Haematopoiesis and Anaemias Flashcards
Main function of red blood cells (erythrocytes)
- transports O2 and CO2
Main function of neutrophils
- phagocytose and destroy invading bacteria
Main function of eosinophils
- destroy larger parasites and modulate allergic inflammatory responses
Main function of basophils
- release histamine (and in some species serotonin) in certain immune reactions
Main function of monocytes
- become tissue macrophages, which phagocytose and digest invading microorganisms and foreign bodies
Main function of B cells
- make antibodies
Main function of T cells
- kill virus-infected cells and regulate activities of other leucocytes
Main function of natural killer (NK) cells
- kill virus-infected cells and some tumour cells
Main function of platelets
- initiate blood clotting
Wright’s stain
- Histological stain that differentiates blood cells
- Eosin bind to basic compounds like proteins in cytoplasm and methylene blue; converting ferric iron in Hb to ferrous iron
Stem Cell Theory of Haematopoiesis
- All cells derived from a pool of stem cells that are self-renewing
- Pluripotential & multipotential stem cells give rise to committed stem cells for each cell line
- Committed stem cells have receptors for specific growth factors
- Respond to stimulation by division & maturation (precursor cell stages) into end-stage cells
Progenitor and precursor cells
- unspecialized or exhibits partial characteristics of specialized cells, but can produce more than one type of specialized cell type
Cell differentiation definitions
- TOTIPOTENT; form all cells including extraembryonic and placental cells
- PLURIPOTENT; give rise to all cell types
- MULTIPOTENT; give rise to more than one cell type but limited
What can multipotent stem cell (MSC) differentiate to?
- Colony Forming Unit-Granulocyte, Erythrocyte, Monocyte, Megaokaryocyte (CFU-GEMM); myeloid cell line - late RBC’s, platelets, granulocytes and monocytes
- Lymphoid stem cell (lymphoid cell line – later lymphocytes and natural killer cells)
Haemopoietic stem cells (HSC)
- HSC are multi-potent stem cells that occur at a
frequency of 1:5000 in bone marrow
Timeline of development of blood cells
- 3 wk : formation of blood islands from yolk sac
- 6 wk : liver becomes hematopoietic organ
- 6-8 wk : spleen (until 8th month)
- ~20wk : bone marrow (life-long)
What is meant by stem cell niche?
- a specific site (microenvironment) in adult tissues where stem cells reside
and undergo renewal and differentiation
What are the 2 haematopoietic niches in bone marrow?
- Osteoblastic niche at the endosteal surface
- Vascular niche involving sinusoidal blood vessels
What is the osteoblastic niche?
- maintains quiescence and harbours the Long Term-HSC
What is the vascular niche?
- supports proliferation, differentiation and mobilization (transendothelial migration) of Short Term-HSC to blood stream in response to physiological demands and act as back up outside the BM for HSC during times of BM stress
Intrinsic v Extrinsic factors controlling haematopoiesis
- Cell fate determination is governed by interactions between extrinsic and intrinsic factors
- Soluble growth factors (extrinsic)
- Transcription factors (intrinsic)
Sequence of erythropoiesis
- proerythroblast
- basophilic erythroblast
- polychromatophilic erythroblast
- orthochromatophilic erythroblast
- reticulocyte
Proerythroblast
- First cell committed to RBC
Basophilic erythroblast
- nucleus becomes smaller
- cytoplasm becomes more basophilic due to the presence of ribosomes
polychromatophilic erythroblast
- produce more haemoglobin
- cytoplasm starts to take up both basophilic and eosinophilic stains
orthochromatophilic erythroblast
- extrudes nucleus
reticulocyte
- cytoplasm containing reticular networks of polyribosomes
- Enters circulation
transcription factors in erythropoiesis
- regulate stem cell survival (e.g. GATA2) or involved in differentiation (e.g. GATA1 – myeloid differentiation)
- can interact to reinforce one programme which may suppress that of another lineage and can induce protein synthesis associated with a specific lineage
soluble factors in erythropoiesis
- act locally or systemically
- May cause proliferation, stimulate differentiation, maturation, prevent apoptosis and affect function
Erythropoietin
- hormone produced in peritubular fibroblast like cells
- anti-apoptotic
- levels increase with decrease in Hb
Red Blood Cell metabolism
- Red blood cells function without a nucleus and mitochondria
- Only nucleated RBC; normoblasts (RBC precursor) and megaloblasts which appear in megaloblastic anaemia
- No nucleus; enhances flexibility, restricts size, increasing O2
carrying capacity - Reduced life span
Pentose Phosphate Pathway
- Generates reduced NAD i.e. NADPH
- NADPH generates reduced glutathione (anti-oxidant)
- Generation of reduced glutathione stimulates glucose metabolism
- help prevent oxidative stress
- to reduce the oxidated form of glutathione
- keep haemaglobin in ferrous state (Fe2+ allow O2 binding)
Methemoglobin reductase pathway
- Maintains iron in Fe2+ state
Leubering Rapaport Bypass
- 2,3-DPG regulates O2 carrying capacity and release
Lactic acid fermentation
- Produces NAD+ and ATP
How do red blood cells make ATP?
- EMBDEN MEYERHOF PATHWAY
- glycolysis of glucose to pyruvate forming ATP and NADH
- lactic acid fermentation on pyruvate forming ATP, NAD+, lactate
Causes of anaemia
- decrease in production
- increase in destruction
- blood loss
WHO definition of anaemia
- < 13g/dL (men)
- <12g/dL (women)
- <11g/dL if pregnant
Classification of anaemias
- by film appearance/morphology
- by cause (underlying morphology)
Diagnosis of anaemia
- Physical examination
- Full blood count
- Reticulocyte count; decreased in states of decreased production, Increased in destruction of red blood cells
- Bone marrow biopsy
RBC Assessment
- Number – Done by automated counters
- Size - Large, normal size, or small; all same size versus variable sizes (anisocytosis). Mean volume
- Shape - Normal biconcave disc, versus spherocytes, versus oddly shaped cells (poikilocytosis)
- Color - Generally an artifact of size of cell
Normocytic anaemia
- Normal size RBC – reduced number
Haemolytic anaemia
- RBC destroyed faster than being synthesised
Normochromic/normocytic (NN) anaemia classification
- reduction in Hb and RBC counts
- normal mean corpuscular volume (MCV), mean corpuscular Hb (MCH) and mean corpuscular Hb concentration (MCHC).
- Due to bleeding from internal or external injury.
- Due to bone marrow failure.
- Many haemolytic anaemias.
Macrocytic (normochromic) (MN) anaemia classification
- MCV of > 100 fl and a normal MCHC. Cells are much larger but the cellular [Hb] is normal.
- Megaloblastic anaemias
- certain haemolytic anaemias.
Microcytic (hypochromic) (MH) anaemia classification
- MCV of < 85 fl and an MCHC of < 30 g/dl.
- Iron deficiency anaemia (most common)
- Sideroblastic anaemias (impaired haem synthesis)
- Thalassaemia syndromes (impaired globin synthesis)
Red blood cell aplasia
- erythroblasts; reduced or increased
- Pure RBC aplasia (PRBCA) most common due to reduced erythroblasts
- Congenital, most common DIAMOND-BLACKFAN ANAEMIA (congenital hypoplastic anaemia), ribosomal protein genes
- Myelodysplastic syndrome-excessive fibroblast growth
Acquired PRBCA
- Causes; Primary or secondary
- infections; virus e.g. HIV, bacteria e.g. staphylococcal
- Solid and haematological tumours
- Autoimmune disease
- Drugs and chemical
Treatments of aplastic anaemia
- transfusions
- corticosteroids
- bone marrow transplant
Macrocytic (megaloblastic) anaemia
- disorder of DNA synthesis, cells undergo incorrect division
- B12 and/or folate deficiency
- dietary or due to malabsorption
- decrease in Hb, increase in mean corpuscular volume
- classical anaemia symptoms plus neurological symptoms
- other rapidly dividing cells (skin GI mucosa, hair follicles etc.) also affected
Anaemia of chronic disease
- normochromic/normocytic (i.e normal cells in reduced numbers)
- mechanism unclear; often seen in malignant disease, chronic inflammation and chronic infection
- only cured by treating underlying cause
Chronic renal failure
- reduced production of erythroid precursors
- caused by lack of EPO production (by kidneys)
- normal cells produced but in greatly reduced number
- normochromic normocytic anaemia
Polycythemia vera
- increase in all blood cells
- causes: unknown mutation in stem cells and JAK2, increased sensitivity to EPO (erythropoietin)
- symptoms: headaches, dizziness, flushed complexion, increased blood viscosity, number of RBCs increased for no other reason
Erythemia
- increase in red blood cells
- phlebotomy is most common treatment
Haemolytic anaemia
- results from increased rate of RBC destruction
- RBC are removed extravascularly by macrophages of reticuloendothelial system in marrow, liver and spleen
- increased haemolysis: symptoms of anaemia, splenomegaly due to increased workload
How doesn’t shortened lifespan always lead to anaemia?
- bone marrow can increase production 6-8 fold
- maintains normal Hb level
- marrow will exhibit hyperplasia
- “compensated haemolytic disease” for haemolytic disorders with reticulocytosis, but no anaemia
Classifying haemolytic anaemia
- intrinsic or extrinsic: is problem within RBCs themselves (membrane, enzymes, globin) or outside (physical, chemical, mechanical, drugs)?
- intravascular or extravascular: site of production - important for diagnosis
- acquired or inherited
Intravascular haemolysis
- RBCs destroyed in circulation
- released Hb in plasma
- can be immune mediated e.g. blood group incompatibility
- iron containing compounds in blood can cause damage
- Free Hb can bind haptoglobin, can reduce haptoglobin levels
Extravascular haemolysis
- premature destruction of RBCs in spleen/bone marrow
- RBC removed by macrophages
- Haem breakdown in macrophage generates bilirubin
- bilirubin released and bound onto albumin to liver for conjugation and excretion in bile
- rise in unconjugated bilirubin
- jaundice
Evidence of increased haemolysis
- damaged RBCs: destroyed released into plasma, osmotic fragility, sickle cells, red cell fragments
- biochemical indicators: bilirubin, haptoglobin, breakdown products
- haemoglobinuria (high Hb in urine) and often linked with haemolytic anaemia
- increased erythropoiesis: reticulocytosis, erythroid hyperplasia
Acquired (extrinsic) anaemia
- immune: autoimmune, HDN, incompatible transfusion, drug induced
- non-immune: mechanical, chemical, infection, burns, toxins
Inherited (intrinsic) anaemia
- membrane defects: e.g. spherocytosis
- globin defects e.g. sickle
- enzyme defects e.g. G6PD deficiency
RBC Membrane defects in haemolytic anaemia
- hereditary spherocytosis; skeletal membrane and lipid bilayer protein interactions, spherical, loss of flexibility
- hereditary elliptocytosis; oval and elliptoid, protein deficiency
- paroxysmal nocturnal haemoglobinuria; mutation in PIG-A, defect in GPI, cells sensitive to complement
Hereditary spherocytosis/elliptocytosis
- abnormal membrane construction
- RBCs are unusual shape and rigid
- readily removed by spleen
- morphology: spherocytes/elliptocytes, reticulocytosis, RBCs smaller than usual
- responds to splenectomy
Globin abnormalities e.g. sickle cell
- defective Hb produced: caused by single amino acid substitution on beta-chain of molecule
- during sickle crises (infection, low O2 tension etc.) Hb becomes rigid: cells distort lifespan 10-12 days
Mechanical part of extrinsic haemolytic anaemias
- RBCs damaged/destroyed by mechanical process
- prosthetic heart valves, laying down of fibrin strands, marching, long-distance running
- lab findings: film shows fragments
Chemical/physical part of extrinsic haemolytic anaemias
- RBCs damaged directly
- Burns victims: heat over 47oC cremates cells
- lead poisoning: direct toxic effect on RBCs
- damaged cells removed by spleen (haemolysis)
Immune-mediated haemolysis
- antibodies react with RBCs and cause destruction
- causes include incompatible blood transfusion, autoantibodies e.g. lupus, drug reactions
- RBCs May show autoagglutination on film
- can be extravascular
Infection of extrinsic haemolytic anaemias
- RBCs removed as spleen defects intracellular infection e.g. malaria
- organism conducts life-span within RBC
