Erythropoiesis Lect 3

8/3/2019 Erythropoiesis Lect 3

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Erythropoiesis

Erythropoiesis is the highly regulated multistep process, the end

product of which is the erythrocytes or red blood cells.


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Modified,Page36,Willams-Hematology


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FACTORS REGULATINGERYTHROPOIESIS

SINGLE MOST IMPORTANT REGULATOR:

TISSUE OXYGENATION

ERYTHROPOIETIN

BURST PROMOTING ACTIVITY

IRON

VITAMINS:

Vitamin B12

Folic Acid

MISCELLANEOUS


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STEM CELLS

These cells have extensive proliferative capacity

and also the:

Ability to give rise to new stem cells (Self Renewal)

Ability to differentiate into any blood cells lines(Pluripotency)

They grow and develop in the bone marrow.

The bone marrow & spleen form a supporting

system, called the

hemopoietic microenvironment


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Pluripotent Stem cells: Has a diameter of 1823 .

Giving rise to: both Myeloid and Lymphoid series ofcells

Capable of extensive self-renewal. Myeloid Stem cells: Generate myeloid cells:

Erythrocytes

Granulocytes: PMNs, Eosinophils & Basophils.

Thrombocytes.

Lymphoid Stem cells: Giving rise only to: Lymphocytes: T type mainly.

STEM CELLS: Types


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PROGENITOR CELLS

Committed stem cells lose their capacity for self-

renewal.

They become irreversibly committed.

These cells are termed as Progenitor cells

They are regulated by certain hormones or

substances so that they can:

Proliferate Undergo Maturation.


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Myeloid

stem cell

BFU-E

CFU-E

Pronormoblast

Erythrocytes

Erythropoiesis


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ERYTHROPOIESIS: SEQUENTIAL CHANGES

I II III IV VVIPRONORMOBLAST

Basophilic

normoblast

Polychromatic

normoblast

RETICULOCYTE

MATURERBC

MITOCHONDRIABASOPHILIAHEMOGLOBIN

Orthochromatic

normoblast


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ERYTHROID PROGENITOR CELLS

BFU-E: Burst Forming UnitErythrocyte:

Give rise each to thousands of nucleated erythroid

precursor cells, in vitro.

Undergo some changes to become the Colony FormingUnits-Erythrocyte (CFU-E)

Regulator: Burst Promoting Activity (BPA)

These are more closely related to the multipotent stem cell.Contain moderately basophilic cytoplasm with occasional pseudopods,.

very fine nuclear chromatin and large nucleoli.


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CFU-E: Colony Forming Unit- Erythrocyte:Well differentiated erythroid progenitor cell.

Present only in the Red Bone Marrow.

Can form upto 64 nucleated erythroid precursor cells.

Regulator: Erythropoietin.

ERYTHROID PROGENITOR CELLS

Cell morphology

Fine nuclear chromatin.

Well defined large nucleolus.

High nuclear cytoplasmic ratio, a perinuclear clear zone

Basophilic cytoplasm with pseudopods.


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Normoblastic Precursors

PROERYTHROBLAST:

Large cell: 1520 microns in diameter.

Cytoplasm is deep violet-blue staining

Has no Hemoglobin.

Large nucleus 12 microns ,occupies 3/4th of the

cell volume.

Nucleus has fine stippled reticulum & manynucleoli.


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Basophilic erythroblast:

Smaller in size.

Shows active Mitosis.

No nucleoli in the nucleus.

Fine chromatin network with few condensation

nodes found.

Hemoglobin begins to form.

Cytoplasm still Basophilic.



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Polichromatic Erythroblast:

Has a diameter of 1014 microns.

Shows active Mitosis.

Increased Hemoglobin content in the cytoplasm

Cytoplasm is Polychromatophilic.



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Orthochromatic Erythroblast:

Diameter is 710 microns.

Nucleus shrinks with condensed chromatin.

Nucleus undergoes the pyknotic degeneration

and exnucleation .

Cytoplasm has a Eosinophilic appearance.



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RETICULOCYTE:

The penultimate stage cell.

Has a fine network of reticulum like a as

clumps of dots The presence of reticulum leads to the term

reticulocytes

In the Neonates, Count is 26/Cu.mm.

Reticulocytosis is the first change seen inpatients treated with Vit B12



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MATUREERYTHROCYTE:

Biconcave disc.

No nucleus. About One-third filled

with Hemoglobin.



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Life Cycle of Red Blood Cells

Figure 17.7


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Erythropoiesis Lect 3