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Hemoglobin synthesis


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What is the normal adult daily iron needed to replace senescent RBCs?
Where does most come from?

What is avg intake?
Normal adult = 21 mg
most comes from recycling iron.
Pregnant/breast feeding/infants need more.

Avg intake = 10-20 mg/day
how much of the total body iron is present as hemoglobin?
How much iron is absorbed from diet and lost daily?
both = 1-2 mg
What factors affect daily Fe requirements?
growth spurts
iron deficiency
where is dietary iron absorption regulated?
in the intestinal mucosa of the small bowel
What is the oxidation state of iron in:
-mucosal cells
Dietary is Ferric - 3+
Stomach is Ferrous - 2+
Mucosa - back to 3+, then complexed with apoferritin to form Ferritin - storage form of iron
What is the primary storage form of iron, and where is it found?

Why is it primary?
-liver, spleen, bone marrow.

Easily mobilized for usage
What is an alternative form of stored iron to ferritin?
After Fe3+ in mucosal cells is complexed with apoferritin, what is the remaining Ferric iron converted to?
Transferrin, via combination with apotransferrin.
what is Transferrin?
an Iron transporter to the organs in the body.
What forms Heme?
Iron plus Protoporphyrin ring
How is iron absorption regulated by mucosal cells?
they only take up ferrous iron, so it has to be converted by the stomach acid to Fe2+. After uptake, its converted back to Fe3+ - ferric.
What is Fe3+ first complexed with in mucosal cells?
apotransferrin, to be transferred to the blood.
What is apotransferrin?
transferrin without Iron. just a glycoprotein Beta-globulin shell without its prosthetic group
What does transferrin do?
transports iron from the gut to the blood
What are the 2 storage forms of iron?
what is the primary protein used to store iron, but without the prostethic group?
what is ferritin?
the storage form of iron - it complexes with Ferric Iron to make it Fe2+
where is ferritin found?
bone marrow
intestinal mucosal cells (some)
what is hemosiderin?
a storage form of ferritin - the ferritin is denatured, but there is excess Fe within it.
what does hemosiderin stain with?
prussian blue.
where is the majority of Fe found in the body?
blood - 65% is in hemoglobin

stored - 30% is in ferritin/hemosiderin
what are 5 types of iron studies?
1. serum iron
2. Total iron binding capacity (TIBC)
3. % saturation of transferrin
4. Serum ferritin
5. Free erythrocyte protoporphyrin (FEP)
What is serum iron?

Reference range?

What is it used for?
How does it vary?
iron bound to protein.

Ref range = 60-160 mg/dl

It has limited use as a single measurement. Diurnal variation - different in the morning vs. night
What is TIBC? what info does it give?
Total Iron Binding Capacity, tells how much transferrin is able to bind Iron.
So, an indirect measurement of transferrin.
What is the ref range of TIBC?
200-360 mg/dl
what does a high TIBC indicate?
That lots of transferrin is free and capable of binding iron - b/c iron to be transferred is low.
what is the % Saturation of Transferrin test?
meausres serum iron/TIBC x 100 to detect if iron levels are too high.
what is serum ferritin?
an acute phase reactant, increased in inflammation.
What info does serum ferritin measurement give?

what is its clinical use?
measurement of body iron stores.

used for monitoring iron therapy.
an acute phase reactant, can be falsely elevated in inflammation.
What does FEP or ZPP stand for?
Free erythrocyte protoporphyrin, or
Zinc protoporphyrin
What does FEP represent?
What is its clinical use?
free erythrocyte protoporphyrin - the non-heme porphyrin in BLOOD. most is actually bound to zinc, so called ZPP.

used to differentiate anemias -ZPP is increased if truly Fe deficient.
what kinds of iron study results are seen in Fe deficiency anemia?
everything is low except
-Iron binding capacity
-Free erythrocyte protoporphyrin
What is characteristic iron study in Anemia of Chronic Infection?
high FEP - no iron is available to bind protoporphyrin so it's bound to zinc.
What is hemociderosis?

What causes it?
Disease where ferritin is degenerated, resulting in excess iron levels.

caused by hemolysis/excess Hb breakdown.
What is hemochromatosus?
What causes it?
What are the symptoms?
How is it treated?
What iron study results are seen?
the most common genetic abnormality i caucasions. Ferritin problem; Iron accumul up to 4g/day!! daily need is in Millig.
caused by 2-gene mutation: C2824, H63D.

Liver cirrhosis, cardiac, diabetic, skin bronzing. BLEED THEM.
what are 4 examples of disease assocaited with iron deficiency or increase?
-Fe deficiency anemia
-Anemia of chronic infection
where is Heme synthesized?
What is heme synthesized from?
glycine and succinyl coenzyme A
In general, how is heme synthesized?
it goes through a biosyntheitc pathway catalyzed by a series of enzymes in both the mitochondria and cytoplasm.

Each enzymatic reaction adds a ring to the heme molecule.
It becomes less H2O soluble as it grows. Lack of an enzyme causes deficiency in heme.
What is the final structure of heme?
a Tetrapyrole ring with Ferrous iron as its core
what controls heme synthesis?
ALA synthase - the rate-limiting step in the pathway.
what affect does Free heme have?
it can be measured in the urine.
What are the porphyrias?
What is their clinical effect?
Defects in porphyrin synthesis.
Free porphyrin precursors are excreted in the urine as:
-urobilinogen in organic layer
-prophyrobilinogen in aqueous layer.
Where does globin synthesis occur?
in ribosomes
what are the 4 types of globin chains?
when is most alpha globin made?
in the fetus
what regulates globin synthesis?
mostly genetics
what is the structure of hemoglobin, and how is it assembled?
a tetramer

-2 alpha chains, 2 non-alpha. either Beta, delta, or gamma.

Tetramer links to heme via the proximal histadine on the polypeptide chain.
what's the most important factor affecting O2 release to tissues?
how is 2,3-dpg generated?
via anaerobic glycolysis
what four things cause a LEFT shift of dissoc. curve?
high Hgb F concentration
meth or carboxyhemoglobin
transfusion of 2,3-DPG depleted blood
what 3 things cause a RIGHT shift?
high altitude
severe anemia
what 3 enzymes play a role in Hgb metabolism?
-enzymes of the Embden Meyerhof produce ATP!!

-G-6-PD catalyze reactions in the hexose monophosphate HMP shunt to prevent buildup of bad peroxides. W/out, Heinz bodies

-Cyto b5 reductase reduces methemoglobin.
what organelle is each synth in?
heme is in mitochondria
globin is in ribosomes.
what regulates heme synthesis?
what is ALA-synthase?
an enzyme that catalyzes the rate-determining step in the heme production pathway
how is heme production regulated?
by a negative feedback system; when heme is present, expression of ALA synthase is downregulated.
what are siderocytes?
cells with precipitated iron, due to abnormal/faulty incorporation of iron into the heme group.
what symptomology is seen in the porphyrias?
metabolic deficiencies; urinary excretion of urobilinogen (organic layer), and prophyrobilinogen (aqueous)
what type of iron studies are seen in iron def. anemia?
decreased everything except TIBC and FEP.
what iron study results indicate anemia of chronic infection?
decreased serum iron, TIBC, and transferrin saturation.
increased serum ferritin and FEP.
what is wrong in anemia of chronic infection?
no problem with iron absorption/storage, but there is faulty delivery of iron to RBC and no incorporation into heme.
-That explains the incr. serum ferritin - it's all stored.
what is hemochromatosis essentially?
overloaded iron stores - a genetic disease.
what iron study results are seen in hemachromatosis?
increased serum iron, Transferrin saturation, serum ferritin.
decreased TIBC and FEP.
what does 2,3-dpg do?
decreases hemoglobin's affinity for oxygen - makes it release.
at what pressure does hgb release oxygen in tissues?
how much is released?
releases 25% of oxygen at 40 mm Hg.
what does temperature increase do to the o2 diss curve?

temp decrease?
increase = shift to right

decrease = shift to left
what does ph decrease (acid) do to the o2 diss curve?

ph increase (alkaline)?
acid = shift to right

alkaline = shift to left
what does increased CO2 do to the o2 diss curve?
shift to left
what does decrease in 2,3 DPG do to the o2 diss curve?
shift to left
what happens to oxygen affinity when curve shifts?
to the right = lower oxygen affinity

to the left = higher oxygen affinity
through what metabolic pathway do RBCs generate energy?
what do RBCs need to protect themselves from?
oxidizing agents that are harmful to protein
what shunt is used to defend the RBC against oxidative injury?
Hexose-Monophosphate shunt
what is the role of glutathione in the hexose-monophosphate shunt?
glutathione reduces oxidative agents and neutralizes them.
what does G-6-PD do?
what is seen if it's deficient?
an enzyme that reduces NADP to NADPH to keep the shunt going.

If deficient, see Heinz bodies.
What is the purpose of Cytochrome b5 reductase?
reduces methemoglobin to make it capable of o2 transport.

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