Hematopoiesis Flashcards
what is hematopoiesis?
formation and development of blood cells
what are the three components of hematopoiesis?
erythropoiesis
leukopoiesis
thrombopoiesis
how are cell numbers maintained?
interaction of hematopoietic organs and humoral regulatory molecules
what organs are involved in hematopoiesis?
bone marrow
thymus
lymph nodes
spleen
mononuclear phagocyte system
liver
where is most hematopoietic activity by birth?
bone marrow
in the embryo, where does erythropoiesis occur?
yolk sac
what functions does bone marrow serve?
major site hematopoiesis in adults
storage/reserve of mature cells
iron storage pool
lipid storage (inactive marrow)
where is active bone marrow retained in older animals?
epiphyses and in flat bones
sternum, pelvis, ribs, vertebrae
what cells is the thymus important for production of?
differentiation of T lymphocytes
production of lymphocytes and cytokines
what functions is the spleen important for?
proliferation lymphocytes
reservoir erythrocytes and platelets
removal/pitting red blood cells
extramedullary hematopoiesis
what is a common site of extramedullary hematopoiesis?
spleen
can occur elsewhere: lymph nodes, liver
what is extramedullary hematopoiesis?
hematopoietic activity in non-bone marrow tissues
what cells are central in the mononuclear phagocyte system?
tissue macrophages
why is the liver important?
vitamin storage
production of coagulation factors
production of erythropoietin precursor
can act as site of extramedullary hematopoiesis
what are the sites of hematopoiesis in fish and amphibians?
kidney
liver
spleen
can disruption of the microenvironment disrupt hematopoiesis, even if the hematopoietic cells themselves are normal?
yes
what cells control the release of blood cells from the marrow into the circulation?
endothelial cells lining the sinuses
what functions does the circulation serve for hematopoiesis?
nutrition
exit route for cells to enter bloodstream
what are some cytokines that control hematopoiesis?
colony-stimulating factors
interleukins
other factors
what does interleukin-1 stimulate?
myelopoiesis
is interleukin-1 pro-inflammatory or anti-inflammatory?
pro-inflammatory especially with TNF
what does interleukin-1 inhibit?
erythropoiesis: contributes to anemia of inflammation
where are stem cells primarily located?
in bone marrow
what are all blood cells derived from?
primitive mesenchymal cells known as pluripotent hematopoietic stem cells
what is differentiation?
commitment of progenitor cells to a particular cell line or lines
what is maturation?
development of a differentiated cell into a functional blood cell
what does myeloid refer to?
may refer to granulocyte +/- monocyte cell lines or all non-lymphocytic hematopoietic cell lines
what is the majority of cells seen in bone marrow examination?
precursor cells
what are precursor cells subdivided into?
mitotic (proliferative)
post-mitotic (maturation and storage)
who has large amounts of active bone marrow?
young animals
can active bone marrow expand back into long bone shafts/extramedullary shafts with increased need for hematopoiesis?
yes
what is pitting and which organ does it?
removal of abnormal structures from red blood cells without cell destruction
spleen
what do nonhematopoietic cells provide?
structural support
nutrients
growth factors
what provides the scaffolding for hematopoietic cells?
reticular cells and trabeculae
what are cytokines?
proteins that modulate the functions of other cell types
what can produce cytokines?
most are produced by macrophages or lymphocytes
also: endothelial cells, epithelial cells, connective tissue cells
can pluripotent hematopoietic stem cells enter circulation?
yes
does maturation or differentiation correspond with morphologic changes in the cells?
maturation
what happens with the size of erythrocytes as they mature?
decrease in size as they mature
at what stage does the cytoplasm of erythrocytes become visible?
rubricyte stage
how do macrophages support red cell precursors?
provide nutrients
phagocytize defective cells and extruded nuclei
what is the first identifiable erythroid cell?
rubriblast
a rubriblast eventually produces about ____________________
16 mature red blood cells
what hormones regulate erythropoiesis?
erythropoietin
interleukin-3 and colony-stimulating factors
other hormones
what is erythropoietin?
glycoprotein
what produces erythropoietin?
peritubular interstitial cells of the kidney
lesser extent hepatocytes and ito cells in liver
what does erythropoietin inhibit?
apoptosis of erythroid progenitor cells
what are platelets produced from in mammals?
megakaryocytes
what are platelets produced from in species other than mammals?
thromboblasts
what is thrombocytosis?
increased platelets or thrombocytes
what is thrombocytopenia?
decreased platelets or thrombocytes
why are megakaryocytes distinctive in bone marrow?
large size
polyploidy
how are platelets released from mature megakaryocytes?
fragmentation of cytoplasmic extensions
what produces thrombopoietin?
bone marrow
liver
kidney
what is the main growth factor involved in megakaryocytes and platelet production?
thrombopoietin
thrombopoietin binds to circulating _____________, and thus the amount of free TPO is regulated by the total ______________________
platelets
platelet mass
what is the first recognizable cell in the granulocytic lineage?
myeloblast
how many nuclear segments does the segmented cell have?
2-4 nuclear segments
what are reticulocytes?
polychromatophilic erythrocytes stained with new methylene blue stain
immature red blood cells
why might chronic renal failure lead to anemia?
decreased erythropoietin levels
what does erythropoietin stimulate?
proliferation of mitotic erythroid precursor cells
release of immature red blood cells into circulation
why can erythropoietin stimulate platelet synthesis?
structurally similar to thrombopoietin
what hormone decreases the response to erythropoietin?
estrogen
where can megakaryocytes be found?
lung
spleen
bone marrow
where does hematopoiesis occur in the fetus?
liver
spleen
thymus
lymph nodes
what does inactive bone marrow consist of?
adipocytes
endothelial cells
reticular cells
what happens in lymph nodes with hematopoiesis?
lymphocytes and plasma cells
can do other cell lines, uncommon
why does extramedullary hematopoiesis occur?
response to anemia/cytopenias
common in normal too
where does hematopoiesis occur in reptiles?
spleen
bone marrow
why are nerves important in bone marrow?
regulate vascular tone
______________ are a type of cytokine, many of which influence hematopoiesis
interleukins
what does interleukin-1 stimulate?
myelopoiesis
what are colony-forming units?
stem cells and committed precursor cells
when does a red cytoplasm in erythrocyte maturation become visible?
rubricyte stage
what is a polychromatophilic erythrocyte?
nucleus has been extruded
cytoplasm is still kind-of basophilic: ribosomes and RNA
what are reticulocytes?
polychromatophilic erythrocytes stained with new methylene blue
what does erythropoietin inhibit?
apoptosis of erythroid progenitor cells
what is granulocyte maturation characterized by?
production of cytoplasmic granules and increasing nuclear segmentation
what does inactive marrow consist of?
adipocytes
endothelial cells
reticular cells
can lymph nodes act as a site for hematopoiesis of cells other than lymphcytes and plasma cells?
rarely
is it common to see extramedullary hematopoiesis in spleens of normal patients?
yes
what was the mononuclear phagocyte system formerly known as?
reticuloendothelial system
what happens in the mononuclear phagocyte system?
removal and destruction of blood cells
hemoglobin degradation
iron storage
secretion of factors influencing hematopoiesis
where is release of blood cells from marrow controlled?
endothelial cells lining sinuses
can pluripotent hematopoietic stem cells enter circulation?
yes
how much of the bone marrow cells are pluripotent hematopoietic stem cells?
<0.2%
what is the morphology of colony-forming units similar to?
small lymphocytes
red blood cell precursors cluster around a _________________ in erythroid islands
macrophage: nurse cell
how many mature red blood cells does a rubriblast eventually produce?
16
with high erythropoietin levels, platelets may decrease as stem cells differentiate into the _________________________________
erythroid, rather than megakaryocyte, pathway
how does thyroxine stimulate erythropoietin production?
indirectly by increasing tissue oxygen demand