Lecture 19: Hematopoisis Flashcards
Define hematopoiesis (hemopoiesis).
The process through which formed elements of the blood are produced
Elements:
▪ Erythrocytes
▪ Leukocytes
▪ Platelets
List the 3 major organs involved in hematopoiesis before birth.
1) Yolk - sac phase
- 3rd week gestation
- “Blood Islands”
2) Hepatic phase
- 2nd trimester
3) Bone marrow phase
- 2nd trimester
List the sites where hematopoiesis is predominant as age advances
After birth:
-Bone marrow
Elderly:
-Most in vertebral and pelvis > sternum > ribs > Lmyph > Femur > Tibia
Describe the histological features of various hematopoietic sites in the body as age progresses
HISTO SLIDE
Describe the characteristics of a stem cell:
Cell plasticity
1) Cell plasticity
- Ability of stem cells to form specialized cell types of other tissues
Hematopoietic stem cells – Neurons & glial cells – Skeletal muscle cells – Cardiac muscle cells – Liver cells
• Bone marrow stromal cells
– Cardiac muscle cells
– Skeletal muscle cells
• Neural stem cells
– Blood cells
– Skeletal muscle cells
Define totipotent, pluripotent and multipotent stem cells
1) Totipotent:
-Ability to develop into all
tissues
(Embryonic germ layers,
Extra-embryonic: Placental, amnion, chorion)
2) Pluripotent:
- Ability to develop into all cells and tissues of the body
- Capable of all blood cell lineages & self – renewal
3) Multipotent:
-Ability to develop into a small
number of different cell types
Define and describe hematopoietic stem cell (HSC)
Function: -Gives rise to multiple colonies of progenitor stem cells ➢Fibroblasts ➢Adipocytes ➢Endothelial cells ➢Osteoblasts
Location:
-Bone marrow (cavity of long & axial bones, surrounded by stroma=support)
Define and describe hematopoietic stem cell niches (Endosteal niche)
A stem cell niche Def:
-A spatial structure (microenvironment) in which
Hematopoietic stem cells are housed
Function:
• Storage of quiescent stem cells
• Self renewal
• Inhibition of differentiation
Location:
-Epiphyseal areas (spongy
bone or “cancellous bone”)
Describe the myeloid and lymphoid lineages
Myeloid Lineage:
Start: Pluripotent Stem cell –> Myeloid Stem cell –> (Diff paths to create the following)
1) CFU-E –> Proerythroblast –> Reticulocyte –> RBC (erythrocyte)
2) CFU-Meg –> Megakaryoblast –> Megakaryocyte –> Platelets (Thrombocytes)
3) Eosinophilic myeloblast –> Basophil (Granular leukocyte)
4) Basophilic myeoblast –> Basophil (Granular leukocyte)
5) CFU-GM –> Myeoblast –> Neutrophil
6) CFU-GM –> Monoblast –> Monocyte –> Macrophages
(Agranular leukocytes)
Lymphoid Lineage:
Pluripotent Stem cell –> Lymphoid Stem cell –> T and B lymphoblasts –> T and B lymphocytes –> B –> Plasma cell
(Agranular leukocytes)
Describe the cellular organization, vascularity and functions of bone marrow
Structure Bone marrow:
1) Reticular fibers, veins, arteries, sinusoids
2) Red bone marrow:
- Active hematopoiesis
3) Yellow bone marrow:
- Fat, capillaries, reticular cells, inactive hematopoiesis
-Hematopoietic stem cells mature they move from endosteal niche (end of bone) to vascular niche (middle of the bone to conduct) hematopoisesis –>
Then do the following:
-Support and promote the differentiation & maturation of progenitors into formed elements of the blood .
-Secretion of growth factors by stromal cells
Describe the role of growth factors, cytokines and hormones involved in hematopoiesis
Role:
-Proliferate and mature progenitor cells (Hematopoietic cells would die without it)
Growth Factors:
1) Erythropoietin (EPO)
- Produced by the kidneys increase erythrocyte precursors
2) Thrombopoietin (TPO)
- Hormone from liver stimulates thrombocyte formation
3) Cytokines are local hormones of bone marrow
-Produced by some marrow cells to stimulate proliferation in other marrow cells
-Colony-stimulating factor (CSF) & interleukin stimulate leukocyte
production
Describe the process of erythropoiesis
- Erthropoiesis:
- Location: Red bone marrow
1) Reduced oxygen levels= Hypoxia occurs (stimulus)
2) Kidneys release Erythropoietin
3) Erythropoietin acts on bone marrow and increases number RBC produced
List & identify the stages of erythrocyte differentiation
1) Proerythroblast
- No hemoglobin
2) Basophilic (early) erythroblast:
- Some hemoglobin
- Nucleus condenses
3) Polychromatophilic erythroblast:
- “Muddy” cytoplasm
4) Orthochromatophilic (late) erythroblast (normoblast):
- Increased hemoglobin
- Nucleus condenses
5) Reticulocyte:
- No nucleus
- Some ribosomes
6) Erythrocyte
- Only hemoglobin
- No ribosomes
Describe the process of thrombopoiesis
Thrombopoiesis:
-Formation of thrombocytes ( platelets)
1) Controlled by thrombopoietin
2) Megakaryoblast
3) Megakaryocyte:
4) Platelets formed by fragments Megakaryocytes
Identify and describe the structure and function of megakaryocytes and formation of platelets
Structure:
(Histo slides)
-Platelets fragmenting off
-Muli-nuclei
Function:
-Forms Platelets from their fragments
