Erythropoiesis & the Erythrogram Flashcards
What is an erythron? What does it include?
red blood cells and their precursors in the bone marrow
- RBCs in blood vessels and sinuses in the spleen, liver, and bone marrow
- precursor cells in the spleen and bone marrow
What is hemoglobin? How much of an erythrocyte is made up of it?
tetramer of 4 globin chains (2 α and 2 β) linked to a separate heme that binds oxygen
95%
What ion is incorporated into each heme molecule of hemoglobin?
iron in the ferrous state (Fe2+)
MUST be reduced, hemoglobin bound to Fe3+ cannot carry oxygen
What is the function of hemoglobin? How should hemoglobin be in healthy individuals?
transports oxygen from lungs to tissues
100% saturated with oxygen in arterial blood
What is the only way to transport oxygen?
Hgb + Fe2+
Why is iron important for red blood cells?
hemoglobin synthesis depends on iron in the series of enzymatic reactions
What are the 3 major sites of iron distribution in the body?
- erythrocyte hemoglobin - 50-70%
- tissue storage and ferritin - 25-40%
- within other molecules, like myoglobin, cytochromes, and enzymes
What is the major rate-limiting enzyme in hemoglobin synthesis? What is required as a cofactor?
5-aminolevulenic acid synthase (5-ALA)
vitamin B6
What inhibits 5-aminolevulenic acid synthase? What does this cause?
lead
accumulation of heme precursor molecules in erythrocytes
What is porphyria?
rare, hereditary disorder of heme synthesis in cattle, pigs, cats, and humans caused by a deficiency in hemoglobin synthesis enzyme, URO synthase, resulting in porphyrin accumulation with incomplete heme synthesis
What is the major energy source in most species? What 4 metabolic pathways in RBCs use it?
glucose
- glycolysis (Embden-Meyerhoff pathway)
- 2,3-DPG (Rapoport-Leubering) pathway
- pentose phosphate pathway
- methemoglobin reductase pathway
What are the 2 major outcomes of glycolysis? What are the 2 most clinically relevant enzymes?
- generates ATP to maintain membrane function and integrity
- generates NADH to reduce methemoglobin (Fe3+ to Fe2+ + Hgb)
- pyruvate kinase
- phosphofructokinase
What is the purpose of the 2,3-DPG pathway in red blood cells?
aids in the oxygen delivery to tissues when anemia is present
What is the purpose of the pentose phosphate pathway and methemoglobin reductase pathway? What do both these pathways also do?
- generates NADPH, a cofactor for glutathione reductase
- reduces iron from Fe3+ to Fe2+
provide protection against oxidative stress
In what dogs is phosphofructokinase deficiency common? What does this cause? How does it present?
- English Springer Spaniels
- American Cocker Spaniels
shortened RBC lifespan due to impaired ATP production and a decreased 2,3-DPG concentration
alkalemia-induced hemolytic anemia (hyperventilation when stressed/excited)
In what animals is pyruvate kinase deficiency common? What does this cause? How does it present?
- Basenjis
- Chihuahuas
- Beagles
- Dachshunds
- Abyssinians
- Somalis
shortened RBC lifespan and an accumulation of 2,3-DPG with reduced ATP production
bone marrow failure
What is erythropoiesis? How does this begin? What stimulates this process?
erythrocyte production occurring mostly in the bone marrow
blast-forming unit-erythroid (BFU-E) —> committed stem cells (CFU-E) —> rubriblasts (first microscopically recognizable erythroid cell)
erythropoietin from the adult kidney and fetal liver
What is the first cell during erythropoiesis that loses its nucleus?
reticulocyte (polychromatophilic erythrocyte) - commonly produced in response to low RBC circulation
(nucleated erythroid cells should only be in the bone marrow)
What are the 6 major erythrocyte development stages?
- rubriblast
- prorubricyte
- rubricyte - basophilic, polychromatophilic
- metarubricyte - last stage that is nucleated
- reticulocyte - large, basophilic, anucleated
- mature erythrocyte
What is the last mitotic stage in erythrocyte development?
rubricyte
What are the 3 major trends in the cells during erythrocyte development?
- cells produce mRNA for hemoglobin synthesis
- cells undergo mitosis to produce more and smaller cells that have progressively more hemoglobin
- DNA synthesis decreases and fewer mitotic divisions occur
About how long does it take for erythropoietic progenitor cells to become a reticulocyte? How long do reticulocytes circulate before maturing into erythrocytes?
5 days
1-2 days
What nutritional factors affect nucleic acid metabolism and cytoplasmic maturation/hemoglobin formation during erythropoiesis?
NUCLEIC ACID: vitamin B12, folate
CYTOPLASM/HGB: vitamin B6, iron, amino acids, copper
What hormonal and bone marrow factors control erythropoiesis?
HORMONAL: erythropoietin from the adult kidney and fetal liver
BONE MARROW: stem cells, stroma, blood supply
What is the RBC lifespan in circulation in birds, cats, dogs, horses, and cows?
BIRDS = 35 days
CATS = 70 days
DOGS = 110 days
HORSES = 145 days
COWS = 160 days
- may not see anemia right away in larger animals
What are the 2 mechanisms of RBC removal?
- MAJOR: phagocytosis by macrophages mainly in the spleen
- MINOR: intravascular lysis with release of hemoglobin into the plasma
What happens to the 2 major parts of the hemoglobin once it’s broken down?
- HEME —> biliverdin, Fe2+, CO —> bilirubin
- GLOBINS —> amino acids
What is the erythrogram? How is it done?
component of the CBC that assesses erythrocytes, leukocytes, and platelets
blood is collected into an EDTA purple top tube containing an anticoagulant and processed through a hematology analyzer
Erythrogram:
What are the 9 major components of an erythrogram?
- RBC - red blood cell count
- Hgb - hemoglobin
- HCT - hematocrit
- MCV - mean corpuscular cell volume
- MCH - mean corpuscular hemoglobin
- MCHC - mean corpuscular hemoglobin concentration
- reticulocytes - reticulocyte count (%), absolute reticulocyte count (absRC), corrected reticulocyte percentage (CRP)
- nRBC - nucleated RBCs
- RDW - red cell distribution width
What are the 2 measured components of an erythrogram? 1 calculated component?
- RBC count - millions, measured by instrument
- hemoglobin - g/dL, measured by spectrophotometry
hematocrit - percentage of blood volume filled by erythrocytes
How is hematocrit calculated? What happens when it is below and above the reference interval?
(MCV x RBC)/10
BELOW = patient is anemic, typically with concurrent decreased Hbg and RBC
ABOVE = erythrocytosis
How does PCV compare to hematocrit?
centrifuged method that is more accurate than HCT if any RBC parameters are falsely altered
should only differ from one another by a maximum of 3%
How should PCV and HCT compare to hemoglobin concentration?
HCT and PCV should be 3x hemoglobin
What are the 3 Wintrobe’s indices in an erythrogram?
- MCV = mean corpuscular cell volume
- MCH = mean corpuscular hemoglobin
- MCHC = mean corpuscular hemoglobin concentration
What does MCV measure? How is it calculated?
volume per average erythrocyte
(HCT x 10)/RBC
What happens when MCV is below or above the reference interval?
BELOW = microcytosis (small RBCs)
ABOVE = macrocytosis (large RBCs)
What does MCH measure? How is it calculated?
quantity of hemoglobin per average erythrocyte, expressed in picograms
(Hgbx10)/RBC
What happens when MCH is below or above the reference interval?
BELOW = hypochromasia
ABOVE = hyperchromasia
What do inaccuracies in RBC count lead to?
MCV and MCH inaccuracies
What does MCHC measure? How is it calculated? How does it compare to MCH?
cellular Hgb concentration per average erythrocyte
(Hgbx100)/HCT
more accurate - not affected by RBC count
What happens when MCHC is below or above the reference interval?
BELOW = hypochromasia
ABOVE = hyperchromasia
How does a short sample (underfilled EDTA tube) or low plasma osmolality (low Na and Cl) influence MCV and MCHC?
falsely decreased MCV and increased MCHC
How does increased plasma osmolality (high Na and Cl) influence MCV and MCHC?
falsely increased MCV and decreased MCHC
How should reticulocytes report in healthy individuals? What is indicated when they are increased?
low numbers in circulation
increased RBC production, indicative of regenerative anemia
How does reticulocyte circulation compare in horses?
horses release few, if any, reticulocytes
How do reticulocytes differ in cattle and small ruminants?
contain basophilic stippling —> dark purple spots, no longer smooth
How is reticulocyte count measured?
instrument uses a special dye for reticulocyte DNA and measures what percentage of ALL erythrocytes are reticulocytes
(can be manually counted using blood smear stained with new methylene blue)
How is absolute reticulocyte count (absRC) calculated?
reticulocyte % x RBC
How is corrected reticulocyte percentage (CRP) calculated?
reticulocyte % x (patient’s HCT/normal HCT for species)
normal HCT for canines = 45%
normal HCT for felines = 35%
In what 2 circumstances are nucleated RBCs (nRBCs) increased? What are the 2 major cells?
- strongly regenerative anemia
- damage to bone marrow endothelium
metarubricytes or rubricytes - earlier stages are indicative of stongly regenerative anemias or leukemia
What does red cell distribution width represent? How is it calculated? What does it indicate?
coefficient of variation of RBC volume distribution
(SDMCV/MCV) x 100
degree of anisocytosis (variation in RBC size)
How is total protein determined? What happens if values are below or above the reference interval?
refractometry
BELOW = hypoproteinemia by loss of lack of production
ABOVE = hyperproteinemia by increased production of hemoconcentration
What is total protein a marker for?
inflammation
When and how is fibrinogen measured? What happens if values are below or above the reference interval?
in large animals using heat precipitation
BELOW = hypofibrinogenemia by loss or lack of production
ABOVE = hyperfibrinogenemia by increased production (inflammation) or hemoconcentration
