Haemopoiesis Flashcards
How many red blood cells are there?
3-5 x 10^12/ litre
How often are red blood cells replaced?
every 120 days
How many white blood cells are there?
2-6 x 10^9/ litre
How often are white blood cells replaced?
every 3-5 days
How many platelets are there?
150- 400 x 10^9/ litre
How often are platelets replaced?
every 10 days
Where is haemopoiesis in the first few days of life?
in the yolk sac
Where is haemopoiesis from 6 weeks to 7 months of life?
in the liver and spleen
Where is haemopoiesis throughout life after 7 months?
in the bone marrow - although can return to liver and spleen if bone marrow is too crowded - as a child it is in all bone marrow but as an adult it is in the axial skeleton
Why is the posterior superior iliac spine a good site for a bone marrow biopsy?
because it is in the axial skeleton so haemopoiesis will always be taking place there
What percentage of bone marrow is fat even when active haemopoiesis is taking place?
50%
Can a pluripotent stem cell be identified in the bone marrow?
no
Can colony forming units be identified in the bone marrow?
no - can only recognise maturational steps beyond colony forming units
If the bone marrow is in constant contact with circulating blood what stops maturing blood cells from entering the circulation prematurely?
the developing blood cells have specific adhesion molecules which bind to the bone marrow stroma to keep them there
What is the bone marrow stroma made up of?
cells and extracellular matrix
What is the role of the bone marrow stroma?
to provide the specific microenvironment for cell maturation
What are haemopoietic growth factors?
glycoprotein hormones which act on specific receptors expressed on the maturing cells to signal maturation - there is a lot of redundancy in the growth factors with multiple growth factors acting on every part of the pathway
Which haemopoietic growth factor acts on the beginning of the pathway at the pluripotent stem cell?
SCF
Which haemopoietic growth factor produces eosinophils?
IL-5
Which haemopoietic growth factor produces neutrophils?
G-CSF
Which haemopoietic growth factor produces monocytes?
M-CSF
Which haemopoietic growth factor produces red blood cells?
EPO
Which haemopoietic growth factor produces platelets?
IL-6
Which haemopoietic growth factors act across all lineages?
IL-3 and GM-CSF
What is the two fold action of GM-CSF?
the actions of GM-CSF depend on the cell that it hits and which receptor its expressing - in the event of sepsis there is an upregulation of GM-CSF which will both activate mature cells to phagocytose and turn on production
What is the mechanism of action of haemopoietic growth factors?
the growth factor binds to an extracellular receptor which turns on an intracellular second messenger system to activate transcription factors for cell proliferation, differentiation or activation
What are haematinics?
agents required for red blood cell production - iron, folate and B12
What are the features of red blood cells?
membrane, haemoglobin and enzymes
What are the causes of iron deficiency?
inadequate diet, blood loss
What are the causes of B12 deficiency?
inadequate diet, poor absorption and rarely an abnormality in a metabolic pathway
Which haematinics are required for all cell production - not just red blood cells?
B12 and folate
What are the causes of a folate deficiency?
inadequate diet (particularly in alcoholics), or drugs such as methotrexate
