Hematopoiesis- Definition, Cells, Growth Factors, Regulation


Hematopoiesis is the process of formation and development of blood cells in the body. Blood cells are essential for various functions such as oxygen transport, immunity, clotting, and homeostasis. Hematopoiesis occurs throughout the lifespan of an individual, from the embryonic stage to adulthood.

The source of all blood cells is a special type of cell called hematopoietic stem cell (HSC). HSCs are multipotent stem cells that have the ability to self-renew and differentiate into various types of blood cells. HSCs are rare and constitute only about 0.01% of the total bone marrow cells in adults.

HSCs reside in a specialized microenvironment within the bone marrow called the niche. The niche provides physical and chemical signals that regulate the survival, proliferation, and differentiation of HSCs. The niche also protects HSCs from stress and damage.

HSCs can be classified into two types based on their differentiation potential: long-term HSCs (LT-HSCs) and short-term HSCs (ST-HSCs). LT-HSCs have a high self-renewal capacity and can generate both ST-HSCs and mature blood cells. ST-HSCs have a limited self-renewal capacity and can only generate mature blood cells.

HSCs can also be identified by the expression of certain surface markers such as CD34, CD38, CD90, and CD133. These markers help to isolate and characterize HSCs from other blood cells using techniques such as flow cytometry and magnetic sorting.

HSCs are responsible for maintaining the homeostasis of blood cell production and replenishing the blood cell pool in response to various stimuli such as infection, inflammation, injury, or chemotherapy. HSCs can also migrate from the bone marrow to other sites of hematopoiesis such as the spleen, liver, or thymus under certain conditions.

HSCs are also important for regenerative medicine and transplantation. HSCs can be obtained from various sources such as bone marrow, peripheral blood, umbilical cord blood, or induced pluripotent stem cells (iPSCs). HSCs can be used to treat various diseases such as leukemia, lymphoma, anemia, immunodeficiency, or genetic disorders by replacing the defective or damaged blood cells with healthy ones.

Hematopoiesis is a complex and dynamic process that involves multiple factors and interactions. Understanding the molecular mechanisms and regulation of hematopoiesis is crucial for developing novel therapies and improving the outcomes of patients with hematological disorders.