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Haematopoiesis: Formation of Blood Cells (Red blood cells, white blood cells, and platelets)

Hematopoiesis_(human)_diagram.png
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source: Wikimedia
The formation of blood cellular components begins in the fetal period in the Yolk sac starting from the third week.

The spleen and liver continue to form blood until the seventh month of the fetal period. The task is limited after this time in Bone marrow.

Blood is formed from the Stem cells CD34 that resides primarily in the Bone marrow, and less in the peripheral blood and Umbilical cord blood of the fetus. That is, the formation of blood, postpartum outside the bone marrow is considered pathological.

Blood consists of:
1. Blood plasma, which accounts for 55% of the total blood volume
2. Cells, make up 45%

Cells in the peripheral blood are normally classified into:
1. Red blood cell, forming about 99.9% of the blood cells
2. White blood cells and Platelets, together constitute only 0.1%

The white blood cells are also classified into Basophils, Neutrophils, Lymphocytes, Monocytes, and Eosinophil.

Pluripotent stem cell
They are non-specialized cells that can differentiate into any type of blood cell.
Its percentage in the bone marrow 1 -2%, in the umbilical cord 10%, and in the blood does not exceed 1% of its percentage in the bone marrow.

These cells have two characteristics:

  • First: it is constantly capable of differentiation
  • Second: they are able to renew themselves

Evolution and differentiation of blood cells in the elderly
The pluripotent stem cell is divided into:

  • common myeloid progenitor
  • common lymphoid progenitor

The direction of the myeloid
A common myeloid progenitor is responsible for the formation of:

  • Megakaryocytes
  • Granulocytes
  • red blood cells
  • Monocytes

The direction of lymphoid
A common lymphoid progenitor is responsible for the formation of:

  • Pre-B Cell: Completes its maturity in the bone marrow itself
  • Pre-T Cell: Maturing in the Thymus

Regulation of Hematopoiesis
It is done through:
1. The microbial environment of the Bone marrow
2. colony-stimulating factor (CSFs)
3. Interleukins
4. Erythropoietin

Erythropoiesis
The colony forming unit-erythroid (CFU-E) is divided into Prorythroblast -» basophilic or early normoblast -» polychromatophilic or intermediate normoblast -» orthochromatic or late normoblast -» reticulocytes stay in the bone marrow 1-2 days and then to peripheral Circulation -» "erythrocytes" or mature red blood cells.

Notes:

  • The erythrocytes cycle takes about 7 days and lasts 120 days.
  • Late normoblast is seen in the peripheral blood in the following cases: Thalassemia major, after splenectomy, Myelofibrosis, and most Hemolysis
  • The central pallor occupies about one-third of the erythrocyte diameter
  • An increase in the diameter of the central pallor is seen in iron-deficiency anemia
  • Lack of diameter of the central pallor or lack of central pallor is seen in Folic Acid Deficiency Anemia or B12 deficiency Anemia, as well as in the early stages of Polycythemia Vera
  • Reticulocytes in the peripheral Circulation can be shown by coloring them with brilliant cresyl blue, where they show clear and within the remains of the RNA

Granulopoiesis
It begins with Myeloblast which is divided to give (Promyelocyte) -» (Eosino/neutro/basophilic myelocyte) -» (Metamyelocyte) -» Band cell (Stab cell) -» Granulocytes (Eosino/neutro/basophil)

If we see in Blood smear examination Increase of lobation in granular cells, we say that we have the Right shift as pernicious anemia and give hydroxyurea.

If we see an increase in the number of immature leukocytes in the peripheral blood we say that we have left shift as in cases, Bleeding Infections and Leukemia due to increased production of leukocytes.

Watching band cells in the peripheral blood is normal unless they exceed 6% of the total granulocytes.

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