Haemopoiesis Flashcards
what is haemopoiesis
blood cell production
continual cellular process of proliferation, differentiation, morphogenesis, functional maturation and finally death
what are the cell types
erythrocytes, neutrophils, lymphocytes, monocytes, eosinophils, basophils, platelets, natural killer cells, dendritic cells …. and so on and so on
what are haemopoietic stem cells and what are their role
all blood cells are derived from precursors in the bone marrow (pluripotent)
stem cell pool
present in very small numbers
process of differentiation and maturation to the morphologically recognisable ‘end’ cells is accompanied by the progressive commitment to a particular cell line
differentiates into commited progenitor cells destined to further differentiate into erythroid, phagocytic, megakaryocytic and lymphoid cells
only cells differentiated beyond stem cell and progenitor cell stage can be recognised morpholigically
what can pluripotent haemopietic stem cells do
thy can replicate themseves and the daughter cellsretain the same proliferative and development potential as original parent cell. they then can differentiate into blood cells.
this is because they have an extensive self maintenance capability that does not appear to decline with age.
they spend most of their time in the go phase
(a long g0 stage means more time for DNA repair)
they can repopulate the bone marrow after injury or irradiation
what are the developmetnal periods
mesoblastic period
hepatic period
myeloid (medullary) period
extramedullary period
what happens in the mesoblastic period
shortly after fertilisation, the blastocyst differentiate into three distinct layers - ectoderm, mesoderm, endoderm
mesoderm gives rise to basophilic cells ‘blood islands’ located in the yolk sac
first detectable at 19-20 days gestation, then through to approximately the 8th week gestation
responsible for red cell production
what happens in the hepatic period
morphological haemopoiesis begins in the liver during the 5th and 6th week of gestation
primary site of blood cell development between the 10th and 30th weeks
remains active until 1st and 2nd week after birth
initially an erythoid organ, by the 2nd month granulocytes and megakaryocytes begin to appear, lymphocytes by 4th month and monocytes by the 5th month
spleen, thymus and lymph nodes also become active in the blood cell production
what happens during the myeloid period
during the 5th month bone cavities begin to form and the bone marrow becomes the main site of blood cell production
after the 1st three week postnatal, the bone marrow becomes the only normal site and remains so throughout life
during the 1st few years - delicate balance exists between the developing bone marrow space and the infants need for blood cells (spleen and liver remain available)
at birth (and early childhood), red marrow is located in most bones
form approximately 4 to 18 years onwards, bone marrow growth exceeds the need for blood cells and red marrow increasingly becomes yellow , fatty marrow
after which, active sites of haemopoiesis are pelvis, sternum and long bones etc
if necessary, yellow fatty marrow can be reactivated in a short period of time
what is extramedullary haemopoiesis
in certain disease states the bone marrow is unable to produce suffecient numbers of haemopietic cells
in these situations the liver and spleen can become active sites for haemopoiesis
what is erythropiesis
red cell production controlled by several growth factors
il-3 and GM-CSF act early on cells not yet committed
once committed, main growth factor is erythroproietin
produced mainly in the kidneys- liver and brain also make small amounts
production is inversely related to the renal oxygen tension
acts by accelerating the commitment of cells to erythoid lineage and enhancing the rate of division and maturation
rate of mitosis is increased and maturation process shortens
what is myelopoiesis
one stimulus is fall in granulocytes in the bone marrow
monocytes produce IL-3 which can stimulate in the microenvironment to produce GM-CSF
GM-CSF increases commitment to granulocyte and monocyte lineages
G-CSF to granulocytes, M-CSF to monocytes and IL-5 to eosinophils
transforming growth factor- beta and macrophage inhibitory factor inhibit the proliferation of progenitor cells
what is thrombopiesis
IL-3 and GM-CSF act early on cells not yet committed
thrombopoietin then stimulates megakaryocytic maturation adn platelet release
TPO produced predominantly in the kidney
speeds up maturation of megakaryocytes - results in less platelet production per cell
