Haematopoiesis Flashcards
Define myelopoiesis in the broad sense and what it can mean more specificially
- The formation of bone marrow and all the cells which arise from the bone marrow
- It can also specifically mean the formation of granulocytes and monocytes
Define granulopoiesis
This is the formation of granulocytes
Define lymphopoeisis
This is the formation of lymphocyes (B&T cells and NK cells)
Define thrombopoeisis and erythropoeisis
Thrombopoeisis = the formation of platelets
Erythropoeisis = the formation of erythrocytes
What is the lifespan of:
- RBC’s
- Platelets
- Neutrophils
- 120days
- 7-10 days
- 7-8 hours
When a name for a cell has blast on the end of it what does this signify ?
That it is a nucleated precursor cell
- Myeloblast = nucleated precursor for granulocytes
- Erythroblast = nucleated precursor for erythrocytes
Define a myelocyte
It is a nucleated precursor between nutrophils and blast
What are the main developmental events in haematopoiesis as you go down the haematopoietic tree
- Self-renewal: a property of stem cells, lost in descendents
- Proliferation: increase in numbers
- Differentiation: descendents commit to one or more lineages
- Maturation: descendents acquire functional properties and may stop proliferating
- Apoptosis: descendents undergo cell death
Are the majority of stem cells always dividing ?
No the majoirty are in a dormant state
What is meant by the term myeloid?
It can mean a number of things:
- Can mean tissue of the bone marrow or marrow malignancy
- It can also be used to describe the lineage of cells as non-lymphoid (refer to pic)
- It can also be used to describe granulocytes and there precursors -myeloid:erythroid
Describe the sites of haematopoiesis
- Haemopoietic stem cells are derived from the mesoderm just after conception
- Yolk sac, the first site of erythroid activity, stops by week 10
- Liver starts by week 6, has stopped producing by birth
- Spleen by week 12 (probably only a small contribution in humans)
- Bone marrow by week 16 – and in an adult is the predominant site, note tibia and femur stop as you get older leaving mainly axial skeleton
What are the different ways in which stem cells can be collected ?
What are the ways in which bone marrow biopsy differs in the age of the person having it done and how it differs from normal stem cell collection?
- Normally stem cells are collected from the blood, you will have weekly injections of growth factor (G-CSF). This encourages the stem cells to move (mobilise) from the bone marrow into the blood. Once mobilised, the stem cells will be collected. This takes between 3-4 hours using a cell-separator machine.
- You may need a bone marrow biopsy e.g. to see if you have cancer in your bone marrow, in adults it is usually collected from the PSIS, in kids usually from the tibia
Where is bone marrow located divide this up into the location of red and yellow marrow
Bone marrow is the soft, spongy, gelatinous tissue found in the hollow spaces in the interior of bones.
- Red marrow is found mainly in the flat bones, such as the hip bone, sternum (breast) bone, skull, ribs, vertebrae, and shoulder blades, as well as in the metaphyseal and epiphyseal ends of the long bones, such as the femur, tibia, and humerus, where the bone is cancellous or spongy.
- Yellow marrow more found in the hollow interior of diaphysis
What is the endosteum ?
The interface between bone and bone marrow
What are the different compartments of the bone marrow ?
Cellular:
- Haemopoietic cells
- Non-haemopoietic cells - (eg adipocytes, ‘fibroblasts’ osteoclasts, osteoblasts)
Connective tissue matrix
Vascular elements
What is the blood supply to the bone and bone marrow ?
Nutrient artery and periosteal network (arteries)
Describe the venous drainage of bone marrow and bone
Arterioles (this is still an artery) drain into ‘sinuses’ (sinusoids) – wide venous vessels, which open into larger central sinuses
Describe the structure of a sinus
Fenestrations increase the permeability of endothelial cells
Describe the release of mature cells from the bone marrow
- Formed blood cells can pass through fenestrations in endothelial cells to enter circulation – refer back to last slide
- Release of red cells is associated with sinusoidal dilatation and increased blood flow
- Neutrophils actively migrate towards the sinusoid
- Megakaryocytes extend long branching processes called proplatelets into the sinusoidal blood vessels
What is the difference between red and yellow bone marrow ?
- Red marrow is where haematopoiesis takes place
- Yellow marrow (inactive)
Define myeloid:erythroid ratio
Relationship of neutrophils and precursors to proportion of nucleated red cell precursors (ranges from 1.5:1 to 3.3:1) – can change (eg reversal in haemolysis as a compensatory response)
What are the 2 main ways in which haematopoeisis can be regulated?
- Intrinsic properties of cells (e.g stem cells vs progenitor cells vs mature cells)
- Signals from immediate surroundings and the periphery (microenvironmental factors)
Give some examples of how haematopoiesis is regulated
Erythropoiesis can also be regulated by EPO from kidneys
What is meant by niches which haematopoietic stem cells occupy ?
An anatomical site where the stem cell recieves signals for expansion, differentiation or dormancy ==> there are different niches
A cell may be dormant in one niche and then move to another where it then recieves signals to differentiate
The ‘niche’ is around vasculature (arteriole or sinusoid) and provides access to different signals (cytokines) these cytokines are what decide what the stem cells are going to do i.e. differentiate or not
