Hematology Flashcards
P50
partial pressure of oxygen at which the oxygen carrying protein is 50% saturated.
P50 for hemoglobin vs. myoglobin under normal conditions
Under normal conditions for temperature (37 C) and pH (7.4), the P50 for hemoglobin is approximately 27 mmHg while the P50 for myoglobin is 2.75 mmHg.
Utility of myoglobin
Intracellular storage of oxygen, where the concentration of oxygen is low enough that myoglobin will let go!
Mnemonic 30-60 60-90 40-75
partial pressure of 30 mmHg, the % saturation is ~60 %, at 60 mmHg it’s ~90% and at 40 mmHg it’s ~75%. Also, at 10 mmHg the % saturation is ~10 %.
Bohr Effect
Increase in pH leads to increased oxygen affinity (Left Shift)
(CO2 and lactic acid make high activity tissues more acidic)
Temperature effect on Hb O2 affinity
Increase in temperature leads to decreased oxygen affinity (right shift) allows oxygen to unload in tissues affected by exercise or fever
2,3 BPG - + Hb O2 affinity
A product of Glycolytic pathway
2,3 BPG binds and stabilizes the T form of Hb, allowing the oxygen to be released into the tissues. (left shift)
Hb Gower 1
Zeta 2 eta 2
Hemoglobin Gower 2
alpha 2 eta 2
Hemoglobin Portland
zeta 2 gamma 2
HbA vs. embryonic Hb
Embryonic Hb has higher Hb affinity
Fetal hemoglobin
alpha 2 gamma 2
Fetal hemoglobin and 2-3 BPT
2,3-BPG binds HbF less well than HbA, so the oxygen affinity is higher
Bohr effect in fetal hemoglobin
Increased by 20%
Fetal blood transfers H+ ions to the intravillous space of the placenta, which leads to increased pH in fetal blood and increased oxygen affinity, promoting transfer of oxygen to blood
Prolonged fetal hemoglobin
premature babies
babies of mothers with diabetes
people with hemolytic anemia
people with diseases like myelodysplasia and leukemia
Hg A2
Same bohr effect, cooperativity, and 2,3 BPG affinity
More heat stable, slightly higher O2 affinity
Heinz bodies
precipitated denatured hemoglobin that can be seen with a special stain.
Caused by mutations producing an unstable hb molecule leading to a mild hemolytic anemia
Hb Chesapeake
Hb with increased O2 affinity
asociated with erythrocytosis
Hemoglobin Zurich
-point mutation that doesn’t affect O2 binding but increases CO affinity
Carboxyhemoglobin levels approach those of smokers
Hemoglobin Koln
Most common unstable HbG. Mild anemia, reticulocytosis, and splenomegaly
Methemoglobin
Fe+2 binds oxygen (ferrous)
Fe+3 does not (ic)
Methemoglobin has Fe 3+ and can’t bind O2
Causes of Methemoglobinemia
1) Methemoglobin overproduction
2) Decreased methemoglobin reduction by NADPH methemoglobin reductase pahtway
3) Heme oxidation by free radicals, H202, NO, or Oh
Acquired Methemoglobinemia
Typically caused by exposure to chemicals (benzocaine, nitrates in drinking water)
Infants are especially at risk
Hereditary methemoglobinemia
Commonly due to homozygous deficiency in cytochrome b5 reductase
Also can be caused due to mutation of Hb that produces HbM by inhibiting reduction of Fe
Methemoglobin Clinical findings
- High amounts of methemoglobin reduces O2 capacity and increases O2 affinity
- People with up to 40% of methemoglobin are typically asymptomatic but cyanotic
Dx of Methemoglobinemia
Suspected: person looks cyanotic but arterial PO2 is normal
-Conclusive - Blood looks chocolate or brown blue and does not change with additional o2 exposure
Treatments
HgM: None
Cytochrome b5 deficient: treat w/ methylene blue or ascorbic acid for cosmetic reasons
Acquired Methemoglobinemia
Levels above 60% can be lethal
Treated by removing chemical and methylene blue (provides electron acceptor for Fe reduction via NADPH pathway)
Dx and treatment of Carbon monoxide poisoning
Dx: Co-oximetry (Pulse oximetry with 4 diodes)
Treatment= oxygen or Hyperbaric oxygen (decreases 1/2 life of CO hemoglobin)
Pulse Oximetry
Photo detector and 2 light diodes (660 nm and 940 nm)
Hemoglobin and Deoxyhemoglobin have different absorption spectrums at the region
Methemoglobin and carboxyhemoglobin aren’t distinguished with this.
