Hemopoesis Flashcards
time it takes to change from reticulocyte to mature RBC
1-2 days
function of normal RBC
transport O2 from lungs and CO2 to the lungs,
Structure of normal RBC
biconcave discs to enable maximal O2 saturation with large surface area and deformability for passage through small capillaries and splenic sinusoids.
Anemia
Def: reduction below normal limits of total circulating red cell mass. determind from Hemoglobin concentration, hemtocrit/packed cell volume. classified by morphological changes and pathophysiological mechanisms. hypochromic, macro,microcytic, spherocytes
Pathogenesis:
- blood loss
- –acute hemorrhage-internal or external, concern is hypovolemia
- –chronic blood loss, rate of loss exceeds RBC regeneration, or when iron stores are depleted
- increased RBC destruction.
- decreasedRBC production.
Clinical Features- asymptomatic when mild.
Symptoms: (related to poor O2 supply to tissues)- weakness, easy fatigability, headaches, fainting, shortness of breath on exertion
Clinical signs: increased pulse, RR, SV, cardiac failure, pallor, nail changes (severe cases)
MCV
Mean cell volume is the average volume of RBC, if it is low it means you have microcytic anemia, if it is high you have macrocytic anemia. femtoliters
MCH
Mean cell hemoglobin(mean corpuscular hemoglobin) average content of hemoglobin per RBC- picograms)
Mean Cell Hemoglobin concentration
average concentration of hemoglobin given volume of packed RBC’s (g/dL). High levels means you have hyper chromic EBV, Low levels means hypochromic
Increased:hereditary spherocytosis.
Red Cell distribution width
coefficient of variation of RBC volume, if it is above average percentage that means there is a wide variety o sizes o RBCs
Hemolytic anemias
Common Features- Shortened RBC life span, increase in erythropoietin, and erythropoesis, accumulation of Hb breakdown
Classified as intravascular or extravascular, or intrinisc or extrnisic to RBCs
intrinsic RBC defect:
- membrane defect- hereditary pherocytosis
- enzyme defect G6PDD, Paroxysymal nocturnal hemoglobinuria
- hemoglobin defect- sickle cell disease, thalassemias
Extrinsic defect
-immune mediated damage- autoimmune , drugs
non immune damage- mechanical trauma, infections, chemicals
-sequestration, due to hypersplenism.
LAB evidence- normochromic normocytic anemia- polychromasia (increased reticulocytes. hyperplasia with increased spherocytes, increased unconjugated bilirubin and free hemoblobin, increased LDH, decreased haptoglobin, Hemosiderinuria and hemoglobinuria.
Intravascular hemolysis
due to mechanical injury of RBC’s eg defective cardiac valves or microvascular thrombi,
complement fixation of antibody coated RBCs
Infections: intracellular parasites, production of toxins.
Extravascular hemolysis
RBC’s less deformable, or rendered foreign by immune system, most cases are extravascular.
Hereditary spherocytosis(intrinsic hemolytic anemia-membrane abnormality))
abnormla critical proteins in RBC skeleton, caused by mutations. as the RBC’s age they become spheroid, less deformable and destroyed by spleen in 10-20 days, Auto-dom. in 75% cases.
Proteins affected- ankyrin Band 4.2(anchors spectrin on inside) Spectrin(main framework) Band 3(transmembrane protein that anchors spectrin to membrane)
Pathogenesis- reduced membrane stability leads to loss of small fragments during normal shearing stresses. the RBC’s become more spherical and can’t get through spleen.
Clinical features- most commonly mild to moderate chronic hemolytic amemia with 25% asymptomatic, and a minority severely affected from birth.) intercurrent infections like parvovirus 19 can cause aplastic or hemolytic crises.
Treatement- splenectomy(anemia corrects but spherocytosis persists.
Diagnosis- family history, evidence of hemolysis, peripheral blood findings and osmotic fragility test, MCHC is INCREASED
osmotic Fragility test
add hypotonic salt solutions, this causes RBC’s to swell and lyse prematurely in 65% of HS patients.
G6PDD
abnormality in the HEXOSE Monophosphate shunt(glutathione metabolism). Leaves RBC’s prone to oxidative injuries
Hereditary form is most important
G6PD A- about 10% American Blacks)- half life of enzyme activity moderately reduced
G6PD mediterranean- mostly middle eastern- half life of enzyme severly reduced.
G6PD B- most common
Pathogenesis- abnormal enzyme variants are misfolded and susceptible to proteolytic degradation. Since mature RBCs hae no nucleus they don’t form new proteins and the enzyme activity falls and older RBC’s not protected against oxidant stresses. Oxidation of SH groups in globin chains cause preciptation of denatured globins on RBC membrane (Heinz bodies). If membrane damage is severe, intravascular hemolysis occur. Less affected RBC’s get through with only a “bite” and become bite cells and spherocytes. these cells are removed by the spleen.
Etiology:
X-linked
may be due to natural selection.
Clinical featuers
- acute hemolysis- 2-3 days afeter exposure to oxidant stress like infection, drungs, foods, (fava beans.
- neonatal jandice-
- chronic low grade hemolyti anemia lacking known environmental triggers.
Hemoglobinopathies
RBC diseases mostly characterized by mutations in globin genes- prodcution of defective hemoglobins- sickle cell disease, Hb C disease.
Sickle Cell disease
Homozygotes have almost 100% HbS
Heterozygotes have about 40% HbS referred to as AS
10% of black americans are heterozygotes.
Etiology: point mutation or missense mutation, glutamic acid replaced by valine, in translated region of Beta globin chain (HbS)
Pathogenesis: Deoxygnated HBS molecules aggregate and polymeraize, further deO2 leads to needle sickling, which is initially refersible but after rpeat, becomes irreversible and leads to RBC stickiness
Factors affecting SCD:
- HbA HbF, alpha thalassemia all decreases sickling (alpha due to less hemoglobin.
- HbC, dehydration, lower pH, long exposre of low O2 tenstion, increase sickling.
Clinical features- intra and extravascular hemolysis, moderate to severe anemia, Hyperplastic bone marrow leading to skull bone changes. Hypersplenism in kids leading to autosplenectomy due to fibrosis. More prone to infections by encapsulated bacteria, H. Influenzae and pneumococcus. Hyperbilirubinemia, gallstones. sickle cell crisis
diagnosis- clinical findings, family history, blood smear, use O2 consuming agent like metabisulfite to dinuce sickling, most common is hemoglobin electrophoresis and prenatal diagonsis-dna screening.
Tx- analgesics, rehydration, exchange transfusions, folic acid, penicilllin prophylaxis if you don’t have a spleen, hydroxyurea to increase HbF. Bone marrow transplant.
outcome- 90% survive til 20 50% survive til 50 infection major death cause in under 5 years, organ failure due to vasoocclusive complications in adults.
Association- small vessel thrombosis.
—-Sickle Cell Crisis—-
caused by infections, dehydration, cold, hypoxia, acidosis, sichemic events in bones, lungs, brain, retina, kidneys(kids young adults), leg ulcers (adults.
- –Sequestration crises: kids/young adults, rapid pooling of blood in spleen
- –Aplastic crises: acute viral infection by parvovirus 19
- –Hemolytic crises.
Thalassemia syndromes
caused by genetic lesions resulting in decreased synthesis of Alpha or Beta globin chains of HbA resulting in low levels of normal Hb
hypocrhomic microcytic RBCs
excess of unimpaired chain leads to aggregates which leads to insoluble inclusions which leads to extravascuar hemolysis.
Beta Thalassemias
diminished Beta globin chians with unimpaired Alpha chain production
Beta+ thalassemia- reduced Beta chains produced- mutation in promoter region of gene
Beta0= no beta chains produced- mutations in splicing or chain temination, frame shift of stop codon mutation.
HYPOCHROMATIC MICROCYTIC anemia
Pathogenesis- reduced survival of RBC’s and RBC precursors, due to cell membrane damage by preciptated alpha cahins. 75% of precursor RBC normoblasts die in hyperplastic bone marrow(inneffective erythropoiesis.
-extramedullary hematopoiesis, if severe,
excessive absortpion of dietary iron.
Clinical syndromes.
- -Beta Major B+/B+ B+/B0, B0/B0- severe transfustion dependant
- -Beta minor/trait: B+/B, B0/B: mild asymptomatic anemia
- -Beta intermedia=milder ariants of 1 severe variants of 2 or 1 combined with alpha thalassemia.
Course: growth retardation and death unless regular blood transfusions.
Treatment: iron chelators given to prevent overload and cardiac failure(important cause of death
Bone marrow transplantation is potentially curative in major, otherwise survial only to 3rd decade.
Diagnosis- Low Hb,VERY Low MCV RDW normal,
Beta thalassemia Major
Mediterranean, parts o Africa, S.E. Asia and immigrants from these areas.
presents 6-9 months after birth when HbF falls, Hb levels 3-6 g/dl
HbF remains elevated and may become major Hb
HbA2 may be normal low or high.
Clinchopathological features:
Expansion of hematopoietic marrow which leads to prominent facial bones, erosion of bony cortex and new bone formation, huge spleen and liver due to EXTRAvascular hemolysis and extramedullary hematopoiessi, Hemosiderosis and secondary hemochromatosis due to iron overolad. (affects heart liver and pancreas)
Beta Thalassemia Minor
Usually asymptomatic with mild HYPOCHROMIC MICROCYTIC anemia hemoblogin EPH will show increase in HbA2 and normal or increased HbF. need to recognize to avoid treating as iron deficiency anemia and to provide genetic counseling.
Alpha Thalassemia
1 deleted gene- silent carrier
2 genes deleted- thalassemia trait (a/a -/-= SE Asian, a/- a/- = african) Only SE Asian can produce offspring with severe Alpha thalassemia
3 genes deleted- Hemoglobin H disease
4 genes deleted- Hydrops fatalis.
Hemoglobin H disease
HbH fromed from tetramers of excess Beta chains, has high affinity for O2 leading to severe tissue hypoxia, HbH is also prone to oxidationwhich will lead to precipitaed inclusions in older RBCS and extravascular heymolysis, moderate anemia.
Hydrops fetalis
Hb Barts,
tetramers of excess gamma chains,
high O2 affinity, no O2 reaches the tissues,
leads to death unless given intrauterine transfusion,
fetus is pale, edematous, and enlarged liver/spleen.