Erythropoiesis

1. Erythropoiesis
Dr. Sai Sailesh Kumar G
Associate Professor
Department of Physiology
RDGMC
DR Sai Sailesh Kumar G 1

2. Learning objectives
 Describe the stages of development of RBCs
 Describe the factors regulating erythropoiesis
 Describe the sources of erythropoietin and its
role in erythropoiesis
DR Sai Sailesh Kumar G 2

3. Introduction
 Erythropoiesis means production of matured
erythrocytes. ( Duration about 7 days)
 RBC count is high in infants and decreases as age
advances
 At birth, RBC count is 8-10 millions/cubic mm of
blood
 Within 10 days after birth, the count decreases due
to rapid destruction of erythrocytes
 Slight increase in serum bilirubin levels
 Physiological jaundice in new born
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4. Why erythropoiesis is needed
 Life span of RBC’s is 120 days.
 Tremendous number of RBC’s are normally,
dying daily in our body.
 These dead RBC’s have to be replenished.
 In our body, the intensity of erythropoiesis is
controlled; that is it can be increased or
decreased depending on need of body
(homeostasis of RBC count).
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5. Site of erythropoiesis
 Blood production starts from 3rd week of intra
uterine life
 Between 3rd week to third month: Erythropoiesis
occurs within the blood vessel in the mesoderm of
yolk sac
 In this stage, erythropoiesis occurs intravascular
 This is the only stage when intra vascular
erythropoiesis occurs
 At all other stages, erythropoiesis occurs extra
vascular DR Sai Sailesh Kumar G 5

6. Site of erythropoiesis
 Between 3rd month to fifth month:
Erythropoiesis occurs mainly in the liver and to
some extent in the spleen and lymph nodes.
 This phase is called hepatic phase
 Hepatic phase stops in the fifth month and from
then, erythropoiesis occurs in the bone marrow
 This phase is called myeloid phase
 By the time baby is born, erythropoiesis occurs
in the bone marrow
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7. IN
FETAL
LIFE
MESOBLASTIC
STAGE
HEPATIC STAGE
MYELOID STAGE
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8. Post natal erythropoiesis
 It occurs in the Red Bone Marrow
 Bone marrow is of two types
 Red bone marrow
 Yellow bone marrow
 At birth, all bone marrows are red.
 As age advances, some of the RBM converted
into yellow bone marrow
 At around 20 years, the adult pattern of
distribution of RBM is established
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9. The adult pattern
 The adult RBM is found only
1. in the flat bones (cranial nerves, ribs, sternum,
vertebrae, pelvic bones)
2. in the upper end of the long bones (humerus and
femur)
 The shaft of the long bones (femur or humerus)
normally contain only yellow bone marrow in the adults
 Yellow bone marrow does not produce RBC’s
 When there is necessity of producing more RBC’s, the
yellow bone marrow is again converted into RBM
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10. Histology of RBM
 Granulocytes and precursors 60%
 Erythrocytes and its precursors 20%
 Lymphocytes, monocytes and their precursors 10%
 Others (non-identifiable, degenerate cells) 10%
 Fat cell: blood cell ratio 1:I ( normally)
 In aplastic anemia and bone marrow depression, fat
cells predominate
 Normal range of myeloid-erythroid ratio is 2.5 to 4
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11. Collection of bone marrow
 For diagnostic purpose, bone marrow may have
to be collected
 RBM is collected by pelvic bone puncture or
sternal puncture
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12. Some important terms
 Stem cells – Ancestral cells. There are several
kinds of stem cells
 Totipotent stem cells: present in embryo. They
have potency to form any kind of cell.
 Totipotent stem cell can develop into
hemopoietic stem cell.
 Hemopoietic stem cells (HSC) also called as
pluripotent stem cells that can produce RBC,
WBC and platelets
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13. Some important terms
 HSC produces committed stem cells
(progenitor cells)
1. Committed stem cell for myeloid series – can
produce RBC, neutrophil, monocyte,
eosinophils and platelets
2. Committed stem cell for lymphocyte series –
can produce T and B lymphocytes
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14. Genesis of blood cells
 The blood cells begin their lives in the bone marrow from a
single type of cell called Pluripotential hematopoietic stem
cell
 Committed stem cells
1. CFU E- colony forming unit erythrocyte –produce RBCs
2. CFU GM – colony forming units that form granulocytes and
monocytes
 Growth and reproduction of different stem cells are
controlled by multiple proteins called growth inducers eg:
Interleukin 3
 Growth inducers promotes only growth but not
differentiation
 Differentiation inducers promotes differentiation
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15. DR Sai Sailesh Kumar G 15

16. Stages of differentiation of RBCs
 The first cell that can be identified as belonging
to red blood series is the pro-erythroblast
 Under appropriate stimulation, large number of
these cells are formed from CFU-E stem cells
 Once, pro erythroblast has been formed, it
divides multiple times, eventually forming many
mature red blood cells
 The first generation cells are called basophil
erythroblast because they stain with basic dyes
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17. Genesis of blood cells
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18. Stages of differentiation of RBCs
 The first generation cells are called basophil
erythroblast because they stain with basic dyes
 The cell at this time has accumulated with very little
hemoglobin
 In the succeeding generations, the cells become
filled with Hb of about 34%
 The nucleus condenses to small size and its final
remnant is absorbed or extruded from the cell
 At the same time, endoplasmic reticulum also
reabsorbed DR Sai Sailesh Kumar G 18

19. Stages of differentiation of RBCs
 The cell at this stage is called reticulocyte because it
still contains small amounts of basophilic material,
consists of remnants of the golgi apparatus,
mitochondria and few other cytoplasmic organelles
 During this reticulocyte stage, the cells pass from the
bone marrow into the blood capillaries by diapedesis
 Diapedesis – squeezing through the pores of the
capillary membrane
 The remaining basophilic material in the reticulocyte
usually disappears within 1-2 days and the cell is then
called mature erythrocyte
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20. Pro erythroblast
 Round or oval in shape
 15-20 micro meter in diameter
 Large nucleus that occupies 80% of cell
 Contains 2-3 nucleoli
 After repeated cell division pro erythroblast/
pro-normoblast differentiate into basophilic
erythroblast/ normoblast
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21. Basophilic erythroblast
 Basophilic normoblast / early normoblast
 12-17 micro meter in diameter
 Chromatin condensation seen
 cytoplasm more and deeply basophilic
 The cell at this time has accumulated with very little
hemoglobin
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22. Polychromatophilic erythroblast
 Intermediate normoblast
 12-15 micro meter in diameter
 Nucleus is very small and assumes a cart wheel
appearance
 Chromatin condensation is more
 Cytoplasm shows both pink and blue color
 Pink color is due to increase in hemoglobin
 Mitosis stops in this phase due to inactivation of
chromosomes DR Sai Sailesh Kumar G 22

23. Orthochromatic erythroblast
 Late normoblast
 8-12 micro meter in diameter
 Smallest of the nucleated precursors
 cytoplasm is pink
 Nucleus undergoes pyknotic degeneration and it
shrinks and becomes irregular
 Finally nucleus is extruded from the cell
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24. Reticulocyte
 8 micro meter in diameter
 Cytoplasm contains cell organells
 Reticulocytes are not seen in a Leishman-
stained blood smear
 Supravital staining with brilliant cresyl blue needed
to stain reticulocytes
 They become mature RBC in 32-48 hours
 Increased reticulocytes - reticulocytosis
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25. Mature erythrocyte
 7.2 micro meter in diameter
 Biconcave shape
 cell organelles ansent
 No nucleus
 No nucleolus
 One pro erythroblast gives rise to 8-32 mature
RBCs
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26. Erythropoietin
 The total mass of RBC in the circulatory system
is regulated within narrow limits, so
1. An adequate red cells are always available to
provide sufficient transport of oxygen from
lungs to tissues, yet
2. The cells do not become so numerous that
they impede blood flow
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27. Erythropoietin
 The principal stimulus for red blood cell production in
low oxygen states is a circulating hormone –
erythropoietin
 It is a glycoprotein with molecular weight about 34,000
 In the absence of erythropoietin, hypoxia has little or no
effect to stimulate red blood cell production
 But when the erythropoietin system is functional,
hypoxia causes a marked increase in erythropoietin
production
 Erythropoietin enhances red cell production until the
hypoxia is relieved DR Sai Sailesh Kumar G 27

28. Erythropoietin
 90% of erythropoietin is formed in the kidneys, 10%
is formed in the liver
 It is not known exactly where in the kidneys
erythropoietin is formed
1. Renal tissue hypoxia
2. Increase in the hypoxia inducible factor 1 (HIF1)
3. HIF-1 serves as a transcription factor for
erythropoietin gene
4. Increase in erythropoietin synthesis
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29. Erythropoietin
 Non-Renal tissue hypoxia
 Non-renal sensor
 Send signals to kidneys
 Increase in erythropoietin synthesis
 Both nor epinephrine, epinephrine and several
prostaglandins stimulate erythropoietin
production
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30. Erythropoietin
 What happens if both kidneys are removed
 Or both kidneys destroyed by renal disease
 The person invariably becomes very anemic
 90% of source of erythropoietin is kidneys
 10% from liver- can cause only one third to one
half of the RBCs formation needed by the body
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32. Regulation of erythropoiesis
 Tissue oxygenation is most essential regulator
of erythropoiesis
 When a person becomes extremely anemic
 Bone marrow begins to produce large
quantities of RBCs
 Destruction of major portions of bone marrow,
especially by X-ray therapy, causes hyperplasia
of remaining bone marrow, in an attempt to
supply the demand for RBCs in the body
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33. Regulation of erythropoiesis
 A very high altitudes, where the quantity of
oxygen in the air is greatly decreased
 Insufficient oxygen is transported to the tissues
 RBC production is greatly increased
 Various diseases of circulation that decrease
tissue blood flow (cardiac failure) or those
cause failure of oxygen absorption by the blood
(lung diseases) – tissue hypoxia
 Tissue hypoxia – increases red cell production
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34. Factors affecting erythropoiesis and
maturation of RBCs
 Hypoxia and
erythropoietin
 Dietary protein and
energy
 Vitamin B12
 Folic acid
 Pyridoxine
 Riboflavin
 Niacin
 Ascorbic acid (vitamin
C)
 Vitamin A
 Vitamin E
 Iron
 Copper
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35. Maturation of RBCs
 Erythropoietic cells of bone marrow are among the
most rapidly growing and reproducing cells in the entire
body
 Therefore, their maturation and rate of production are
affected greatly by the person’s nutritional status
 Two vitamins are essential for final maturation of RBCs
 Vitamin B12 and folic acid
 Both of these are essential for synthesis of DNA
 Lack of either of these cause abnormal or diminished
DNA
 Failure of nuclear maturation and cell division
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36. Maturation of RBCs
 Erythroblastic cells fail to proliferate rapidly
 Produce larger cells than RBCs
 Macrocytes- cell itself has a flimsy membrane
and is often irregular, large and oval in spite of
biconcave disc
 These poorly formed cells can carry oxygen
after they enter the circulation
 But their fragility causes them to have a short
life
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37. Pernicious anemia
 Common cause for red blood cell failure is failure
to absorb vitamin B12 from GIT
 This is seen in pernicious anemia
 Atrophic gastric mucosa that fail to secrete normal
gastric secretion
 The parietal cells of gastric glands secretes a
glycoprotein called intrinsic factor
 Intrinsic factor combines with vitamin B12 in the
food and makes it available for the absorption by
the gut DR Sai Sailesh Kumar G 37

38. Intrinsic factor
 IF binds tightly with vitamin B12
 In this bound state Vit B12 is protected from
digestion by gastro intestinal secretions
 If binds to specific receptor sites on the brush
border membranes of mucosal cells in the ileum
(terminal part)
 Vitamin B12 is transported into the blood during
the next few hours by pinocytosis, carrying both IF
and vit B12
 Lack of IF causes decrease in absorption of Vit B12
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39. Vitamin B12
 Once vitamin B12 is absorbed from GIT, it is first
stored in large quantities in liver
 Then released slowly as needed by bone marrow
 Minimum amount of vit B12 required to maintain
normal maturation of RBC is 1-3 mcg
 Normal storage in the liver is about 1000 times this
amount
 Therefore 3-4 years of defective vitamin B12
absorption usually required to cause maturation
failure anemia DR Sai Sailesh Kumar G 39

40. Folic acid
 Normal constituent of green leafy vegetables, fruits,
meat (especially liver)
 However, it is easily destroyed during cooking
 People with gastro intestinal absorption
abnormalities, such as sprue often have serious
difficulty in absorption of both folic acid and
vitamin B12.
 In many cases of maturation failure, deficiency of
intestinal absorption of both folic acid and vitamin
B12 is seen
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41. Summary of factors
 Hormones- Erythropoietin, androgens, thyroid
hormones, corticosteroid hormones
 Vitamins: Vitamin B12 (intrinsic factor), Folic
acid, pyridoxine and vitamin C(helps iron
absorption)
 Minerals : Iron and copper
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42. DR Sai Sailesh Kumar G 42

43. THANK YOU
DR Sai Sailesh Kumar G 43