The basics of hematopoiesis

Question 1

What is the origin of all the circulating cellular components of the blood

Answer 1

They are derived from hematopoietic stem cells (HSC) that originally develop in a region of embryonic mesoderm

- Mesoderm also forms the skeletal muscle, skeleton, dermis, connective tissue, urogenotal system, heart, kidney and spleen

Question 2

What is the future of the stem cells

Answer 2

The stem cells undergo massive expansion in the fetal liver (the main hematopoietic organ at this stage)

Then they colonize the spleen and lymph nodes, the bpne marrow and thymus

Question 3

What is the particular feature of hematopoietic stem cell

Answer 3

HSCs are self-renewing
- That is when they proliferate at least some of their progeny remain as stem cells, whereas others commit to the myeloid or lymphoid progenitor pathways
- Once committed, these cells cannot then self-renew due to changes in gene expression

Question 4

How is hematopoieisis regulated

Answer 4

Hematopoiesis is regulated by:
- stem cell factor (SCF) as well as colony stimulating factors (CSF) in the case of granulocytes

- erythropoietin for RBCs

- thrombopoietin for the formation of megakaryocytes

- as well as a variety of other cytokines such as interleukin (IL)-3

Question 5

Where does hematopoiesis take place in the body

Answer 5

Hematopoiesis occurs within the bone marrow

Occasionally, often in response to hypoxia, it can occur outside the marrow, most commonly in the liver and spleen (extramedullary hematopoiesis)

Question 6

Describe the pathway conducting from a stem cell to a lymphocyte

Answer 6

Stem cell transforms in common lymphoid precursor which in turn gives the 3 types of lymphocytes (T cells, NK cells, B cells)

Question 7

Describe the pathway conducting from a stem cell to erythrocytes or megakaryocytes

Answer 7

Stem cell transforms in common myeloid precursor which in turn will transform in Megakaryocyte-erythrocyte progenitor and then, that last one will trnsform in erythrocytes or megakaryocytes

Question 8

Describe the pathway conducting from a stem cell to granulocytes

Answer 8

Stem cell transform in granulocyte-monocyte progenitor which in turn will transform in granulocytes, resident monocytes and inflammatory monocytes

Monocytes will transform in macrophages and dendritic cells in tissues