Hematopoiesis

Question 1

Mesoblastic/Yolk Sac Phase

Answer 1

• 2/3 to 8 weeks of gestation
• Blood islands in wall of yolk sac
• Form endothelium of vessels and nucleated RBCs

Question 2

Hepatic Phase

Answer 2

• 2-7 months of intrauterine life
• Production of anucleate erythrocytes
• Megakaryocytes, granulocytes
• Hematopoiesis between hepatocytes and endothelium in “Space of Disse”

Question 3

Splenic Phase

Answer 3

• 10th week to 6-7 months of intrauterine life

- Occurs during Hepatic Phase

Question 4

Myeloid/Bone Marrow Phase

Answer 4

• 6 month intrauterine until death

- Begins after marrow spaces develop in bones

Question 5

Red Marrow

Answer 5

• Site of active hematopoiesis
• Birth to 4-5 years
• More hematopoietic cells than fat cells (adventitial reticular cells)
• Found only in certain bones during adulthood (ilia, sternum, ribs, clavicles, skull, ends of femur/humerus)

Question 6

Yellow Marrow

Answer 6

• Replaces red marrow after 4-5 years of age
• Less active hematopoiesis than red marrow
• Contains many large, fat-filled, adventitial reticular (stromal) cells
• Lipogenesis is stimulated by glucocorticoids

Question 7

Vascular Compartment (CV system)

Answer 7

• Nutrient arteries pass through and enter marrow cavity
• Sinusoids drain into collecting sinuses which drain into central longitudinal vein
• CLV drains into veins that leave bones alongside feeding arteries
• Newly formed blood cells leave via sinusoids

Question 8

Hematopoietic Compartment

Answer 8

• Surrounds the sinusoids in the marrow
• Adventitial reticular cells have elongated processes that extend into hematopoietic compartment
• Reticular fibers form mesh around areas of blood cell formation
• Macrophages found as part of erythroblastic islets
• Macrophages phagocytize new RBC nuclei and old/deteriorated RBCs

Question 9

Pluripotent Hematopoietic Stem Cell (PHSC)

Answer 9

• Gives rise to all elements of formed blood
• During division, one daughter cell remains a PHSC while the other becomes a progenitor cell
• Stem cell population capable of self-renewal
• Express CD34

Question 10

Differentiation of PHSCs

Answer 10

1) PHSC
2) Multipotential progenitor cells
3) Lineage-specific precursors (committed precursor cells)
4) Morphologically identifiable stages typical of that cell type

Question 11

Multipotential progenitor cells

Answer 11

• No longer capable of self-renewal

- Can develop into several types but not all cell types

Question 12

Erythropoiesis

Answer 12

• Occurs in cell clusters called erythroblastic islets-
• Central macrophage surrounded by multiple cells in varying stages of development
  1) Proerythroblast
  2) Basophilic Erythroblast
  3) Polychromatophilic Erythroblasts
  4) Orthochromatic Erythroblast (normoblast)
  5) Reticulocytes
  6) Mature erythrocytes

Question 13

Granulopoiesis (Neutrophils)

Answer 13

Common myeloid progenitor can produce all 3 granulocytes

1) Myeloblasts
2) Promyelocytes
3) Neutrophilic Myelocytes
4) Metamyelocytes
5) Neutrophilic band/stab cell
6) Mature neutrophil

Question 14

Metamyelocytes

Answer 14

-Contain v-shaped indentations of the nucleus

Question 15

Myelocyte

Answer 15

• Earliest recognizable/distinguishable stage of granulopoiesis
• Eosinophilic - Synthesize eosinophilic specific granules containing crystalloid
• Basophilic - Synthesize large basophilic granules that obscure the nucleus
• Neutrophilic - Relatively hard to distinguish granules
• Last stage capable of mitosis

Question 16

Monopoiesis

Answer 16

1) CFU-M
2) Promonocytes
3) Can differentiate monocytes or form a pool that can be quickly matured to meet special demand
4) Tissue macrophages

Question 17

Thrombopoiesis

Answer 17

1) CFU-Meg
2) Megakaryoblast
3) Megakaryocyte
4) Platelet

Question 18

Lymphopoiesis

Answer 18

1) CFU-L
2) CFU-LyB or CFU-LyT
3) Mature small lymphocytes
4) Blast transformation to increase size