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Clinical Pathology > Erythropoiesis & the Erythrogram > Flashcards

Erythropoiesis & the Erythrogram Flashcards

1
Q

What is an erythron? What does it include?

A

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
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2
Q

What is hemoglobin? How much of an erythrocyte is made up of it?

A

tetramer of 4 globin chains (2 α and 2 β) linked to a separate heme that binds oxygen

95%

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3
Q

What ion is incorporated into each heme molecule of hemoglobin?

A

iron in the ferrous state (Fe2+)

MUST be reduced, hemoglobin bound to Fe3+ cannot carry oxygen

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4
Q

What is the function of hemoglobin? How should hemoglobin be in healthy individuals?

A

transports oxygen from lungs to tissues

100% saturated with oxygen in arterial blood

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5
Q

What is the only way to transport oxygen?

A

Hgb + Fe2+

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6
Q

Why is iron important for red blood cells?

A

hemoglobin synthesis depends on iron in the series of enzymatic reactions

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7
Q

What are the 3 major sites of iron distribution in the body?

A
  1. erythrocyte hemoglobin - 50-70%
  2. tissue storage and ferritin - 25-40%
  3. within other molecules, like myoglobin, cytochromes, and enzymes
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8
Q

What is the major rate-limiting enzyme in hemoglobin synthesis? What is required as a cofactor?

A

5-aminolevulenic acid synthase (5-ALA)

vitamin B6

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9
Q

What inhibits 5-aminolevulenic acid synthase? What does this cause?

A

lead

accumulation of heme precursor molecules in erythrocytes

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10
Q

What is porphyria?

A

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

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11
Q

What is the major energy source in most species? What 4 metabolic pathways in RBCs use it?

A

glucose

  1. glycolysis (Embden-Meyerhoff pathway)
  2. 2,3-DPG (Rapoport-Leubering) pathway
  3. pentose phosphate pathway
  4. methemoglobin reductase pathway
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12
Q

What are the 2 major outcomes of glycolysis? What are the 2 most clinically relevant enzymes?

A
  1. generates ATP to maintain membrane function and integrity
  2. generates NADH to reduce methemoglobin (Fe3+ to Fe2+ + Hgb)
  3. pyruvate kinase
  4. phosphofructokinase
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13
Q

What is the purpose of the 2,3-DPG pathway in red blood cells?

A

aids in the oxygen delivery to tissues when anemia is present

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14
Q

What is the purpose of the pentose phosphate pathway and methemoglobin reductase pathway? What do both these pathways also do?

A
  • generates NADPH, a cofactor for glutathione reductase
  • reduces iron from Fe3+ to Fe2+

provide protection against oxidative stress

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15
Q

In what dogs is phosphofructokinase deficiency common? What does this cause? How does it present?

A
  • 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)

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16
Q

In what animals is pyruvate kinase deficiency common? What does this cause? How does it present?

A
  • Basenjis
  • Chihuahuas
  • Beagles
  • Dachshunds
  • Abyssinians
  • Somalis

shortened RBC lifespan and an accumulation of 2,3-DPG with reduced ATP production

bone marrow failure

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17
Q

What is erythropoiesis? How does this begin? What stimulates this process?

A

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

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18
Q

What is the first cell during erythropoiesis that loses its nucleus?

A

reticulocyte (polychromatophilic erythrocyte) - commonly produced in response to low RBC circulation

(nucleated erythroid cells should only be in the bone marrow)

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19
Q

What are the 6 major erythrocyte development stages?

A
  1. rubriblast
  2. prorubricyte
  3. rubricyte - basophilic, polychromatophilic
  4. metarubricyte - last stage that is nucleated
  5. reticulocyte - large, basophilic, anucleated
  6. mature erythrocyte
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20
Q

What is the last mitotic stage in erythrocyte development?

A

rubricyte

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21
Q

What are the 3 major trends in the cells during erythrocyte development?

A
  1. cells produce mRNA for hemoglobin synthesis
  2. cells undergo mitosis to produce more and smaller cells that have progressively more hemoglobin
  3. DNA synthesis decreases and fewer mitotic divisions occur
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22
Q

About how long does it take for erythropoietic progenitor cells to become a reticulocyte? How long do reticulocytes circulate before maturing into erythrocytes?

A

5 days

1-2 days

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23
Q

What nutritional factors affect nucleic acid metabolism and cytoplasmic maturation/hemoglobin formation during erythropoiesis?

A

NUCLEIC ACID: vitamin B12, folate

CYTOPLASM/HGB: vitamin B6, iron, amino acids, copper

24
Q

What hormonal and bone marrow factors control erythropoiesis?

A

HORMONAL: erythropoietin from the adult kidney and fetal liver

BONE MARROW: stem cells, stroma, blood supply

25
Q

What is the RBC lifespan in circulation in birds, cats, dogs, horses, and cows?

A

BIRDS = 35 days
CATS = 70 days
DOGS = 110 days
HORSES = 145 days
COWS = 160 days

  • may not see anemia right away in larger animals
26
Q

What are the 2 mechanisms of RBC removal?

A
  1. MAJOR: phagocytosis by macrophages mainly in the spleen
  2. MINOR: intravascular lysis with release of hemoglobin into the plasma
27
Q

What happens to the 2 major parts of the hemoglobin once it’s broken down?

A
  1. HEME —> biliverdin, Fe2+, CO —> bilirubin
  2. GLOBINS —> amino acids
28
Q

What is the erythrogram? How is it done?

A

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

29
Q

Erythrogram:

A
30
Q

What are the 9 major components of an erythrogram?

A
  1. RBC - red blood cell count
  2. Hgb - hemoglobin
  3. HCT - hematocrit
  4. MCV - mean corpuscular cell volume
  5. MCH - mean corpuscular hemoglobin
  6. MCHC - mean corpuscular hemoglobin concentration
  7. reticulocytes - reticulocyte count (%), absolute reticulocyte count (absRC), corrected reticulocyte percentage (CRP)
  8. nRBC - nucleated RBCs
  9. RDW - red cell distribution width
31
Q

What are the 2 measured components of an erythrogram? 1 calculated component?

A
  1. RBC count - millions, measured by instrument
  2. hemoglobin - g/dL, measured by spectrophotometry

hematocrit - percentage of blood volume filled by erythrocytes

32
Q

How is hematocrit calculated? What happens when it is below and above the reference interval?

A

(MCV x RBC)/10

BELOW = patient is anemic, typically with concurrent decreased Hbg and RBC

ABOVE = erythrocytosis

33
Q

How does PCV compare to hematocrit?

A

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%

34
Q

How should PCV and HCT compare to hemoglobin concentration?

A

HCT and PCV should be 3x hemoglobin

35
Q

What are the 3 Wintrobe’s indices in an erythrogram?

A
  1. MCV = mean corpuscular cell volume
  2. MCH = mean corpuscular hemoglobin
  3. MCHC = mean corpuscular hemoglobin concentration
36
Q

What does MCV measure? How is it calculated?

A

volume per average erythrocyte

(HCT x 10)/RBC

37
Q

What happens when MCV is below or above the reference interval?

A

BELOW = microcytosis (small RBCs)

ABOVE = macrocytosis (large RBCs)

38
Q

What does MCH measure? How is it calculated?

A

quantity of hemoglobin per average erythrocyte, expressed in picograms

(Hgbx10)/RBC

39
Q

What happens when MCH is below or above the reference interval?

A

BELOW = hypochromasia

ABOVE = hyperchromasia

40
Q

What do inaccuracies in RBC count lead to?

A

MCV and MCH inaccuracies

41
Q

What does MCHC measure? How is it calculated? How does it compare to MCH?

A

cellular Hgb concentration per average erythrocyte

(Hgbx100)/HCT

more accurate - not affected by RBC count

42
Q

What happens when MCHC is below or above the reference interval?

A

BELOW = hypochromasia

ABOVE = hyperchromasia

43
Q

How does a short sample (underfilled EDTA tube) or low plasma osmolality (low Na and Cl) influence MCV and MCHC?

A

falsely decreased MCV and increased MCHC

44
Q

How does increased plasma osmolality (high Na and Cl) influence MCV and MCHC?

A

falsely increased MCV and decreased MCHC

45
Q

How should reticulocytes report in healthy individuals? What is indicated when they are increased?

A

low numbers in circulation

increased RBC production, indicative of regenerative anemia

46
Q

How does reticulocyte circulation compare in horses?

A

horses release few, if any, reticulocytes

47
Q

How do reticulocytes differ in cattle and small ruminants?

A

contain basophilic stippling —> dark purple spots, no longer smooth

48
Q

How is reticulocyte count measured?

A

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)

49
Q

How is absolute reticulocyte count (absRC) calculated?

A

reticulocyte % x RBC

50
Q

How is corrected reticulocyte percentage (CRP) calculated?

A

reticulocyte % x (patient’s HCT/normal HCT for species)

normal HCT for canines = 45%
normal HCT for felines = 35%

51
Q

In what 2 circumstances are nucleated RBCs (nRBCs) increased? What are the 2 major cells?

A
  1. strongly regenerative anemia
  2. damage to bone marrow endothelium

metarubricytes or rubricytes - earlier stages are indicative of stongly regenerative anemias or leukemia

52
Q

What does red cell distribution width represent? How is it calculated? What does it indicate?

A

coefficient of variation of RBC volume distribution

(SDMCV/MCV) x 100

degree of anisocytosis (variation in RBC size)

53
Q

How is total protein determined? What happens if values are below or above the reference interval?

A

refractometry

BELOW = hypoproteinemia by loss of lack of production
ABOVE = hyperproteinemia by increased production of hemoconcentration

54
Q

What is total protein a marker for?

A

inflammation

55
Q

When and how is fibrinogen measured? What happens if values are below or above the reference interval?

A

in large animals using heat precipitation

BELOW = hypofibrinogenemia by loss or lack of production
ABOVE = hyperfibrinogenemia by increased production (inflammation) or hemoconcentration

Clinical Pathology (33 decks)

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