Hematopoiesis Flashcards
T or F. Hematopoiesis is regulated at both levels of differentiation and cell division.
T
How is a pluripotent stem cell defined?
By its ability to salvage all the elements of hematopoiesis after it has been wiped out by irradiation or chemotherapy.
How can pluripotent stem cells be identified?
Characteristic cell surface markers (CD34+ CD38-). Cannot be identified by morphology.
T or F. Pluripotent stem cells are common.
F. <1 in 20 million.
T or F. Pluripotent stem cells express receptors for key growth factors.
T
T or F. Pluripotent stem cells are critical for bone marrow transplants and gene therapy methods.
T
What does BFU stand for?
Burst Forming Units
What does CFU stand for?
Colony Forming Units
BFU and CFU are currently defined by their responsiveness to what?
A handful of key known growth factors.
What are the 4 key growth factors in hematopoiesis?
- TPO
- EPO
- G-CSF
- GM-CSF
What are the 5 cells in the morphologic maturation of granulocyte precursors?
- Blast
- Promyelocyte
- Myelocyte
- Metamyelocyte
- Bands and Neutrophils
What is the key regulator of granulopoiesis?
G-CSF
What are the 3 ways in which disease states can affect granulopoiesis?
- Increase in overall numbers
- Shifted left or right
- Maturation arrest (blocked part way through)
What cell is responsible for platelet production?
Megakaryocytes
What is special about megakaryocytes?
They are polyploid. Their nuclei have divided multiple times, so instead of being diploid (2n) they contain an average of 16-32 haploid genomes.
How do megakaryocytes make platelets?
They extend snake-like tubes called proplatelets into fenestrated bone marrow blood vessels (sinuses). Mature platelets are shed off one at a time from the ends of proplatelets.
What is the major regulator of thrombopoiesis?
TPO (thrombopoietin)
T or F. TPO is synthesized at a constant rate in the liver.
T
What cells can TPO bind to?
Both platelets and megakaryocytes.
What happens when TPO binds to megakaryocytes?
Stimulates platelet production from immature precursors and mature megakaryocytes.
What allows more TPO to bind to megakaryocytes thus stimulating thrombopoiesis?
Low platelet count.
What are the 5 cells in erythryopoiesis?
- Blasts
- Pronormoblasts
- Basophilic erthyroblasts
- Polychromatophilic erythroblasts
- Normochromic erythroblasts
How many cell divisions are there in erythropoiesis?
5
Nascent red cells are known as what?
Reticulocytes (polychromasia)
As a patient ages, the cellularity of the bone marrow does what?
Declines
What are the 4 requirements for red cell production?
- Heme synthesis
- Globin synthesis
- DNA synthesis
- Regulation
What are the 4 requirements for heme synthesis?
- Iron
- B6
- Succinyl CoA
- Glycine (which requires B12 and folate)
What are the 2 requirements for globin synthesis?
- Normal globin genes (alpha and beta)
2. Amino acids
What 2 things can cause problems with globin production?
- Malnutrition
2. Gene mutations (more common in ‘Merica)
T or F. The nucleus must be replicated several times in red cell production.
T
What is required in DNA synthesis in red cell production?
Adequate nutrition and deoxynucleoside triphosphates (which requires ribonucleotide reductase and thymidine). Thymidine requires B12 and folate.
What hormone regulates red cell production?
EPO (erythropoietin)
Where is EPO produced?
Kidneys
What 2 things are required for EPO?
- Normal kidneys
2. Normal bone marrow micro-environment
Is anemia a diagnosis?
No. It is a labratory finding. It remains undiagnosed until you find a cause for it.
What are the 3 ways in which a patient can become anemic?
- Losing red cells
- Not making enough red cells
- Both
What is the morphology of an anemic patient’s red blood cells?
Small without much hemoglobin. Microcytosis=small red cells. Hypochromic=loss of color bc of low hemoglobin.
Lots of variation in size and shape. Anisocytosis=varying size. Poikilocytosis=varying shape.
In regards to anemic red blood cells on a peripheral blood smear, what is the rule of thumb for the area of central pallor?
If the diameter of the enlarged central pallor area is greater than 1/3 of the red cell’s diamter, the cell is hypochromic aka lacking hemoglobin.
What is another characteristic (besides microcytic hypochromic) of anemic red cells?
Lots of variation in size and shape. Anisocytosis=varying size. Poikilocytosis=varying shape.
What form is dietary iron in?
Ferric (Fe3+). Must be reducted to ferrous (Fe2+) in the stomach before it can be taken up in the small bowel.
What 2 things are required for dietary iron to be reduced from Fe3+ to Fe2+?
- Low pH
2. Ascorbate
What molecule handles the transport of iron in the plasma?
Transferrin
What oxidizes ferrous iron in the plasma to its ferric state so it can be bound to transferrin?
Serum oxidases
Why would free iron in the plasma be a bad thing?
- Augment bacterial growth
2. Catalyze formation of superoxide radicals from oxygen
What are the 2 fates of iron bound to transferrin?
- Transferred to red cell precursors in the BM via transferrin receptor
- Transferred to ferritin for the iron storage pool
Where is the storage pool of iron located?
Bound to ferritin in macrophages located in the BM, liver, and spleen.
How is serum iron measured?
It is a direct measure of transferrin-bound iron.
T or F. A measurement of transferrin-bound iron does not directly assess iron stores.
T
What does the soluble transferrin receptor amount measure?
Measurement of the small number of transferrin receptor molecules that get sloughed off the storage pool cells and into the plasma.
How is the amount of storage pool iron measured?
Measured by the trace amount of ferritin present in the serum. This value is directly proportional to the amount of storage pool iron in the body.
T or F. Serum ferritin is the most useful measure of iron metabolism.
T: used for assessment of anemias of unknown etiology.
What is the measurement of the total amount of transferrin in circulation called?
Total iron binding capacity
Patients with poor iron intake show a reduced level of what?
Serum iron. Careful though, this can be seen in other conditions.
What happens to the soluble transferrin receptor value when the iron storage pool is depleted?
It is increased bc when iron stores are depleted, macrophages increase the amount of transferrin receptors on their surface.
With iron deficiency, what happens to the total iron binding capacity (TIBC) and serum ferritin levels?
TIBC: increased (bc transferrin production is increased)
Serum ferritin: decreased
T or F. In anemias due to chronic blood loss, the combined flux of dietary iron and iron store mobilization is insufficient to keep up with the red cell loss.
T
Describe the lab findings in a patient with an anemia due to chronic blood loss.
They are identical to the lab values seen when iron deficiency results from poor dietary intake.
What is thalassemia?
Reduced globin production resulting from genetic mutations (alpha or beta).
What is the morphology of red cells in Beta Thalassemia?
- Microcytosis, hypochromia (just like iron deficiency)
2. Frequent target cells (non-specific)
What are the main differences in red cell morphology of beta thalassemia compared to iron deficiency?
- Smaller: MCV < 70 pL (normal=90-100 pL)…note this is not always true
- Presence of target cells on PBS
What are target red cells also commonly seen in association with?
Liver disease. Remember: target cells are non-specific.
What is the difference between homozygous and heterozygous beta globin chain mutations?
Homozygous: can be severe.
Heterozygous: can be mild and not clinically obvious.
What is a reliable clue to let you know if a patient with a microcytic anemia has a thalassemia or an iron deficiency?
The NUMBER of red cells. In iron deficiency, the number of red cells is decreased. In thalassemias, the number of red cells is normal or increased.
What test needs to be ordered to confirm that a patient has a thalassemia?
Hemoglobin Electrophoresis Test
The beta globin locus is located on which chromosome?
Chromosome 11
What are the 6 beta globin forms?
- Epsilon
- g-Gamma
- a-Gamma
- Psi-Beta
- Delta
- Beta
Which 3 beta globin forms are expressed in utero?
Epsilon, g-gamma, and a-gamma.
Which beta globin form is primarily expressed in the fetus and has a low level of expression after birth?
Delta (all the others besides beta are expressed in the fetus too)
Which beta globin form is expressed in adults?
Beta
What happens to the relative amount of delta globin if expression of a beta globin allele is impaired due to a mutation?
Increased, sometimes to high levels.
What is the predominant adult form of hemoglobin?
Hemoglobin A: 2 alpha chains, 2 beta chains.
What is hemoglobin A2 composed of?
2 alpha chains and 2 delta chains.
To confirm beta thalassemia, what is seen on hemoglobin electrophoresis?
Increased Hemoglobin A2. Hemoglobin A2 forms bc of the increased expression of delta globin and migrates differently on electrophoresis than Hemoglobin A.
In severe cases of beta thalassemia, what other form of hemoglobin is detected on electrophoresis?
Hemoglobin F (for fetal): 2 alpha chains, 2 gamma chains.
The alpha globin locus is located on what chromosome?
Chromosome 16
What are the 4 forms of alpha globin?
- Zeta 2
- Zeta 1
- Alpha 2
- Alpha 1
Which 2 forms of alpha globin are primarily expressed in the fetus? Adult?
Fetus: Zeta 1 and Zeta 2.
Adult: Alpha 1 and Alpha 2.
A patient with a heterozygous alpha2 mutation?
Alpha thalassemia 1 trait. Results in almost no clinical/lab findings.
A patient with homozygous alpha 1 mutations?
Alpha thalassemia 2 trait.
A patient with alpha thalassemia 2 trait presents with what type of anemia?
Mild microcytic anemia.
At birth, what type of Hgb do alpha thalassemia 2 trait patients have excess numbers of?
Hgb Bart’s (4 gamma chains)
T or F. Alpha thalassemia 2 trait patients have a normal Hgb electrophoresis as adults.
T
What tests are used to diagnose alpha thalassemia 2 trait?
PCR based: electrophoresis and/or sequencing.
Alpha thalassemia 2 trait is seen in 3% of what ethnic group?
African Americans
A patient with both alpha 1 alleles mutated and one alpha 2 allele mutation have what disease?
Hemoglobin H disease
Hemoglobin H is composed of?
4 beta globin chains
Hemoglobin H disease shows what in regards to lab findings?
- Variable degree of microcytic anemia
2. Hgb electrophoresis shows 15-30% Hgb H
What can Hgb H disease be misdiagnosed as?
Iron deficiency
A patient with no function allele of either alpha 1 or alpha 2?
Hgb Bart’s
T or F. Hgb Bart’s is lethal in utero or shortly after birth.
T: fetus/baby dies before normal expression of beta globin can produce significant amounts of Hgb H.
Where is Hgb Bart’s common?
Southeast Asia
What are the biochemical requirements for DNA synthesis?
Ribonucleoside triphosphates have to be reduced to the deoxy form and UTP has to be methylated to TTP. Methylation requires B12 and folate.
What are the 3 consequences of impaired DNA synthesis in regards to red cell production?
- Fewer cells are produced
- Normal/enhanced maturation of cytoplasm
- Impaired nuclear maturation
T or F. Impaired DNA synthesis in red cell production holds up production after one or two cell divisions resulting in cells with large nuclei and chromatin that is not condensed into heterochromatin.
T
If DNA synthesis is impaired in red cell production, what color are the resulting cells? What is the name for the appearance of these cells?
Red (instead of blue). As the cytoplasm continues to mature, RNA which stains blue is degraded and Hgb’s reddish color takes over. This is termed megaloblastic.
What are the 4 causes of megaloblastic anemia?
- Impaired B12 uptake
- Impaired folate uptake
- Drug effect
- Intrinsic bone marrow dysfunction
T or F. Most megaloblastic anemias can be diagnosed without a BM biopsy.
T
What is a megaloblastic anemia due to impaired B12 uptake called?
Pernicious anemia
What are the causes of impaired folate uptake?
Malabsorption or malnutrition.
What 2 types of drugs can cause megaloblastic anemia?
- Nucleoside analogs (HAART)
2. Ribonucleotide reductase inhibitors (hydroxyurea)
What intrinsic bone marrow dysfunction can cause a megaloblastic anemia?
Myelodysplastic syndrome
T or F. Red cell production is regulated by organs outside the bone marrow and can be impaired by dysfunction of those organs.
T: ex. anemia as a result of renal failure bc the kidneys synthesize EPO.
How is EPO production regulated?
Oxygen sensors
Where are the oxygen sensors located that regulate EPO production?
Peritubular cells in the renal cortex. They secrete EPO
What does hepcidin impair?
Iron store mobilization
Hepcidin is secreted by what organ?
Liver
What stimulates the production of hepcidin?
IL-6 that is produced in response to chronic inflammatory conditions. So infection and inflammation impair utilization of iron stores.
What is increased in the bone marrow due to increased hepcidin production?
Increased bone marrow iron stores
How is the transferrin saturation calculated?
Serum iron divided by TIBC.
What 3 things happen in anemia of chronic inflammation in regards to iron transport?
- Iron not mobilized from storage
- Iron not absorbed well from GI tract
- Transferrin pulled out of circulation
What happens to the transferrin saturation value in anemia of chronic inflammation?
Increased (bc TIBC is reduced).
T or F. The net flux of iron through the system is reduced in anemia of chronic inflammation.
T
What cell type is affected by anemia of chronic inflammation?
Red cell precursors bc there isn’t as much iron to bind to their transferrin receptors (even if macrophages are full of ferritin).
If you suspect anemia of chronic inflammation, what must be ordered to confirm it?
Bone marrow biopsy bc CBC and iron labs do not rule out other bad things happening in the bone marrow like acute leukemia, lymphoma, metastases, or a large number of granulomas.
In anemia of chronic inflammation/disease, what 4 things are seen in the labs and tests?
- Normocytic anemia
- Increased ferritin
- Reduced or normal serum iron
- Increased bone marrow iron stores
T or F. AIDS, TB, RA, or any type of cancer can result in an anemia of chronic inflammation/disease.
T
