RBC metabolism and Disorders Flashcards
What do RBC’s need energy for maintaining?
High intracellular K+, low Na+, and very low Ca++
Hgb in reduced form
High levels of reduced glutathione
Membrane integrity and deformability
What pathway is 90-95% of the glucose consumption utilized by?
Embden-Meyerhof pathway
What are the products of the Embden-Meyerhof pathway?
Glucose is metabolized to lactate = 2 moles of ATP per glucose molecule
What is ATP needed for?
Needed to maintain RBC shape, flexibilty, osmotic equilibrium and membrane integrity through cation pumps
What does decreased ATP production cause?
Increased osmotic fragility
What happens in the Hexose Monophosphate (HMP) shunt?
Pathway produces reduced nicotinamide adenine dinucleotide phosphate (NADPH) and reduced glutathione (GSH) necessary for maintaining hemoglobin in the reduced functional state
HMP shunt is functionally dependent on G6PD
What happens when the HMP shunt is defective?
Hgb sulfhydryl groups are oxidized = Heinze bodies
Damaged RBC’s are removed by spleen
What deficiency is a result from defective HMP shunt?
G6PD deficiency
What does GSH do?
High concentrations present to protect RBC against oxidants by inactivating these oxidants
Oxidants are produced by macrophages during infecting or RBC in the presence of some drugs
What is the Methemoglobin Reductase Pathway essential for?
Maintains heme iron in reduced state, Fe++
What is hemoglobin in Ferric state known as?
Fe+++ is methemoglobin and can’t bind O2
What 2 pathways protect heme iron from Oxidation?
Methemoglobin reductase and Embden-Meyerhof pathway
What happens if the methemoglobin reductase can’t keep up with challenges by oxidant drugs?
High levels of methemoglobin = cyanosis due to increase concentration of deoxyhemoglobin
What is the Rapoport-Leubering Shunt?
Part of Embden-Meyerhof pathway
Produces 2,3-DPG
What is function of 2,3-DPG?
When hemoglobin binds 2,3-DPG O2 is released
An increase in 2,3-DPG = increase release of O2 to tissues = decreased affinity for O2
What is Pyrvate kinase deficiency?
Defect in glycolytic pathway?
What are characteristics of G-6-PD deficiency?
Seen during WWII, antimalarial drugs caused severe hemolysis; 10% of african americans were affected
GSH levels fall because NADPH synthesis is decreased = oxidants damage cell = denatured Hgb precipitates as Heinze bodies = Extravascular hemolysis
What G6PD variants are associated with hemolysis?
GdA - Most common; 10% of African Americans
Gdmed - 2nd most common; seen in caucasions
GdB - normal genotype and present in 70% of caucasusions
What are triggers for hemolysis?
Infection
Oxidant drugs therapy
Favism - severe hemolytic episode after eating fava beans (occurs in Gdmed)
What is heme?
An iron-chelated porphyrin ring that functions as a non-amino acid component of a protein
Porphyrin ring is composed of a tetrapyrrole ring with Fe++ inserted in the center
What forms of hemoglobin are found in the Embryo?
Gower 1
Gower 2
Portland
-not detectable after the 3rd month of gestation
What is the primary hemoglobin in the fetus?
Hgb F (2 alpha + 2 gamma)
90-95% until 34-36 weeks
50-85% at birth
What is the primary hemoglobin found in adults?
Hgb A
2 alpha chains + 2 beta chains)
At what age does an infant reach adult levels of hgb A?
By one year
What is hemoglobin A2?
Normal variant of Hgb A
2 alpha chains + 2 delta chains
1% in newborn and 2-4% in Adults
How much Hgb F is found in normal adult?
2% - most is restricted to 8% of all RBC called F cells
The switch from Hgb F to Hgb A is incomplete and reversible
What regulates hemoglobin production?
ALAS enzyme
Negative feedback of heme
Concentration of Iron
Regulation of Globin chain synthesis
What is the function of Hemoglobin
Transport and exchange gasses; primarily O2 and CO2
What is P?
Partial pressure each gas exerts into the atmostmphere
Why is O2 released to tissues?
oxygen is released because the PO2 (partial pressure of oxygen) in blood is more than in the tissues, and CO2 diffuses into the blood because PCO2 (partial pressure of carbon dioxide) is greater in tissues than in blood.
Gas goes from greater to less
Lungs have high partial pressure
Tissues have low partial pressure
What does increased O2 affinity mean?
Hemoglobin has a high affinity for O2 and does not give it up
What is P50?
Oxygen affinity of hemoglobin is expressed as PO2 where 50% of the Hemoglobin is saturated with O2.
Normal P50 is 26 mm HG
How many O2 molecules can one hemoglobin bind?
4 O2 molecules
What does a right shift oxygen dissociation curve cause?
O2 affinity is decreased - More O2 released to tissues Increase temp Increas 2,3 DPG Decreased pH Increased P50
What does a left shift oxygen dissociation curve cause?
O2 affinity is increases - less O2 released to tissues Decreased temp Decreased 2,3 DPG Decreased P50 Increased pH
What is the difference of oxygen affinity of HgB F and HgB A?
Hgb F has a higher O2 affinity than Hgb A
Hgb F does not readily bind to 2,3-DPG
What is the Bohr effect?
The effect of pH on oxygen affinity
What changes occur is stored blood?
pH goes down due to lactic acid from anaerobic glycolysis and K+ increase
2,3-DG decreases = decrease affinity for O2 - Hgb doesn’t release)
What kind of hemoglobinopathy is sickle cell?
Qualitative hemoglobin disorder
What kind of hemoglobinopathy is thalassemia?
Quantative hemoglobin disorder
What are the types of qualitative globin chain abnormalities?
Substitution of a amino acid for another
Deletion of AA from the globin chain
Addition of AA to the globin chain
Globin chain fusion
What is hemoglobin electrophoresis?
Uses a red cell hemolysate
Two types are required because some Hb variants migrate to the same position on one type but will separate on the other type.
- Cellulose acetate: pH 8.4 – 8.6
- Citrate agar: pH 6.0 – 6.2
Interpretation: based on known migration patterns of variant Hb and comparison with controls
What are the normal hemoglobin electrophoresis values?
HbA (A1): 96 – 98%
HbA2: 1.5 – 4.0%
HbF: 60-90% immediately after birth
<2% after age 1
What are the characteristics of Hereditary Persistance of Fetal Hemoglobin?
Benign
Large amts of fetal hemoglobin in adult
Caused by suppression of beta chain synthesis so increase in gamma chains = Hgb F
What are the test for hemoglobin F?
- Alkali denaturation: fetal hemoglobin is more resistant to denaturation under alkaline conditions strong alkali such as NaOH or KOH used
- Kleihauer-Betke (acid elution)
- Flow Cytometry: detects intracellular HbF
What is the amino acid substitution for Hgb S?
ß2 6GLU→VAL
- Mutation in SIXTH position of A3 helix of the ß-chain > from POLAR glutamic acid to NON-POLAR valine (net decrease in negative charge)
- Change in electrophoretic mobility
What causes cells to sickle in Hgb S?
The HbS molecule undergoes gelation (crystallization) causing sickling of the red cells when the oxygen tension is reduced
HbS is less soluble than HbA
Hgb crosslinks itself
What does the hgb electrophoresis look like in HgB S?
80% Hgb S
Up to 20% of Hgb F
3-4% of Hgb A2
NO Hgb A because abnormal Beta chain
What is the half life of sickle cells?
10-20 days