Origin of blood cells Flashcards
Define and describe haematopoiesis
βIt is the formation of blood cells.
βSTEM CELLS β PROGENITORS β IMMATURE PRECURSORS β MATURE CELLS.
βthis is a one way process
βThroughout the process of making specialised cells from stem cells, growth factors are added throughout.
Give three examples of precursors and the mature cells that they produce
β Ξ²-LYMPHOCYTES make PLASMA CELLS
βMONOCYTES make MACROPHAGES
βMEGAKARYOCYTES make PLATELETS
what are megakaryocytes?
megakaryocytes are large polyploid cells which platelets bud off of
What are the different sites of haematopoiesis throughout a humanβs lifetime?
βIN THE EARLY FOETUS: in the yolk sac βIN THE FOETUS: in the liver βIN AN INFANT: throughout the bone marrow βIN AN ADULT: β central skeleton β vertebrae βribs and sternum β skull β sacrum β pelvis β in the proximal ends of the humerus and the femur
Describe the bone marrow
βThe bone marrow is a spongey, jelly-like tissue.
β It has many blood vessels which bring nutrients and take away new blood cells.
βIt is a metabolically active, highly innervated organ.
what are the two different types of bone marrow?
βRED MARROW: where active haematopoiesis takes place
βYELLOW MARROW: where it is filled with fat cells
What is the difference between a bone marrow trephine biopsy and a bone marrow aspiration?
βBONE MARROW TREPHINE BIOPSY: - bone marrow is removed in pieces ( 1 or 2cm core of bone marrow) used to examine the bone marrow architecture
βBONE MARROW ASPIRATION: - bone marrow cells are sucked out in a syringe - used to examine cellular morphology
how many red blood cells does adult bone marrow produce?
2x10^11 RBC
how many neutrophils does adult bone marrow produce?
5x10^10 neutrophils
why is haematopoeisis a one way process?
as an anti cancer mechanism
What are the most common cells seen in the bone marrow?
β myelocytes and myeloblasts.
Describe the formation of neutrophils (myelopoiesis)
βmyeloblast β promyelocyte β myelocite βmetamyelocyte β band β segmented neutrophil (Caps ones are more important)
what are the steps of erythropoeisis?
β PROERYTHROBLAST β BASOPHILIC ERYTHROBLAST β POLYCHROMATIC ERYTHROBLAST β PYKNOTIC ERYTHROBLAST β RETICULOCYTE βMATURE RED BLOOD CELL As we go along, the nucleus shrinks and the cytoplasm gets pinker
what are the steps of platelet formation?
β MEGAKARYOBLAST (to the next step, there is only DNA replication, no cell division)
βMEGAKARYOCYTE
β BLOOD PLATELETS
what do high level of reticulocytes in the blood mean?
β that the bone marrow is working overtime to produce new red cells
what are the steps of lymphocyte formation?
βSTEM CELL
β forms a COMMON LYMPHOID PROGENITOR
β forms either a T-LYMPHOCYTE or a B-LYMPHOCYTE
Where does T-Cell formation occur?
β T-Cell formation occurs in the thymus ( in the chest)
β The early progenitor migrates to the thymus and T-Cell receptor gene arrangement occurs
β Positive (check that they work) and negative selection also occur
Where does B-Cell formation occur?
βB-Cell formation occurs in the bone marrow.
βImmunoglobin gene arrangement occurs.
βexpression of surface IgM (immunoglobulin)
βThe immature B-Cell migrates to the secondary lymphoid organs (lymph nodes) for maturation and antigen selection.
why are progenitors considered undifferentiated?
βundifferentiated because you cannot tell the difference between them morphologically
since they donβt show the characteristics of mature cells.
why are progenitors considered committed?
βthey are committed to what they will become when they produce mature cells
Why are progenitors called Colony Forming Units (CFUs) and how many cells can be in a colony?
βProgenitors grow to form colonies of mature cells.
β from 32 to hundreds or thousands of cells in a colony.
what are some examples of some colony forming units?
β CFU- G granulocyte progenitor β CFU- GM granulocyte/monocyte progenitor β CFU - E erythroid progenitor β CFU- bas β CFU-eo β CFU - MK megakaryocyte progenitor
why do some erythroid colonies look like they have burst and what are they called?
β because they are mobile
β BFU - E (burst forming unit)
What are CSFs?
Factors which were discovered to stimulate colony growth were named Colony Stimulating Factors or CSFs
List some examples of CSFs
βG-CSF: granulocyte-CSF
β M-CSF: monocyte-CSF
βGM-CSF: granulocyte/monocyte-CSF
what is G-CSF used for?
β used for patients that are not making neutrophils due to chemotherapy
what are the steps for bone marrow transplantation?
β completely ablate haemopoeisis with radiation and drugs
β infuse compatible donor bone marrow cells
β haemopoeisis can be completely restored
what are the requirements for bone marrow transplantation?
β donor must be HLA matched (human lymphocyte antigen) could be a sibling or unrelated donor
β or autologous BMT
reinfuse the patients with their own bone marrow
what cells can give long term engraftment in bone marrow transplantation?
βonly haematopoietic stem cells can give long term engraftment
βnot progenitors
β not precursors
what are the applications of bone marrow transplantation?
β leukaemia, lymphoma, myeloma
β intensified chemotherapy for solid tumors
β thalassemia and SCID
what are the risks of bone marrow transplantation?
β significant mortality while waiting for engraftment
β infection due to neutropenia (low neutrophil count)
β bleeding due to thrombocytopenia (low platelet count)
βGraft versus Host disease (long-term risk in which the graft starts attacking the body)
what is the benefit of bone marrow transplantation?
β only curative treatment
how can haematopoietic stem cells can be described as pluripotent and self-maintaining?
β considered pluripotent because they can give rise to cells of every blood lineage.
β considered self-maintaining because a stem cell can divide to produce more stem cells.
How did we prove that haematopoietic stem cells are pluripotent?
β proved via mice.
βStem cells were marked by retrovirus insertion.
βthen transplanted into irradiated mice with a small number of stem cells.
βThe same marked stem cells gave rise to neutrophils, lymphocytes, etc.
Describe chronic myeloid leukaemia (CML)
βChronic Myeloid Leukaemia (CML) is caused by a chromosome translocation in a stem cell. 9 and 22
βexcess production of neutrophils and neutrophil precursors
βCML mostly affects neutrophil lineage, but the Philadelphia chromosome is also found in T-lymphocytes and other lineages.
What cells present the CD34 antigen, and why?
βStem cells and early progenitors carry the cell surface antigen CD34.
β used to purify stem and progenitor cells.
what are haematopoietic growth factors and what do they do?
βThey are polypeptide growth factors (cytokines).
βThey bind to the cell surface transmembrane receptors.
βThey stimulate the growth and survival of progenitors.
Describe the specificity of haematopoietic growth factors.
βsome stimulate early progenitors (eg. IL-3, stem cell factors (SCF)
βsome stimulate late progenitors (eg. M-CSF (monocyte-CSF)
βsome are specific to one lineage (eg. erythropoietin) βsome stimulate several different lineages
describe erythropoietin
βproduced in the kidney in response to hypoxia. It βincreases RBC production by increasing the survival of erythroid progenitors (CFU-E).
βspecific to one lineage (erythroid) and acts on late progenitors.
what are the clinical applications of erythropoietin?
CLINICAL APPLICATIONS:
β treating anaemia of kidney failure
β an alternative to blood transfusions in Jehovahβs Witnesses
Describe G-CSF
βproduced by many cell types in response to inflammation.
βacts on mature neutrophils in the periphery.
βacts as a chemoattractant
βpromotes neutrophil maturation
βpromotes neutrophil activation
βIt stimulates neutrophil production in the bone marrow.
βstimulates neutrophil progenitors (CFU-G)
βhelps stimulate progenitors of other lineages, but only in combination with other growth factors
βmobilizes cells in the bone marrow
what are the clinical applications of GCSF?
CLINICAL APPLICATIONS:
βstimulates neutrophil recovery after bone marrow transplantation
β stimulates neutrophil recovery after chemotherapy
βtreatment of hereditary (and other cases of) neutropenia (because G-CSF also helps to stimulate other cell lineages, it will also stimulate platelet recovery after bone marrow transplantation)
How does G-CSF treatment contribute to Peripheral Blood Stem Cell Transplantation (PBSCT) and how is PBSCT used?
βG-CSF treatment causes stem cells to be released from the bone marrow into the circulation.
βThis is seen by the appearance of CD34 on cells in the circulation.
βWe can collect the stem cells by leukapheresis.
why can PBSCT be used as an alternative to bone marrow for transplantation?
Itβs less traumatic for the donor, as it is so painless that it does not require a general anaesthetic.
What is reticulocyte?
βImmature RBC that just left the bone marrow.
βStill has some RNA, ribosomes.
βQuickly loses these to make a mature RBC.