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ypoornima
06-08-2006, 02:02 AM
Why is the Fetal Hb content more than tht of the adults?

md90
06-08-2006, 12:12 PM
I don't know if I understand your question... but what I know about Fetal Hb:
1. contains alpha and gamma chains
2. helps to have a greater affinity for oxygen.. so that they can get it from the mother in the womb
3. attraction is based with or without 2,3-BPG
4. will continue the higher attraction until the adult Hb can fully matured and functional which is around 32-36 weeks post-conception
5. also provides a protective factor--in relation to sickle cell disease
6. b/c of the higher attraction, left-shift the oxygen dissociation curve (not needing the 2,3-BPG)

ypoornima
06-11-2006, 12:27 AM
Wht I meant to ask was ... Compared to adult Hb levels why is the Fetal Hb more? ( ie a normal adult has a Hb level Of 12-16gm% n the normal fetal Hb is more than tht)


Here is the explanation for it:
The fetus has to get the oxygen fm mother thru the placental surface, the surface area of which is very less. Hence, the fetus has to grab as much as oxygen as possible for which it needs to have high affinity for the oxygen. Since,this Hb has high affinity for oxygen, it will not be able to release the O2, so the tissue is now in hypoxic state. This signal is sent to the kidney to synthesize erythropoietin, which in turn synthesizes the HbF. This is a vicious cycle. Therefore the HbF content is more.

Same is the reason for giving HbF in Sickle cell anemia

Hope u got it.

Billy BA
06-13-2006, 07:19 PM
There is no "signal sent to the brain". The peritubular capillaries in the kidney detect the low oxygen content of the blood (due to the increased affinity of HbF) and release erythropoietin. HbF is NOT given to in sickle cell disease. Methotrexate is given to induce the production of HbF in the bone marrow which has a much decreased tendency to sickle.

Billy BA
06-13-2006, 11:39 PM
One further thing, HbF has a decreased affinity for 2,3 BPG thereby left-shifting the disassociation curve which increases it's affinity for O2. It is not that they "need" or are "allowed" to not bind 2,3 BPG.

Billy BA
06-14-2006, 06:39 AM
My error on the methotrexate treatment, it is hydroxyurea that increases HbF production.

tRmedic21
06-14-2006, 06:51 AM
Also, just as a note, some people DO still give HbF for acute sickle cell crisis. It was told to me on my FP rotation that this is the case, and there are many current studies out there which are reviewing the protective factor of HPFH (Herditary Persistance of Fetal Hemoglobin) in conjunction with sickle cell trait.







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