Erythropoiesis is the process of red blood cell formation that occurs in bone marrow. It involves stem cells maturing through several stages over 7-9 days to become reticulocytes and then erythrocytes. The cytoplasm changes color as maturation occurs and cell size decreases as the nucleus is lost. Erythropoietin produced by kidneys is the major hormonal regulator of erythropoiesis, stimulating stem cell development and red blood cell maturation. A variety of nutritional and environmental factors can also influence erythropoiesis.

1. ERYTHROPOIESIS
Dr. JILSHA

2. OBJECTIVES
To get a better understanding of :
 Definition of erythropoiesis
 Stages of erythropoiesis
 Description of various cell stages
 Duration of erythropoiesis
 Factors affecting erythropoiesis
 Description of erythropoietin

3. INTRODUCTION
 The process of formation of Red Blood Cells
(RBCs) is called Erythropoiesis.
 It is a part of the process of development of
blood cells called Hematopoiesis which
include:
 Erythropoiesis
 Leucopoiesis – formation of White Blood
Cells
 Thrombopoiesis – formation of platelets

4. STAGES OF ERYTHROPOIESIS
 There are three stages of erythropoiesis:
 Mesoblastic stage
 Medullary stage and
 Hepatic stage
 MESOBLASTIC STAGE
 During intrauterine life, erythropoieisis first
takes place in the mesoderm of yolk sac &
mesoderm of the body. This is mesoblastic stage.
 During this stage, erythropoiesis is
intravascular.
 This takes place in the first 2 months of
gestation.

5. CONTD..
 HEPATIC STAGE
 From the 5th week of gestation, erythropoiesis
takes place in the liver & spleen. This is the
hepatic stage.
 MEDULLARY STAGE
 From the 5th month of gestation, erythropoiesis
takes place in the bone marrow – medullary
stage.
 It is usually slow in the 2nd trimester and
becomes more effective in the third trimester.

7. CONTD..
 After birth bone marrow becomes the sole site
of erythropoiesis.
 In young children, active hematopoietic bone
marrow is found in both axial skeleton and
bones of extremities.
 The active hematopoietic bone marrow is red
in color due to marked cellularity – Red bone
marrow.
 However, there occurs a progressive fatty
replacement throughout the long bones
converting red bone marrow to the yellow
bone marrow.

8. CONTD..
 After 20-30 years, erythropoiesis is mostly
limited to sternum, ribs, vertebrae, skull, pelvic
and pectoral girdles.

10. STEPS OF ERYTHROPOIESIS
 There are four major cell stages
 Stem cells
 Progenitor cells
 Precursor cells and
 Mature cells.
 During erythropoiesis, following cellular changes takes
place :
 Cell size progressively decreases.
 Size of nucleus and no. of nucleoli decreases.
 Chromatin material condenses and nucleus
disappears.
 Staining reaction of cytoplasm – deep basophilic to
acidophilic

11. STEM CELLS
 Pluripotent stem cells are the mother stem
cells that form stem cells for different cell
lines.
 It possess two fundamental properties :
 Self replication – they are capable of
giving rise to more stem cells
 Differentiation – they have the ability to
differentiate into specialized cells called
progenitor cells.

13. COMMITED STEM CELLS
 These cells develop from pluripotent stem
cells.
 They are of two categories :
 Myeloid stem cell and
 Lymphoid stem cell
 Myeloid stem cells form erythroid series,
monocytic granulocytic series and
megakaryoid series.
 Erythroid stem cells give rise to progenitor
cells for erythroid cell lines.

15. PROGENITOR CELLS
 Have the ability to give rise to clones.
 They are of two types:
 BFU – E (Burst Forming Units)
 CFU – E (Colony Forming Units)
 BFU – E & CFU – E develop from CFU –
Mg/E (Megakaryoid/Erythroid)
 BFU – E give rise to large number of CFU –
Erythroid cells.
 CFU – E give rise to Blast cells.

16. PRECURSOR CELLS/BLAST CELLS
 The precursors for erythrocytes –
erythroblasts or normoblasts.
 Normoblasts develop from pronormoblasts.
 Normoblasts have three successive forms :
 Early normoblasts
 Intermediate normoblasts and
 Late normoblasts.

17. PRONORMOBLAST
 First blast cells to appear in the Bone Marrow and
the first identifiable cells of erythroid series.
 MORPHOLOGICAL FEATURES
1. Size : 15 – 20 µm.
2. Shape : irregularly rounded or slightly oval
3. Cytoplasm : Less, Basophilic due to the
presence of polyribosomes, high content of
RNA.
4. Nucleus : Large, multiple nucleoli.
5. Mitosis +
6. Hb : not yet formed.

19. EARLY/ BASOPHILIC NORMOBLAST
 Pronormoblast progresses into early
normoblast.
 MORPHOLOGICAL FEATURES
1. Size : 12–16µm.
2. Shape : irregularly rounded or slightly oval
3. Cytoplasm : Scanty, Blue, Basophilic.
4. Nucleus : Large, Chromatin strands are
thicker.
5. Mitosis +
6. Hb : not present.

21. INTERMEDIATE NORMOBLAST
 This appears following mitotic division of
early normoblast.
 Also called as polychromatophilic
normoblast.
 MORPHOLOGICAL FEATURES
1. Size : 10 – 14 µm.
2. Cytoplasm : polychromatophilic (contains
admixture of basophilic RNA and
acidophilic Hb )

22. 3. Nucleus : Coarse, condense, deeply
basophilic with no nucleoli.
4. Mitosis +
5. Hb : appears.

23. LATE NORMOBLAST
 Last nucleated cell of erythrocyte series.
 Also called as orthochromatophilic normoblast.
 MORPHOLOGICAL FEATURES
1. Size : 8 – 10 µm.
2. Cytoplasm : Deeply acidophilic with diffuse
basophilic hue. It gives an appearance of an
orthochromatic cell.
3. Nucleus : Small, pyknotic with dark chromatin.
4. Mitosis : absent.
5. Hb +

25. RETICULOCYTES
 Immediate precursors of red cells.
 Also called as juvenile red cells.
 MORPHOLOGICAL FEATURES
1. Size : 7 – 7.5 µm.
2. Cytoplasm : Contains small amounts of RNA. With
supravital stains like brilliant cresyl blue, the RNA
appears in the form of reticulum and hence the cell is
called reticulocyte.
3. Nucleus : absent
4. Mitosis : absent.
5. Hb : increases.

27. ERYTHROCYTES
 Final cells in erythropoiesis.
 Reticulocytes spends 1 – 2 days in the marrow
and circulate for 1 – 2 days in the peripheral
blood before maturing to form erythrocytes.
 MORPHOLOGICAL FEATURES
1. Size : 7.5 µm.
2. Shape : Biconcave disc
3. No nucleus
4. Hb : +

30. FATE OF ERYTHROCYTES
 Ageing erythrocytes are destroyed, often in
the spleen, after an average life span of 120
days.
 The phagocytic cells of reticulo endothelial
system degrade the haemoglobin released,
with iron from the haem and amino acids
from the globulin molecules being recycled.
 The porphyrin ring is converted into
bilurubin, which is further metabolized by
the liver and then excreted in the bile.

31. APPLIED ASPECTS
Increase in erythrocytes –
polycythemia
Decrease in erythrocytes –
Anemia

32. DURATION
 The total period of erythropoiesis is 7 – 9
days.
 It takes 5 – 7 days for progenitor cells to
become reticulocytes and another 2 days
for reticulocytes to become red cells.

33. FACTORS CONTROLLING ERYTHROPOIESIS
 Hormonal
 Erythropoietin (EPO)
 Interleukins and GM – CSF
 Androgen and estrogen
 Dietary
 Iron
 Vit B12 and folic acid
 Proteins
 Vitamin C
 Copper, cobalt
 Other factors
 Environmental
 Drugs and chemicals

34. HORMONAL FACTORS
ERYTHROPOIETIN
 In 1906, Carnot and Deflandre proposed an alternate
mechanism for hypoxic induction of erythropoiesis.
They observed an increase in red blood cell counts
following infusion of normal rabbits with serum from
anemic animals and concluded that erythropoiesis is
regulated by a humoral “factor” in the plasma which
they called hemopoietin.
 in 1948 two Finnish scientists, Bonsdorff and Jalavisto
continued work on red blood cell production and
called the hemopoietic substance "erythropoietin“.
 In 1957, Jacobson and co-workers found that EPO is
produced by kidneys.

35.  ERYTHROPOIETIN (EPO)
 Also known as hematopoietin.
SOURCE
 Produced mainly by the interstitial cells in
peritubular capillary bed of kidneys.
 Also produced by juxtaglomerular cells and
extraglomerular mesangial cells .
 Kidney – 85% of EPO secretion; Kuppfer cells and
prevenous hepatocytes in Liver – 15% of EPO
production.

36. EPO
STRUCTURE
 EPO is a glycoprotein containing 165 amino acids.
 Molecular weight – 34,000 Dalton.
STIMULUS FOR PRODUCTION
 RBC function – supply O2 to the tissues.
 Whenever there’s hypoxia / decrease in the no. of
RBCs, there occurs a release of renal erythropoietin
factor.
 If the no. of RBCs is more, EPO formation is less.

37. EPO
MECHANISM OF ACTION
 Hypoxia → ↑ release of Hypoxia Inducible Factor
(HIF -1)
 HIF – 1 binds to Hypoxia Response Element (HRE)
of EPO gene that ↑ synthesis of EPO.
 EPO binds to receptors in the target cells.
 The receptors have tyrosine kinase activity and
activates a cascade of serine and threonine kinases
resulting in the growth & development of target
cells.
 Thus, EPO ↑ committed stem cells which mature to
erythrocytes.

39. APPLIED ASPECT
As kidney is the main source of EPO,
chronic renal diseases that reduce renal
mass produce anemia.
Anemia is also caused following
nephrectomy since the amount
produced by Liver doesn’t meet the
needs.

40. EPO
FUNCTIONS
 Stimulates BFU – E & CFU – E to form pro
normoblasts.
 Enhances mitosis.
 Facilitates maturation of normoblasts.
 Increases Hb synthesis in normoblasts.
 Acts on stem cells to promote their transformation
towards erythroid series.
 Stimulates early release of reticulocytes in
circulation.

41. EPO
REGULATION
Factors that ↑ EPO
 Hypoxia, Anemia, ↓ Blood volume, Lung diseases.
 Hormones like epinephrine, nor epinephrine,
androgen, thyroxine, prolactin.
Factors that ↓ EPO
 Estrogen, theophylline.
METABOLISM
 Inactivated mainly in the liver.
 Half life in circulation is about 5 hrs.

42. HORMONAL FACTORS
 INTERLEUKINS AND GM – CSF
 IL – 1, 3 and 5 produced from T- cells act on stem
cells and convert them to progenitor cells.
 GM – CSF stimulates the production of committed
stem cells.
 ANDROGEN AND ESTROGEN
 Androgen stimulate erythropoiesis. Hence males
have ↑ RBCs
 Estrogen inhibit erythropoiesis by ↓ EPO
production and ↓ hepatic synthesis of globulin.

43. DIETARY FACTORS
 IRON
 Iron is the raw material for synthesis of heme
component of hemoglobin.
 Iron deficiency results in microcytic hypochromic
anemia.
 VIT B12 & FOLIC ACID
 Necessary for the maturation of red cells as they
promote DNA synthesis.
 For synthesis of DNA, thymine is required &
Tetrahydrofolate (THF) is necessary for thymine
synthesis which is formed from folic acid.

44. DIETARY FACTORS
 Folate deficiency leads to arrest of mitosis in
the absence of DNA synthesis.
 Vit B12 promotes conversion of methyl
tetrahydro folate (MTHF) to its active form.
 In Vit B12 deficiency, MTHF accumulates
which leads to arrest of chromosomal
division.
 Megaloblasts are produced in the BM
instead of normoblasts resulting in
Megaloblastic anemia.

45. DIETARY FACTORS
 PROTEINS
 Proteins are essential for the synthesis of globin
component of hemoglobin.
 Protein deficiency is invariably associated with
hypochromic anemia.
 OTHERS
 Vit C helps in absorption of Iron. Vit C deficiency
hence leads to anemia.
 Deficiency of copper and cobalt also leads to anemia.

46. APPLIED ASPECTS
IRON DEFICIENCY ANEMIA
microcytic, hypochromic anemia. Erythrocytes smaller than
normal and contain less hemoglobin than normal.
MEGALOBLASTIC ANEMIA
macrocytic anemia Abnormal erythrocytes precursors
(abnormally large erythrocytes) are found in the marrow.

47. OTHER FACTORS
 ENVIRONMENTAL FACTORS
 High altitude leads to hypoxia which
increases erythropoiesis.
 DRUGS & CHEMICALS
 Catecholamine, thyroxine, cobalt salts etc
influence erythropoiesis.

48. DYSERYTHROPOIESIS
Defective erythropoiesis is known
as dyserythropoiesis in which red blood cells
produced in the bone marrow are destroyed
before their release or have short life span after
entering circulation. Dyserythropoiesis
includes irregular nuclearity, budding nuclei,
multinuclearity, megaloblastoid changes, and
ring sideroblasts. Seen in megaloblastic anemia,
thalassemia, congenital dyserythropoietic
anemia etc.,

49. SUMMARY
 The process of formation of Red Blood Cells is
called Erythropoiesis which is a part of
hematopoiesis.
 Bone marrow becomes the sole site of
erythropoiesis in adults.
 The stem cells give rise to normoblasts which
mature to reticulocytes and then erythrocytes.
 The cytoplasm changes from basophilic to
acidophilic, the cell size decreases, nucleus
disappears and Hb appears.
 There are several factors affecting erythropoiesis
and EPO plays a major role.
 RBCs are destroyed in the spleen.