Hematopoiesis

Hemopoiesis
• Hemopoiesis (haematopoiesis) (hee-moh-poi-ee-sis) n.

• Hemopoiesis encompasses proliferation, differentiation and functional

maturation of stem cells to terminally differentiated blood cells.
• The process of formation of blood cells.

• It consists of: 1. Erythropoiesis

2. Granulopoiesis
3. Megakaryopoiesis
4. Lymphopoiesis
Total volume of haemopoietic tissue in adult is: 1-2l, this is known as red marrow
because of its macroscopic appearance.
Yellow marrow also occupies a volume of 1-2L and it serve as a reserve space
into which haemopoietic tissue can expand to an increased demand for red cells
production.
Site of haematopoiesis:
*Fetus- 0-3 months (yolk sac)
3-6 months (Liver, Spleen)
4-9 months (bone marrow)
*After birth: Bone marrow (An Exception -Lymphocyte production.)

*Newborn: Particularly all bones.

*Adult: Proximal ends of femur and humerus, vertebrae, pelvis, skull
bones and bones of the thorax.
Stem Cells
Stem cells are the cells which maintain their numbers by self-
replication and also give rise to precursors of all types of cells.

• All blood cells arise from “mother” (stem) cells

–Self renewing
–Safe from harm
–Pluripotent
–Normally in G0 phase of cell cycle
Stem cells types:
1. Embryonal
2.Adult

Heamatopoietic Stem Cells

1. Myeloid cells
2. Lymphoid cells

Myeloid lineage give rises to all blood cells except lymphocyte.

Lymphoid lineage give rises to lymphocytes.
❑ Progenitor cells

•Encompasses from immediate progeny of stem cells to

differentiation cells committed to one lineage.
•Progenitor cells become progressively more restricted in
their differentiation and proliferation capacity.
Erythropoiesis
▪The process of red blood cells production.
▪Stages:

Pro erythroblast (14-20 µm)

↓
Basophilic erythroblast (12-16 µm)
↓
Polychromatic erythroblast (12-14 µm)
↓
Orthochromatic erythroblast (8-12 µm)
↓
Reticulocyte ( 7-10 µm)
↓
Erytrocyte (7-8 µm)
Proerythroblast or pronormoblast:
▪14-20 µm
▪Cytoplasm: More basophilic than in the myeloblast.
▪Nucleus contain fine clumps of chromatin & several nucleoli .
Early normoblast (Basophil erythroblast):
▪Smaller than the pro erythroblast, 12-16µm in size.
▪ More basophilic cytoplasm.
▪Nucleus contain coarse & thick chromatin but no nucleoli.
Intermediate erythrooblast (polychromatic erythroblast) –
▪Smaller than the basophilic erythroblasts, 12-14 micron in size.
▪Polychromatic cytoplasm (Mixture of acidophilic hemoglobin and basophilic RNA)
▪It this stage proliferation ceases and maturation start ( early stage active proliferation later stage
absence of proliferation).
▪Nucleus is small & deeply stained with coarse thick clumps of chromatin.

Orthochromatic erythroblasts (Late normoblast) –

▪Smaller than the previous stage, 8 -12 micron in size.
▪Final stage of maturation.
▪ Nucleus is small and pyknotic.
▪Cytoplasm predominantly acidophilic with some basophilic tint.
Reticulocyte- (7-10 µm)
▪ When the nucleus is extruded from the orthochromatic
erythroblasts to form the reticulocyte. So reticulocyte are
the freshly released red cells from the marrow which still
contain RNA.
▪ Reticulocyte are slightly greater volume and diameter than
erythrocyte.
▪ Its biconcave shape, flat, non nucleated cell.
▪ Cytoplasm are similar in staining that of orthochromatic
erythroblast, it contain diffuse basophilic hue that are
absent in erythrocyte.
▪Stain used for reticulocyte are: Supravital stain such as;
New methylene blue
Brilliant cresyl blue

▪Normal reticulocyte count: 0.5-2%

▪High reticulocyte indicate increase erythropoietic activity in bone marrow .

High reticulocyte count ( reticulocytosis)
found in: Low reticulocyte found in :
1. Haemolytic anaemia 1. Aplastic anaemia
2. Following haematinic therapy 2. Pure red cell aplasia
in neutritional deficiency anaemia. 3. Fanconi’s anaemia
3. Leukemia 4. Aplastic crisis in sickle cell anaemia
4. Lymphoma 5. Hereditory spherocytosis
5. Secondary carcinoma
6. Haemorrhage
7. Haemolysis
➢ Erythrocyte (Mature RBC):
▪ Size- 7-8 µm.
▪ Anucleate, biconcave disc and possess a central one-third pallor.
▪Orange red cytoplasm.
▪RNA lost.
▪ Lack of cytoplasmic structure like endoplasmic reticulum, mitochondria and lysosomes.
▪Life span 120 days.
❑ Factor influencing erythropoiesis:
▪ Erythropoietin.
▪Nutritional factor like Iron, vitamin B12, Folic acid, vitamin B6, vitamin C, copper, cobalt
▪Protein and aminoacid
▪Charbohydrate
▪Hormone: Androgen, Thyroxine, GH, Corticosteroid
Erythropoietin:
Heat stable glycoprotein
Produce mainly in kidney (90%), liver, spleen
Mechanism of action:
1. It stimulate BFU-E, CFU-E and proerythroblasts to proliferate and differentiate.
2. Stimulate rate of maturation
3. Stimulate Hb synthesis
4. Stimulate release of cell into circulation from marrow.
❑ Causes of increased erythropoietin secretion:
1. Hypoxia: High altitude, cvs disease chronic pulmonary disease.
2. Anaemia
3. Renal disease: Hydronephrosis, tumor cyst.
4. Adrenocortical hormone
5. Drugs: Androgen, corticosteroids, thyroxine

❑Causes of decreased erythpoietin secretion:

1. Renal failure
2. Oestogen
3. Polycythemia
4. Secondary anemia due to chronic disease.
❑ Granulopoiesis:
Process of formation of granulocyte ( Neutrophil, eosinophil, basophil).
▪Stage:
Myeloblast (15-20 µm)
↓
Pro myelocyte ( 10-20 µm)
↓
Myelocyte (10-18 µm)
↓
Metamyelocyte (10-18 µm)
↓
Band or stab form (10-16 µm)
↓
Segment or polymorphoneucler granulocyte: Neutrophil, Eosinophil, Basophil
 Myeloblast:
▪ Large cell with large neucleus (15-20 µm)
▪ Nucleus round to oval and occupying a larger portion of the
cell.
▪ Fine network of neuclear chromatin
▪ Prominent nucleoli 2-3 usual number but there may be upto
6 neucleoli.
▪ Cytoplasm : basophilic.
▪ No granule in cytoplasm.
❑ Promyelocyte:
▪ Large cell like myeloblast (15-20µm).
▪ Nucleoli present.
▪Cytoplasm deep blue contains a few granules ( Primary or azurophilic granule).

❑ Myelocyte-
▪10-18 m
▪Prominent cytoplasmic granules.
▪No nucleoli present
▪Cytoplasm less basophilic, chromatin are more aggregated.
❑ Metamyelocyte-
▪ Similar to myelocyte but nucleus is indented assumed kidney shaped.
▪Granule are prominent in cytoplasm.

❑Band or stab form-

▪Nucleus having indentation greater than 50% of nuclear diameter.
▪Pink cytoplasm.

❑Segmented form ( Granulocyte): Neutrophil, eosinophil, basophil.

❑ Neutrophil:
o12-14µm in diameter
▪ Lobulated nucleus contain 2 to 5 lobes of clumped chromatin.
▪Cytoplasm contain fine granules.
❑ Eosinophil:
▪ Slightly larger than neutrophil up to 16µm in diameter.
▪Nucleus are usually bilobed occasionally contain three lobes.
▪Cytoplasm contain coarse orange granules.

❑Basophil:
▪Smaller than eosinophil with a diameter of 10-14 µm.
▪Presence of basophilic coarse cytoplasmic granules that overlie and obscure
the nucleus.
❑ Lymphopoiesis:
The process of formation of lymphocyte.
Stage:
Lymphoblast
↓
Pro lymphocyte
↓
Lymphocyte:
Small lymphocyte
Large lymphocyte
❑ Lymphoblast-
▪Lymphoblast are large cell but slightly smaller than myeloblast.
▪2-3 indistinct nucleoli.
▪Dense chromatin.
▪Auer rods absent
▪Nuclear- chromatin ratio is more.
❑ Small lymphocyte
▪ 9-12 µm in diameter (size near to RBC).
▪Nucleus- Round with clumped chromatin.
▪Thin rim of basophilic cytoplasm

❑Large lymphocyte:
▪12-15 µm in diameter.
▪Round to oval nucleus.
▪More cytoplasm than small lymphocyte and usually pale blue.
▪The chromatin is more clumped than in the small lymphoblast.
❑ Monocyte macrophage series:
▪ Stage:
Monoblast
↓
Promonocyte
↓
Monocyte
↓
Macrophage
❑ Monocyte
▪Large cell 15-20µm in diameter.
▪Nucleus ranges from almost round to sufficiently indented to produce a lobulated, reniform
appearance (kidney shaped).
▪Cytoplasm is abundant of a pale grey blue tint and may be vacuolated.
▪ Thrombopoiesis/ Megakaryopoiesis:
- Process of formation of platelets.
▪Stage:
Megakaryoblast
↓
▪Pro megakaryocyte
↓
▪Megakaryocyte
↓
▪Platelets
❑ Megakaryoblast:
•Morphologically resembles myeloblast.
•Size: 10-15µm
•Cytoplasm: blue non-granular.
•Kidney shaped nucleus with multiple nucleoli.

❑Promegakaryocyte:
•Larger than megakaryoblast.
•Deeply basophilic cytoplasm
•Nucleus may be lobulated.
•Chromatin is deeply basophilic.
Megakaryocyte:
▪30-90 µm in diameter.
▪Contain 4-16 nuclear lobes with coarsely clumped chromatin
▪The cytoplasm is light blue and contains many red purple granules.

▪Platelets are formed by protrusion into the bone marrow sinusoids of pseudopods of
megakaryocytes cytoplasm which detach into the bloodstream and fragmented to small discoid
platelets.
Platelets:

▪ Anucleate.
▪ 1-4µm in diameter.
▪ Discoid shaped.
▪Cytoplasm: light blue and contain small red-purple
azurophilic granules.