erythropoisis. red blood cells blood and blood products

DEFINITION
• Erythropoiesis is the process of
the orogin, development and
maturation of erythrocytes.
• Hemopoiesis or Hematopoiesis
is the process of origin,
development and maturation of
all the blood cells.

SITE OF ERYTHROPOIESIS
IN FETAL LIFE- Erythropoiesis
occurs in three stages.
Mesoblastic Stage- During the
first 2 months of intrauterine life,
the RBCs are produced from
mesenchyme of yolk sac.

Hepatic Stage- From third month
of intra-uterine life, liver is the
main organ that produces RBCs.
Spleen and Lymphoid organs are
also involved in erythropoiesis.
Myeloid Stage- during the last
three months of intrauterine life,
the RBCs are produced from the
red bone marrow and liver.

IN NEW BORN BABIES,
CHILDREN AND ADULTS
Up to the Age of 20 Years: RBCs are
produced from the red bone marrow
of all the bones (long bones and flat
bones).
After the Age of 20 Years: RBCs are
produced from membranous bones
like vertebrae, sternum, ribs,
scapula, iliac bones and skull bones

Though bone marrow is the site of
production of all blood cells,
comparatively 75 % of the bone
marrow is involved in the production
of leukocytes and only 25 % is
involved in the production of
erythrocytes.

PROCESS OF
ERYTHROPOIESIS
STEM CELLS
• Stem cells are the primary cells capable of
self-renewal and differentiating into
specialized cells.
• Hemopoietic stem cells are the primitive
cells in the bone marrow, which give rise to
the blood cells.
• Hemopoietic stem cells in the bone marrow
are called uncommitted pluripotent
hemopoietic stem cells (PHSC).
• PHSC is defined as a cell that can give rise

CONT.
Committed PHSC- These cells are restricted
to give rise to one group of blood cells.
Committed PHSC are of two types:
Lymphoid Stem Cells (LSC) & Colony
forming Blastocytes.
Lymphoid Stem Cells- It gives rise to
lymphocytes and natural killer cells.
Colony forming blastocytes gives rise to
myeloid cells. Myeloid cells are the blood
cells other than lymphocytes.
Myeloid cells when grown in cultures, these
cells form colonies hence the name new
colony forming blastocytes.

Different units of colony forming cells
are
 CFU– E Means Colony Forming Unit
– Erythrocytes. Cells of this unit
develop into erythrocytes.
 Colony Forming Unit Granulocytes /
Monocytes (CFU – GM): These cells
gives rise to granulocytes
(Granulocytes, basophills, and
eosinophills) and Monocytes.
 Colony Forming Unit-

CHANGES DURING
ERYTHROPOIESIS
• Cells of CFU– E pass through different
stages and finally become the matured
RBCs, during these stages four important
changes are noticed.
1. Reduction in size of the cell (from the
diameter of 25 to 7.2 microns).
 Disappearance of nucleoli and nucleus.
 Appearance of hemoglobin.
 Change in the starting properties of the
cytoplasm.

STAGES OF
ERYTHROPOIESIS
Various stages between CFU
– E Cells and matured RBCs
are-
1. Pro-erythroblast
2. Early Erythroblast
3. Intermediate Normoblast
4. Late Normoblast
5. Reticulocyte

PRO-ERYTHROBLAST
(MEGALOBLAST)
• It is the first cells derived from CFU – E.
• It is very large in size with a diameter of
about 20 microns.
• Its nucleus is large and occupies the cell
almost completely.
• The nucleus has two or more nucleoli and a
reticular network.
• Pro-erythroblast does not contains
hemoglobin.
• The cytoplasm is basophilic in nature.
• Pro-Erythoblast multiplies several times
and finally forms the cell of next stage.

EARLY NORMOBLAST
• This cell is smaller than pro-
erythroblast with a diameter of about 15
microns.
• In the nucleus, the nucleoli disappear.
• Condensation of chromatin network
occurs.
• The condensed network becomes dense.
The cytoplasm is basophillic in nature.
• Hence this cell is also called as
Basophillic erythroblast.

INTERMEDIATE
NORMOBLAST
• Cell is smaller than the early
normoblast with a diameter of 10 to 12
microns.
• The nucleus is still present, but the
chromatin network shows further
condensation.
• The hemoglobin starts appearing.
• Cytoplasm is already basophilic.
• The cell develops into next stage called

LATE NORMOBLAST
• Diameter of the cell decrease further to
about 8 to 19 microns.
• Nucleus becomes very small with very
much condensed chromatin network
and it is known as ink – spot nucleus.
• Quantity of hemoglobin increases.

• Cytoplasm becomes almost acidophilic,
so the cell is called as orthochromic
erythroblast.
• In the final stage of late normoblast
just before it passes to next next stages.
• The nucleus disintegrates and
disappears.
• The process by which nucleus
disappears is called Pyknosis.

RETICULOCYTE
• It is otherwise known as immature
RBC.
• It is slightly larger than matured RBC.
• The cytoplasm contains the reticular
network.
• Due to the presence of reticular
network it is called as reticulocyte.

MATURED ERYTHROCYTE
• Reticular network disappears and the
cell becomes the matured RBC and
attains the bioconcave shape.
• The cell decreases in size to 7.2 microns
in diameter.
• The matured RBC is with hemoglobin
but without nucleus.

• It requires 7 days for the development
and maturation of RBC from pro-
erythroblast.
• It requires 5 days up to the stage of
reticulocyte.
• Reticulocute takes 2 more days to
become the matured RBC.

Function of blood
1. Nutritive function
2. Respiratory function
3. Excretory function
4. Transport of hormones and enzyme
5. Regulation of water balance
6. Regulation of acid base balance
7. Regulation of body temperature
8. Storage function
9. Defensive function

1. Nutritive Function- Nutritive
substances like glucose, amino acids,
lipids and vitamins derived from
digested foods are absorbed from
gastrointestinal tract and carried by
blood to different parts of the body for
growth and production of energy.
2. Respiratory Function- transport of
respiratory gases is done by blood. It
carries oxygen from alvioli of the
lungs to different tissues and carbon

3. Excretory Function- Waste products
formed in the tissues during various
metabolic activities are removed by blood
and carried to the excretory organs like
kidney, skin, liver etc. for excretion.
4. Transport of hormones and enzyme-
Hormones which are selected by ductless
(endocrine) glands are released directly
into the blood. The blood transports these
hormones to their target organs/tissues.
Blood also transport enzymes.
5. Regulation of water balance- Water
content of the blood is freely

6. Regulation of acid base balance-
Plasma protiens and hemoglobin act
as buffers and help in the regulation
of acid base balance.
7. Regulation of body temperature-
Because of the high specific heat of
blood, it is responsible for
maintaining the thermoregulatory
mechanism in the body i.e. the
balance between heat loss and heat
gain in the body.

8. Storage function- Water and some important
substances like protiens, glucose, sodium and
potassium are contantly required by the
tissues. Blood serves as a readymade source of
these substances. These substances taken from
blood during the conditions like starvation,
fluid loss, electrolyte loss etc.
9. Defensive function- Blood plays an important
role in the defense in which white blood cells
are responsible for this function. Neutrophils
and monocytes engulf the bacteria by
phagocytosis. Lymphocytes are involved in
development of immunity. Eosinophils are
responsible for detoxification, disintegration

erythropoisis. red blood cells blood and blood products

erythropoisis. red blood cells blood and blood products

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