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Characteristics of RBCs:
- Uniform
- Flattened
- Biconcave disks
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Erythropoiesis:
RBC production
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Hemoglobin synthesis requires 3 basic components:
- Amino acids
- Iron
- Vitamins B12 and B6 and Folic Acid
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Functions of RBCs:
- Transports oxygen from lungs to tissues.
- Transports CO2 from tissues to the lungs.
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Erythropoietin:
Glycoprotein hormone (growth factor) that stimulates erythropoiesis.
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Where does erythropoietin happen?
85% in kidneys, 15% in liver
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Erythropoietin synthesis is stimulated by and located on chromosome:
hypoxia, 7
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Decreased blood oxygen (hypoxia) is detected by special kidney cells, which:
Stimulates them to produce erythropoietin
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Erythropoietin is secreted into the:
blood and travels to the bone marrow
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Can RBCs counts get too high?
Yes, blood becomes so thick, heart can not pump leads to clot/blood vessel.
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Polycythemia:
Increased RBC concentration
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Absolute Polycythemia:
- Secondary.
- Increased numbers of RBCs (High erythropoietin, smokers, chronic lung disease, abnormal hemoglobin molecules, renal tumors, genetic disorders)
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Relative polycythemia:
- Primary.
- Decreased plasma volume (Not related to high erythropoietin, RBC numbers are not increased, Dehydration from burns, diarrhea, decreased fluid intake or exposure to excessive heat)
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Developement and maturation of RBCs:
- Rubriblast (Pronormoblast): Fine chromatin, 0-2 nucleoli, basophilic cytoplasma, receives iron from hemoglobin.
- Prorubricyte (Basophilic normoblast):Thicker chromatin, no nucleoli
- Rubricyte (Polychromatic normoblast): Coarse chromatin, "muddy grey" cytoplasm 1st visible hemoglobin
- Metarubricyte (Orthochromatic normoblast): Pyknotic nucleus (dark solid), pinkish cytoplasm
- Reticulocyte: Anuclear RBC with bluish tint
- Erythrocyte (Mature RBC): Anuclear, pink-red cytoplasm
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Megaloblastic maturation
- Delayed nuclear maturation but normal cytoplasm maturation.
- Immature nucleus and mature cytoplasm.
- The nucleus and cytoplasm are asynchronous
- Common cause of megaloblastic maturation is B12 deficiency.
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Reticulocyte (retic):
- RBC after nucleus is lost.
- Briefly retains RNA, causing bluish discolorization (Wright stain)
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When is the RNA lost in a reticulocyte?
1-2 days after release
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Under normal conditions in retic:
- Bone marrow retics replace old RBCs removed from circulation.
- # marrow RBCs=# Blood retics=#RBCs removed from blood
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Stress retics:
- Reticulocytes released earlier than normal to meet increased demand.
- Immature, larger than normal and have a
- darker bluish color.
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Retic count:
- Common test to measure bone marrow erythropoiesis.
- RNA will stain a smooth light blue color with the Wright Stain.
- RNA is precipitated and stains as bluish granules (speckled appearance) with Methylene Blue stain.
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Retics are expressed as a _____.
% of total RBCs
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Retic counts are performed in 2 ways:
- Microscopic exam of Methylene blue stained blood smear.
- Automated analysis of Methylene blue stained whole blood
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What is the corrected retic formula?
(patient HCT/Normal HCT) retic %
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Uncorrected Retic formula:
#retics/#RBCs x 100
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(RPI) Reticulocyte Production Index:
Corrected Retic count/Maturation time
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RPI is done to correct:
For apparent increase in erythropoiesis
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Hemoglobin is a large, coiled, conjugated protein molecule that is composed of:
- 4 polypeptide chains composed of amino acids.
- 4 heme groups
- 4 iron molecules, 1 in each heme group
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Adult hemoglobin:
2 alpha-2 beta chains
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2-3 DPG:
- Molecule found inside the RBCs
- 2-3 DPG is high the oxygen will leave the RBC cell to the other cells (good).
- If low it will soak up the oxygen.
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Increased 2-3 DPG _________ affinity:
Decreases
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Increased PO2 _______ affinity.
increased
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Increased temp _________ affinity.
decreases
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Increase pH __________ affinity
Increases
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Increase O2 affinity:
Shift to Left
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Decreased O2 affinity:
Shift to right
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Fetal hemoglobin has _______ O2 affinity than HGB A. Pulls O2 across placenta from mother to fetus.
Greater
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Hemoglobin F:
- 2 Alpha-2 gamma
- Synthesis begins at 5 weeks gestation and associated with hepatic hematopoiesis
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Carbon Dioxide Transport. Hemoglobin is also needed to transport carbon dioxide from the tissues back to _______ for removal.
Lungs
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Carbon dioxide transported 3 different ways:
_____ Indirect RBC pathway (conversion of CO2 to HCO3)
____ Direct pathway
____ Dissolved in plasma
75%, 20%, 5%
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Porphyrias:
Disorder of heme synthesis
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Causes of porphyrias:
- Genetic deficiencies of enzymes required for heme synthesis.
- Acquired deficiencies from substances that damage heme synthesis.
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Porphyrias are diagnosed:
From detection of heme pre-cursors molecules in the urine
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Ferric iron is transported to the immature marrow RBCs by the protein ______.
Transferrin
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Transferrin delivers ____ to the immature RBC membrane and then returns to the plasma.
Fe3+
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Excess iron is stored as ________ in tissues and plasma.
Ferritin
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Ringed sideroblasts
Excess iron may accumulate in immature RBCs
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Hemoglobin A2:
2 alpha-2 delta
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Hemoglobin S:
2 alpha-2 beta (6 Glucose--Valence
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Hemoglobin C:
2 alpha-2 beta (6 glucose-lysine)
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Carbon monoxide:
- Hemoglobin affinity for CO >200 x that of oxygen.
- Hgb binds CO and releases it very slowly.
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Can carboxyhemoglobin transport oxygen?
NO
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Sulfhemoglobin:
- Hemoglobin combined with sulfur compounds.
- Hemoglobin shape altered, preventing oxygen transport.
- May denature and precipitate to form Heinz Bodies.
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Common causes of sulfhemoglobin:
- Drugs
- Bacterial infections
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Methemoglobin:
- Hemoglobin with ferric iron.
- Caused by genetic defects/oxidizing drugs
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Hemoglobin electrophoresis:
- Analytical technique that separates substances according to their different migration rates (movement) in an electric field.
- Commonly used to confirm a hemoglobinopathy diagnosis.
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What are the 2 most common hemoglobin electrophoresis technique:
- Cellulose acetate
- Citrate agar
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Cellulose acetate has a pH of:
8.6
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Citrate agar has a pH of:
< 7.0
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Fetal Hemoglobin stain or Hemoglobin F stain is also known as:
- Kleihauer-Betke Stain
- useful to ID fetal blood in the maternal circulation
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Embden-Meyerhof Pathway:
Main energy source/ATP from glucose
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Hexose Monophosphate Shunt:
Prevents oxidative denaturation of hemoglobin and Heinz Body formation
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Methehemoglobin reducatase pathway:
prevent oxidation of hemoglobin iron to Fe3+
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Luebering-Rappaport Pathway:
Regulates 2-3 DPG concentration in the RBCs
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What is the average lifespan of RBCs?
4 months
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As RBCs age what happens:
- Membrane become less flexible
- Enzyme activity decreases.
- Cell loses membrane-RBC hemoglobin increases
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Cup of grace Coup de grace:
- As RBC's become stiff, they get stuck passing through the spleen.
- Phagocytized and removed from the circulation by the spleen.
- RBCs are destroyed.
- The components of the RBCs must be re-utilized or excreted.
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Extravascular catabolism (Intracelluar):
- Happens in spleen. Inside the RE cells of spleen.
- Heme is broken apart and concerted into bilirubin and excreted into the GI tract by the liver.
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Intravascular catabolism (in the circulating blood):
RBCs hemolyze, releasing the cytoplasm into the plasma.
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Haptoglobulin:
- Plasma protein binds polypeptide chains, preventing their loss in the urine.
- Haptoglobin-protein complexes removed by the liver.
- Additional unbound plasma hemoglobin oxidized to methemoglobin.
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MCV (fL):
- Mean Corpuscular volume
- How big, average
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MCH (pg):
- Mean Corpuscular Hemoglobin
- How much hemoglobin in cell.
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MCHC (g/dl):
- Mean Corpuscular Hemoglobin Concentration
- Concentration of hemoglobin
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Formula for MCV:
HCT/RBC (10)
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Formula for MCH:
HGB/ RBC (10)
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Formula for MCHC:
HGB/HCT (100)
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