ALL THE BLOOD CELULAR COMPONENTS IS DERIVED BY HEMATOPOIETIC STEM CELLS
HEMATOPOIETIC STEM CELLS (HSC)
IS LOCATED AT BONE MARROW.
HSC - HAS SPECIAL CHARACTERISTIC WHERE IT CAN SELF-RENEWING
ONCE HSC PROLIFERATE,THERE PRODUCE 2 DAUGHTER CELL.
# 1 STEM CELL WILL REMAIN .
# OTHER STEM CELL WILL PRODUCE EITHER
LYMPHOID STEM CELL(LSC) AND MYELOID
STEM CELLS THAT GIVES RISE TO ALL BLOOD CELLS TYPES IS INCLUDING:-
1. LYMPHOID STEM CELL:
# NATURAL KILLER (NK-CELL)
- IS THE TYPE OF CYTOXIC LYMPHOCYTES.
2. MYELOID STEM CELL:
# MEGAKARYOCYTES ---- PLATELETS
Erythroid cells Lymphoid cells Myeloid cells
Oxygen carrying RBC - Cornerstone of the - Granulocytes,
Reticulocytes and adaptive immune system megakaryocytes and erythrocytes are - T-cells and B-cells. macrophages functional and are - Innate immunity, released into the blood adaptive immunity, and blood clotting.
Before birth, hemopoiesis first occurs in the yolk sac of an embryo and later in the liver,spleen,thymus and lymph nodes of a fetus. Red bone marrow becomes the primary site of haemopoiesis in the last 3 months before birth and continues as the source of blood cells after birth and throughout life. However,maturation , activation and some proliferation of lymphoid cells occurs in secondary lymphoid organs (spleen, thymus,and lymph nodes). In children, haematopoiesis occurs in the marrow of the long bones such as the femur and tibia. In adults, it occurs mainly in the pelvis, cranium, vertebrae, and sternum. LOCATION OF HAEMATOPOIESIS
In some cases, the liver, thymus, and spleen may resume their haematopoietic function, if necessary. This is called extramedullary hematopoiesis . It may cause these organs to increase in size substantially.
Blood cell “Maturation”
As a stem cell matures it undergoes changes in gene expression that limit the cell types that it can become and moves it closer to a specific cell type.
These changes can often be tracked by monitoring the presence of proteins on the surface of the cell.
Each successive change moves the cell closer to the final cell type and further limits its potential to become a different cell type .
Blood cell “Determination”
Cell determination appears to be dictated by the location of differentiation.
For the stem cells and other undifferentiated blood cells in the bone marrow, the determination is generally explained by the determinism theory of hematopoiesis.
Saying that colony stimulating factors and other factors of the hematopoietic microenvironment determine the cells to follow a certain path of cell differentiation.
The ability of the bone marrow to regulate the quantity of different cell types to be produced is more accurately explained by a stochastic theory:
Hemopoietic growth factors
are hormone-like substances (protein) that
stimulate bone marrow to produce blood cell and
promote the proliferation of blood cells
Is produces primarily by cells in the kidney that
lie between the kidney tubules ( peritubular interstitial
- red blood cell production
Increases the number of red blood cell precursors
Required for a myeloid progenitor cell to become
Thrombopoietin ( TPO)
hormone produced by by the liver
stimulates the formation of platelets from megakaryocytes (megakaryocytopoiesis)
Growth factors initiate signal transduction pathways, altering transcription factors and activate genes that determine the differentiation of blood cells.
The early committed progenitors express low levels of transcription factors that may commit them to discrete cell lineages.
Which cell lineage is selected for differentiation may depend both on chance and on the external signals received by progenitor cells.
Several transcription factors have been isolated that regulate differentiation along the major cell lineages.
For instance, the Ikaros, Aiolos and Helios transcription factors play a major role in lymphoid development.
HAEMATOPOIESIS – RBCs
Characteristics seen in erythrocytes during erythropoiesis
The following characteristics can be seen changing in the erythrocytes when they are maturing:
They show a reduction in the cell size
The cytoplasmic matrix increases in amount
Staining reaction of the cytoplasm changes from basophilic to acidophilic
Initially the nucleus was large in size and contained open chromatin. But with the maturation of RBC's the size of the nucleus decreases and finally disappears with the condensation of the chromatin material