Erythrocytes must maintain hemoglobin in a reduced state. How is this accomplished?
They reduce methemoglobin (Fe3+) to hemoglobin (Fe2+)
Erythrocytes must resist oxidant stress to protect themselves from the harmful effects of oxygen. How is this accomplished?
They maintain Glutathione in its reduced state
How many molecules of oxygen can each hemoglobin molecule carry? What molecule binds the oxygen?
What is the predominant hemoglobin in utero?
Hgb F (Fetal Hemoglobin): α2 γ2
When are normal adult levels of hemoglobin met?
On what chromosome is the alpha-gene cluster on? How many alphas are on each chromosome?
2 alphas each for a total of 4
On what chromosome is the beta-gene cluster on? How many betas are on each chromosome?
1 beta per chromosome for a total of 2
The ___________ structure of the hemoglobin molecule allows it to slide around, which alters the affinity of hemoglobin for oxygen. What is this measured as?
P50: partial pressure at which hemoglobin is 50% saturated with oxygen
A DECREASED O2 affinity ____________ O2 unloading to tissues. This causes a ____________ shift in the O2 saturation curve, and a ___________ P50.
What is this known as?
An INCREASED O2 affinity ______________ O2 unloading. This causes a ____________ shift in the O2 saturation curve, and a _________ P50.
What is this known as?
What molecule regulates hemoglobin-oxygen affinity? This molecule decreases oxygen affinity by ___________ tissue oxygen supply. An increase in the concentration of this molecule causes a(n) _________ in affinity.
Does acidosis increase or decrease O2 affinity? What is this known as?
Does alkalosis increase or decrease O2 affinity?
Does an increased temperature increase or decrease O2 affinity?
What is the rate-limiting step of heme synthesis? On what chromosome is this enzyme located? What does it require? A deficiency in this enzyme can cause what two disease states?
Requires Pyridoxal 5'-phosphate
Sideroblastic Anemias & Inherited Porphyrias
Normal Oxygenation of Hemoglobin:
Oxyhemoglobin (Fe2+) --> Deoxyhemoglobin + O2
(reverse reaction also occurs)
What harmful products are formed from the spontaneous oxidation of Oxyhemoglobin?
What enzyme catalyzes the reverse reaction, back to hemoglobin (thus protecting the RBC from harm)? What molecule is required for this reaction to take place, and where is it generated from?
When Oxyhemoglobin (Fe2+) is spontaneously oxidized to methemoglobin and superoxide, what enzyme converts the superoxide to H2O2?
H2O2 itself must then be reduced:
2 GSH + H2O2 --> GSSG + 2 H2O
What is GSH known as? What enzyme reduces GSSG back to GSH, to conserve the molecule? What molecule is needed for this reverse reaction, and where is it generated from?
Glutathion (GSH) is "reducing back" for RBC -- protects them from harmful effects of superoxide ion by reducing it
Requires NADPH generated by hexose monophosphate shunt
What pathway is responsible for producing 2,3-Diphosphoglycerate (2,3-DPG), which is the primary regulator of hemoglobin-O2 affinity?
After approximately 120 days, most erythrocytes are trapped and phagocytosed by what system, and where is it located? This is an example of __________ hemolysis.
In extravascular hemolysis, hemoglobin dissociates into the globin protein and heme molecule. What is removed from the heme ring, and recycled back to marrow or stored within macrophage? The protoporphyrin ring is then opened. What does this result in?
Biliverdin & CO2
In extravascular hemolysis, the protoporphyrin ring is opened, resulting in biliverdin and CO2. What is the biliverdin then converted to? This is known as unconjugated or "indirect". What conjugates it?
An excess production of this molecule can result in a build-up of its unconjugated form. What can this result in?
Increase in RBC breakdown
In intravascular hemolysis (occurs in <10% of hemoglobin cells), the hemoglobin tetramer dissociates to what? What molecule do these then complex to, and what removes them from circulation?
Excess hemoglobin in intravascular hemolysis may be phagocytosed by what cell type? They also may appear in urine as _______ __________ or ____________
Renal Tubular Cells
Free Hemoglobin or Methemoglobin
How long is a RBC normally a reticulocyte?
4 days: 3 in marrow, 1 in blood
Reticulocytes are normally counted as % of RBCs. What is a normal reticulocyte count? How is this calculated?
Ratio of reticulocytes to total RBCs X 100
In anemia, the total RBC count is decreased. If the absolute reticulocyte count is unchanged, the ratio will _________ -- falsely suggesting _________ reticulocyte production. Therefore, the reticulocyte count must be corrected for this factor. How is this accomplished?
Corrected Reticulocyte Count: Patient retic count (%) X (Patient Hematocrit/ Normal Hematocrit)