Hematopoiesis Flashcards
what produces hematopoietic stem cells (HSCs) and endothelial cells?
common embryonic stem cells called hemangioblasts
where do embryonic hematopoietic stem cells (HSCs) originate?
in the yolk sac and aorta-gonad-mesenephros (AGM) region of the embryo
what species is the exception when it comes to blood cell types in utero?
cats - they produce a wider spectrum of blood cell types
describe the appearance of embryonic cells
they are huge and nucleated
when does bone marrow organization begin?
during the second trimester
describe bone development in 4 steps
- *
1. cartilage is calcified
2. chondroclasts degrade mineralized cartilage
3. vessels invade marrow space that is created
4. osteoblasts form bony trabeculae - *
what two things form a connective tissue meshwork?
- vascular sinuses
2. extravascular mesenchymal stromal cells
when do hematopoietic cells from liver form circulating blood cells?
once hematopoietic microenvironment forms
what is extravascular space?
space between the vascular sinuses in bone marrow
what does extravascular space create?
a hematopoietic microenvironment
what does the extravascular space contain?
- stromal elements (cells and extracellular matrix)
- osteoclasts, plasma cells, mesenchymal stem cells, mast cells (rare)
- accessory cells for hematopoiesis
- hematopoietic cells
what cells are produced in the vascular space in birds?
erythrocytes and thrombocytes
where are all blood cells created in mammals? where do blood cells then go?
in extravascular space. they then have to migrate through the endothelium and into sinus, then circulatory system once its developed
where are quiescent hemaopoietic stem cells (HSCs) concentrated?
near endosteal and trabecular bone (osteoblasts)
where are more active HSCs and hematopoietic cells found?
near vascular sinuses
where are erythroid cells found?
around macrophages
where are megakaryocytic cells found?
near sinusoidal endothelial cells
where are granulocytic cells found?
near stromal cells located away from vascular sinuses
what cells are found in bone marrow stroma (connective tissue)?
- endothelial cells
- stromal cells
- adipocytes
- autonomic nerves
- extracellular matrix
what is the function of bone marrow endothelial cells?
they synthesize hematopoietic growth factors
what do bone marrow endothelial cells regulate?
** they regulate transendothelial movement of cells to and from the extracellular space**
what do bone marrow endothelial cells and stromal cells produce?
extracellular matrix components
describe some characteristics of bone marrow stromal cells
- fibroblastic-type or vascular smooth muslce like cells
- extensive branched cytoplasmic processes that provide structural support for the bone marrow
what is the function of bone marrow stromal cells?
** they synthesize collagen fibers and other extracellular matrix components **