Anemia Flashcards
Hemoglobin Structure
Tetramer composed of two unlike pairs of globin polypeptide chains (one pair of alpha-globin and one pair of non-alpha globin)
Oxygen in its Ferrous vs Ferric form
Ferrous = Fe+2 (reduced) BIND O2
Ferric = Fe+3 (oxidized) CAN’T bind O2
Iron is reduced from ferric to ferrous by Cytochrome Reductase
Allostery of Hemoglobin
When O2 binds to hemoglobin at one site, hemoglobin changes in configuration, which alters the binding affinity of additional O2
Taut form of Hemoglobin
Deoxygenated form, under conditions where oxygen concentration is low (none of the 4 binding sites are occupied). T-configuration is present due to inter- and intra-salt bonds, H-bonding, and hydrophobic interactions
Relaxed form of Hemoglobin
Oxygenated form. As oxygen becomes more available, 1 oxygen binds, configuration changes and other sites have higher binding affinity. Breaking of salt bonds lead to R-conformation
Neumonic for %oxygen saturation with various pO2
mmHg/%
30-60, 60-90, 40-75 (100-98)
How does pH affect the hemoglobin dissociation curve?
Low pH = decreased O2 affinity = shift to right
High pH = increased O2 affinity = shift to left
Known as BOHR EFFECT
How does CO2 concentration affect the hemoglobin dissociation curve
CO2 + H20»_space; carbonic acid»_space; bicarbonate and H+
This leads to a lower pH, initiating Bohr Effect. O2 will be unloaded in tissues with high metabolism (more CO2=more acidic=less O2 affinity)
How does Temperature affect the hemoglobin dissociation curve?
Higher Temp = Lower O2 affinity
How does 2,3-BPG concentration affect the hemoglobin dissociation curve?
Increase in BPG = Lower O2 affinity
BPG is the product of anaerobic glycolytic pathway
Hemoglobin vs Myoglobin
Myoglobin is a MONOMER and cannot undergo allosteric regulation. Has very high O2 affinity at very low O2 concentrations. Good for STORAGE
What are conditions that would create a Right-shift on hemoglobin dissociation curve?
Functional abnormal hemoglobin variants
Increase in BPG: High altitude, Pulmonary hypoxemia, Severe anemia, Congestive heart failure, Hepatic cirrhosis
What conditions would create a Left-shift on hemoglobin dissociation curve?
Functionally abnormal hemoglobin variants
CO poisoning
Decrease in BPG: Septic shock, Severe acidosis, Blood transfusion of stored blood, BPG-mutase deficiency
Alpha-like globin chains
4 gene copies on chromosome 16
Beta-like globin chians
2 gene copies on chromosome 11
Fetal Hemoglobin
Have distinct hemoglobin with high O2 affinity:
At 4-14 weeks gestation: Gower I, Gower II, Portland
At 8 weeks gestation: Fetal hemoglobin. Binds BPG poorly, putting the hemoglobin in a permanent relaxed state. Also increase in Bohr Effect
Hemoglobin at birth
65-95% HbF and 20% HbA
Hemoglobin after age 5
96-97% HbA
2% HbA2
1% HbF
HbA2
Functions much like HbA, has the same Bohr effect, same response to Bohr effect. Is more heat stable and has slightly higher O2 affinity
Hemoglobin Variants
More than 500 identified, ~200 are clinically significant
Most common HbS, HbC, HbE. Can lead to unstable hemoglobins or with altered O2 affinity
High Affinity Hemoglobin
Hemoglobin Chesapeake: single point mutation. Erythrocytosis because O2 delivery is reduced
Low Affinity Hemoglobin
Presents with cyanosis and mild anemia
Unstable Hemoglobin
Spontaneously denature, may or may not bind O2
Ex: Hemoglobin Zurich (single point mutation, increases O2 binding). Also Hemoglobin Koln (mutation in Beta-chein, increase O2 affinity. Mild anemia, reticulocytosis, splenomegaly). Finally, Hemoglobin Poole (mutation in gamma chain, infants with hemolytic anemia that resolves in a few months)
Methemoglobinemia
Fe+3 (ferric) cannot carry oxygen. The curve shifts to the left and p50 drops. Can be acquired (drugs and chemicals) or genetic (homozygous, think of the inbred blue-skinned family in KY). No treatment is needed for genetic, only cosmetic. For acquired, the higher the methoglobin level the more severe the symptoms (above 70% not compatible with life.
CO poisoning
240x more affinity to hemoglobin than O2. Normally have 3% CO, smokers have 10-15%. Causes curve to shift left. Leads to headache, malaise, nausea, dizziness., coma, MI. NOT cyanotic, instead is “cherry red”
Basic definition of Anemia, and the measurements to define it
Insufficient red cell mass to adequately deliver oxygen to peripheral tissues. Measure Hemoglobin concentration, Hematocrit, RBC count. Values will differ based on age, gender and geography
Reticulocyte Count
Is the percentage of reticulocytes with 1,000 RBC are counted. An increase in RBC destruction (or loss of blood) will raise the Reticulocyte count
Know the chart of Anemia by heart, OK?
OK!
Symptoms of Anemia
Shortness of breath, fatigue, rapid heart rate, dizziness, pain with exercise, pallor
Where do you find iron in the body?
Most iron is in hemoglobin, but about 25% is stored in Ferritin and Hemosiderin
Fe solubility
More soluble at low pH.
In aqueous solutions, forms insoluble hydroxides unless bound to protein (ie Heme)
Iron Absorption
Occurs in DUODENUM. Gastric pH maintains solubility until it reaches the duodenum. Enters duodenum as FERRIC ion and is concerted to FERROUS ion by surface reductase. Absorption controlled by intraluminal and extraluminal factors
Intraluminal factors for Iron Absorption
Gastric factors (low pH, gastroferrin), Presence of proteins and AA, Vitamin C, Amount of iron ingested. Phytates and oxalates DECREASE absorption
Extraluminal factors for Iron Absorption
Increased erythropoietic activity will increase Fe absorption
Iron Cycle, Transport
Transferrin. Binds 2 mole Fe+3. High binding affinity. Binds specific receptors
Iron Cycle, Storage
Ferritin. Intracellular storage protein. Multimeric structure. Center contains ferric salts/protein molecules and up to 4500 atoms of Fe with are biologically available
Iron Cycle
Allows iron to be re-used, limiting the amount needed from diet. Absorbed through mucosal cell and binds to Transferrin. Goes to bone marrow, enters through clatherin-coated pits. Endosome become acidfied, releasing iron. Iron become incorporated to hemoglobin, RBC circulates for 120 days. RBC removed my macrophages in spleen, macrophages sequester iron in Ferritin iron stores. Iron stores can be released and rebound to Transferrin
Hepcidin
A 25aa peptide in liver produced in response to high iron intake and for inflammation/infection. Production reduced by anemia or hypoxia. LOW hepcidin=INCREASED iron absorption. Negative regulator of iron absorption. Can be implication for iron resistant iron deficiency anemia
Characteristics of Iron Deficiency
Decrease Hgb synthesis, Decrease cell proliferation. Anemia. Mild defect in muscular performance or neuropsych dysfunction. Ridges on nails. Dysphagia. Gastritis. Immune dysfunction.
Diagnosing Iron Deficiency
Decrease in O2 carrying capacity. Decrease reticulocyte production. Microcytosis (Decrease MCV). Hypochromia (Decrease MCHC). Wide range of cell size (Increase RDW). Low serum Fe, Low Ferritin. High Total Iron Binding Capacity
Ddx for Iron Deficiency
Anemia of chronic inflammation/infection
Anemia of chronic disease
Thalassemia
Sideroblastic anemias
Iron Overload
From high iron diet, high iron absorption, or repeat transfusions. Can cause organ damage (cardiac arrhythmia, cardiac failure, liver dysfunction/failure, diabetes). Treatment through iron chelators or therapeutic phlebotomy
Features of Anemia due to chronic infection/inflammation
Tumor Necrosis Factor decreases iron availability from stores and decreases EPO production. INF-beta inhibits erythropoiesis. Patient may have fever, arthritis, fatigue. Other symptoms present consistant with infection. Labs show mild-mod anemia. Normal ferritin stores, but DECREASE in serum Fe, TBIC, EPO for Hct, and retic count.