1. Hemopoietic bone marrow is initially found in many locations but becomes restricted to the axial skeleton after puberty. 2. Bone marrow contains hematopoietic stem cells that differentiate into the erythroid, thrombocytic, granulocyte-monocyte, and lymphoid lineages. 3. Bone marrow is located in the medullary canals of long bones and cancellous bone cavities, and contains reticular connective tissue, hematopoietic cords, and sinusoidal capillaries that allow new blood cells to enter circulation.

4. Sites:
Hemopoietic bone marrow occurs in
many locations through puberty, but
then becomes increasingly restricted to
components of the axial skeleton.

14. Hemopoietic stem cells

15. 1- Erythroid lineage
2- Thrombocytic lineage
3- Granulocyte-monocyte lineage
4- Lymphoid lineage

19. Bone marrow
• Found in medullary canals of long bones and small cavities of cancellous bone
• Two types
1- red bone marrow
2- yellow bone marrow due to accumulation of fat ( adipocyte )
• Bone marrow contain
1- reticular connective tissue stroma
2-hemopoietic cords or islands ( c )
3- sinusoidal capillaries
• The hematopoietic niche in marrow includes the stroma, osteoblasts, and
megakeryocytes
• Between the hematopoietic cords run the sinusoids, which have discontinuous
endothelium, through which newly blood cells and platelets enter the circulation.

24. proerythroblast (P)
basophilic
erythroblast (B)

25. polychromatophilic
erythroblasts
orthochromatophilic erythroblast
reticulocytes

36. - Larger than erythrocyte
- Mutilobulated ( 3-5 )
- Also called polymorphonuclear
leukocytes

58. (a)Megakaryoblasts (Mb) are very large, fairly rare cells in bone marrow, with very basophilic cytoplasm.
(b) Megakaryoblasts undergo endomitosis (DNA replication without intervening cell divisions), becoming
polyploid as they differentiate into megakaryocytes (M). These cells are even larger but with cytoplasm
that is less intensely basophilic.
(c) Micrograph of sectioned bone marrow in which a megakaryocyte (M) is shown near sinusoids (S).
• Complex process extend many long, branching pseudopodia-like projections called proplatelets,
from the ends of which platelets are pinched off almost fully formed.