Hematopoiesis

Question 1

hematopoiesis

Answer 1

formation and development of blood cells

Question 2

The hematopoietic system

Answer 2

lymph nodes

• thymus
• liver
• spleen
• bone marrow

Question 3

three phases of hematopoiesis

Answer 3

1. mesoblastic phase (2-12 wks): blood islands from primitive erythroblasts
2. hepatic phase (5 wks to birth):
   - liver is major site of hematopoiesis during 2nd trimester
   - spleen, kidney, thymus and lymph nodes also
   - granulocytes, monocytes, lymphocytes, and megakaryocytes appear
3. medullary phase (5 mos to remainder of life):
   - bone marrow takes over production
   - major site by wk 24

Question 4

T or F. Active bone marrow decreases as we age

Answer 4

T!

Estimated BM cellularity: 100 - age (+/- 10%)

Question 5

requirements for hematopoiesis

Answer 5

• adequate micro-environment (stroma)
• hematopoietic stem cells
• nutrients (iron, vitamin B12, folate)
• hematopoietic growth factors and cytokines
• feedback inhibition mechanisms

Question 6

Stromal cells include (7)

Answer 6

• endothelial cells: control flow of particles entering/leaving
• macrophages: phagocytosis, secrete cytokines/growth factors
• osteoblasts: bone-forming cells
• osteoclasts: bone-resorbing cells
• fibroblasts: form supporting lattice, secrete extracellular matrix
• adipocytes: fat cells, secrete cytokines/growth factors
• lymphocytes: cytokines/growth factors
• critical role in the regulation of hematopoietic stem cells

Question 7

Hematopoietic Stem Cells (HSCs)

Answer 7

• capable of self renewal
• pluripotent
• can give rise to differentiated progeny
• are able to reconstitute the hematopoietic system of lethally irradiated host
• 3 fates: self-renewal, differentiation, apoptosis

Question 8

hematopoietic growth factors and cytokines

Answer 8

• regulate proliferation, differentiation, and maturation of hematopoietic precursor cells (method of INTERcellular communication
• may exert a positive or negative effect on proliferation
• prevent apoptosis of precursor cells
• includes CSF (colony stimulating factors), IL, and chemokines + interferons

Question 9

glycoprotein hormone produced in the renal peritubular interstitial cells

Answer 9

EPO (erythropoietin)

Question 10

EPO

Answer 10

• stimulates proliferation of committed erythroid cells
• regulates rate of erythropoiesis: early release of reticulocytes from bone marrow, prevents apoptosis for RBC precursors, reduces time needed for RBC precursors to mature
• induces hemoglobin synthesis

Question 11

nutritional requirements for erythropoiesis

Answer 11

1. protein and amino acids: building blocks of Hb
2. vitamin B12 and folic acid: DNA synthesis
3. vitamin B6 (pyridoxine): heme synthesis
4. vitamin C: iron absorption
5. iron: hemoglobin synthesis & cell proliferation
6. copper: intracellular iron utilization
7. cobalt: component of vitamin B12

Question 12

Erythropoiesis summary

Answer 12

occurs with maturation:

• decrease in cell size
• condensation of nuclear chromatin
• loss of nucleoli
• decrease in N:C ratio
• decrease in RNA and mitochondria
• increase in Hb

Question 13

Granulopoiesis summary

Answer 13

with maturation:

• decrease in size
• condensation of nuclear chromatin
• change in nuclear shape
• change in cytoplasm colour
• appearance and disappearance of primary granules
• appearance of secondary granules

Question 14

platelets are derived from megakaryocytes in a process called

Answer 14

endomitosis

• nucleus is duplicated but no cell division occurs
• polyploid cell
• cytoplasm of megakaryocytes becomes platelets

Question 15

Granulopoiesis pools (3) of developing cells in bone marrow

Answer 15

1. stem cell pool: HSCs (self-renewing)
2. proliferation pool: CMP, GMP, myeloblasts, promyelocytes, myelocytes
3. maturation pool: metamyelocytes, bands, segmented granulocytes

Question 16

Granulopoiesis pools (2) of developing cells outside bone marrow

Answer 16

1. circulating pool (blood)
2. marginating pool (tissues or on capillary walls)

after cells have matured, can migrate between these pools

Question 17

in late stage of this stage of erythropoiesis, nucleus is ejected and engulfed by macrophages

Answer 17

orthochromic normoblast

- chromatin is completely condensed = pyknotic