Formation of blood cells in bone marrow

1. HEMATOPOIESIS

2. HEMATOPOIESIS
 Hematopoiesis is the process of formation of blood cells in the body, occurring primarily
in the bone marrow.
 This process includes the production of
 Red blood cells,
 White blood cells,
 Platelets
 The term hematopoiesis originates from Greek, hemato (BLOOD) and poiesis meaning
(PRODUCTION or FORMATION)

3. SITE OF ERYTHROPOIESIS (IN FETAL LIFE)
 1. Mesoblastic Stage: During first two months of intrauterine life, RBCs are produced
from mesenchyme
 2. Hepatic Stage: From third month of intrauterine life, liver is the main organ that
produces RBCs
 3. Myeloid Stage: During last three months of intrauterine life, the RBCs are produced
from red bone marrow and liver

4. SITE OF ERYTHROPOIESIS
 In newborn babies, children and adults: RBCs are
produced from the red bone marrow
 1. Up to age of 20 years: RBCs are produced
from red bone marrow of all bones (long bones
& all flat bones)
 2. After age of 20 years: RBCs are produced
from membranous bones like vertebra,
sternum, ribs, scapula, iliac bones & skull bones
and from ends of long bones

5. CELLULAR PATHWAY OF HEMATOPOIESIS
 STEM CELLS
PROGENITOR CELLS
PRECURSORS CELLS
EFFECTOR CELLS

6. STEM CELL
 Stem cells play a crucial role in hematopoiesis, Hematopoietic stem cells (HSCs) are
multipotent stem cells found in the bone marrow that can differentiate into various
types of blood cells, including
 red blood cells (erythrocytes)
 white blood cells (leukocytes)
 and platelets (thrombocytes).
 These stem cells have the remarkable ability to self-renew, ensuring a constant supply
of blood cells throughout life. They are essential for maintaining the body's immune
system and ensuring proper oxygen transport, clotting, and defense against infections.

7. PROGENITOR CELLS
 In hematopoiesis, progenitor cells are intermediate cells derived from hematopoietic stem cells (HSCs) and give rise to
specific blood cell lineages. Here are the main progenitor cells involved:
 Myeloid Progenitor Cells:
 Common Myeloid Progenitor (CMP):
 Gives rise to erythrocytes (red blood cells), platelets, granulocytes (neutrophils, eosinophils, basophils), and monocytes/macrophages.
 Megakaryocyte-Erythroid Progenitor (MEP):
 Differentiates into megakaryocytes (which produce platelets) and erythrocytes.
 Granulocyte-Monocyte Progenitor (GMP):
 Produces granulocytes (neutrophils, eosinophils, basophils) and monocytes (which become macrophages upon migration into tissues).

8. CONT.
 Lymphoid Progenitor Cells:
 Common Lymphoid Progenitor (CLP):
 Gives rise to lymphocytes, including T cells, B cells, and natural killer (NK) cells.
 These progenitor cells undergo further differentiation and maturation steps under the
influence of various growth factors, cytokines, and microenvironmental cues in the bone
marrow niche. This process ensures the continuous production of all types of blood cells to
maintain homeostasis and respond to physiological needs and challenges.

9. PRECURSORS CELL
 In hematopoiesis, precursor cells are intermediate stages of differentiation between progenitor cells and fully
mature blood cells. These precursor cells are committed to a specific lineage and undergo further maturation
to become functional blood cells. Here are some key precursor cells involved in hematopoiesis:
 Proerythroblasts:
 Precursors of red blood cells (erythrocytes).
 They contain cytoplasmic hemoglobin and gradually decrease in size as they mature.
 Megakaryoblasts:
 Precursors of platelets (thrombocytes).
 They undergo a process of endomitosis to become polyploid megakaryocytes.

10. CONT.
 Myeloblasts:
 Precursors of granulocytes (neutrophils, eosinophils,
basophils).
 They exhibit prominent nucleoli and a high nuclear-to-
cytoplasmic ratio.
 Monoblasts:
 Precursors of monocytes, which mature into tissue
macrophages.
 They have a less condensed chromatin compared to
myeloblasts.
 Lymphoblasts:
 Precursors of lymphocytes (T cells, B cells, natural killer
cells).
 They undergo rearrangements of their antigen
receptor genes during maturation.

11. EFFECTOR CELLS
 In hematopoiesis, effector cells are fully differentiated blood cells that perform specific functions within the
bloodstream or tissues. Here are the main effector cells in hematopoiesis:
 Erythrocytes (Red Blood Cells):
 Responsible for oxygen transport from the lungs to tissues and carbon dioxide transport from tissues to the
lungs.
 Lack a nucleus and most organelles, allowing for maximum space for hemoglobin, the oxygen-carrying
protein.
 Platelets (Thrombocytes):
 Essential for blood clotting (hemostasis) to prevent excessive bleeding.
 Form clots at the site of vascular injury, sealing the damaged blood vessel and initiating the repair process.

12. CONT.
 Granulocytes:
 Neutrophils:
 First responders to bacterial infections.
 Engulf and destroy bacteria through
phagocytosis.
 Eosinophils:
 Involved in allergic reactions and
defense against parasitic infections.
 Release toxins to kill parasites and
modulate allergic responses.
 Basophils:
 Release histamine and other mediators of inflammation.
 Contribute to allergic reactions and inflammatory responses
 Monocytes/Macrophages:
 Monocytes circulate in the bloodstream before migrating
into tissues, where they differentiate into macrophages.
 Macrophages are involved in phagocytosis, antigen
presentation, and tissue remodeling.
 Play key roles in immune defense, wound healing, and
maintaining tissue homeostasis.

13. CONT.
 Lymphocytes:
 T Cells:
 Involved in cell-mediated immunity.
 Recognize and eliminate infected or abnormal cells
and regulate immune responses.
 B Cells:
 Responsible for humoral immunity.
 Produce antibodies (immunoglobulins) that
neutralize pathogens and mark them for destruction.
 Natural Killer (NK) Cells:
 Provide rapid responses against virus-infected cells
and tumor cells.
 Induce apoptosis (cell death) in target cells.

18.  Lymphocytes are involves in the production of new lymphocytes, including B
lymphocytes, T lymphocytes, and natural killer (NK) cells. B lymphocytes
primarily produce immunoglobulins, also known as antibodies, and are key
effectors of humoral immunity.
 Life span = average lifespan of a week to a few months, but some live for years.

20. REFERENCE
 https://www.slideshare.net/LadiAnudeep/hematopoiesis-70137084
 https://www.slideshare.net/amenullah1/hematopoisis
 https://my.clevelandclinic.org/health/articles/24287-hematopoiesis
 https://www.medicalnewstoday.com/articles/319544