week 3 part 1 Flashcards
Haemopoiesis
the production of blood cells and platelets, which occurs in the bone marrow.
Erythropoiesis
Produces red blood cells (erythrocytes),
Lymphopoiesis
Refers to the production of new lymphocytes, including B lymphocytes, T lymphocytes, and natural killer (NK) cells.
Neutrophils lifespan
7-8 hrs
Platelets lifespan
7-10 days
What do “blasts” mean at the end of cells - e.g. erythrobasts?
Nucleated precursor cell
Megakaryocytes
platelet precursor, polyploid
Reticulocytes
Immediate red cell precursor
Myelocytes
nucleated precursor between neutrophils and blasts
Where do these precursor cells come from?
Progenitors, and ultimately all haemopoietic cells come from haemopoietic stem cells (HSC)
What are the sites of haemopoiesis?
Embryonically, haemopoietic stem cells originate in the mesoderm
Circulating committed progenitors detectable as early as week 5
Yolk sac, the first site of erythroid activity, stops by week 10
Liver starts by week 6
Bone marrow by week 16
In adults, haemopoiesis is restricted to the marrow within axial skeleton, pelvis and proximal long bones
Venous sinuses
Arterioles drain into ‘sinuses’ – wide venous vessels, which open into larger central sinuses
In contrast to capillaries, ‘sinuses’ are larger and have a discontinuous basement membrane
Release of mature cells from marrow
Formed blood cells can pass through fenestrations in endothelial cells to enter circulation
Release of red cells is associated with sinusoidal dilatation and increased blood flow
Neutrophils actively migrate towards the sinusoid
Myeloid:erythroid ratio
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)
How do we assess haemopoiesis?
non-lymphoid mature cells
- Routinely undertaken- blood count, cell indices (by non-specialists), morphology (blood film-specialist)
- Less common (specialist)-bone marrow
examination
Immunophenotyping
Identify patterns of protein (antigen) expression unique to a cell lineage
Use antibodies (in combination) specific to different antigens
What regulates haemopoiesis?
Intrinsic properties of cells (e.g stem cells vs progenitor cells vs mature cells)
Signals from immediate surroundings and the periphery (microenvironmental factors)
Specific anatomical area (‘niche’) for optimal developmental signals
What happens in Malignant Haemopoiesis?
Malignant haemopoiesis is usually characterised by increased numbers of abnormal & dysfunctional cells & loss of normal activity
What causes haematological malignancies?
Genetic, epigenetic, environmental interaction
ACQUIRED somatic mutations in regulatory genes [driver mutations vs passenger mutations (‘noise’)]
Recurrent cytogenetic abnormalities (eg deletions, chromosomal translocations etc): NOT causal in most, but contributory
What are clones?
Clone: population of cells derived from a single parent cell
This parent cell has a genetic marker (driver mutation or chromosomal change) that is shared by the daughter cells
Clones can diversify but contain a similar genetic ‘backbone’
Normal haemopoiesis is polyclonal; malignant haemopoiesis is usually monoclonal
Driver’ mutations
Confer growth advantage on the cells and are selected during the evolution of the cancer
A term used to describe changes in the DNA sequence of genes that cause cells to become cancer cells and grow and spread in the body.
Passenger mutations
Do not confer growth advantage, but happened to be present in an ancestor of the cancer cell when it acquired one of its drivers
Passenger mutations are defined as those which do not alter fitness but occurred in a cell that coincidentally or subsequently acquired a driver mutation, and are therefore found in every cell with that driver mutation.
Types of haematological malignancies based on:
- Lineage: Myeloid, Lymphoid
- Developmental stage
- Blood involvement: leukaemia
- Lymph node involvement with lymphoid malignancy: lymphoma
- Myeloma: plasma cell malignancy in marrow
Features of clinical aggression
rapid progression of symptoms
Features of histological aggression
Large cells with high nuclear-cytoplasmic ratio, prominent nucleoli, rapid proliferation
Difference between histology and presentation of acute leukaemias/high-grade lymphomas and chronic leukaemias/low-grade lymphomas
acute leukaemias & high-grade lymphomas are histologically and usually clinically more aggressive than chronic leukaemias & low-grade lymphomas