblast
(Rubriblast)
 Pronormoblast is the earliest morphologically
recognizable red cell precursor.
 Size: 20-25m in diameter.
 Nucleus:
 large, round to oval
 contains 0-2 light bluish, indistinct nucleoli
 The chromatin forms a delicate network giving the
nucleus a reticular appearance.
 Cytoplasm:
 there is a narrow (about 2m) rim of dark marine blue
cytoplasm
 There may be a perinuclear halo
 The N:C ratio is about 4:1

68. Basophilic Normoblast/prorubricyte
 Size: 16-18m in diameter.
 Nucleus:
 Round or oval and smaller than in the previous stage
 The chromatin forms delicate clumps so that its
pattern appears to be denser and coarser than that
seen in the pronormoblast.
 No nucleoli are seen.
 Cytoplasm:
 Slightly wider ring of deep blue cytoplasm than in the
pronormoblast
 There may be a perinuclear halo
 The N:C ratio is about 4:1

69. Polychromatophilic Normoblast/
Rubricyte
 Size: 12-14m in diameter
 Nucleus:
 smaller than in the previous cell
 has a thick membrane
 contains coarse chromatin masses
 Cytoplasm:
 as the nucleus is shrinking the band of cytoplasm is
widening
 It has a lilac (polychromatic) tint because of beginning
of hemoglobinization (blue layered with tinges of
orange red
 The N:C ratio varies from 2:1 to 4:1.

70. Orthochromatic Normoblast
 Size: 10-12m in diameter.
 Nucleus:
 small and central or eccentric with condensed homogeneous
structureless chromatin.
 It is ultimately lost by extrusion.
 Cytoplasm:
 a wide rim of pink cytoplasm surrounds the shrinking nucleus
 The entire cell is somewhat smaller than the polychromatophilic
normoblast
 The N:C ratio varies from 1:2-1:3.

71. Reticulocyte
 Is a large somewhat basophilic anuclear cell formed
after the expulsion of the nucleus
 Remnants of RNA visualized as reticulum,
filamentous structure, in chains or as a single dotted
structure when stained with new methylene blue
 In Wright’s stain seen as large bluish-red cell,
Polychromatophilic macrocytes
 This network is responsible for the name of the cell
and consists of precipitated ribosomes.

72. Reticulocyte cont’d
 As the bone marrow reticulocyte matures the
network becomes smaller, finer, thinner, and finally
within 3 days disappears
 About 1% of reticulocytes enter the peripheral
circulation
 Size: 8-10m in diameter
 Nucleus: the reticulocyte does not contain a
nucleus.
 Cytoplasm: faintly basophilic (blue)

73. Mature erythrocyte
 Size: 7-8m in diameter
 Cytoplasm:
 Biconcave disc-shaped cell filled with hemoglobin
 orange-pink with a pale staining center occupying
one-third of the cell area (central pallor)

74. Erythropoiesis cont’d

75. Regulation of Erythropoiesis
 Erythropoietic activity is regulated by the hormone
erythropoietin which in turn is regulated by the level of
tissue oxygen
 Erythropoietin:
 a heavily glycosylated hormone (40% carbohydrate)
with a polypeptide of 165 amino acids
 Normally, 90% of the hormone is produced in the
peritubular (juxtaglomerular) complex of the kidneys
 10% in the liver and elsewhere
 There are no preformed stores of erythropoietin
 the stimulus to the production of the hormone is the
oxygen tension in the tissues (including the kidneys)

76. Regulation cont’d
 Erythropoietin production increases when there is tissue
hypoxia due to:
 Low blood hemoglobin levels (e.g., anemia)
 Impaired oxygen release from hemoglobin for some
structural or metabolic defects (e.g., the
hemoglobinopathies)
 Poor blood flow as in severe circulatory defects
 Low atmospheric oxygen (e.g., high altitude)
 The produced erythropoietin stimulates erythropoiesis
by increasing the number of progenitor cells committed
to erythropoiesis

77. Regulation cont’d
 Erythropoietin accelerates nearly every stage of red cell
production:
 It increases the rate at which the committed stem cells
divide and differentiate
 It increases the rate of cell division
 It speeds up the incorporation of iron into the
developing red cells
 It shortens the time cell maturation, and
 It hastens the entry of reticulocytes into the peripheral
circulation

78. Regulation cont’d
 On the other hand, reduced erythropoietin activity is due
to increased oxygen supply to the tissues resulted from:
 Increased red cell mass (e.g., polycythemia)
 Ability of hemoglobin to release oxygen to the tissues
more readily than normal

79. Ineffective erythropoiesis/Intramedullary
hemolysis
 Erythropoiesis is not entirely efficient since 10-15% of
eryhtropoiesis in a normal bone marrow is ineffective,
 the developing erythroblasts die within the marrow
without producing mature cells
 Together with their hemoglobin, they are ingested by
macrophages
 This process is substantially increased in a number of
anemias.

80. Megaloblastic Erythropoiesis
 Megaloblasts are pathologic cells that are not present
in the normal adult bone marrow
 their appearance is caused by a deficiency in vitamin
B12 or folic acid or both
 Deficiency of these vitamins leads to defective DNA
synthesis
 In megaloblastic erythropoiesis, the nucleus and
cytoplasm do not mature at the same rate
 Thus nuclear maturation lags behind cytoplasmic
hemoglobinization

81. Megaloblastic Erythropoiesis cont’d
 This nuclear lag appears to be caused by
interference with DNA synthesis while RNA and
protein synthesis continue at a normal rate
 The end stage of megaloblastic maturation is the
megalocyte which is abnormally large in size (9-
12m in diameter).

82. Formation of white blood cells
(Leukopoiesis)
 Granulopoiesis and Monocytopoiesis
 Neutrophils and monocytes arise form a common
committed progenitor
 The myeloblast is the earliest recognizable precursor
in the granulocytic series
 on division the myeloblast gives rise to promyelocyte
 The promyelocyte contain abundant dark “azurophilic”
primary granules that overlie both nucleus and
cytoplasm
 with subsequent cell divisions these primary granules
become progressively diluted by the secondary, less
conspicuous “neutrophilic” granules that are
characteristic of the mature cells.

83. Granulopoiesis cont’d
 This concomitant cell division and maturation
sequence continues form promyelocytes to early
myelocytes, late myelocytes, and then
metamyelocytes
 As the metamyelocyte matures the nucleus becomes
more attenuated and the cell is then called a “band” or
“stab” form
 Subsequent segmentation of the nucleus gives rise to
the mature neutrophil or polymorphonuclear leucocyte.

84. Granulopoiesis cont’d
 The average interval from the initiation of
granulopoiesis to the entry of the mature neutrophil
into the circulation is 10 to 13 days.
 The mature neutrophil remains in the circulation for
only about 10 to 14 hours before entering the tissue,
where it soon dies after performing its phagocytic
function.

85. Myeloblast
 is the earliest recognizable precursor in the granulocytic
series
 Size and shape:
 12-20 m in diameter
 round or oval in shape.
 Nucleus:
 large, oval or round, and eccentric.
 has a thin nuclear membrane
 has finely dispersed, granular, purplish, pale chromatin
with well-demarcated, pink, evenly distributed
parachromatin
 2-5 light blue-gray nucleoli surrounded by dense
chromatin are seen

86. Myeloblast cont’d
 Cytoplasm:
 is small in comparison to the nucleus
 High N:C ratio of 7:1
 stains basophilic (bluish) and shows a small indistinct,
paranuclear, lighter staining halo (golgi apparatus)
 the cytoplasm lacks granules.

87. Promyelocyte
 larger than the myeloblast
 Size and Shape:
 15-20m in diameter and round or oval in shape.
 Nucleus:
 still large but is beginning to shrink
 round or oval, eccentric, possibly slightly indented,
and surrounded by a thin membrane
 1-3 nucleoli may be faintly visible within the finely of
granular purplish pale chromatin,

88. Promyelocyte cont’d
 Cytoplasm:
 pale blue
 some what larger than in myeloblast, so the
nuclear/cytoplasmic ratio is 4:1 or 5:1
 the basophilia is not quite as intense as in
myeloblasts
 contain abundant dark “azurophilic” primary granules
that overlie both nucleus and cytoplasm
 these non-specific, peroxidase-containing azurophilic
granules are characteristic of the promyelocyte stage
of development

89. Myelocyte
 Is the last stage capable of cell division
 Size and shape:
 10-18m in diameter and round.
 Nucleus:
 Condensed, oval, slightly indented, and eccentric
 The chromatin is coarse
 Nucleoli are absent.
 Cytoplasm:
 Light pink and contains neutrophilic granules
(brownish)
 Granules that may cover the nucleus and are
coarse in the younger cells but become finer as the
cell matures.
 The N:C ratio is about 2:1 or 1.5:1

90. Metamyelocyte (Juvenile cell)
 Size and shape:
 10-15m in diameter and round.
 Nucleus:
 Eccentric, condensed, and indented or kidney-shaped
 The nuclear membrane is thick and heavy, and the
chromatin is concentrated into irregular thick and thin
areas.
 Cytoplasm:
 abundant and pale or pink
 contains both specific and non-specific (few) granules
that in the neutrophilic metamylocytes vary in size,
whereas the basophilic and eosinophilic granules are
large and equal in size.
 The NC ratio is 1:1

91. Band Granulocyte (Stab Cell)
 The juvenile cell or the band cell are the youngest
granulocytes normally found in the peripheral blood.
Size: 9-15m in diameter
Nucleus:
 elongated, curved and usually U shaped, but it may be
twisted
 It is not segmented but may be slightly indented at one
two points
 The chromatin is continuous thick and coarse, and
parachromatin is scanty.
Cytoplasm:
 contains specific and a few non-specific granules
 is pink or colorless.
 The N:C ratio is 1:2

92. Segmented granulocyte
 Size:
 0-12m in diameter.
 Nucleus:
 eccentric with heavy, thick chromatin masses
 It is divided into 2-5 lobes connected to each other by thin
bridges of chromatin membrane
 The ratio of segmented to band forms is of clinical significance
and is normally about 10:1.
 Cytoplasm:
 abundant and slightly eosinophilic (pinkish) or colorless, and
 contains specific granules
 The neutrophilic granules are very fine in texture and do not
overlay the nucleus
 The N:C is 1:2

93. Eosinophilic Granulocyte and
Precursors
 Eosinophils mature in the same manner as neutrophils.
 The eosinophlic myeloblast is not recognizable as such.
 In the eosinophilic promyelocyte stained preparation the
granule are at first bluish and later mature into orange
granules
 The mature eosinophilic granules are
 larger than neutrophilic granules
 round or ovoid
 prominent in the eosinophilic myelocyte.

94. Mature Eosinophil
 Size and shape:
 10-16m in diameter, slightly larger than a
segmented polymorphonuclear granulocyte.
 Nucleus:
 Eccentric
 usually bilobed
 rarely single- or tri-lobed and contains dense
chromatin masses.
 Eosinophils with more than two nuclear lobes are
seen in
 vitamin B12 and folic acid deficiency and
 in allergic disorders.

95. Eosinophil cont’d
 Cytoplasm:
 densely filled with orange-pink specific granules.
 The granules are
 uniform in size
 Large and individualized
 do not cover the nucleus
 Highly metabolic and contain histamine and other
substances

96. Basophilic Granulocyte and Precursors
 The early maturation of the basophilic granulocyte is
similar to that of the neutrophlic granulocyte.
 Mature Basophil
 Size:
 Somewhat smaller than eosiniphils
 measuring 10-14m in diameter
 Nucleus:
 Indented giving rise to an S pattern.
 It is difficult to see the nucleus because it contains less
chromatin and is masked by the cytoplasmic granules.

97. Basophils cont’d
 Cytoplasm:
 Pale blue to pale pink
 contains granules that often overlie the nucleus but
do not fill the cytoplasm as completely as the
eosinophilis granules do

98. Monocytes and their Precursors
Monoblast
 Since the monoblast cannot be differentiated from the
myeloblast on morphologic or histochemical criteria, one
may assume that the myeloblast can give rise to myeloid
and monocytic cells.
 Size: 15-20m in diameter.
 Nucleus:
 Round or oval and at times notched and indented
 The chromatin is delicate blue to purple stippling with
small regular, pink, pale or blue parachromatin areas
 The nucleoli (3-5 in number) are pale blue, large and
round

99. Monoblast cont’d
 Cytoplasm:
 Relatively large in amount
 May contains a few azurophilic granules (rare)
 Stains pale blue or gray
 The cytoplasm filling the nucleus indentation is lighter
in color than the surrounding cytoplasm
 The surrounding cytoplasm may contain Auer bodies.

100. Promonocyte
 Is the earliest monocytic cell recognizable as
belonging to the monocytic series
 is capable of mitotic division
 Its product, the mature monocyte, is only capable of
maturation into a macrophage
 Size:
 12-20m in diameter.

101. Promonocyte cont’d
 Nucleus:
 Large
 ovoid to round, convoluted, grooved, and indented
 The chromatin forms a loose open network containing
a few larger clumps
 there may be two or more nucleoli.
 Cytoplasm:
 sparse, gray-blue, contains fine azurophilic granules
 N:C ratio is about 3:1

102. Monocyte
 Size:
 12-20m in diameter.
 Nucleus:
 Eccentric or central
 Takes different shapes from brainy convolutions to
lobulated and S shaped (often lobulated)
 The chromatin network consists of fine, pale, loose,
linear threads producing small areas of thickening
at their junctions
 No nucleolus is seen
 The overall impression is that of a pale nucleus
quite variable in shape.

103. Monocyte cont’d
 Cytoplasm:
 Abundant, opaque, gray-blue with moderate
granules
 unevenly stained and may be vacuolated
 N:C ratio 1:1

104. Lymphopoiesis
 The precursor of the lymphocyte is believed to be the
primitive mulipotential stem cell that also gives rise to the
pluirpotenital myeloid stem cell for the granulocytic,
erythyroid, and megakaryocytic cell lines
 Lymphoid precursor cells travel to specific sites
 There, they differentiate into cells capable of either
expressing cell-mediated immune responses or
secreting immunoglobulins
 The influence for the former type of differentiation in
humans is the thymus gland;
 the resulting cells are defined as thymus-dependent
lymphocytes, or T cells.

105. Lymphopoiesis cont’d
 The site of the formation of lymphocytes with the
potential to differentiate into antibody-producing cells
has not been identified in humans, although it may be
the tonsils or bone marrow
 In chickens it is the bursa of Fabricius, and for this
reason these bursa-dependent lymphocytes are called
B cells
 B cells ultimately differentiate into morphologically
distinct, antibody-producing cells called plasma cells.

106. Lymphocytes and Precursors
Lymphoblast
 Size:
 10-20m in diameter.
 Nucleus:
 Central, round or oval
 the chromatin has a stippled pattern
 The nuclear membrane is distinct and one or two pink
nucleoli are present and are usually well outlined
 Cytoplasm:
 Non-granular and sky blue
 may have a deep blue border
 It forms a thin perinuclear ring.
 N:C ratio 4:1

107. Prolymphocyte
 Size:
 9-18m in diameter.
 Nucleus:
 Oval but slightly indented
 may show a faint nucleolus
 The chromatin is slightly condensed into a mosaic
pattern.
 Cytoplasm:
 Gray blue, mostly blue at the edges
 may show a few azurophilic granules and vacuoles

108. Lymphocytes
 There are two varieties
 the morphologic difference lies mainly in the amount of
cytoplasm
Small Lymphocyte
 Size:
 7-18m in diameter.
 Nucleus:
 round or oval to kidney shaped
 occupies nine tenths of the cell diameter
 The chromatin is dense and clumped
 A poorly defined nucleolus may be seen.

109. Lymphocytes cont’d
 Cytoplasm:
 It is basophilic and forms a narrow rim around the
nucleus or at times a thin blue line only with few
azurophilic red granules
 N:C ratio is 4:1
 Distinguishing characteristics of a small lymphocyte:
 clumping of chromatin around the nuclear membrane
may help to distinguish this from a nucleated red cell

110. Large Lymphocyte
 Size:
 9-12m in diameter
 Nucleus:
 the dense, oval, or slightly indented nucleus is
centrally or eccentricity located
 Its chromatin is dense and clumped.
 Cytoplasm:
 Abundant
 gray to pale blue, unevenly stained, and streaked at
times
 A few azurophilic granules are contained in 30-60% of
the cells.
 These are large granular lymphocytes (LGLs).

111. Large Lymphocyte cont’d
 N:C ratio is 4:1
 Distinguishing characteristics: Cytoplasm is mor
abundant with tendency for azurophilic granules

112. Formation of platelets (Thrombopoiesis)
 Platelets are produced in the bone marrow by
fragmentation of the cytoplasm of megakaryocytes
 The precursor of the megakaryocyte-the
megakaryoblast-arises by a process of differentiation for
the hemopoietic stem cell
 The megakaryoblast produces megakaryocytes,
distinctive large cell that are the source of circulating
platelets.
 Megakaryocyte development takes place in a unique
manner.
 The nuclear DNA of megakaryoblasts and early
megakaryocytes reduplicates without cell division, a
process known as endomitosis.

113. Thrombopoiesis cont’d
 As a result, a mature megakaryocytes has a polyploidy
nucleus, that is, multiple nuclei each containing a full
complement of DNA and originating from the same
locust within the cell.
 Mature megakaryocytes are 8 n to 36 n.
 The final stage of platelet production occurs when the
mature megakaryocyte sends cytoplasmic projections
into the marrow sinusoids and sheds platelets into the
circulation.

114. Thrombopoiesis cont’d
 It takes approximately 5 days from a megakaryoblast to
become a mature megakaryocyte.
 Each megakaryocyte produces from 1000 to 8000
platelets.
 The platelet normally survives form 7 to 10 days in the
peripheral blood.

115. Morphology of the Platelets and their
Precursors
Megakaryoblast
 Size:
 ranges from 10-30m in diameter.
 The cell is smaller than its mature forms but larger
than all other blast cells.
 Nucleus:
 the single, large, oval or indented nucleus has a loose
chromatin structure and a delicate nuclear membrane
 Multi-lobulated nuclei also occur representing a
polyploid stage.
 Several pale blue nucleoli are difficult to see
 The parachromatin is pink.

116. Megakaryoblast cont’d
 Cytoplasm:
 the cytoplasm forms a scanty, bluish, patchy, irregular
ring around the nucleus
 The periphery shows cytoplasmic projections and
pseudopodia like structures.
 The immediate perinuclear zone is lighter than the
periphery.

117. Promegakaryocyte
 Size:
 ranges from 20-50m in diameter.
 It is larger than the megakaryoblast
 in the process of maturation it reaches the size of the
stage III cell.
 Nucleus:
 large, indented and poly-lobulated.
 the chromatin appears to have coarse heavily
stained strands and may show clumping
 The total number of nucleoli is decreased and they
are more difficult to see than in the blast cell.
 The chromatin is thin and fine.

118. Promegakaryocyte cont’d
 Cytoplasm:
 intensely basophilic
 filled with increasing numbers of azurophilic
granules radiating from the golgi apparatus toward
the periphery sparing a thin peripheral ring that
remains blue in color.

119. Granular Megakaryocyte
 The majority of the megakaryocytes of a bone marrow
aspirate are in stage III which is characterized by
progressive nuclear condensation and indentation and the
beginning of platelet formation within the cytoplasm.
 Size:
 ranges from 30-100m in diameter
 is the largest cell found in the bone marrow.
 Cytoplasm:
 a large amount of polychromatic cytoplasm produces
blunt, smooth, pseudopodia-like projections that contain
aggregates of azurophilic granules surrounded by pale
halos
 These structures give rise to platelets at the periphery of
the megakaryocytes.

120. Platelets
 Size:
 varies from 1-4m in diameter.
 Nucleus:
 no nucleus is present.
 In Wright - Giemsa stained films, platelets appear as
small, bright azure, rounded or elongated bodies with
a delicately granular structure.

121. Review Questions/Summary
1. What is hemopoiesis and how is the process regulated?
2. What are the hemopoietic tissues during fetal life, in
infancy, in childhood and in adulthood?
3. What are the effects of the hormone erythropoietin on
red cell development and maturation.
4. Describe the microenvironment briefly.
5. Explain megaloblastic erythropoiesis.
6. Describe general Characteristic feature of cells during
maturation (nuclear , cytoplasmic, etc )
7. State the composition of blood.
8. State the main functions of blood.
9. List main characteristics of blood.
10. What is extramedulary hemopoiesis and when does it
occur?