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What is the hematopoiesis ?

[wp-svg-icons icon=”point-right” wrap=”i”]Hematopoiesis is the production, Development and the maturation of various cellular components of the blood

[wp-svg-icons icon=”point-right” wrap=”i”]The cellular components of blood are developed from the Hematopoietic stem cells also known as Pluripotent Stem cells or totipotent stem cells which further differentiate and mature into typical blood cells.

[wp-svg-icons icon=”point-right” wrap=”i”]The Pluripotent stem cells give rise to two types of Stem cells or lineages –

  • Myeloid stem cells/Lineage – Differentiate in the Redbone marrow and form Erythrocytes, Granulocytes (Neutrophils, Eosinophils, and Basophils), Monocytes and Thrombocytes
  • Lymphoid stem cells/Lineage – differentiates in the Redbone marrow and then migrates to the lymphoid tissue. They form T- and B- Lymphocytes.

[wp-svg-icons icon=”point-right” wrap=”i”] The production of erythrocytes is called as Erythropoiesis; the leukocytes are called as Leucopoiesis and that of platelets is Thrombopoiesis.

[wp-svg-icons icon=”point-right” wrap=”i”] Leucopoiesis is further subdivided into –

  • Granulopoiesis – formation of granulocytes
  • Monopoiesis – formation of monocytes
  • Lymphopoiesis – formation of lymphocytes

What are the Sites of Hematopoiesis ?

  • The site of Hematopoiesis depends on the age of the person as follows –
  • In human embryo – Yolk sac is the main site of Hematopoiesis
  • By the 3rd to 7th month of Intra-uterine life – Hematopoiesis occurs in liver and spleen.
  • By the 7th month till birth – it starts in the bone marrow.
  • From birth till maturity – occurs in bone marrow, spleen, and liver.
  • In adults – Hematopoiesis occurs in the Central skeleton (Vertebrae, Sternum, Ribs, Skull, Sacrum, and pelvis), proximal ends of the long bones like Femur, Tibia, and Humerus.

What is Erythropoiesis?

[wp-svg-icons icon=”point-right” wrap=”i”] It is the process of formation, development, and maturation of Red blood cells in the bone marrow.

[wp-svg-icons icon=”point-right” wrap=”i”] Sites of production –

  • The red bone marrow is the prime site for the production of RBC’s from birth till age 20
  • After the age of 20 years, RBCs are mainly produced in the marrow of Vertebrae, Sternum, Ribs, and Pelvis
  • After the gradual structural and functional maturation – the cells are released in peripheral circulation.

Regulation of Erythropoiesis – Erythropoietin is the hormone produced mainly by the kidneys, helps to regulate the process of Erythropoiesis so that the number of RBCs is sufficient to sustain adequate tissue oxygen levels.

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[wp-svg-icons icon=”point-right” wrap=”i”] Reticulocytes are called as the juvenile RBCs or Immature RBCs.

[wp-svg-icons icon=”point-right” wrap=”i”] Reticulocytes spend 1-2 days in the marrow than 1-2 days in circulation where it gets mature into Erythrocytes and attains biconcave shape.

[wp-svg-icons icon=”point-right” wrap=”i”] Normal range of Reticulocytes –

  • Adults – 0.5 – 2.5%
  • Infants – 2 – 6%

What is Leukopoiesis?

[wp-svg-icons icon=”point-right” wrap=”i”] It is the process of formation or production of leucocytes which normally occurs in the blood-forming tissue of the bone marrow. There are 3 independent series, which leads to the formation of 3 different types of white cells –

  • Granulocytes – Granulopoiesis
  • Lymphocytes – Lymphopoiesis
  • Monocytes – Monopoiesis/ Monocytopoiesis

[wp-svg-icons icon=”point-right” wrap=”i”] The formation of White Blood cells is regulated by –

  • Stimulation by cytokines and Colony stimulating factor.
  • Produced by Macrophages & T – lymphocytes.
  • Activated by coming in contact with foreign organisms.

What is Granulopoiesis?

[wp-svg-icons icon=”point-right” wrap=”i”] Granulopoiesis is the process of formation or production of Granulocytes that are the  type of White blood cells that contains the granules in their cytoplasm, which begins at the Myeloblast and passes through the stages of a Promyelocyte, Myelocyte, Metamyelocyte and Band cells and ultimately results in the formation of 3 types of Granulocytes – Neutrophils, Eosinophils & the Basophils.

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What is Lymphopoiesis?

Lymphopoiesis is the process of formation or production of Lymphocytes, a type of white blood cells that lack the granules in their cytoplasm, which begins at the Lymphoblast and passes through the stage of Prolymphocyte and ultimately results in the formation of mature Lymphocytes.

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What is Monopoiesis / Monocytopoiesis?

Monopoiesis or Monocytopoiesis is the process of formation of production of Monocytes, a type of White blood cells that lack the granules in their cytoplasm, which begins at the Monoblast, passes through the stage of Promonocyte and ultimately results in the formation of mature Monocytes.

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What is Thrombopoiesis?

Thrombopoiesis is the formation or production of Thrombocytes or Platelets in the bone marrow which is formed by fragmentation of mature Megakaryocyte membrane projections, begins at Megakaryoblast and passes through the stages of Promegakaryocyte and then the Megakaryocytes ultimately results in the formation of mature Thrombocytes or Platelets.

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